The Preparation of Plantation Rubber
by Sidney Morgan · English · Gutenberg #35510 · 661,529 chars · public domain (US)
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Title: The Preparation of Plantation Rubber
Author: Sidney Morgan
Contributor: H. P. Stevens
Release date: March 7, 2011 [eBook #35510]
Language: English
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| TRANSCRIBER'S NOTES: |
| |
| * Minor typographical and lay-out errors have been corrected. |
| * Inconsistencies in spelling (e.g. hyphenated vs. non-hyphenated |
| words) have not been corrected. |
| * Italics are represented by underscores as in _text_. |
| * The original book uses a V symbol to describe V-shaped cuts. These |
| V symbols are represented as [V]. |
| * Changes made to original text: |
| * Table of Contents: |
| * "Early collection of latex transport" changed to "Early |
| collection of latex--Transport". |
| * "Roof brick built houses" changed to "Roof--Brick built |
| houses". |
| * The order of the sections under Chapters XII and XXII has been |
| changed slightly to reflect the order of the sections in the |
| text. |
| * "Tephrosia candiad" changed to "Tephrosia candida". |
| * "Archiev" changed to "Archief". |
| * "about 1/2 square" changed to "about 1/2 inch square". |
| * "asbesto-slate" changed to "asbestos-slate" as elsewhere. |
| * "Formaline" changed to "Formalin" as elsewhere. |
| * Footnotes moved to under the paragraph they belong to. |
| * Page 141: "The lengths of crepe were weighed carefully at 8 a.m. |
| and 4 a.m." should probably read "The lengths of crepe were weighed|
| carefully at 8 a.m. and 4 p.m." |
+----------------------------------------------------------------------+
THE PREPARATION OF PLANTATION
RUBBER
THE PREPARATION
OF
PLANTATION RUBBER
BY
SIDNEY MORGAN, A.R.C.S.
VISITING AGENT FOR ESTATES IN THE EAST; FORMERLY SENIOR SCIENTIFIC OFFICER
AND NOW HONORARY ADVISER TO THE RUBBER GROWERS' ASSOCIATION
IN MALAYA
WITH A PREFACE AND A CHAPTER ON VULCANIZATION
BY
HENRY P. STEVENS, M.A. (OXON.,) PH.D., F.I.C.
CONSULTING CHEMIST TO THE RUBBER GROWERS' ASSOCIATION IN LONDON
CONSTABLE & CO. LTD.
LONDON : BOMBAY : SYDNEY
1922
PRINTED IN GREAT BRITAIN BY
BILLING AND SONS, LTD., GUILDFORD AND ESHER
PREFACE
Mr. Sidney Morgan's work on Plantation Rubber in the East is so well known
that he hardly needs introduction.
An earlier book, published in 1914, by the Rubber Growers' Association,
entitled "The Preparation of Plantation Rubber," was well received and
widely read. This book dealt in a very practical manner with problems with
which the industry had to contend. A second edition was subsequently
published. Both editions are now out of print. The present opportunity was
therefore taken to revise the original work, with the result that it has
been enlarged and practically rewritten. The information given is brought
up-to-date, and covers the whole process of production, commencing with the
planting of the tree, passing on to the collection, coagulation, and curing
of the rubber, and concluding with the packing for export. In the course of
his work for the Association, Mr. Morgan carried out a great deal of
industrial research in rubber production, including lengthy experiments on
tapping, the use of different coagulants and different conditions of
coagulation, and also on varying modes of rolling, drying, and smoking
rubber. He also went very fully into the types of construction and details
of the machinery and buildings employed on estates.
Much of this valuable work has escaped notice, owing to its having been
published in reports with limited circulation. Also a great deal of
information was supplied to planters in a quiet and unobtrusive fashion, in
interviews, visits to estates, and on other similar occasions. The
knowledge and experience thus accumulated has been embodied in the present
volume. The subject-matter should interest not only those actually engaged
in rubber planting, but those otherwise directly or indirectly connected
with the industry, such as importers, brokers, and particularly the rubber
manufacturers in this country and in America. My experience has been that
manufacturers as a whole have but a vague idea as to the methods employed
in the preparation of plantation rubber, and this work provides them with
the opportunity of obtaining an insight into the actual operations on the
estates. It is most desirable that a closer bond should unite the
plantation and manufacturing rubber industries. Such a result is best
promoted by a better understanding of the problems with which each is
confronted. Perhaps I may go so far as to suggest that some leading
scientific officer in the employment of one of the large manufacturing
concerns may take in hand a book which will give the planters the
equivalent of information in regard to the manufacturing industry which the
planters are now offering to the manufacturers.
The photographs in the earlier part of the book will give the layman some
conception of the enormous amount of labour that must be expended in the
opening up, planting, trenching, and weeding the plantations which have
replaced the virgin jungle. The authors are indebted for most of these
photographs to Mr. H. Sutcliffe, one of the mycologists of the Rubber
Growers' Association. The pictures of spotless coagulating tanks and tiled
verandahs regularly hosed down will indicate the cleanliness necessary for
the preparation of the beautifully clean sheet and crepe rubber which
became available with the advent of plantation rubber. These results are
largely due to the work of Sidney Morgan and his colleagues, on whom the
planters have relied for technical guidance and advice.
As regards my own contribution this is confined to a general outline of the
subject. I have, therefore, omitted reference to a number of matters which
would have been dealt with in detail had space permitted. The information
given is based on researches on vulcanisation carried out for the Rubber
Growers' Association by the writer over a period of nine or ten years. It
was not found practicable to give detailed references in all cases. The
reports on which the conclusions are based will, however, be found among
the regular quarterly reports made by the writer for the Association up to
June, 1919. Subsequent reports have been published in the Monthly Bulletin
of the Rubber Growers' Association. We are indebted to the Association for
permission to publish details from these reports, and also for the use made
of numerous earlier reports published both in London and in the East.
CONTENTS
PART I
_FIELD OPERATIONS_
PAGE
CHAPTER I
PLANTING
Seeds--Seed selection--Strain improvement by bad propagation--
Nurseries--Stumps--Seed at stake--Basket plants--Preparation
of land--Danger of disease--Clean clearing--Loss of top-soil--
Silt-trenches on slopes 1
CHAPTER II
FIELD MAINTENANCE
Clean weeding--Selective weeding--Loss of top-soil--Grass
ridges--Lallang eradication--_Mimosa gigantea_ (_M.
invisa_)--Green cover-plants--Connection between weeding,
soil conservation, and soil improvement 13
CHAPTER III
THINNING OF AREAS
Original planting per acre--Ultimate stand per acre--Close-
planting _versus_ wide-planting--When to commence
thinning operations--How to select in preliminary rounds--
Later selections based on yields of individuals--Yields per
tree, present and future--Trees per acre 19
CHAPTER IV
TAPPING SYSTEMS
Former methods--Former systems--Tendency to reduce number of
tapping cuts and frequency of tapping--Period allowed for
bark-renewal--Modern systems--Superimposed cuts--Single cuts,
etc.--Tapping experiments--R.G.A. experiment--Alternate-daily
_versus_ daily tapping 28
CHAPTER V
TAPPING AND COLLECTING
Tapping knives--Personal equation in use of knives--Choice of
latex cups--Cleaning of cups--Water in cups--Premature
(spontaneous) coagulation--Prevention of spontaneous
coagulation--The use of anti-coagulants in the field--
Collecting pails--Payment by result--Methods for calculation
of yields per coolie--Tree-scrap, oxidation of--Prevention of
oxidation--Bark-shavings--Collection and storage of shavings--
Treatment of shavings--Collection of earth-scrap 38
CHAPTER VI
TRANSPORT OF LATEX AND COAGULUM
Percentages of "first" latex and other grades--Early
collection of latex--Transport, nature of--Light railways--
Motor-lorries--Bullock-carts--Care of transport vessels--Use
of an anti-coagulant during transport--Transport by coolie--
Coagulation centres (stations)--Transport of coagulum 59
PART II
_FACTORY OPERATIONS_
CHAPTER VII
PRELIMINARY TREATMENT OF LATEX
Reception at store--Receptacles--Jars--Tanks--Necessity for
close supervision--Need for utmost cleanliness--Straining of
latex--Strainers--Facilitation of straining--Bulking of latex
--Standardised dilution of latex--Facilities for receiving and
handling latex--Reception verandahs--Receiving vessels--Types
of installations 65
CHAPTER VIII
COAGULATION
Choice of coagulant--Strength of acid solution--Making stock
solution--Quantity for use--Quantities under modern
requirements--Care in mixing--Method of mixing with latex--Use
of sodium bisulphite as an anti-oxidant--Quantities for use--
Formulae--Abuse of the chemical--Residual traces in the dry
rubber--Use of sodium sulphite as an anti-coagulant,
quantities for use--Formulae--Use of Formalin as anti-coagulant
--Formulae for use 74
CHAPTER IX
PREPARATION OF SHEET RUBBER
Pale (air-dried) sheets--Uniformity of product--Pans _versus_
tanks--The ideal tank--Modern installations--Care of tanks--
Standardised dilution of latex--Variation in dimensions and
density of coagulum--Standardising instruments--Method of
using--Skimming latex--Style of sheets--Standard sheets--
Rolling and marking--When to work the coagulum--Hand-rolling--
Power smooth-rolling--Marking rolls--Preparation for smoke-
curing--Caution against accumulation of wet sheets--Hot-water
treatment--Dripping in the open air--When to place in smoke-
house 89
CHAPTER X
PREPARATION OF CREPE RUBBER
First consideration, fine pale crepe--Standardised dilution of
latex--Coagulation and coagulant--Quantities of coagulant--
Colour of rubber--Sodium bisulphite (use of)--Evaluation and
deterioration of the bisulphite and sulphite of sodium--To
distinguish between these two chemicals--Care of sodium
bisulphite--Mixing solution with latex--Former methods of
making pale rubber--Working the coagulum--Lower grades of
crepe--Naturally coagulated lump--Skimmings and washings--
Tree-scrap--Bark-shavings--Earth-scrap--Fibrous matter in low-
grade rubbers--Scrap-washers--Compound crepes--Increased care
with lower grades--Block rubber from crepe--Smoked crepe
_versus_ sheet clippings 110
CHAPTER XI
DRYING OF RUBBER
Air-drying of crepes--Artificial driers for crepes--Vacuum
drying--Hot-air driers--Michie-Golledge system--Rate of air-
drying--When drying takes place--Increase in weight of drying
crepe--Differences in weight--Aids to normal drying--Smoke-
curing of sheet rubber--Instruments for recording temperature
--Temperatures of smoke-house--Period of drying--Fuels for
smoking--Sun-drying of sheet rubber--Artificial driers for
sheet rubber 132
CHAPTER XII
SORTING, GRADING, AND PACKING
Reducing number of grades--Reduction carried too far--R.G.A.
recommendations--Care in sorting--Choice of packing cases--
Bags--Bales--Folding of crepe--Mechanical folders--Care in
assembling--Methods of packing--Weight of contents--Short
weights 150
PART III
_MACHINERY AND BUILDINGS_
CHAPTER XIII
MACHINES
Quality of metal in rolls--Nature of roll-bearings--Brass
liners--Liners of alloy or of cast-iron--Adequacy of machines
--Arrangement of battery--Speed of machines--Gear ratios--
Grooving of rolls--Heating of rolls--Sheeting machines--
Lubrication--Trays--Position of battery--Drainage of battery--
Access to back of machines--Engines--Power 159
CHAPTER XIV
FACTORIES
General construction--Plenty of light--Floors--Drainage of--
How many storeys--Verandahs--Tanks, situation of--Designs and
lay-out--Drains--Water supply 172
CHAPTER XV
OTHER BUILDINGS
Drying-houses for crepe rubber--How many storeys--Ventilation
--Windows--Effect of light--Effect of direct sun-rays--Hot-air
houses--Smoke-houses--Various types--Ordinary smoke-houses--
General ventilation--Windows--Racks of supports--Floors--
Furnaces in general--Pit-fires--Pot-fires--Iron stoves--
Horizontal drum-furnaces--Rate of combustion--Brick stoves--
Pataling type of--Consumption of fuel--Floor of furnace room--
Roof--Brick built houses--"Third Mile" type--Jackson cabinet--
Devon type--Detailed description of--Barker patent design 178
CHAPTER XVI
OTHER BUILDINGS (_continued_), AND SITUATION OF BUILDINGS
Sorting-room--Packing room--Store rooms--Storage of rubber--
Need for special accommodation--Floor of store room--Local
conditions--Temperature and humidity--Incidence of moulds--
Effect upon smoked sheets--Tool-sheds and stores--Situation of
buildings--Position with respect to points of the compass--
Choosing a factory site--Centralisation--Decentralisation 211
PART IV
_THE FINISHED RUBBER_
CHAPTER XVII
DEFECTS IN CREPE RUBBERS
General style of finish--Dirty edges--Iron-stains--Rust-stains
--Oil-marks--Trays--Dirt--Holes--Greenish and tacky streaks--
Not due to oil _per se_--Tackiness and copper--Cotton and
other fibre--Bark and grit--Sand--Oxidation streaks--Yellow
streaks--Bisulphite streaks--Spot disease--Cause of--Influence
of rate of drying--Percentage of moisture--Humidity of
atmosphere--Prevention of disease--Infection by contact--
Outbreak of dormant spores--Rules to be observed--Surface
moulds or mildew--Tackiness in general--Full discussion of--
Experimental reproduction--Lack of uniformity in colour--
Defects in block rubber 223
CHAPTER XVIII
DEFECTS IN SHEET RUBBER
Defective coagulation--Coloured surface blotches--General
darkening of surface--Soft coagulum--Spongy underface--Tearing
--"Pitting" of surface--Thick ends or edges--Mis-shapen sheets
--Thick patches--Torn sheets--"Dog-ears"--Creases--Greasiness
of surface before smoking--Surface blemishes--Uneven
appearance--Variation due to oxidation--Colour when dry--
Surface gloss--Dull surface--Moist glaze and greasiness--
Virgin spots--Surface moulds or mildew--Black streaks or spots
--White or grey streaks--Rust--Theories on formation of--
Prevention of--Two methods--Other views on causation--Bubbles
--Causes of formation--In the field--In the factory--Blisters
--"Spot" disease in sheet rubber--Support marks--Stickiness--
Surface pattern--Sheet clippings--Other infrequent defects--
Dirt--Ash--Bark--Splinters 249
PART V
_GENERAL_
CHAPTER XIX
CHOICE OF COAGULANT
Acetic acid in general use--Is a coagulant necessary?--Acetic
acid--Formic acid--Citric acid--Tartaric acid--Oxalic acid--
Sulphuric acid--Hydrochloric and nitric acids--Hydrofluoric
acid--Alum--Pyroligneous acid--Smoked water--Chinese vinegar--
Sulphurous acid--Sugars--Various salts--Proprietary compounds
--Carbonic acid gas--Alcohol--Vegetable extracts 278
CHAPTER XX
SPECIAL METHODS OF PREPARATION
Da Costa process--Byrne curing process--Freezing process--
Wickham process--Derry process--Spontaneous coagulation--
Definition of--Discussion of types--AErobic--Anaerobic--
Organisms--Maude-Crosse patent--Method of operation--
Accelerating action of sugars--Accelerating action of soluble
calcium salts--Ilcken-Down process--Slab rubber 290
PART VI
_VULCANISATION_
CHAPTER XXI
INTRODUCTORY DEALING WITH TREATMENT AND VULCANISATION
Wild rubber contrasted with plantation rubber--Milling and
mixing--Preparation for vulcanising--Vulcanising 301
CHAPTER XXII
TESTING OF PLANTATION RUBBER
Tests on raw rubber--Breaking strain--Behaviour of rubber
during milling, etc.--Preparation for testing--Tests on
vulcanised rubber--Choice of a formula--Physical tests 309
CHAPTER XXIII
THE PROPERTIES OF RUBBER
Raw rubber--Physical tests--Vulcanised rubber--"Inner
qualities" of raw rubber--Defects of crepe and sheet--
Variation in physical properties--Rate of cure--Influence of
various factors in raw rubber on rate of cure--Other types of
plantation rubber--Fine para 313
INDEX 327
LIST OF ILLUSTRATIONS
PAGE
SEEDS, SHOWING VARIABLE SIZE, SHAPE, AND MARKING 2
FELLING LIGHT (SECONDARY) JUNGLE 3
SEEDLING, SHOWING ROOT-SYSTEM WITH SEED STILL ATTACHED 4
NEW CLEARING 5
TYPICAL YOUNG CLEARING, AGED ABOUT THREE YEARS, PLANTED ON
VIRGIN SOIL. ORIGINAL JUNGLE TIMBER SLOWLY ROTTING 6
LIGHT JUNGLE 7
DENSE JUNGLE 8
CLEARING READY FOR PLANTING 9
NEW CLEARING: SLOPES "HOLED" FOR PLANTING; FLAT AREA BEING
DRAINED 11
TYPICAL YOUNG CLEARING, WITH TIMBER 15
TYPICAL YOUNG CLEARING, WITH TIMBER 17
TYPICAL YOUNG PLANTED AREA 20
ANOTHER EXAMPLE OF A RECENTLY PLANTED AREA 21
WIDELY PLANTED YOUNG AREA, JUST READY TO BE BROUGHT INTO
TAPPING 24
FIELD OF OLD RUBBER TREES IN WHICH THINNING HAD BEEN DELAYED
TOO LONG 25
TWO CUTS ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE 31
THE SINGLE CUT ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE AND
ON RENEWED BARK 33
SINGLE CUT ON HALF CIRCUMFERENCE (HALF-SPIRAL) 35
A [V]-CUT ON HALF THE CIRCUMFERENCE 37
SINGLE CUT ON TWO-FIFTHS OF CIRCUMFERENCE 41
EFFECTS UPON RENEWED BARK OF PREVIOUS TAPPING 44
ANOTHER EXAMPLE SHOWING THE EFFECTS OF PREVIOUS TAPPING 45
1. SHOWING EFFECT OF "WINTERING" 48
2. NEW GROWTH OF YOUNG LEAF ON SAME TREE 49
EFFECTS OF DISEASE--"MOULDY ROT" 50
EFFECTS OF DISEASE--"MOULDY ROT" 51
EFFECTS OF DISEASE--"MOULDY ROT" 52
EFFECTS OF DISEASE--"MOULDY ROT" 53
RAISED VERANDAH FOR RECEPTION OF LATEX; LIKEWISE EQUIPPED WITH
FACILITIES FOR CALCULATING INDIVIDUAL DAILY "YIELD PER
COOLIE" BY SAMPLING OF LATEX 66
END-SECTION SKETCH OF VERANDAH, ETC., SHOWING A GOOD METHOD
FOR RECEIVING LATEX AND FILLING TANK 70
RAISED VERANDAH FOR RECEPTION AND HANDLING OF LATEX 71
ANOTHER SET OF DILUTION TANKS ON RAISED VERANDAH 72
TWO VIEWS OF DILUTION AND MIXING TANKS 81
UNIT MODERN COAGULATING TANK (TWO VIEWS) 91
ANOTHER BATTERY OF TANKS, WITH DILUTION TANKS, RAISED, ON THE
RIGHT 92
CLOSER VIEW OF FOREGOING 93
ANOTHER BATTERY OF TANKS, WITHOUT DILUTION TANKS OR MEANS OF
GRAVITATING LATEX 95
A SHEETING TANK CONTAINING COAGULUM FOR CREPE PREPARATION 96
A "BATTERY" OF SHEETING TANKS (PATALING ESTATE). DILUTION
TANKS, RAISED, ON THE LEFT 97
THE OLD METHOD OF "DRIPPING" FRESHLY ROLLED SHEETS WITHIN THE
FACTORY 108
THE NEWER METHOD OF HANGING IN THE OPEN AIR 109
THREE GRADES OF CREPE RUBBER 111
A WASHING SHED 112
DRYING GRAPH. PALE CREPE (THIN) 140
A SHIPMENT OF RUBBER, PACKED AND READY FOR TRANSPORT 155
ON ITS ROAD TO THE RAILWAY: BULLOCK-CART TRANSPORT 157
A BATTERY OF MACHINES 165
"THIRD MILE" TYPE; HORIZONTAL DRUM 190
"THIRD MILE" TYPE OF FURNACE, USED IN CONJUNCTION WITH "THIRD
MILE" SMOKE-HOUSE 190
SIDE SECTIONAL ELEVATION (PATALING TYPE OF FURNACE) 193
PATALING TYPE OF FURNACE 193
LARGE SMOKE-HOUSE OF ORDINARY CONSTRUCTION, WITH SHIELDED
VENTILATORS PERMANENTLY OPEN 194
BRICK AND CEMENT SUPERSTRUCTURE OF FURNACE INSIDE THE
BUILDING, BUT FED FROM OUTSIDE 195
GENERAL VIEW OF SHELTERS COVERING APPROACHES TO FURNACES 196
NEAR VIEW OF SHELTER 197
"THIRD MILE" TYPE OF SMOKE-HOUSE 199
GENERAL VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE 201
GENERAL VIEW OF DOUBLE "DEVON" SMOKE-HOUSE AND FACTORY
BUILDINGS 202
VIEW OF PLATFORM OF "DEVON" SMOKE-HOUSE; DOORS OF COMPARTMENTS
OPEN, AND ONE RACK PARTIALLY WITHDRAWN 203
DOUBLE "DEVON" SMOKE-HOUSE OF BRICK, WITH ROOF OF CHINESE
TILES, SHOWING LOADING PLATFORMS WITH RACKS WITHDRAWN FROM
SMOKING CHAMBERS 204
SIDE-VIEW OF PRECEDING PHOTOGRAPH, SHOWING EXTERNAL
ARRANGEMENT FOR STOKING FURNACES 205
FRONT VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE 206
SIDE-VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE 207
THE NEW "BARKER" TYPE OF SMOKE-HOUSE: A SMALL UNIT 210
SUGGESTED ARRANGEMENT OF BUILDING 218
THREE SPECIMENS OF FINE PALE CREPE SUFFERING FROM "SPOT"
DISEASE 237
THE PREPARATION OF PLANTATION RUBBER
PART I
FIELD OPERATIONS
CHAPTER I
_PLANTING_
To criticise the methods of the pioneer planters of _Hevea Brasiliensis_
presents no difficulty in the light of present comparative knowledge, and
to be "wise after the event" is a failing which is not confined to those
interested in modern planting methods. Looking at the matter broadly,
however, it must be acknowledged that the pioneers, wrong though they may
have been on some points, did remarkably well, considering that there
existed no real knowledge on the subject and that the methods employed were
perforce of an empirical nature. Although we know a little more concerning
the scientific aspects of rubber planting, the sum total of that knowledge
does not justify any drastic criticism of the methods employed by our
predecessors. In fact, although we may be of opinion that on general lines
there is little now to be learned regarding the planting of _Hevea
Brasiliensis_, our present knowledge does not preclude the possibility that
future investigations may bring against us charges similar to those
sometimes levelled at the earlier planters.
The main theme of the present volume is that of the preparation of rubber
for the market. Hence it is not proposed to deal in detail with the work
attaching to the opening and development of rubber estates. For this the
reader is referred to the literature dealing specifically with rubber
planting. Certain points in connection with planting may advantageously be
treated in a general way according to modern knowledge, and of these it is
proposed to discuss a few in the following pages.
[Illustration: SEEDS, SHOWING VARIABLE SIZE, SHAPE, AND MARKING.]
SEEDS.--The view is now generally held that many areas were planted from
seed which was not collected in a discriminate manner; and that probably
the comparatively low yields obtained on areas of some estates may be due
to the employment of seed from a poor strain. To be able to decide whether
such explanation fits the case demands a full knowledge of all the possible
factors governing the question of yields. It may, or may not, be a fact
that seed from a poor strain is wholly or partially accountable for low
yields; but whatever the degree in which the seed influences the result, it
is an axiom that to obtain the best results in all planting industries a
most judicious selection of seed should be made. In short, seed obtained
from good-yielding specimens by selective treatment will eventually produce
progeny of good-yielding strain.
[Illustration: FELLING LIGHT (SECONDARY) JUNGLE.]
The recognition of these principles as applied to the planting of _H.
Brasiliensis_ has focussed recent attention upon the desirability of
planting nurseries with seeds obtained from those trees which are known to
be good producers of latex of normal consistency. It does not follow that
the tree of most rapid growth and development is necessarily the best
yielder; such is often not the case. In the matter of selection, therefore,
one has to take other standards than that of size; and the issue is
narrowed chiefly to a consideration of the yields of latex given by
individual trees. It has been found by various experimenters that there is
no necessity to proceed to such a refinement as the determination of the
actual weight of rubber yielded. The dry rubber content of latices from the
same trees is found to be so comparatively regular, allowing for climatic
changes, that it is sufficient for the purposes of selection to measure the
volumes of latex yielded by individual trees.
[Illustration: SEEDLING, SHOWING ROOT-SYSTEM WITH SEED STILL ATTACHED.]
Unfortunately the industry is so young that the question of seed selection
yet awaits study. The task presents certain practical difficulties, and
would be by no means so easy to control as in the case of seed selection
from other plants. It will be obvious that several generations of trees
raised from selected seed would have to be under observation before any
sound deductions could be made from statistics obtained in the course of
the work. Thus the problem of seed-selection as it concerns the
establishment of a high-yielding strain would involve many years of
observation on the part of a trained man. Unfortunately neither the man nor
the facilities for such experimental work exist at the present moment in
the Federated Malay States. On the scientific side the industry is
incommensurably staffed, and most of the workers' time is occupied with
routine work connected with estate practice.
[Illustration: NEW CLEARING.
In the middle distance, felled trees awaiting burning; in the foreground, a
flat and wet area with main drainage outlined.
(_By courtesy of the manager of Membakut Estate, British North Borneo._)]
[Illustration: TYPICAL YOUNG CLEARING, AGED ABOUT THREE YEARS, PLANTED ON
VIRGIN SOIL. ORIGINAL JUNGLE TIMBER SLOWLY ROTTING.]
SELECTION.--It is possible, however, that the question of strain
improvement will be solved in another manner than that of successive
breeding from the seeds of high-yielding trees. Such investigatory work is
now occupying the attention of scientific organisations in the East, and
credit is due to the stations in Java which have begun experimental work in
this direction. In brief, the scheme may be outlined as follows. Trees
known to be uniformly good yielders are kept under observation, and the
seeds gathered carefully. These seeds are germinated in a special nursery,
and the best-grown seedlings are selected for further operations. At a
certain stage a bud is taken from a high-yielding parent tree and grafted
upon the stem of the seedling. When this has "struck" the original head of
the seedling is removed. This ensures that one has in the seedling both the
stem and future branch system of the same strain as the parent
high-yielding trees. It is possible to go a step farther, and by certain
processes induce a new root system to grow above the existing roots, which
are then removed. One is then able to guarantee that the roots, stem, and
branches will be of the original high-yielding strain. An objection
sometimes made against the third operation of inducing a new root system is
that the original tap-root is removed and that the subsequent system
consists only of laterals. Against this argument may be quoted the observed
fact that in actual development any one of the laterals may under such
circumstances function eventually as a tap-root.
[Illustration: LIGHT JUNGLE.]
On the whole, this system of propagation receives the approval of
investigators, and removes the objections which may be advanced against the
development of a scheme entirely founded upon successive breedings from
selected seed. The course of the investigations, also, are thereby
shortened considerably. Care must be exercised in the work of obtaining and
grafting the buds, but it has now been proved that by exercising reasonable
precautions which are not beyond the intelligence and ability of
subordinates, an extremely high percentage of success can be attained.
[Illustration: DENSE JUNGLE.]
Until such time as this process becomes practicable the inception of a
planted area must follow the lines usually adopted.
NURSERIES.--The usual practice is to obtain seeds from some estate which
has a reputation for good yields and for exercising care in the gathering
and shipping of seeds. The seed is planted in specially prepared beds, and
the percentage of germination noted for future reference. The plants should
be tended carefully, and close observation made for the detection of
disease or pests. It is not uncommon to find that owing to lack of care in
the preparation of the seed-bed, the young plants are attacked by disease.
[Illustration: CLEARING READY FOR PLANTING.
Surface timber removed, but stumps remaining.]
STUMPS.--At a stage, varying according to the requirements of the estate,
when the plants are from twelve to eighteen months old, they are lifted
from the earth. The roots and head are cut off, and the "stump" is ready
for immediate planting in the field. Naturally any appreciable delay in
planting, or unfavourable weather conditions, will militate against the
chances of successful "striking"; and it is not uncommon to find that a
certain number of "supplies" will be necessary.
SEED AT STAKE.--A method sometimes adopted is to put out seed in the field,
in prepared holes which indicate the exact position of the future trees.
Usually three seeds are placed in each hole, and if two or three germinate,
the plant having the healthiest appearance is retained, and the others
removed. The possible objections to this method of planting are obvious to
those acquainted with field conditions, but in actual practice planting
seed "at stake" has often proved highly successful. Naturally the results
obtained must depend upon the selection of good seeds, the care exercised
in the preparation of the "holes," weather conditions, and the
discrimination exercised in the selection of the plants to be
retained--apart from such disabilities as the depredations of rats and
other pests.
BASKET PLANTS.--Yet another and perhaps the most popular method at present
is the germination and growth of seedlings in baskets specially constructed
for the purpose. These plants are kept under observation until of the
required age and growth. They are then conveyed to the field, and the
baskets are planted in prepared holes. The baskets, being of vegetable
material, are liable to be attacked by various diseases while in the
nursery or after planting. It is considered advisable, therefore, to treat
them by dipping into some disinfectant such as tar, or a mixture of tar and
one of the common proprietary disinfectants. Otherwise a disease may be
conveyed from the basket to the seedling.
PREPARATION FOR PLANTING.--There can be no other opinion than that ideally
all land required for planting should be perfectly clear of timber of every
description. After felling and burning, under ordinary conditions a certain
amount of clearing is effected, but in actual practice this amounts to
comparatively little. Big logs and stumps are left because the cost of
clean clearing is judged to be prohibitive and non-economic. Surface timber
is gradually cleared in the course of development, and usually large stumps
are the last to be tackled. The objection to this procedure is really not
strong, but unfortunately an important point is generally overlooked.
Granted that most of the dreaded diseases travel beneath the surface of the
ground by means of buried timber, it is plain that as far as stumps are
concerned, the chief source of danger lies in the existence of the roots.
If these were carefully exposed and removed, the isolated stumps would then
not be such potential infection points. It follows from this argument that
the importance of removing buried timber cannot be too strongly insisted
upon. It is not uncommon to find that some years after the opening of an
estate, and after surface timber has been removed, a large number of trees
are affected with _Fomes lignosus_ (formerly known as _Fomes semitostus_).
Such cases are directly attributable to the existence of buried timber, and
no local treatment will be successful unless the whole of the area is dug
over carefully, and all pieces of timber removed.
[Illustration: NEW CLEARING; SLOPES "HOLED" FOR PLANTING; FLAT AREA BEING
DRAINED.
(_By courtesy of manager, Membakut Estate, British North Borneo._)]
SILT CATCHMENT TRENCHES.--Granted the ultimate necessity of clean clearing,
it becomes necessary to take some precautions to prevent loss of soil by
"wash" in young areas planted on sloping land. An argument often used in
extenuation of the practice of allowing large surface timber to remain
until it becomes rotten is that it is an aid in preventing loss of soil by
wash. Its removal necessitates the institution of some method of preventing
"wash." The establishment of terraces on steep slopes tends to the
achievement of the desired result, but this method is not extended to more
moderate slopes where loss by wash is still considerable. It is the opinion
of the writers and others that the general case calls for the institution
of silt catchment trenches, which, as the name denotes, fulfil the duty of
catching any surface soil and of retaining rainwater. These trenches are
usually laid out on contour, and do not exceed a length of 20 feet. They
are usually from 18 inches to 2 feet wide and deep, and are so arranged on
the slope that they occupy overlapping positions. The actual number of
trenches required will depend upon the angle of slope; the steeper the
slope the greater the number required--_i.e._, the shorter will be the
length of slope between any two trenches. Given a clean area, it is obvious
that the momentum acquired by running water (and hence the amount of soil
removed) on any one slope will depend upon the distance travelled. It is
advisable, therefore, to place a larger proportion of the trenches on the
upper part of the slope than on the lower, so as to guard against the
breaking down of the trench system under an abnormal downpour of rain.
On land thus prepared the writer has seen areas successfully planted,
which, under ordinary conditions, were condemned as being too steep for
planting. It is true that these trenches necessitate continual upkeep until
the soil becomes well shaded by trees, but the actual amount of work
demanded in cleaning and maintaining the trenches will depend largely upon
the thoroughness with which the original work was planned and executed.
Whatever may be the weaknesses exposed as a result of providing an
insufficient number of trenches of inadequate dimensions, there can be no
question that they are a necessity.
CHAPTER II
_FIELD MAINTENANCE_
CLEAN WEEDING.--Intimately connected with the growth and development of the
rubber tree one has to consider the conditions under which it is allowed to
mature. The argument has been used that, since the habitat of _Hevea
Brasiliensis_ is in the jungle, we should be proceeding against nature by
introducing conditions unlike those under which the "wild" rubber tree
grows. It is difficult to treat such an argument seriously, as by quoting
parallel instances in arboriculture it could be shown that growth,
development, and yields are improved by cultivation of "wild" plants.
It needs small experience with rubber-tree plantations to be convinced of
the necessity for dealing with other growths, which would otherwise soon
surround and overshadow young rubber trees.
Apart from checking and preventing woody undergrowths it is considered
advisable to keep the ground more or less free from light vegetable
growths, which are roughly grouped under the heading of "weeds."
Naturally, if these weeds are allowed to flourish and seed, their eventual
eradication may be a matter of extreme difficulty and expense. It is the
aim, therefore, of properly conducted estates generally to institute such a
system of work that the weeding-gangs cover the whole estate at regular
intervals; and, as a general rule, it may be accepted that the shorter the
interval between successive visits by the gang to any particular area, the
easier it is to keep weeds in check, and the cheaper the work will
eventually be done. This procedure defines roughly what is implied by the
term "clean weeding," and it is the policy adopted by most estates.
Strict adherence to this practice in rubber cultivation has been inculcated
by the older school of planters who obtained their experience in the
cultivation of other crops such as tea, coffee, tobacco, etc.
In latter years the wisdom of scrupulous clean weeding under all conditions
has been questioned; and there can be no doubt that under certain special
conditions a continuation of the policy of clean weeding is calculated to
produce, in course of time, more harm than benefit. As an instance, the
case might be cited of steep slopes on poor land. Continual clean weeding
on such areas will lead eventually to a great loss of the surface soil,
unless some precautions are adopted for catching and retaining the fine
silt particles. It is to be noted that such a type of soil and slope, when
the shade is appreciable, often produces no weeds heavier in growth than a
very light grass. It is urged that the necessity for strict clean weeding
on such soils does not exist, and, in fact, that it would be an injurious
policy. Such arguments appear to be well founded in experience, and the
writers are in thorough agreement that such special cases deserve special
consideration. Rigid adherence to a policy of clean weeding, without regard
to special conditions, would be most inadvisable.
Nevertheless, such exceptional cases do not detract from the wisdom of
clean weeding in general. Every planter of experience realises how easily
fields become infested with weeds if the regular work is suspended or
delayed. It is probably quite true that the harm due to the presence of
some weeds on an occasion is negligible; but apart from this debatable
point, there is the solid fact that if once an area is allowed to become
weedy it may soon demand a much greater expenditure to bring it back to
normal condition than if it had been regularly weeded. This is common
experience, and for that reason alone a general policy of clean weeding is
thoroughly sound; especially if combined with some system of
silt-retention.
GRASS SQUARES.--On some estates the practice of clean weeding is undertaken
in combination with a system of silt-retention, which depends upon the
development and maintenance of ridges. These are built up from the debris
of weeding in the form of hollow squares. Grass is allowed to sprout and
grow in these ridges, and when it attains a certain height it is trimmed
down so as to keep it within bounds. The soil within the hollow square is
clean weeded; and it is maintained that loss of soil by wash is avoided.
Under certain conditions there is a great deal to be said in favour of the
method, but in the opinion of the writers it should be regarded only as a
method of expediency. It is not to be preferred to the more thorough
practice of soil-retention by means of silt-trenches, although the latter
method may be slightly more expensive in the end.
[Illustration: TYPICAL YOUNG CLEARING, WITH TIMBER.
Planted "rubber-stump" in foreground.]
"LALLANG" ERADICATION.--The greatest bugbear of the planter in connection
with weeding is the incidence of lallang. Many proposals have been put
forward at various times for the complete eradication of this pest; but at
present, under ordinary circumstances, there would seem to be no better
method than by heavy and deep digging, followed by regular attention. The
method is acknowledged to be expensive, but any half-hearted measure
otherwise taken will eventually prove to be even more costly.
One has to differentiate, of course, between the incidence of lallang
attributable to negligence on the estate itself, and the occasional
outbreaks near boundaries, due to seeds having been wind-borne from patches
of lallang outside the boundaries But, in general, it would be safe to
remark that the appearance of lallang could be taken as evidence of a
failure to cover the area at sufficiently short intervals.
As already intimated, the usual method of eradication of areas of lallang
is by thorough digging, and the exposure of the strong root system to the
sun. As a matter of interest it may be noted that recently some success has
been obtained by another method[1] on areas which one may have in view for
planting at some future date.
[1] "Eradication of Lallang," W. P. Handover, _The Planter_, Vol. I., No.
1, August, 1920.
It consists in the employment of _Mimosa gigantea_, which eventually
smothers the growth of lallang.
The seeds are sown broadcast, in drills, or in pockets, amongst the
lallang. In the course of about three months it overtops the grass and
proceeds to travel. At this stage the whole mass is pressed down, and the
pressing is repeated at regular intervals. Under favourable conditions, in
about twelve months, an impenetrable mat has been formed, which gradually
forms a good mulch. When it is desired to remove the Mimosa, the mass
(pressed down) is cut and rolled up like a carpet. Cleared in this manner,
the area then needs regular weeding, in order to check the development of
any stray lallang shoots. In actual practice it was found that the cost of
this method was approximately two-thirds that of the usual digging method.
GREEN COVER PLANTS.--Some years ago it was quite common to find green
cover-plants employed on estates with the primary idea of minimising
weeding costs. With most of these it was found later that their value was
not real, and that they harboured diseases, and pests. Moreover, when they
were removed, it was often found that an abundant crop of lallang and
weeds resulted.
There can be no question that certain plants can be employed with
advantage, not only in the control of weeds, but also by reason of benefit
to the soil in which they are established. These plants are leguminous, and
their use is restricted almost entirely to young areas, inasmuch as they
will not continue to grow when shade becomes marked. Of those best known in
modern practice might be mentioned _Tephrosia candida_ (Boga bean),
_Centrosema Plumerii_, and _Dolichos Hoseii_ (Sarawak bean).
[Illustration: TYPICAL YOUNG CLEARING, WITH TIMBER.
Young rubber plants in foreground. Two of these are easily distinguishable,
both with small crowns of leaves.]
It is wrong to imagine, however, that the establishment of such leguminous
cover-plants obviates weeding. So far is this from being the case, that in
practice it is found that the weeding "rounds" must be conducted at first
with the same regularity as in ordinary working, but that naturally there
is much less work to be done.
As the plants develop, they can be pruned or dug into the soil, as the case
may be. The addition of the green material to the soil, either by digging
or by burying in open trenches, is calculated to cause improvement in the
condition of the soil. There may thus be a close connection between
weeding, soil conservation, and soil improvement.
CHAPTER III
_THINNING OF AREAS_
On this subject there is unanimity regarding the necessity for the
operation. Divergence of opinion exists only as to a matter of degree.
On the one hand there is the school of planters who would advocate the
advisability of planting up to, say, 200 trees per acre, with subsequent
thinning out by selection. At the other extreme there is the opinion that
we should plant only a few more trees per acre than it is intended
eventually to maintain, the argument being that by this method the growth
and development of individual trees will be so much greater than in close
planting that the necessity for drastic thinning out will not arise.
Unfortunately for the latter school, a very important point is
overlooked--viz., that size and general development are not criteria of
yielding capacity. It might thus follow that a stand of ninety well-grown
trees per acre might give very disappointing yields per acre. In a few
instances this has been noted with 30 by 30 feet planting, but it is
doubtful whether the factor influencing such results has been appreciated.
The apostles of close-planting have this in their favour: that if the trees
to be removed are selected on proper lines, it is possible to have all
remaining trees of comparatively high-yielding strain. This is a very sound
argument, but its practicability is limited very largely by the question of
early growth and development. It would seem the sane course in any event
not to plant more trees per acre than may grow normally, and without branch
or root interference up to the fifth year (the normal first year of
tapping).
Before this stage has been reached, stunted or deformed trees will have
been noted and removed, so that in the first year of tapping thinning
proper can be commenced. In the past this has been effected wholly by
selection of trees according to their general appearance and situation; but
it is now safe to predict that future operations will be based upon sounder
and more scientific lines.
Trees will be selected for removal according to their individual yields, a
standard which we have been advocating for years without much practical
success. In Java and Sumatra much good work has been done in this
direction, and recently a commencement has been made in the F.M.S.
[Illustration: TYPICAL YOUNG PLANTED AREA.
Heavy original jungle timber.]
It is within the daily observation of all planters that certain trees
regularly give greater yields than others, and that such trees are not to
be distinguished by size or general development. Moreover, with slight
variations, it has been found that a good yielding tree is consistently a
good yielder, and the converse holds true.
If, therefore, measurements of individual yields are taken at intervals,
and the results recorded during the first year of tapping of an area, an
excellent guide is obtained for the first round of thinning. It is found
in actual practice that five, or even three, readings during the year are
sufficient to give the indication required. It is not essential that
simultaneous readings should be taken over a large area; in fact, such a
step is really impracticable at first. The simplest method is to employ
either--
(_a_) A small uniform vessel in which the latex is measured by means of a
thin slip of bamboo upon which graduations are marked.
(_b_) A glass measure graduated regularly.
[Illustration: ANOTHER EXAMPLE OF A RECENTLY PLANTED AREA.]
In both cases it is immaterial what units are represented by the
graduations--whether cubic centimetres, quarter ounces, half-ounces, or
ounces, as long as the unit is not too large. It is preferable to employ a
fairly small unit, so that in taking readings from young trees a wider
range may be obtained between poor yields and good yields. In the case of
older trees a larger unit may be taken.
The first stage in the operations is to number all trees in the field to
be tested, and to prepare a rough register, with three or five vacant
columns opposite each tree number.
It is not advisable to commence the record of yields until the panel of
bark has been under tapping for a month or two. It is found that an
intelligent coolie can be taught the method of measuring and rough
recording. The latter is accomplished by means of marks made upon the
virgin bark of the tree above the tapped area. The marks may be made with a
tapping knife, by means of paint, or with a lead pencil. The simplest form
of record consists in putting one mark for each graduation of reading.
In practice it is found that, commencing about an hour after the first tree
has been tapped (in the case of young trees) and following the course taken
by the tapper, the measurer of yields is able to do about 2 full tasks (650
to 750 trees) per diem. Each day progress is made through the field.
Obviously on such a small scale and utilising only one measuring coolie the
comparison is restricted very much; but in any case this is immaterial as,
owing to the personal equation of the tapper, comparison strictly should be
limited and internal--_i.e._, it should really be confined to one task only
at a time. In this way the worst trees in any task are indicated.
The keeping of the records may be entrusted to a field clerk, but is better
placed in the hands of a European. The register is taken into the field and
the rough records found on the trees are noted in the columns against the
tree number.
Most planters are aware in a general way of the disparity between the
yields of individual trees, but they would probably be surprised if they
undertook the institution of such records.
The following figures must not be taken as typical. They represent the
average results from several tasks in a young field from which all
ill-grown and deformed trees had been removed. It is immaterial what the
units represent, as they are purely arbitrary and were selected for the
purpose of obtaining a fairly wide range.
Any trees which failed to yield sufficient latex to reach the first mark
were registered at zero. The following percentages were obtained:
Zero 3 per cent.
Above mark 1 6 "
" " 2 16 "
" " 3 42 "
" " 4 12 "
" " 5 14 "
" " 6 6 "
" " 7 0 "
" " 8 1 "
" " 9 0 "
---
100 "
It may be remarked that, judging by ordinary standards, it was impossible
to discriminate between good yielders and others, and if thinning were to
be done on the usual lines it is quite possible that some of the best
yielding trees would be removed.
Taking the mark No. 5 as the datum line, it will be noted that 79 per cent.
of the trees come below and 21 per cent. above. In the latter proportion
the majority lie close to the datum line. It will be seen that there are
outstanding yielders even amongst these young trees, and that it would be
possible to mark about 10 per cent. of the stand per acre at once for
removal in the first round of thinning.
In the case of old trees it is possible that one would encounter greater
extremes of yields than those shown in the foregoing table, especially if a
certain amount of thinning had been done previously on empirical lines.
Sufficient has been written to show that the only reasonable basis for
selection of trees in thinning is that of yields; and it is obvious that if
the method be adopted the future yield per acre of any area is bound to be
in excess of the same area as thinned on rule-of-thumb lines.
YIELDS PER TREE.--A great feature is made in estate reports of the figure
showing the average yield per tree per annum. Assuming an area to be
yielding at the average high rate of 540 lbs. per acre per annum, with an
average stand of ninety trees per acre, the yield per tree per annum
averaged over all trees is 6 lbs. Keeping in mind the test-figures on a
previous page, it will be obvious that some of these trees may have given
very much more than 6 lbs. during the year, and some less. In view of
present information it would not be surprising to find that a few might
have been yielding upwards of 15 lbs. per annum. Unfortunately this
information is only to be obtained by individual tests, and under normal
estate conditions the facts escape notice. Cases are known in which
out-standing individual trees have been known to yield at the rate of 25
lbs. and more per annum.
[Illustration: WIDELY PLANTED YOUNG AREA, JUST READY TO BE BROUGHT INTO
TAPPING.]
[Illustration: FIELD OF OLD RUBBER TREES IN WHICH THINNING HAD BEEN DELAYED
TOO LONG.
Note height and comparative lack of girth.]
FUTURE YIELDS PER TREE.--It has been shown that by selective methods based
on yields, poor trees can be eliminated. Whether by a process of
seed-selection or by means of propagation based on bud-grafting and
marcotting, it needs no great stretch of imagination to forecast future
conditions under which trees may be bred which will be capable eventually
of giving an average yield of 25 lbs. per annum over any given area.
Yields of 1,000 lbs. per acre per annum should be obtained easily.
TREES PER ACRE.--This brings us to the question as to how many trees one
should leave to the acre after thinning operations. Figures have been given
by various authorities, but it appears to the writer at the present time to
be impossible to lay down a general rule. So much depends upon conditions.
In certain cases where the soil is admittedly poor, the average growth
below normal, and thinning has been postponed too long, the writer has been
forced to the conclusion that it would be most inadvisable, and
commercially unsound, to reduce the stand of trees below 120 per acre. In
such instances the average yield per tree equalled only 3 lbs. per annum,
and although the trees were upwards of nine or ten years old the crowns
were small and sparse. It is doubtful whether such trees will ever exhibit
any further development, and to thin them further would probably lead only
to a diminution in the crop per acre.
Under normal conditions of growth an arbitrary figure of eighty trees per
acre has been selected as a standard by many estates. In these cases it
would probably be correct to state that thinning was undertaken on almost
purely empirical lines--_i.e._, that trees were not selected by tests of
individual yields. As far as such a method retained the apparently most
vigorous trees it was successful; but in view of what has been written it
might explain some of the disappointing results which have followed upon
such a system of thinning.
It will be clear that any decision regarding the number of trees to be
retained must be derived from a study of the detailed results of individual
tests. If the large majority of the trees appear to be fairly uniform in
yields the first thinning must be confined to comparatively few trees.
Where there is, on the other hand, a good percentage of high-yielding trees
the final stand per acre may be appreciably less. Unless and until such
information is available, one cannot give any definite opinion as to the
requisite number of trees to be retained per acre.
Similarly, intelligence must be displayed in deciding which of several
uniformly-yielding trees should be removed. In the average sense of this
consideration one must pay no attention to symmetry of spacing, but when
dealing with trees of fairly uniform yields one needs to study the
characteristic development of the trees individually, in order to retain
those which would appear to be most favourably situated with regard to
surrounding trees.
CHAPTER IV
_TAPPING SYSTEMS_
Broadly there are only two methods employed in obtaining the latex from
_Hevea Brasiliensis_. The first is that employed in South America, where
incisions are made by means of a light axe. The other is the system of
excision, or paring, of the bark practised on plantations in the East.
In the early days of the plantation industry, the South American method
seems to have been employed, and the writer has knowledge of trees on one
of our best-known estates in Malaya which still exhibit the outward and
visible signs of that method. At a comparatively early stage, however, the
method of excision was introduced. Curiously enough there appears to be no
record of its inception or of the individual who was responsible for the
substitution of this method. We have been so accustomed to regard it as one
of the ordinary facts of estate procedure, that this point seems to have
escaped notice and enquiry.
As a variant of these two main methods, a slight vogue was for a short
while obtained by the operation known as "pricking." This was generally
combined with excision of bark, and was then known as the "paring and
pricking" method; but the simple operation of pricking alone had its
adherents, and various forms of instruments were designed to achieve the
object. As a means for obtaining a flow of latex, pricking may have been
effective, but the general difficulties attaching to the collection of the
latex was such as to put the method out of favour.
In the employment of "paring and pricking," a thin shaving of bark was
excised on one occasion. At the next tapping no bark was excised, but a
pricking instrument was used along the previously cut surface. It was not
proved that any advantage was gained by this method, which was more
commonly employed in Ceylon than elsewhere, and it would be surprising to
find it in use at the present day.
In the ordinary way the method of excision is practised in such a manner
that the "cut" gradually descends to the base of the tree.
Planters with original views, and of an enquiring nature, often query the
common practice; and it has been suggested that "as the latex descends by
the force of gravity," one's paring should be done in an upward direction,
thus obtaining a greater pressure of latex--and hence a greater flow. It
will be obvious that it would be no simple matter to collect effectively
the latex thus obtained from the under edge of a sloping cut, but apart
from this the argument would appear to be founded upon what is now accepted
to be a fallacy--viz., that the latex _per se_ is manufactured in the
leaves and gravitates down the tree.
FORMER SYSTEMS OF TAPPING.--To hark back ten years in the plantation rubber
industry is equivalent to delving into history, since development has been
so rapid. It was then thought necessary to place upon the trees a number of
simultaneous cuts which the modern planter would judge to be inconceivably
excessive. Were it not for evidence in the shape of photographs extant, it
would be difficult to convince a young planter that such systems were
employed.
It was not uncommon for trees to have from six to ten cuts, sometimes all
placed on one half of the tree in a herring-bone fashion, and sometimes
divided into two portions, each of which tapped the opposite quarter panel
of the tree's circumference. Such superimposed cuts were spaced from 1 foot
to 18 inches apart.
On other occasions, a spiral cut was employed, commencing at a height of,
say, 5 feet, and gradually descending to the cup at the base of the tree.
Later systems varied from several cuts on a half-circumference, or on a
quarter of the tree, tapped either daily, or on alternate days, to cases in
which one-third or one-fifth of the tree was employed. Also popular were
the systems of the [V] and half-spiral cuts on half the circumference.
It did not take long to be recognised that with all these systems demanding
a number of simultaneous parings from the same panel of bark, the rate of
excision was so heavy that the period available for the renewal of bark was
insufficient for continuous tapping.
As a result most of the systems specified have fallen into desuetude, and
the tendency has since been to reduce the number of cuts, or the
periodicity of tapping, so as to allow for increasing periods of bark
renewal.
In the earlier days, a period of four years was thought to be an extremely
generous allowance, whereas six years is now becoming recognised as a
minimum necessity. Eight years is not regarded as extravagant, while with
older bark on some estates periods of ten and twelve years have to be
allowed for full renewal. Even so no finality has been reached, and no
general rule can be laid down. Local conditions of planting and growth
exercise great influence, and the writers have in mind instances in which a
period of eight years has proved to be insufficient even for a first
renewal after the excision of virgin bark.
In the main the most popular systems of tapping are:
(_a_) One cut on a quarter of the tree, tapped daily.
(_b_) One cut on a third of the tree, tapped daily.
(_c_) One cut on half the circumference, tapped on alternate days.
(_d_) A [V] cut on half the circumference, tapped on alternate days.
Variants and extremes are:
(1) One cut on a quarter, tapped on alternate days.
(2) One cut on a half, tapped daily.
Superficially viewed the latter is four times as strenuous as the former,
and the relative position seems to be inexplicable. It may be explained
that as a rule the former system is practised on old trees with poorly
renewed bark, in order to allow for adequate bark renewal; and the latter
is employed in opening young trees just brought into tapping, when the rate
of bark renewal is at a maximum.
[Illustration: TWO CUTS ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE.]
A few estates in this country still continue to tap trees by means of two
superimposed cuts on a quarter of the tree. This was a very popular system
some four or five years ago, but it has come to be recognised by practical
experience that any system employing superimposed cuts leads to a high
consumption of bark without proportionate increase in yield. For instance,
if one compares the system of two cuts on a quarter tapped daily with a
similar system employing only one cut, one finds that the major quantity of
latex is yielded by the lower cut, and that the single-cut system which
excises approximately half the amount of bark gives about 80 per cent. of
the yield obtained by the tapping of two superimposed cuts.
Of experiments to test the relative values of different systems of tapping
there have been many. Most of them suffered from the initial handicap that
they dealt with systems which were then popular. In order to obtain any
valid result they had to be undertaken over a long period. Meantime there
was a progressive movement in actual estate practice towards a greater
conservatism in bark removal, and hence the experiments as originally
planned lost value.
Moreover, in Malaya it was difficult for experimenters to obtain practical
support in the form of areas of trees suitable for experiment. As a result
experiments were often confined to small blocks of trees, and a small
number of blocks, from which any conclusions derived were subject to
considerable errors of experiment. Often comparisons were made between only
two blocks, and no allowance was made for varying factors, such as initial
differences in yielding capacities of the trees, soil conditions, or the
personal equation of the tappers. As a general rule, therefore, the results
were vitiated to a very appreciable extent.
All these factors were later taken into consideration in an experiment
undertaken on behalf of the Rubber Growers' Association. In this instance
unique facilities were provided by the London Asiatic Rubber Company on
their property at Semenyih Estate, and it is only fitting that the company
should receive the recognition which its enterprise deserves.
It would have been a great advantage to have included in that experiment
other features which have since come into prominence, but the original
scope of the experiment had to be confined to the point of comparing yields
obtained in making comparative tests based on one system of tapping with
different frequencies. Such data were required as a check upon a Ceylon
tapping experiment which had attracted much attention. In that experiment
trees were tapped at intervals ranging from one day to seven days; and it
was concluded that after a period of three and a half years trees tapped
with greater intervals gave yields equalling or exceeding those obtained
from trees tapped with shorter intervals.
[Illustration: THE SINGLE CUT ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE
AND ON RENEWED BARK.]
In the Semenyih experiment the system chosen was that which had the
greatest contemporary vogue--viz., two superimposed cuts on a quarter of
the tree. The various blocks were tapped respectively every day, every
second day, and every third day.
It was found that the conclusions drawn from the Ceylon experiment were not
confirmed. After a period of three and a half years' continuous tapping
neither the alternate-day system nor the third-day system gave results in
any way approximating to the yield of the daily system.
The actual average yields from these systems over the whole period were in
the order of--
_Daily._ _Two Days._ _Three Days._
100 per cent. 60 per cent. 45 per cent.;
and throughout the course of the experiment neither of the other sections
showed any appreciable improvement in position relative to the daily
section.
In actual yields "per tapping" over the whole period the alternate-day and
the third-day divisions showed advantages of 20 and 35 per cent.
respectively over the daily portion.
At the beginning of the second year of experiment another section of blocks
was opened with a single cut on a quarter, tapped daily. This enabled
direct comparison between the values of one cut and two cuts on a quarter
in daily tappings and between a daily single cut and two cuts tapped
alternate daily.
It appeared that the daily single cut yielded over the period of experiment
80 per cent. of that obtained by tapping two cuts daily; and that in the
comparison between two cuts tapped alternate-daily and a single cut tapped
daily the latter had an advantage of about 40 per cent. in yield.
This result has been used by advocates of daily tapping generally, but it
does not constitute a fair argument, inasmuch as the single cut was tapped
twice as often, and its position was always relatively low on the hole of
the tree. It has been shown in the comparison between the daily single cut
and the two cuts daily that the influence on yields of the superimposed cut
is relatively small. A fairer comparison would have been obtained if the
two cuts tapped alternate-daily had been either amalgamated to form one
long cut on half the tree or to form a [V] on half the tree, thus placing
the cuts in the opposing sections on the same level. With the knowledge
that the yield obtained from cuts is _always greater per tapping_ by using
the alternate-daily system, it would appear to be plain that the one long
cut on half the tree would at least equal the yield of the single short cut
tapped daily on a quarter tree.
[Illustration: SINGLE CUT ON HALF CIRCUMFERENCE (HALF SPIRAL).
_Note._--In this particular instance the cut is changed to the opposite
half of the tree every half-year.]
Unfortunately no opportunity has been afforded up to the present of
definitely proving this point by prolonged experiment under strict
conditions. It is true that the view is held strongly in some quarters as a
result of the experience of managers, chiefly on their own estates, that
alternate-daily tapping generally gives better yields than daily tapping.
In a number of instances this view is probably correct, and the writers are
in agreement; but it is necessary to clear away some misconceptions which
confuse the issue. In the main there are two schools, one of which plumps
for alternate-daily tapping, while the other adheres strongly to daily
excision. Great confusion exists, inasmuch as in many instances the
disciples of these schools are really discussing different matters. In the
case of managers who argue for alternate-daily tapping their experience is
gained, with very few exceptions, from systems in which the excision covers
half the circumference of the tree; whereas in almost all cases daily
tapping is confined to a single cut on a quarter of the girth. Bearing on
such a comparison there are, as far as the writers are aware, no reliable
published experimental results. To compare the results obtained from one
system practised on one estate with the results of the other system
established on another estate is not strictly permissible, as we know that
conditions generally may vary to an enormous degree.
The controversy has raged, however, to such an extent that many who are not
directly engaged in estate practice have obtained confused impressions. For
instance, it appears to be the belief in some quarters that alternate-daily
tapping, when applied to a single cut on a quarter of the tree, will yield
more than an exactly similar cut tapped daily. In support of such a
statement there does not appear to be any confirmation under normal
conditions; although such a result might be obtained in the case of old
trees which have been heavily over-tapped in the past, and on which the
rate of bark renewal has been appreciably retarded. It might also be the
case eventually when trees with the opposing frequencies have been tapped
for a period extending into many years; but it is the opinion of the
writers that under normal conditions such a result would be extremely
doubtful.
When we come, however, to a comparison of daily tapping on a single cut on
a quarter with double the length of that cut on half the circumference, at
the same height, tapped alternate-daily--whether in the form of one long
cut or in the form of a [V]--we arrive at a contrast which gives a clear
issue. As already stated, facts and figures of reliable experiment are
wanting; but it is the opinion and experience of the writers that the
alternate-daily system at least suffers no disadvantage on the point of
yields, and in other respects, such as conservation of labour and costs, is
superior to the daily system.
[Illustration: A [V]-CUT ON HALF THE CIRCUMFERENCE.]
CHAPTER V
_TAPPING AND COLLECTING_
TAPPING KNIVES.--The choice of a tapping knife is a subject upon which
there is much divergence of opinion. This must be so because no known knife
has such apparent outstanding superior features or claims as would enable
one to settle the point. Moreover, the personal factor is so large that, as
far as the knives in common use are concerned, it appears to exert the
greatest influence. The possibility of obtaining the ideal knife, which
will go to sufficient depth into barks of varying thickness to yield the
maximum quantity of latex without wounding, is quite as remote at the
present time as it was some years ago. Meanwhile the search for that ideal
knife continues, and occasionally one learns of the alleged merits of some
new instrument which, it is said, fulfils all requirements. It is only to
be regretted, both for the sake of the inventor and for the expectant
buyers, that the claims always fail in some one or more particulars.
In Malaya probably the number of different types of tapping knives may
amount to a half-dozen, but those most commonly in use are:
(1) The gouge--straight or bent.
(2) The ordinary farrier's knife.
(3) Modifications of the farrier's knife, such as the "Jebong."
Argument on the respective merits of knives is popular, and discussion
seems endless. It is claimed for the bent gouge that it is superior to the
straight instrument, because, the leverage being downwards on the handle,
the tendency is to lift the cutting edge upwards and out of the bark,
whereas with a straight gouge the tendency is to push the knife downwards
into the bark. It is claimed, therefore, that the average shavings taken
off by the bent gouge should be thinner than those obtained by the use of
the straight instrument.
For similar reasons it is asserted that the "Jebong" and other
modifications are superior to the original form of the farrier's knife.
These points are generally accepted without great argument, but when
comparisons are made between the gouge and the farrier's knife (with its
modifications) the opinions of planters are so varied and conflicting as to
be almost irreconcilable. Two opinions based on experience with both types
of knives are often wholly contradictory.
There can be no doubt that the likes and dislikes of operative coolies have
a considerable influence in determining the measure of success obtained
with any one knife. Should coolies have been accustomed to the use of a
particular form of instrument they become quite expert, and any proposed
change creates in the minds of coolies a prejudice which is considerable in
effect on the quality of the handicraft. Such prejudice may be overcome in
course of time, but in the interval not a little damage may have been done
in the shape of tapping wounds. So considerable is this question of
personal favour that even on estates where a standard pattern of knife is
issued coolies often modify that knife slightly on their own accord. Such
alteration is ignored by the superintendents as long as the quality of the
tapper's work is maintained at a high standard.
Naturally there is a limit to such leniency, and this limit is soon reached
in the case of knives having adjustable parts controlled by screws, or nuts
and bolts, etc. Some knives of this description really merit a much wider
use than is afforded them at present; but in view of the potential damage
which might be done as a result of adjustments made by the coolies these
knives do not become popular.
It is not proposed here to enter into a description of even recent
instruments for which strong claims are being made by their inventors or
vendors. If they possess the merits attributed to them they will soon find
favour, as managers are always keen on studying the points of any new knife
which will lead to a conservation of bark and a reduction in the number of
wounds. On the whole, it may be advanced that the best general results are
obtained by the adoption of a simple non-adjustable knife and the retention
of its use.
THE CHOICE OF LATEX CUPS.--It has come to be recognised that the maximum
possible cleanliness is essential in all details of estate work, and the
younger generation of planters could scarcely be aware that a few years ago
it was deemed sufficient to use coco-nut shells for the reception of latex
on individual trees.
Terne-plate cups ousted the coco-nut shell, and they had the merit of being
cheap. The interior coating of tin did not last long if the cups were
properly cleaned. The iron being exposed, with a minutely roughened
surface, each microscopic projection served as a point around which latex
coagulated. Scrapping the film of interior rubber became more and more
difficult, and often the cups were burnt in order to get rid of the
accumulation of rubber. The last state of such cups was worse than the
preceding one. On some estates fairly successful attempts were made to keep
these cups clean by making the coolies bring them into the store each day.
Terne-plate cups are not now in common use.
Aluminium cups have their advocates, but much the same argument applies to
the difficulty of keeping them clean as was used in the foregoing
paragraph. On many estates, however, they are used with success, the usual
method of treatment being to make the coolies bring them into the store and
clean them there. Owing to the comparative lightness of the material such a
scheme is more feasible than was the case with terne-plate cups.
The cups now most in general use are either of glass or white-ware, and
probably those of glass are the most extensively employed. There are many
details to be studied in the choice between these two types of
cups--_e.g._, percentage of breakage in transport and in the field, price
when breakage is taken into account, etc.; but these apart the glass cups
have one advantage--namely, the ability of the superintendents to see
whether the cups have been properly cleaned. In the case of white-ware cups
this means an inspection and handling of individual cups, whereas in the
case of glass the point is settled by visual examination at a comparative
distance.
[Illustration: SINGLE CUT ON TWO-FIFTHS OF CIRCUMFERENCE.
The opening cut covers two-fifths. Subsequent cuts occupy one-fifth of
circumference.]
Glass cups are made in two patterns, one having a flat bottom and the other
a conical base. The latter is convenient for use when wire supports are
employed, the cup fitting into a loop placed beneath the spout. Used on the
ground its shape is an obvious disadvantage, as, unless a hole is scooped
for its reception, it has to be propped up with sticks or stones. Often a
touch is sufficient to upset the balance, and latex is lost.
The flat-bottomed cup, on the other hand, may be used with success equally
on a wire support or on the ground. It is sometimes said that owing to its
shape the ease of cleaning, as compared with the half-spherical cup, is
diminished, and that if the cups when not in use are kept inverted upon
sticks placed near the foot of the tree the breakage is apt to be high.
This latter objection is being rapidly removed as the practice of using
these sticks is losing vogue for various reasons, and wire cup-holders will
be in general use as soon as the cost of material becomes normal.
There are on the market, and in fairly wide use, cups of Chinese and
Japanese manufacture. These generally consist of brown earthenware with an
interior glass finish. These are cheap in comparison with glass and
white-ware cups, but it is a pity that the glass does not extend over the
whole of the cup. The outer surface has a tendency to collect rubber and
dirt. On some few estates small china bowls or saucers are still used and
are quite satisfactory, except for the favour with which they are regarded
by natives on the outskirts of the estates.
CLEANING CUPS.--The question of cup-cleaning would appear to be a very
simple one; but in practice it is quite a source of worry to managers,
especially where a mixed labour force is employed. Tamil coolies can be
made to clean their cups in the day's task and at odd times. Chinese
coolies, more often than not, either refuse to give the necessary attention
or else demand extra pay for the work.
The method of cup-cleaning employed more popularly within recent years was
that of daily washing. The tapper carried two buckets, one for receiving
the latex and the other containing water. Pouring the latex in the bucket
the coolie then added a little water to the cup and added these rinsings to
the latex collected. The cup was next washed hastily in the bucket of water
and replaced. By the time the coolie has emptied and washed some 200 cups
(about half the task generally) the water has the consistency of dilute
latex, and the wet cup when replaced becomes coated with a thin film of
rubber. If the latex is always collected in one direction it will be clear
that, while the cups at one end of the task are comparatively clean, those
at the other end have the chance of being correspondingly dirty.
Controversy has raged respecting this question of cup-washing, and many
estates have abandoned it as a daily practice. Coolies have not to carry an
extra bucket of water. The contents of the cups are poured into the
latex-bucket, and the bulk of the latex film remaining is also removed by
the aid of a finger. The cup is then replaced, a thin skin of rubber
forming on the interior surface. As a general rule this is easily removed
on the next occasion, except perhaps in dry weather. It is the custom on
most estates employing this practice to have all cups receive special
attention at regular intervals.
There are certain economic factors entering into the difference of opinion
regarding the two broad methods employed. In some cases--_e.g._, on old
areas--it would be practically impossible to follow the older method of
daily cup-washing, as the tappers have to employ two buckets for the
collection of the latex. The employment of special coolies for cup-washing
would be necessitated, such as may be seen sometimes on estates working
Chinese "squatter" labour--where the man taps, a child assists in
collecting, and another child, or the mother, washes the cups. It may be
pointed out that in such instances the helpers are not paid by the estate.
Their services merely mean a saving in time which is spent in the
squatter's garden, and perhaps the permission to the tapper to work a
larger number of trees than would be allotted ordinarily to a task.
Again, on some estates, the tappers, while not being required to carry a
bucket of water for cup-washing, are given an increased number of trees to
tap. Furthermore, on hilly areas under tapping, it is often manifestly
unfair to expect the tapper to be able to carry two buckets during
collection, when the slope is such, as to make the manipulation of even one
bucket a matter of difficulty.
It will be seen, therefore, that there is no clear issue for argument
concerning the two methods, and that the point must be decided on the
economic factors peculiar to each estate or district.
[Illustration: EFFECTS UPON RENEWED BARK OF PREVIOUS TAPPING.
Note uneven surface and callosities.]
[Illustration: ANOTHER EXAMPLE SHOWING THE EFFECTS OF PREVIOUS TAPPING.]
WATER IN CUPS.--Much discussion used to take place regarding the necessity
or otherwise for placing a small quantity of water in the cups when
tapping. It was recognised that the permission to use water (with the idea
of preventing coagulation) led to much abuse, apart from the question as to
the utility of the method. Dirty water was often used, although clean water
may have been placed in the buckets when coolies left the muster-ground.
The small quantity of water often exceeded the actual yield of pure latex
by hundreds per cent., with the result that on arrival at the factory the
diluted latex was below the standard desirable for the preparation of a
good sheet-rubber.
PREMATURE COAGULATION.--Other opinion to the contrary it is now generally
acknowledged that the possibility of premature coagulation in the cup or
bucket is at least not diminished by the addition of even clean water. The
use of water often obtained from estate drains clearly led to increased
trouble. The extent to which such premature coagulation takes place varies
greatly under the influence of many factors--_e.g._:
(_a_) Cleanliness of cups and spouts (the latter an important item
often overlooked, and involving the presence of certain organisms
which effect coagulation).
(_b_) Climatic conditions.
(_c_) Rate and volume of flow of latex.
(_d_) Size of tappers' tasks (involving the length of interval between
tapping, and the collection of latex).
(_e_) Distance to be traversed between the site of the task and the
store.
(_f_) Care in collecting, to exclude extraneous matter.
(_g_) Nature of transport; agitation of the latex to be reduced to a
minimum.
(_h_) Nature of the soil, and situation of the estate.
The last mentioned factor is of great importance. As a general rule it is
noted that premature coagulation is less marked on estates situated on
comparatively hilly land. The greatest effect is remarked on estates
situated on the flat lands of the coastal area where peaty soils are a
feature. On many such estates, in spite of the observance of all ordinary
precautions, it is not possible to receive the latex at the factory without
a large percentage of prematurely coagulated rubber being found in the
transport vessels.
ANTI-COAGULANTS.--For this reason on these (and other) estates, the use of
small quantities of anti-coagulants is common. The effect of these is to
keep the latex liquid and thus render possible the preparation of a higher
percentage of first-grade rubber than would be otherwise obtained.
Among the better known agents which have such an effect upon latex,
formalin and sodium sulphite (not bisulphite) are the chief. The latter is
the more popular as it is slightly cheaper and much more stable. As now
used, it is in the form of an easily soluble powder (anhydrous sodium
sulphite). The ordinary crystalline form of sodium sulphite as used in
photography is not recommended, on account of its comparative lack of power
and its poor keeping qualities.
It will be obvious that, given two equal quantities of different latices,
different amounts of an anti-coagulant may be required to produce the same
effect. Hence it should be remembered that a formula which suits the needs
of one field or one estate will not necessarily prove suitable in the case
of another field or estate. Unless this point is appreciated trouble may
ensue. On some estates it has been the custom to give equal quantities of
sodium sulphite solution to all coolies irrespective of the ages of the
trees in the fields to be tapped. Thus it happened that the latex from one
field was found to have insufficient anti-coagulant present, while that
from another field could only be coagulated by the addition of an excess of
acid. In this matter the experience of the preliminary trials should have
caused some discrimination to be exercised as to the quantities of solution
to be issued in each field or division. It has been found sometimes that a
moist glossiness in the smoked sheet could be attributed to the use of an
excess of sodium sulphite. Traces of the salt remained in the rubber, and
as the substance is hygroscopic, moisture was being absorbed from the air,
to cause a surface deposit which often returned even after the sheets were
surface-washed and re-dried.
If sodium sulphite is to be used in the field, the following formula, which
is in wide use, may serve as a basis for trials.
_Formula for Use of Sodium Sulphite in the Field._
(_a_) Dissolve anhydrous sodium sulphite in water at the rate of 1
pound to 3 gallons.
(_b_) Of this solution each coolie is given about 3/4 pint. This is
usually sufficient for a task of 350 trees. The solution is used by
shaking a few drops into the cup or, diluted with an equal volume of
water, it is run down the main channel when the latex flows.
[Illustration: 1. SHOWING EFFECT OF "WINTERING."]
On some estates it is found either unnecessary or impracticable to use the
solution in this manner. Instead the anti-coagulant is placed in the bottom
of the bucket prior to the commencement of collection. The solution is made
as in (_a_) above, and roughly half an ordinary latex-cupful is placed in
each bucket.
[Illustration: 2. NEW GROWTH OF YOUNG LEAF ON SAME TREE.]
COLLECTING PAILS.--All vessels intended for the transport of latex should
have a smooth and curved interior, so that cleansing may be easy.
Preferably the interior and exterior surfaces should be glazed, but it is
often found that the enamel chips easily, and that the handles are too
frail in construction. The shoulder-pieces, to which the handles are
joined, are often too lightly attached to the bucket. Something stouter in
the shape of enamelled ware is required, without an appreciable increase in
weight. Until such a utensil is available, the heavily galvanised and
brass-bound milk-pails used on some estates are as good as anything at
present in vogue, providing they are kept scrupulously clean.
[Illustration: EFFECTS OF DISEASE--"MOULDY ROT."
(_a_) Note on right hand the panel next in order for tapping; a hopeless
position.]
[Illustration: EFFECTS OF DISEASE--"MOULDY ROT."
(_b_) The present cut badly infected; above there is no renewal of bark.]
The collecting pails should be kept under cover, when not in use, either at
the muster grounds or at the factory. On some estates coolies are allowed
to take them to their quarters, where they are used for various purposes.
Curious effects of this practice have sometimes been noticed. As an
example might be quoted an instance in which premature coagulation was
found to take place to a surprising degree. It was discovered eventually
that the coolies (Javanese in this case) were in the habit of utilising the
buckets for the preparation of their food. A liquid extract of a popular
fruit was often made. This extract was very markedly acid in character,
and as the buckets were not afterwards thoroughly cleansed, the latex of
the following day suffered.
[Illustration: EFFECTS OF DISEASE--"MOULDY ROT."
(_c_) As in (_b_); another tree.]
Preferably all buckets should have a lid of slightly funnel shape. This is
inverted during collection, and thus prevents much dirt falling into the
latex.
[Illustration: EFFECTS OF DISEASE--"MOULDY ROT."
(_d_) At close quarters. Note wounds due, apparently, to bad tapping, but
really caused by the disease.]
PAYMENT BY RESULT.--The arguments for and against the institution of this
practice are many. In actual result there can be no question that a higher
yield is obtained by the adoption of a scheme under which the coolie is
either given a bonus based on result or is paid at a definite rate per
pound. It is fully recognised, both by advocates and opponents of payment
by result, that the personal equation of the tapper is a very important
factor. A good skilled tapper will always obtain a higher yield than an
ordinary individual from the same task of trees, and without any more
injury to the trees. It is argued, therefore, that such an operative should
be given the benefit of his skill. Apart from this, it is claimed that even
the average tapper does not do his best work if he knows that he will get
his daily wage, no matter what his yield may be, as long as he does not
injure the trees by wounding. It is claimed that this sense of security
leads to shallow tapping which, while it has an agreeable appearance, does
not produce the available amount of rubber.
On the other hand, it is advanced in opposition that under a scheme of
payment by result the tappers' only consideration is the matter of
obtaining rubber, and that considerable damage in the form of wounds is
done by over-deep tapping. That there is a great deal of truth in these
statements is not to be doubted. Much, of course, depends upon the amount
and quality of the supervision possible, and upon the standard demanded. It
is a notable fact, however, that on estates which first introduced the
system some years ago the quality of the tapping compares favourably with
that of average estates, and in a few instances within the experience of
the writer the tapping is of a high standard. Possibly these are
exceptional instances, and there can be no doubt that the opposition of
many managers of considerable experience is founded upon the deterioration
in the standard of tapping which often follows the institution of payment
of tappers by result.
It will be recognised by planters that apart from the personal factor in
tapping, the worker might be so unfortunate as to be placed in an area from
which the yield is naturally low, either by reason of its youth or from
other natural causes. Obviously such individuals are entitled to special
consideration in respect of the rate per pound paid for the rubber
obtained. Again, on very hilly land it may be not humanly possible for a
worker to tap the usual number of trees. Hence to place him on a parity
with other tappers, as far as wage-earning capacity is concerned, a higher
rate than ordinary must be given. It will be plain, therefore, that on any
one estate it is generally impossible to set a standard rate per pound for
payment by result; the rate may vary, for example, from, say, 3 cents per
pound in old and high-yielding tasks to 12 cents or more per pound on young
areas of the same estate.
Naturally the actual rates paid will primarily depend upon the average
yield per tree or yield per acre, and the lower the average yield the
higher the rates to be paid per pound. Thus, on low-yielding properties
where the natural conditions render a high yield impossible the rate per
pound may reach a figure of 22 cents (approximately 6d.).
The methods of arriving at the yield of rubber brought in by individual
tappers vary, but broadly they fall into two classes:
(_a_) That in which the volume of latex is ascertained (either by
measuring or by weighing), a sample is drawn, and the final
calculation made from the weight of the more or less dry sample.
(_b_) That in which, after noting the volume, the calculation is based
upon a reading of the dry rubber content of the latex, obtained by
means of an instrument such as the "Metrolac," or any other instrument
working on the same principle.
Quite a number of estates which have not adopted the full system of payment
by result yet employed some such method of checking the yields of
individual coolies, as the observed results act as a great deterrent
against various malpractices, such as neglecting to tap trees, adulteration
of the latex, etc.
TREE-SCRAP.--The thin film of latex which coagulates naturally upon the
surface of the tapping cut after the latex has ceased to flow is known as
"tree-scrap." Normally it is collected on all estates, but the method of
collection varies according to the class of labour employed. On most
estates, where the labour is Tamil or Javanese, it is supposed to be
removed as fully as possible before the tapping cut is reopened. The narrow
strips are then placed in a bag or basket carried by the tapper. Chinese
tappers usually decline to follow this practice of first peeling off the
scrap, and remove it by the operation of tapping, with the result that the
scrap when brought into the store has adhering to it various shavings of
bark. Unless these can be thoroughly cleaned off the scrap cannot truly be
classed as "tree-scrap."
OXIDATION OF TREE-SCRAP.--It is often noted that some scrap is dark in
colour, and in this condition it is generally spoken of as "oxidised"
scrap. The oxidation is probably due to an enzyme, and also to the presence
of chemical substances of a phenolic nature. In the course of laboratory
experiments with normal latex, it was found possible to reproduce this
darkening due to oxidation by the addition of very small quantities of
various phenols used in general chemical processes, and the rapidity with
which the darkening was effected depended upon the quantity of the phenol
added. If this rapidly oxidising latex be mixed with normal latex, it would
seem that the whole bulk of the latex is affected by this tendency to rapid
oxidation. It is observed that this condition under which any tree may
yield rapidly oxidising latex is not a permanent one.
CARE OF TREE-SCRAP.--As these scraps eventually give a grade of rubber
which compares well with other and better-looking grades care should be
exercised in collection and treatment so that its quality is not impaired
in any way.
TO PREVENT OXIDATION.--As a rule the scraps are picked over, and heavily
oxidised pieces are sorted out; otherwise the crepe rubber prepared
exhibits black streaks. The scraps should not be allowed to remain in the
sun (which induces "tackiness"), and if they have to be kept over night
they may be placed in a weak solution (1 per cent.) of sodium bisulphite to
arrest oxidation. It should be recognised that such a solution will not
"bleach" already darkened scrap-rubber, and the nature of its action is
only anti-oxidant.
BARK SHAVINGS.--In the matter of collecting bark-shavings much depends upon
the organisation and nature of the labour force. Probably, on the majority
of estates bark-shavings are collected systematically, but on quite a
number considerable laxity in this respect has been noted. This may arise
from lack of adequate supervision or from the peculiar systems of working
which seem to pertain to Chinese labour. Granted that the trees are well
"scrapped," and that the percentage of rubber obtained from shavings under
such circumstances would be extremely small (say 2 per cent. by weight on
the total output), it does not need much calculation to see that annually
the loss of rubber to the estate must be considerable. It would also seem
to follow that, if the adult labour declines to pick up bark-shavings
carefully, it might pay to employ children for the purpose. Or, as is done
in some places, the adult labour might find it advantageous to collect
bark-shavings at low rates per pound.
It is a well-known fact that if bark-shavings be allowed to accumulate in a
heap for any but a short period, a fermentative and heating action is set
up. The heat developed in these piles of shavings is so considerable that
it is impossible to keep the hand in a heap for more than a second or two.
Should this be allowed to persist, as would happen in the case of a
breakdown of engine or machines, it usually results in the final crepe
rubber becoming tacky when approaching dryness.
To avoid this heating effect it is necessary to have spare jars or proper
tanks in which the shavings may be soaked in water. In this condition
bark-shavings may be kept for many days.
For the same reason (_i.e._, the heating effect and consequent tackiness)
the custom followed on some estates of allowing coolies to keep
bark-shavings in their "lines" until they have accumulated a fair quantity
cannot be commended, quite apart from the possibility of actual loss by
theft, which is thus rendered easy.
It will be clear that where the trees are scrapped efficiently before
tapping, the amount of rubber to be obtained from the treatment of pure dry
shavings would be almost nil, and would scarcely repay the cost of
collection and working. In actual practice, however, it is not possible to
guarantee that the shavings are free from some scrap-rubber. Shavings
brought in by Tamils and Javanese carry only a small amount of rubber,
whereas where Chinese tappers are employed the yield of rubber may be as
high as 35 to 40 per cent. upon the total weight of the material treated.
Few estates now are not equipped with "scrap-washers"--machines specially
designed for removing the bark from the rubber--and if they function
efficiently the resulting crepe should be free from bark-particles.
COLLECTION OF EARTH-SCRAP.--This, the lowest grade of rubber, is found at
the base of the tree. Theoretically, if proper precautions are observed,
the amount should be comparatively small, but in actual practice it may be
very appreciable. The usual contributory causes are:
(_a_) Failure to replace cups beneath the spouts of trees which
continue to drip latex after collection.
(_b_) Collection of latex at too early a stage.
(_c_) Failure on the part of the tapper to ensure the flow of latex,
by means of the spout, into the cup.
(_d_) Flowing of latex over the edge of the cut before it reaches the
vertical channel.
(_e_) "Wash-cuts" on wet days, when the volume of rainwater down the
tree is sufficient to wash the latex out of the cup.
The amount of earth-scrap collected on any estate will depend, all other
things being equal, upon the labour expended in its collection. Certainly
on well-organised estates, having ample labour, the amounts collected are
huge in comparison with other estates. The ground at the base of the tree
below the latex-spout is systematically turned over with pointed sticks and
large clots of rubber are often picked up. Here, again, it is advised that
the collected earth-scrap should not be allowed to remain in heaps upon the
floor of the factory. It should be placed in suitable tanks containing
water, and quite a considerable portion of the cleansing work is thus taken
from the machines.
CHAPTER VI
_TRANSPORT OF LATEX AND COAGULUM_
PERCENTAGE OF FIRST LATEX AND OTHER GRADES.--One of the problems
confronting any manager is the question of the percentage of first-grade
rubber calculated upon the whole output. Inquiries are constantly being
received for advice as to what the various percentages of each grade of
rubber should be. This is a question to which no definite list of figures
can apply. There are so many little factors influencing the result. Some
estates are not particularly careful in collecting tree-scrap. Hence quite
a quantity of tree-scrap finds its way into the crepe made from
bark-shavings. On the other hand, bark-shavings are not collected
systematically on some estates, and the total output is thereby diminished.
In consequence the first-grade rubber shows a higher percentage than it
would otherwise. Again, if the earth-rubber is not regularly collected the
percentages of the best grades are higher than they should be. In comparing
the percentages of each grade of rubber from any two estates, therefore,
one should have all the information possible as to the various working
details of the estates. Without wishing to lay down any definite
proportions which can be applied to all estates it might be said that,
taking averages over a large number of estates, the percentages to be aimed
at are:
First-grade latex 75 per cent. to 80 per cent.
Other grades 20 " " 25 "
For these figures one promises that all lower grades are collected and
accounted for carefully and regularly. The distribution of the lower grades
will depend upon the field practices of the particular estate, but the
following list might be given for an estate keeping all lower grades
distinctly separate:
First-grade latex 75 per cent.
Cup-washings }
Coagulated lump, etc. } 10 "
Tree-scrap 9 "
Bark-shavings 4 "
Earth rubber 2 "
---
100 "
Emphasis is again laid on the statement that these figures must not be
accepted as a standard. Nevertheless, they may prove of some service to
managers in giving an idea of what the general line of percentages may be.
There are special circumstances, such as distance of transport and the
nature of the land, which at present would render the attainment of more
than 75 per cent. first-grade rubber impossible on some estates. Still the
fact remains that if the percentage is low through distance of transport,
etc., some method will have to be discovered by means of which the
difficulty maybe overcome. On a few estates the percentage of first-grade
rubber obtained sometimes reaches 85, but these results are rather out of
the ordinary. An estate which collects all lower grades properly is doing
well if the percentage of first-grade rubber is 75 or over.
EARLY COLLECTION.--As already noted in the preceding chapter, one of the
factors influencing premature coagulation is that of the interval elapsing
between the commencement of tapping and the collection of latex. It will be
seen that this ordinarily would depend, in turn, upon such considerations
as the size of the tappers' tasks, the spacing of the trees, and the
natural conformation of the land over which the tappers have to perform
their tasks. In general it need only be remarked that every possible
consideration should be given to this question, and that any delay should
be avoided.
TRANSPORT.--Wherever possible it is endeavoured to convey latex from field
to factory by man-power. Tamil coolies, as a rule, place the bucket on the
head; Chinese and Javanese coolies like to use a balanced carrying-pole.
Where distance renders these methods too costly in time and labour, it is
usual to have field centres where the latex is collected and dispatched to
the factory generally (_a_) by means of vessels conveyed on light railways;
(_b_) in large cans placed on motor-lorries; (_c_) in cylindrical
galvanised drums supported on two wheels and drawn by bullocks. There may
be variants, but these are the chief means of transport in bulk over a
distance.
Where possible, the best system is that employing a trolley-line, as great
agitation of the latex is avoided, and the time in transit is much reduced.
The usual method of transport by bullock power is slow, and as estate roads
(and even Government roads) are often below the standard expected in this
country, the jolting undergone by the latex is, to say the least, not
calculated to afford a high yield of first-grade rubber. The late Mr. F. W.
F. Day advocated the use of a circular perforated wooden grid, to be
floated on the latex, in order to moderate the wave effect produced by
jolting.
Whatever the means of bulk-transport employed, it should be the care of
those in charge to see that vessels are not allowed to remain in the sun
longer than is necessary. Even during the journey they should be shaded in
the best possible manner.
These large transport vessels usually receive what is really only
perfunctory attention in the matter of cleaning. They should receive the
same care as would be exercised in dealing with milk cans in other
countries. Ordinary sluicing with water is not sufficient, and if they
cannot be sterilised by means of boiling water, they should be treated,
after ordinary washing, with a 5 per cent. solution of sodium bisulphite
every day.
ANTI-COAGULANT FOR TRANSPORT.--When anti-coagulants are not used in the
cups or buckets, it is advisable to use them in the bulk-transport vessels.
Either formalin or sodium sulphite is of service, but the great objection
advanced against the former is its loss due to evaporation while the carts
are going to the fields or waiting at the centres. For this reason sodium
sulphite is now generally employed.
_Formula for Use of Sodium Sulphite in Transport._
(_a_) Dissolve 1 pound of powder in 3 gallons of water.
(_b_) Of this solution, place half a gallon in the vessel for every 30
to 40 gallons of latex.
TRANSPORT BY COOLIE.--As already pointed out, the extent to which man-power
can be used in transport of latex is generally limited. On small estates it
is an easy matter for coolies to carry the latex to the factory, but on
larger estates many difficulties may arise, which may also militate against
the successful use of other means of transport. It is not uncommon to find,
therefore, that a policy of decentralisation has been adopted.
COAGULATION CENTRES.--Divisions of the estate have their own small stations
at which latex is received and coagulated. In this way it is possible to
receive latex without much delay, and with benefit to the resultant rubber,
especially if prepared in sheet form. Much controversy has arisen regarding
these decentralised establishments, but the fact remains that on large
estates, which are efficiently controlled, the scheme has been highly
successful from all points of view. On the other hand, it is alleged that
this method of working increases costs, and often gives an unsatisfactory
quality of rubber. Concerning the latter point it seems to be reasonable to
expect that the European in charge of any division should be conversant
with the method of preparation required, and should be capable of seeing
that no mistakes are made. Given uniform equipment in all stations, and
uniform rules for treatment of the latex, there does not appear to be any
valid reason why the product of one station should be inferior to that of
the others. Neither is it so in the case of several estates which might be
quoted.
In the matter of costs of working the writer has had to investigate several
cases regarding which there was dissatisfaction. In some instances it was
found that the stations had not been placed advantageously with respect to
a water-supply; and instead of one or two coolies pumping for an hour or
two, a larger number had to be employed for hours in the carriage of water
from the nearest available source. This meant that, as the coolies were on
daily wage, the force appeared to be much bigger than that usually
required. In other cases there were too many store coolies, when often the
place of some could have been taken for the necessary period by tappers
arriving early from the nearer fields. Sometimes costs were increased by
reason of the use of an excess of chemicals, owing to the lack of uniform
rules throughout the several stations. In spite of all that has been
written, and the verbal instructions that have been given, it was not
uncommon to find unstable chemicals such as sodium bisulphite exposed to
the moist air. In this way not only was there waste of material, but also
the probability of inferior rubber being made.
TRANSPORT OF COAGULUM.--On the whole if it is a question between the
transport of latex and the transport of coagulum, the writer would always
favour the latter, for reasons which have possibly been made clear in the
preceding paragraphs. In effect, it should be recognised that the less
handling and transport the latex receives the better the general result.
If proper precautions are taken, the transport of coagulum intended for the
preparation of crepe should present no difficulty, and should have no
injurious effect upon the quality of the resultant rubber. It is only too
common, nevertheless, to note defects, in the finished crepes, which can
only be attributed to a failure to observe reasonable care in the transport
of the coagulum. For example, it has been observed that a mass of coagulum
from a coagulation station has been conveyed on the floor of a
bullock-cart, or motor-lorry, previously used in the carriage of other
materials. Unless the boards have been most scrupulously cleansed, the
coagulum is found to be contaminated, often to a marked degree. Again,
although the cart may be clean, it may have to travel some distance on
roads carrying a fair amount of motor traffic. Even should the cart have a
canopy, road-dust is often whirled through the open sides of the cart; and
in the districts where red laterite roads are common, the stain of such
dust often persists in the finished crepe. It scarcely need be remarked
that coagulum should be transported in closed wooden boxes or in galvanised
iron drums fitted with lids; and that preferably sufficient water should
be present in these receptacles to allow the coagulum to float. All such
containers should receive the same scrupulous attention as the vessels
employed in the transport of latex.
The successful transport of coagulum for sheet-making is fraught with much
greater disabilities, and it is usual to note on most estates that the
resulting sheets from out-stations are always inferior, in final result, to
those coagulated and prepared at the central factory. If the flat pieces of
coagulum are placed in piles of any height it is common to find, on arrival
at the factory, that much adhesion has been caused. There is great
difficulty in separating the pieces, and often the successful operation is
impossible. It is usual to hand-roll the coagulum before transport, but it
is often found that by the time the rubber reaches the factory it has
become too hard for subsequent good results.
One of the strong arguments in favour of the establishment of divisional
stations is to be found in the preceding paragraph. Sheet-making, as it
necessitates the employment of only light machines suitable for hand-power,
is a feasible proposition in a field station. There is no reason for sheets
made thus to be in any way inferior to those made at a central factory; in
fact, they are often better, as the latex has the chance of being treated
when comparatively fresh.
If it is found necessary to transport sheet-coagulum, every possible
precaution should be taken against piling the pieces.
After hand-rolling some estates bring the rubber from the field-stations to
the central factory in drums of water, others in shallow boxes containing
not more than half a dozen sheets in a pile. A method proposed long ago,
but not in practice, was to have a number of shallow trays subdivided so
that each compartment held one sheet only. If these trays were properly
made and carefully fitted there appeared to be no reason why they should
not form sliding parts of a large box, in which squeezing and adhesion of
the pieces of coagulum would be avoided. Naturally any such device would
increase appreciably the weight to be transported, and on this ground would
not find popular favour except where motor-power is used for road
transport.
PART II
FACTORY OPERATIONS
CHAPTER VII
_PRELIMINARY TREATMENT OF LATEX_
RECEPTION OF LATEX AT THE STORE.--Bearing in mind the remarks in Chapter
VI. on the conditions under which latex is transported, it follows that
nothing but the very best and most suitable vessels should be used in the
store. A point to which adequate attention is not given in many factories
might be mentioned here. Considering the importance attached to colour in
the dry rubber by brokers and consumers, and knowing how extremely trivial
are the causes which may mar the colour, it is rather surprising that
better provision is not made for the reception and handling of latex in
factories. Too often the receiving vessels are placed on the floor of the
store close to the entrance. Coolies bringing in latex cannot avoid
bringing with them quite a considerable amount of dirt. Presuming that a
hose-pipe has been installed, and that the floor is constantly being
sluiced down with water, no great harm will result. But would it not be
ever so much better if the dirt were kept out? In how many factories is
provision made for this? Such an arrangement is not difficult to make, and
is already in practice on a few estates. A verandah is built outside the
wall of the factory and all latex is received there. In another place open
chutes are provided which terminate in the straining sieves. The coolie
thus stands on the verandah where he removes coagulated lump and impurities
from the latex, which is then poured down the chute, passing through the
sieve into large coagulating jars or tanks.
Too often it would appear, from the writers' observation, there is a lack
of adequate supervision on the arrival of latex at the store. Much can be
learned from an inspection of the coolies' buckets, and the cause of small
defects in the finished rubber can often be thus traced. Leaves, stems,
bark-shavings, and dirt appear in the buckets, and it is a source of
constant surprise to imagine how even unintelligent coolies can allow such
things to happen. These objects are removed before or during straining, but
still they ought not to be there in the first place, and the fact that such
a state of things exists is evidence of neglect on the part of the coolies
or lack of supervision. Efforts are made in a large number of cases to cope
with these troubles, but on some estates things are allowed to proceed in
the same slipshod way, and too much responsibility is thrown on the
straining process.
[Illustration: RAISED VERANDAH FOR RECEPTION OF LATEX; LIKEWISE EQUIPPED
WITH FACILITIES FOR CALCULATING INDIVIDUAL DAILY "YIELD PER COOLIE" BY
SAMPLING OF LATEX.]
It is suggested that it should be the business of a European to supervise
the reception of latex every day. This is at present quite impossible on
some estates, but it does not alter the fact that this supervision should
be provided, and is extremely necessary.
It is surprising how the point is overlooked in many factories--not that
they are in a dirty state, but they fall short of being classed as clean
factories for want of the little that makes the difference. Possibly those
in charge do not believe that all this fuss need be made, but the writers
can assure them, from a practical knowledge of a very large number of
factories, that cleanliness does pay.
It might not be credited to Tamil coolies, but yet it is probably true,
that the moral effect of working under the cleanest and best conditions has
an influence upon the store coolies, and that their work is better in
consequence. Everything which will tend to simplify the cleansing of the
factory should therefore be installed. Hose-pipes, glazed tiles, clean
floors, plenty of light and air are not fads or fancies, but considerable
factors in determining the final quality of the rubber. There is
considerable truth in the suggestion that the coagulating room and machine
room should be as "spick and span" as a modern home dairy.
STRAINING OF LATEX.--This is a most necessary process, and one which
usually entails much trouble and time which one could wish avoided. It will
be admitted that the trouble could be reduced greatly if the regulation of
field processes could be made more stringent. In spite of knowledge that
impurities must not be allowed to enter the cups, coolies will ignore the
rule that the cup must not be placed in position until the bark shaving has
been cut. The result is that pieces of bark fall into the cups, and coolies
are generally too careless or too hurried to remove them.
Again, when cups are placed on the ground, it is easy to see that dirt may
adhere to them. In the collection of latex some of this dirt may fall into
the bucket. Since the introduction of cup-holders on many estates the
trouble from this source has decreased considerably, but, nevertheless, it
may be taken for granted that even under the best of conditions all latex
requires straining.
The best type of strainer has yet to be evolved. Usually it consists in
principle of a piece of fine brass mesh contained in some form of holder.
Theoretically such a strainer should work well, but in actual practice
nearly all strainers are a source of continual worry. Undiluted latex, as
received at the factory, is of a rich consistency, containing very fine
particles of dirt and often minute particles of prematurely coagulated
rubber. The latter soon clog a fine mesh strainer, while the former may
pass through. When the flow through the strainer becomes slow, the coolie
in charge generally rubs the top surface of the sieve with a piece of
coagulum, thus forcing material through the mesh. He then rubs the
under-surface, with the result that undesirable matter falls into the
strained latex. In theory it seems a simple matter to have a number of
sieves ready so that a clean one may be substituted for a clogged one,
which should be cleansed at once with water. In practice the factory coolie
will probably only carry out instructions when the eye of the
superintendent is alert. As a result of the rubbing and consequent strain,
the brass mesh usually breaks away from its support and the fracture may
not be detected for some time, during which irreparable damage may have
been done to the resultant rubber.
In view of the presence of the fine particles of dirt, to which allusion
has been made, fine sieving of the latex appears to be essential,
especially when sheet-rubber is to be prepared. The fine sieves are
generally of the type known as "60 mesh," and they do not usually give
thoroughly satisfactory results even when the gauze is supported and
strengthened by means of cross-wires placed underneath. The general fault
with these strainers is that a sufficiently wide "selvage" is not allowed
in the clamped edges of the gauze, or that the edges of the support are so
sharp and abrupt that the strands of the gauze are soon severed by the
strain imposed in vigorous cleaning.
Many estates use two strainers; the first a more robust one containing "30
mesh" gauze, and the second the fine "60 mesh." Even this device does not
bring about the desired immunity from trouble. Relief could be obtained if
the latex were always in a more freely fluid form. Estates employing
anti-coagulants in the field benefit in this respect. Other estates,
although finally using the finest of mesh, experience far less trouble than
most estates by reason of a difference in method of working. This can be
explained by an outline of the system adopted on a particular estate:
(_a_) On arrival of the rich latex at the store, all visible
coagulated lumps and other extraneous matter are removed by the
tapper.
(_b_) Each tapper's latex is diluted with a quantity of water.
(_c_) The diluted latex passes through two sieves, one above the
other. The top sieve is of stout perforated zinc sheet, with 10
circular holes to the inch. This removes all large particles. The
lower is of "30 mesh" brass gauze, and practically no rubbing is
required. The latex is now in glazed-tile tanks, in which it is
further diluted to the required standard by means of a recording
instrument.
(_d_) The latex flows by means of a chute into the coagulating tanks,
passing through a large "60 mesh" sieve.
It is not guaranteed that this method will furnish a complete absence of
very fine particles of dirt in sheet rubber, as the human element enters so
largely into the question; but it can be stated that no complaints have
been received on the point of "specks of dirt" since this system was
inaugurated.
On the same estate fine sieving in the preparation of pale crepe has been
abandoned as an unnecessary refinement. The two coarse sieves mentioned
above are employed only, and it is to be acknowledged that the results
justify the procedure.
BULKING OF LATEX.--Not long ago advanced estates used to combine all latex
before coagulation, in order to obtain uniformity of product. Previously it
had been the custom to deal only with comparatively small separate volumes
of latex, with obviously great disadvantage.
Since the introduction of instruments such as the "Metrolac," by means of
which any volume and all volumes of latex may be reduced to a common
standard of dry rubber content, the necessity for "bulking" has passed. It
is not now necessary to keep latex standing, perhaps for two hours,
awaiting the arrival of other latex from distant fields.
STANDARDISATION OF LATEX.--In modern practice, as already pointed out, it
is possible now to handle any volume of latex with a view to its reduction
to any required standard of dilution for the purpose of obtaining a
uniform product. For the reception and subsequent handling of the latex
various schemes have been devised, and they are usually planned in
connection with coagulating tanks used in the preparation chiefly of sheet
rubber.
[Illustration: END-SECTION SKETCH OF VERANDAH, ETC., SHOWING A GOOD METHOD
FOR RECEIVING LATEX AND FILLING TANK.
T, Sheet coagulation tank; C, cylinder for reception and dilution of latex;
GG, gutter; PP, raised platform on verandah; SS, steps leading to platform;
W, dwarf wall; EE, expanded metal partition; OO, open.]
In the successful working of a tank it is necessary, in order to obtain the
best results, to standardise all latex. This cannot be effected properly in
the tank itself, and hence it is the practice to dilute each lot of latex
to standard before it is run into the tank. In the ordinary way this would
entail a great deal of labour in handling the diluted latex. To obviate
this, the scheme outlined in the accompanying sketch has been suggested on
several occasions and in various quarters. Such a scheme or modification of
it has been put into successful practice on several estates. Although the
drawing was made some considerable time ago when estates were not then
prepared to go so far in this direction, subsequent modifications show only
minor differences which, while leaving the original principle intact,
testify to a fertility of resource in adapting the idea to existing
circumstances and buildings. The drawing is _in toto_ almost a replica of
the original installation now in successful use on the Kinrara Estate of
the Ledbury Rubber Company. On this company's Ledbury Estate likewise a
similar system is employed, except that the reception verandah is part of a
natural formation and needed no such direct raising. Several other estates
have now adopted the scheme, which has been proved to be of practical
value. The writers make no claim to originality in the idea, which might
have occurred to many independently on the introduction of coagulating
tanks.
[Illustration: RAISED VERANDAH FOR RECEPTION AND HANDLING OF LATEX.]
VERANDAH.--In reproducing the drawing it is believed that the sketch will
convey practically all the information required. It may be explained that
the coolies are allowed to enter only the outer part of the verandah. The
buckets are handed across the low wall into the care of factory coolies,
who strain the latex through gauze sieves into the latex cylinders.
LATEX RECEPTION VESSELS.--These cylinders may be similar to the tanks
commonly used for transport of latex from distant fields to the factory. An
80-gallon cylinder is easily mounted by its trunnions on a suitable iron
framework which is superimposed on a skeleton truck.
[Illustration: ANOTHER SET OF DILUTION TANKS ON RAISED VERANDAH.]
The latex is diluted down to standard in the cylinders, the truck is moved
opposite the compartment to be filled, and a light movable gutter is placed
beneath the vent of the outlet pipe. This pipe is fixed in the bottom of
the cylinder, and is provided with a large stop-cock which is operated by a
spanner key. The stop-cock should be of the simplest type, capable of being
taken apart and assembled in a minute or so. The orifices should be large
enough for a coolie to insert at least two or three fingers so as to
facilitate cleaning, and the pipe should have no right-angle bends.
On the inside of the cylinder a scale of gallons may be painted, so that
one may possess a knowledge of the quantities run into, or required for the
completion of, any compartment.
A SCREW PLUG UNSATISFACTORY.--It may be of benefit to managers who
contemplate such an installation to know that the adoption of a stop-cock
in the vent pipe of the cylinder is the outcome of experience. In one
instance the vent pipe as designed was fitted with a screw plug at the end.
Unfortunately with this arrangement the flow could not be regulated, and
owing to the "head" of the latex it dashed violently down the gutter,
struck the bottom of the coagulating tank, and thence was scattered over
the factory.
ANOTHER INSTALLATION.--In another type of installation, in place of the
vessels travelling upon a raised verandah platform, the standardised latex
is conveyed to the coagulating tanks by means of drums supported by hooks
to a chain-block and pulley which travels on an overhead gantry. This
method is practicable, but may be regarded as less satisfactory in general
working than the verandah method of treatment.
A MODERN INSTALLATION.--In the most recent scheme for dealing with the
reception of latex, its standardisation, and conveyance to the coagulating
tank, the main principle of the first system outlined is retained; but the
receptacles are not mobile. Glazed-tile tanks are employed, the capacity of
each being approximately equivalent to that of each unit coagulating tank.
The accompanying illustrations show the general arrangement and some
details of the system of reception tanks employed on the well-known
Pataling Estate.
CHAPTER VIII
_COAGULATION_
Whether it is necessary to employ any coagulant, or whether latex should be
allowed to coagulate naturally, will not be discussed at this stage.
Neither will mention be made of any patent processes of coagulation which
employ other than acid mediums. These subjects will be treated in a
subsequent section of the book.
CHOICE OF COAGULANTS.--It is not proposed here to enter into a discussion
as to the merits of the dozens of known coagulants. Suffice it to state
that acetic acid, although the oldest general coagulant, still remains the
best and safest at the present time. There is a deal to be said in favour
of the use of another organic acid, formic acid. It is equally as safe as
acetic acid, and quite efficacious; the only drawback is that, taking all
things into consideration, it is very slightly more expensive. Acetic acid,
therefore, will always be implied in this chapter when the word "acid" is
used.
STRENGTH OF ACID SOLUTION.--In the old days it was the rule rather than the
exception to find pure, undiluted acid used in coagulation. In many cases
no harm resulted, for the simple reason that, owing to the large proportion
of water in the latex, the acid was thereby very much diluted. The estates
had to thank the over-dilution of the latex for the non-injury of the
resulting rubber.
Some estates make up a stock solution of 1 part acid to 20 of water, and
use this with success because of the fair amount of added water present in
the latex.
It must be understood that what is being referred to now is not the
absolute quantity necessary for coagulation, but the proportions--_i.e._,
the respective volumes of acid and water in the solution of acid made up
every day. That the strength of the acid solution, as well as the quantity
used, has an effect upon coagulation can be easily demonstrated in the
following way:
Take separate and equal lots of the same latex, and to each add the same
quantity of pure acid, but in each case diluted with varying quantities of
water. It will be found that coagulation is quickest where pure acid is
employed, and slowest where the acid is most dilute. It will also be found
that, providing the quantity of acid employed was sufficient for
coagulation, the best and most uniform coagulation is obtained from the use
of the most dilute acid, within limits. It will often be found that where
pure acid has been employed coagulation is local--_i.e._, we have lumpy
coagulation, and often a very milky remaining liquor. This is due to the
fact that, as coagulation is immediate upon the spot which is first touched
by the pure acid, a deal of the acid is enclosed within the rubber at that
spot, and hence other portions of the latex are deprived of acid. It is in
such cases that most air-bubbles are enclosed.
As the dilution of the acid solution is increased the mixing is more
thorough and uniform. Coagulation is slower, and air-bubbles can escape to
the surface.
METHOD OF MAKING STOCK SOLUTION.--Experiments have been repeatedly made in
the laboratory with acid solutions of varying dilution, from pure acid down
to 1 part of acid in 500 parts of water. While it has been found that a 1
in 5 solution can be used where the latex is very dilute (say, 1 part of
latex to 5 parts of water), and a 1 in 20 solution may be used in fairly
dilute latex (for crepe-making), it is undoubtedly a fact that for latex as
generally "standardised" on estates a much more dilute solution of acid
should be used--_e.g._, 1 in 100, or even 1 in 200, of water. It must be
borne in mind that the quantity of acid necessary for coagulation is not
changed, but merely the dilution. Let us take a concrete case to illustrate
the point:
On an estate at present the stock solution is made up by diluting 1
pint of acid with 20 pints of water, and 1 gallon of this is necessary
to coagulate 50 gallons of pure latex.
It is desired to use a stock solution of 1 pint of acid to 100 pints
of water. Evidently, therefore, 5 gallons of this stock solution
contain only the same quantity of pure acid as 1 gallon of the old
solution contained, and it will be necessary to add 5 gallons for
every 50 gallons of pure latex. Thus:
1 to 20; 1 gallon necessary for 50 gallons pure latex.
1 to 100; 5 gallons necessary for 50 gallons pure latex.
It may be pointed out that the quantities worked out in the foregoing
examples are not absolutely and mathematically correct, but they are quite
close enough for all practical purposes.
It may be advanced by someone that if a dilute solution of acid, such as 1
in 100, is used the bulk of this stock solution (5 gallons to 50 gallons of
latex) is very great, and might be injurious to the quality of the
resulting rubber. A moment's consideration will show that, after all, the
volume of acid solution is only one-tenth that of the volume of latex. This
can have no effect upon the quality of the rubber. Even dilution of the
pure latex with half its bulk of water in the factory will have no effect
upon the quality of the resulting rubber. It is to be remembered that,
except in cases where the proportion of added water to latex is absurdly
large, the main argument against putting water into the latex-cups is
against the possible poor quality of the water rather than against the
actual small quantity theoretically added. It is acknowledged that, where
the water to be put into the cups can be guaranteed to be of good quality,
no great objection would be raised against placing the smallest possible
quantity of such water in the cups. But how many estates have such good
water easily available to the coolies, and how many estates can be sure
that only that smallest possible quantity would be used? It is a notorious
fact that, even on estates where the quantity of water used was supposed to
be a minimum, the proportion of water to latex in some cups often exceeded
even three or four to one. In any case it may be stated as an elementary
truism that the absence of water is more to be desired than water of
doubtful quality.
QUANTITY OF ACID.--As a result of repeated experimental work it has been
found that, for pure average latex, the quantity of acid necessary for
complete coagulation, reckoned in parts of pure acid to parts of latex, is:
1 part pure acid; 1,000 parts average latex.
Where the latex is rather richer than average (above 30 per cent. dry
rubber) probably a little more acid would be required, and similarly if the
dry rubber content is lower the quantity of acid must be less.
It used to be a common belief that the more dilute the latex the greater
the quantity of acid necessary, but this would only apply to cases of
extreme dilution of latex.
As a matter of fact, up to certain limits of added water, the reverse is
actually the case--_i.e._, the more water in the latex the less acid must
be added, assuming that for pure latex the proportion of pure acid to latex
is taken as 1 part to 1,000 parts. This was found to be the case up to
dilutions of three or four times the volume of latex. To take concrete
examples which will perhaps make the truth more clear:
Assuming we commence by making up our stock solution of acid by adding
100 parts of water to 1 part of pure acid, this gives us a mixture of
1 to 100. For 1 gallon of pure latex it would be necessary to add
one-tenth of its volume of the above mixture--_i.e._, 16 ozs.
Suppose we take a gallon of pure latex and add a gallon of water, we
now have 2 gallons of so-called latex. But we still have only 1 gallon
of real latex present in the diluted latex, and it is only necessary
to add sufficient acid to coagulate this gallon--_i.e._, 16 ozs.
Further, if 1 gallon of latex be diluted with 2, 3, or even 4 gallons
of water it is still only necessary to add 16 ozs. of the acid
mixture.
At dilutions beyond this limit, however, it is necessary to add a
little more acid to obtain complete coagulation.
In the process of preparing sheet rubber it is very necessary to see that
the minimum quantity of acid is used, otherwise visible defects are caused.
But in coagulating latex intended for preparing crepe, where the rubber
undergoes protracted washing on the machines, the presence of a slight
excess of acid in coagulation is not calculated to cause any deterioration
in the quality of the rubber. Advantage must not be taken of this statement
to argue that more than a slight excess may be used without injury to the
rubber, as it can be shown that the use of a large excess of acid results
in an inferior rubber.
QUANTITIES NECESSARY FOR MODERN REQUIREMENTS.--It may be commended to the
notice of the beginner that any further experimental work as to the
quantity of acetic acid necessary for complete coagulation would only
involve a waste of time and energy.
The general figure given in a preceding paragraph (1 part pure acid to
1,000 parts of latex) may be accepted as the rough basis for working. In
modern practice, however, undiluted latex is usually diluted to a standard
which may vary on different estates from 1-1/4 lbs. to 1-1/2 lbs. dry
rubber per gallon.
Latices of these strengths can be coagulated at a ratio of 1 part pure acid
to 1,200 parts of standardised latex; and this quantity need not be
exceeded, except in cases where an appreciable amount of some
anti-coagulant is present in the latex. The proportion may then be raised
to 1 in 1,000.
If considered advisable the acid may be used in a 1/2 per cent. solution
for sheet preparation; but in any case it is advised for the sake of
uniformity that a 1 per cent. solution should be employed in the
preparation of both sheet rubber and crepe rubber. In most modern
factories, measuring vessels of various capacities are to be found, and it
is always more satisfactory to have the solution made up in approximately
correct strength at the rate of 1 oz. of pure acid to 5 pints of water.
Often, however, on some estates European supervision of this work is not
possible, and the preparation of the acid solution has to be left in the
hands of a (more or less) skilled coolie. It is thus necessary to find some
less fine, but still approximately correct, method of procedure. In the
East the kerosene tin is in universal favour for the carriage of water, and
there is no reason why it should not be utilised as a standard measure for
preparing the dilute acid solution, _providing it is not allowed to become
rusty_. The capacity of the tin is 4 gallons (640 fluid ozs.), so that a
one-hundredth part would be approximately 6-1/2 ozs. It is suggested that
this quantity should be measured out by means of a glass graduated vessel,
and then that an aluminium cup should be cut down so as to hold the exact
quantity.
This would reduce the making of a solution, sufficiently approximate to 1
per cent. strength for all practical purposes, into a simple operation of
mixing pure acid and water in the ratio of one cupful of acid to 1 kerosene
tin of water.
The actual quantity of solution required for the coagulation of any volume
of standardised latex can be calculated easily from the ratio 1:1,200. As
the strength of solution is 1:100 it will be seen that the quantity to be
taken is _always one-twelfth_ that of the volume of latex--_e.g._:
(_a_) If the latex tank holds 90 gallons of standardised latex, 7-1/2
gallons of dilute acid solution are required.
(_b_) A tank containing 120 gallons of latex would need 10 gallons of
the 1 per cent. acid solution.
It is assumed that all estates, not only in the preparation of sheet
rubber, but also in the making of crepe rubber, always employ the system of
standardising latex in order to obtain uniformity. They are ill-advised if
they do not follow this practice; but in case average undiluted latex is
treated in coagulation, the quantity of acetic acid to be used should be
calculated from the ratio 1:1,000.
If the acid solution is to be employed in 1 per cent. strength, _one-tenth_
of the volume of latex to be treated will indicate the required quantity of
solution necessary for complete coagulation unless anti-coagulants have
been used, when the quantity must be increased as experience directs. It
will be recognised, of course, that undiluted latex may only be used in any
case for the preparation of crepe rubber; or in some exceptional case, such
as the special preparation of "slab" rubber.
CARE IN MIXING.--It is essential that the mixture of dilute acid and latex
should be thoroughly intimate. This can only be attained by careful
manipulation, especially in the case of sheet preparation. Where crepe
rubber is to be made it may be permissible to employ a solution stronger
than 1 per cent., but it is not advised. The acid should be poured into
the latex while stirring, and the agitation should continue for such a
period as to ensure thorough mixing in all parts.
It will be appreciated that in the preparation of sheet rubber this period
may not be unduly prolonged, otherwise the latex will have begun to
coagulate before skimming and the placing of the partitions in their
respective slots can be effected. Furthermore, while in the preliminary
treatment for crepe rubber, the formation of enclosed bubbles and surface
froth is immaterial. For sheet preparation it is essential that the
stirring shall be done so carefully as to try to avoid internal bubbles and
to reduce surface froth to a minimum. For crepe-making a perforated board,
with handle attached at right angles to the face of the board, may be used;
but in shallow sheet-coagulating tanks, broad paddles (which may or may not
be perforated) give good results as long as there is a sufficient number
used to cover the area of the tank in reasonable time. Obviously also,
where the area of any tank or compartment is of any appreciable size, the
dilute acid solution should be poured in from various points so as to
obtain a good even distribution. In some cases the acid is distributed from
a sprinkling can, but this is a refinement which experience shows to be
unnecessary. In actual practice, working on a tank measuring 12 ft. by 4
ft., no difficulty is found if coolies pour in acid solution from four
points. The degree of success depends entirely upon experience and
efficient supervision. This remark applies equally to the use of various
devices, such as rakes with broad teeth, used as stirring implements. There
is room for display of ingenuity in this direction, and it is found often
that, while they are used successfully on one estate, they may be condemned
on another.
[Illustration: TWO VIEWS OF DILUTION AND MIXING TANKS.
Below, on the right, coagulating tanks. At the far end strainers. Each
dilution tank is of equal capacity to the corresponding coagulating tank.]
USE OF SODIUM BISULPHITE.--Some few years ago a demand for pale crepe
rubbers sprang up, and this demand has been maintained. The total quantity
of pale rubber put on the market previously could only have amounted to
very little, and that little was obtained by luck and various tricks in
manipulation. It must be premised that if coagulation is allowed to take
place, either naturally or with the aid of acetic acid, the resulting
rubber will almost inevitably oxidise on the surface, except in the cases
of very dilute or young latices. Even supposing that this darkening of the
surface does not take place in the wet stage, it is often found that a
rubber expected to dry to a pale colour does not fulfil expectations, and a
dull neutral shade results. This darkening of crepe rubber may be
attributed to a slow process of oxidation, which continues until the rubber
is dry. From these remarks it will be seen that the process of oxidation is
a natural one, and that any pale rubber formerly shipped was the outcome of
circumstances outside the control of the estate, except in such cases where
boiling of the coagulum, etc., was resorted to. The fact that one rubber
happened to be a shade darker than another was absolutely no criterion as
to the value of the rubber, but apparently the market thought, and still
thinks, otherwise, although the actual necessities of manufacturers for a
pale crepe to be employed in special processes must be comparatively small.
The prevention of this natural oxidation was a problem which exercised the
minds of all responsible for the preparation of pale rubbers, and much time
and thought were expended upon it. Various theories were propounded, and
the chief conclusion arrived at was that the darkening of rubber was to be
prevented by excluding all the light possible from the drying houses. To
this end windows were to be kept shut, or else they were provided with
ruby-coloured glass, which incidentally kept out the air. In spite of these
precautions, little success attended the expenditure of so much energy and
thought. It was absolutely necessary that some chemical agent should be
discovered which would make the preparation of pale crepe possible for any
estate. This chemical would have to fulfil several requirements before it
could become popular:
1. It must be a simple substance capable of being easily handled.
2. It must be very soluble, so that solutions could easily be made up
by inexpert workers.
3. It must be cheap.
4. It must be quite innocent of any harmful effect upon the quality of
the rubber.
After months of investigation into the properties of other chemicals the
writers decided that the only one which satisfactorily answered all
requirements was sodium bisulphite. The writers make no pretension to any
claim of having discovered the properties of this substance, which was a
common chemical, and widely known. Even its action on latex was suspected
before they engaged upon the work. These matters are only mentioned because
the credit, if any, should be given to the laboratories of the Rubber
Growers' Association.
As soon as it began to be known on the market that sodium bisulphite was
being used in the preparation of pale crepe, a great outcry was made, and
estates were warned that no more rubber prepared in this way would be
accepted. It was said that the chemical would destroy the "nerve" of the
rubber,[2] and it was definitely stated that rubber prepared with this
chemical was brittle. It must be remembered that brokers had some
legitimate excuse in raising objections to the introduction of new and
strange chemicals for preparing rubber, as they were quite without means of
judging whether the rubber had suffered harm or not. Still, on the other
hand, private tests had been made in conjunction with Messrs. Beadle and
Stevens for fully eight months before the name of the chemical was
mentioned in reports, and they had decided from the results of
vulcanisation tests that the chemical was quite innocuous. Then, and only
then, did we consider it advisable to recommend the use of sodium
bisulphite in general estate practice. Owing to the initial prejudice
against rubber prepared with sodium bisulphite, the results of our
preliminary work were published by permission of the Rubber Growers'
Association.[3] The original instructions to estates regarding the proper
employment of this chemical were given in the private reports issued by the
Rubber Growers' Association in 1911. At the present time it is probably
accurate to state that it is now used by all estates preparing fine crepes.
Representatives of manufacturers have sometimes given us to understand
that the question of paleness of colour in such rubber is of no such
importance as is impressed upon us as producers. While we are prepared to
believe, we can only plead that from our point of view the supply arises
from the demand. Such are the conditions governing the sale of rubber that,
irrespective of the requirements of the ultimate user, we have to market
rubber which is valued almost completely upon its appearance at the time of
sale.
[2] Williams, International Rubber and Allied Congress, London, 1914.
[3] "The Employment of Sodium Bisulphite in the Preparation of Plantation
Rubber," Beadle, Stevens, and Morgan, _India-rubber Journal_, August 2,
1913.
As long as such conditions prevail estates must continue to adopt any
device of proved harmlessness, in order to obtain the best possible price
for their product, and not because we desire to continue a practice which
some assure us to be unnecessary, and which, moreover, adds somewhat to the
cost of production.
QUANTITIES OF SODIUM BISULPHITE.--It must be premised that, although sodium
bisulphite is employed on some few estates in the preparation of sheet
rubber, we do not advise the practice. It is unnecessary, and may lead to
some little trouble and delay in drying. In any case, sodium sulphite gives
the results desired for sheet rubber (see following). It must be
understood, therefore, that we are concerned here, in the case of sodium
bisulphite, with its employment in the preparation of fine pale crepe only.
As the dry rubber contents of latices vary with the age of the trees, the
general health of the trees, the seasons and general climatic conditions,
the relative strain imposed by depletion of reserves through tapping, etc.,
it will be clear that the effect produced by a definite quantity of sodium
bisulphite in any given volume of latex will also vary--_i.e._, the effect
depends upon the potential amount of rubber present. A dilute latex needs
less sodium bisulphite than a richer latex to produce the same effect in
colour.[4]
[4] Incidentally there are certain occasions, as in the opening of areas of
bark rested for long periods, when the latex is of a rich yellow colour.
Sodium bisulphite will not "bleach" this colour, and it is well to remark
again at this stage that the action of the chemical is only to avoid or
arrest oxidation (darkening).
Hence it follows that if in any factory uniform quantities of the solution
are used for any given volume of undiluted latices from different areas of
the estate, the effect upon the dry rubbers will vary. This explains why
some estates obtain different shades of rubber in their fine pale crepes.
The remedy obviously is to reduce the variation in latices by diluting them
all to a standard rubber content as is done in sheet preparation. One is
thus assured that the prescribed quantities of sodium bisulphite will meet
requirements in every case, and that waste will be avoided.
Working with a standard of 1-1/2 lbs. dry rubber per gallon the following
formula should serve as a _maximum_:
_Formula for Use of Sodium Bisulphite._
(_a_) Dissolve sodium bisulphite in water at the rate of 1 lb. to 10
gallons.
(_b_) Of this solution use 1 gallon to every 10 gallons of latex.
MAKING A SOLUTION.--The making of a solution of the chemical would seem to
be a simple matter, but to judge by the ill-effects sometimes observed in
the dry rubber the simplicity of the operation appears to have been
overrated. Great care must be exercised in preparing the solution, and the
work should not be left to the few minutes preceding its actual
requirement; such has been found to be the case in several factories, so
that it is not surprising if the rubber is defective.
The powder should be added gradually to water with thorough stirring, which
should be continued for five minutes at least. Even then there may often be
seen at the bottom undissolved particles, sand, and other impurity. It is
necessary, therefore, in such cases to decant the solution through a piece
of cotton cloth before using. No solid particles should be allowed to enter
the latex.
ABUSE OF SODIUM BISULPHITE.--It is now generally recognised that the abuse
of sodium bisulphite, in the form of an excess, leads mainly to delay in
the period of drying and the production of an overpale rubber.[5] It is
probable that few estates, if any, now experience trouble due to this
non-observance of the rules and quantities laid down for use.
[5] "The Preparation of Plantation Rubber," Morgan, 1913, p. 74.
RESIDUAL TRACES OF SODIUM BISULPHITE.--The prolongation of the drying
period was attributed to the fact that traces of substances caused by the
decomposition of sodium bisulphite remained in the rubber if the rubber
were not sufficiently worked and washed on the rolls. These traces must
have been very minute, but they were sufficient to retard the progress of
drying. That much depended on the care exercised in washing is evident from
the fact that samples prepared with varying quantities of the chemical show
varying results on extraction. These samples were tested for the presence
of sulphates. Of the series tested that sample prepared with bisulphite in
the proportion of 1 part to 600 parts latex showed only a trace of sulphate
present; while the one prepared 1:2,400 gave an equal quantity.
Intermediate samples contained no trace of sulphate. On the whole,
therefore, the presence of sulphate in crepe rubber is adventitious, and
properly washed crepe prepared with moderate quantities of bisulphite may
be taken as free from any residual quantities. Meanwhile there cannot
possibly be any doubt of the advantages gained by the use of sodium
bisulphite, and it would not be very wide of the mark if the statement were
made that, in the event of this chemical being discarded, most contracts
for pale crepe could not be fulfilled.
SODIUM SULPHITE.--It would not be amiss to insist upon the point that while
the nature of sodium _bisulphite_, as employed in the preparation of
rubber, is anti-oxidant, sodium sulphite is employed chiefly for its
anti-coagulant property. It is not used, therefore, in the making of crepe
rubber, but is of service in the preparation of sheet rubber, where the aim
is to keep the latex in good fluid condition as long as is necessary, and
to retard coagulation slightly so that enclosed bubbles of gas or air may
escape. Formulae have been given for its use in the field when required. On
some estates this practice is not found necessary, but a quantity of
solution is always placed in the bottom of the reception vessels prior to
the straining of latex into them. Only a small quantity is used, and as a
working basis the following formula may be adopted:
_Sodium Sulphite: For Use in the Factory._
(_a_) Dissolve 2 ozs. of anhydrous sodium sulphite in a gallon of
water.
(_b_) The gallon of solution, placed in the bottom of the reception
jar or tank, is sufficient for the treatment of 40 gallons of
standardised latex (1-1/2 lbs. dry rubber per gallon).
The warning previously given regarding the necessity for thoroughness in
the preparation of solutions is here reiterated. Stirring should be
thorough, say for five minutes, and if there is any sediment or undissolved
matter the solution should be strained through cloth before using.
Where uniform jars or tanks are in use, the majority of which will contain
uniform quantities of latex daily, the practice of using the chemical can
be made almost fool-proof even in the hands of coolies. A calculation is
made of the quantity of powder required for each vessel daily. The
necessary number of lots is weighed out each morning and each placed in an
envelope. The process is thus simplified by the fact that the contents of
an envelope, neither more nor less, are required for each unit reception
vessel. Even the weighing can be done by a coolie if he is given a
counterpoise (of lead, for example) equivalent to the required weight.
It will not be found necessary to do any vigorous stirring of the solution
with the latex, as the latter is strained into the solution and the
continued addition of successive quantities is sufficient to give a good
mixture.
USE OF FORMALIN.--Few estates now use formalin (formaldehyde) as an
anti-coagulant. It must be acknowledged that when not abused there are
points in favour of its employment in preference to sodium sulphite, but
these are outbalanced by certain disadvantages. The argument may be stated
thus:
_Points for_: (1) If made up freshly it is an effective
anti-coagulant.
(2) Formalin being the solution of a gas in water, there is no
residual substance left in the rubber to delay drying.
(3) Its use gives a bright clear rubber.
_Points against_: (1) Its cost at all times is greater than that of
sodium sulphite.
(2) If the jar is not sealed there is loss by evaporation, thus
increasing the cost.
(3) Its effect upon the rubber is uncertain. Even in normal quantity
it is said to cause "brittleness" or "shortness."
Certain few estates, however, have continued its use, and no trouble is
claimed to ensue. The following formula is stated to give satisfactory
results in the preparation of sheet rubber, when applied as in the
preceding paragraphs bearing on the employment of sodium sulphite:
_Formula for Use of Formalin (Formaldehyde)._
(_a_) 1 pint of formalin is diluted with 5 gallons of water.
(_b_) Of this solution 1 gallon is required for 50 gallons of
standardised latex.
In noting this formula the writer gives no recommendation regarding its
use. Whatever may be the actual facts regarding the effect of formalin upon
the vulcanisation of rubber, when used in minimum proportions, there can be
no question concerning its injurious effect if used in excess. Beyond this
the factors of cost and loss militate against its wider employment.
CHAPTER IX
_PREPARATION OF SHEET RUBBER_
PALE SHEET.--The first form in which plantation rubber was prepared was as
"biscuits" or sheets. This form remained in favour for some years. The
first biscuits or sheets were rather dark in colour owing to the natural
oxidation which followed. Then it was discovered that by diluting the latex
the degree of oxidation was diminished, and later it was found that if the
soft coagulum were placed in almost boiling water for a short time the
resulting rubber was pale. Thus there arose gradually a demand for pale
sheet. With our present knowledge we are in a position to state that the
pale biscuits were not in any way superior to the darker ones, and they
were in most cases actually inferior.
It was found also as time progressed that sheet rubber, on air-drying,
became covered with external surface moulds, and that, more often than not,
the smell of the drying rubber was the reverse of pleasant. Even when dry
the sheets had to be continually brushed free from moulds, and by the time
the rubber reached the market it was again usually mouldy. Such are, even
now, the handicaps under which those who prepare pale sheets have to
labour. Few, however, are the estates making pale sheets, and they are
confined almost entirely to native holdings.
To those accustomed only to the preparation of crepe rubber, where
coagulation can be effected in large batches, the preparation of sheet
rubber always seems to demand much more labour. As a matter of fact,
although the preliminary operations certainly do demand more care and
labour than in crepe-making, there are compensating advantages in the
machining stage. For the preparation of sheet of the highest quality on any
but the largest scale, elaborate installations of machinery are quite
superfluous, as equal results can be obtained with pairs of rolls worked by
hand.
UNIFORMITY OF PRODUCT.--There will be no need to enter again into a
discussion of the preliminary operations of receiving and straining latex
for sheet-making. They have been fully dealt with in Chapter VII. It used
to be the general custom to mix the acid and latex in each individual dish,
and in some small or non-progressive factories that is still the procedure.
Quite apart from the question of labour entailed, the process is quite
unnecessary. Even if comparatively small volumes of latex are handled,
standardisation by dilution should be the rule, and the acid solution
should be added to the bulk. It is possible to stir in the acid and to
ladle out uniform quantities in each pan or dish from a bulk volume of up
to 40 gallons if the organisation is efficient.
On any but a small scale the labour entailed in the handling and cleaning
of pans is excessive, and shallow tanks are now employed on most estates.
The reception and standardisation of latex by dilution has already been
discussed in Chapter VII. The combination of this practice with the
employment of shallow coagulating tanks has simplified working and reduced
the cost of labour. It is not intended to enter into any lengthy discussion
relative to the merits of sheets made in pans as against those made in
tanks. It is granted that it is possible to make a "pan" sheet superior in
appearance to the general average of "tank" sheets; but from an economic
standpoint the introduction of the use of tanks into all but the smallest
factories is only a matter of time, if the demand for this class of rubber
persists.
THE IDEAL TANK.--Even the most modern installations of sheet-coagulating
tanks must be regarded as merely temporary devices, as, given facilities,
the room for improvement is so wide.
The first tanks made erred in being too large, and as the result of
experience the size of units has now been reduced to a maximum of 12 feet
by 4 feet by 1 foot deep.
[Illustration: UNIT MODERN COAGULATING TANK (TWO VIEWS).
Construction of brick and cement with lining of glazed tiles. Note slots
incorporated in side tiles. Partition boards in piles in the background.]
Tanks are at present constructed either of hard timber or of brick and
cement faced with glazed tiles; both types have inherent drawbacks. The
wooden tanks are difficult to keep clean and in "sweet" condition. The
glazed tiles, unless extremely well laid, allow the acid serum (from which
the rubber is removed) to percolate between the interstices. Thus "pockets"
of liquid collect beneath the tiles, and in process of the decomposition of
certain constituents dissolved in the serum evil-smelling gases are set
free.
[Illustration: ANOTHER BATTERY OF TANKS, WITH DILUTION TANKS, RAISED, ON
THE RIGHT.
Note drainage cocks, chute, and sieve in position.]
It should not be a matter of difficulty for manufacturers to make sheets of
thick glass sufficiently large to form the bed-plate and side-pieces
necessary in the lining of a tank. If such adjuncts could be secured, the
disabilities indicated above would be perhaps wholly removed. Unless there
is a demand from estates, however, it is idle to expect a supply to be
forthcoming.
An even greater improvement would take the form of unit tanks cast in
glazed white-ware with the necessary slots incorporated in the sides. At
present no known firm makes such tanks of sufficient size. A unit could
measure (internally) 6 feet by 4 feet by 1 foot deep, with slots 1-1/2
inches apart, and 3/8 inch in width. The tanks might be reinforced with
iron bars, so that they could either be used alone or embedded in the usual
brick structure. The junctions of the bed-plate and side-pieces could be
finely rounded so as to facilitate cleaning, and at one end a draining-hole
could be made, say, 1 inch in diameter.
[Illustration: CLOSER VIEW OF FOREGOING.
Note partitions in position and coagulum being removed.]
Meantime both the hard-wood tanks and those of glazed tiles find their
particular applications. The former is generally employed in smaller
factories, or where future large increases of crop preclude the present
installation of a fixed system. The latter find use in large factories, or
where no new areas remain to come into bearing.
MODERN INSTALLATION.--As an example of a modern installation of coagulating
tanks, we can do no better than offer reproductions of the system now in
use on Pataling Estate.
A warning must be given against employing all tanks of stone-ware or cement
unless well glazed. Almost without exception, irrespective of the material
used in the construction of coagulating tanks, wooden partitions are
employed. In the few exceptional cases the partitions are either of glass
or of aluminium. The former would appear to be the ideal substance, were it
not for initial cost and loss by breakage. These disabilities may possibly
be overcome in course of time.
CARE OF TANKS.--The use of aluminium would have been wider had it not been
for lack of supplies and the question of cost during the War. A novel
method of employing aluminium partitions was introduced in the factory of
Tremelbye Estate. There were no slots in the sides of the glazed-tile
tanks, but the necessary slots were very ingeniously created by means of
aluminium "distance-pieces," the two long edges of which were turned at
right angles to the face of each piece to a depth of about 1/4 inch. The
ends of the thin aluminium partition moved in the slot thus formed between
two adjacent "distance-pieces." The friction between the surfaces was
sufficient to allow all the partitions, when in position, to be raised well
above the floor of the tank, so that a uniform level of latex was obtained.
Slight hand-pressure only was then required to push the partitions down.
Naturally the cleansing of glass or aluminium partitions presents no
difficulty, but in the case of wood failure to ensure thorough cleanliness
leads to possible defects in the finished dry rubber. Provided the wood
could be made waterproof, no trouble would ensue, and hence various
measures have been tried with that object in view. When new the boards have
been surface-waxed or varnished, and the treatment has been repeated on
occasions. But in course of time the surface film of waterproof material
has disappeared, partially or wholly, and the trouble recurs. When
partitions become sodden with serum, the surfaces are liable to be coated
with a slime, consisting largely of organic growths which have an effect
upon the latex, causing "pitting" on the surface of the coagulum and
enclosed bubbles within.
[Illustration: ANOTHER BATTERY OF TANKS, WITHOUT DILUTION TANKS OR MEANS OF
GRAVITATING LATEX.]
It is recommended, therefore, that wooden tanks, after ordinary cleansing
daily, should be swabbed out with a 5 per cent. solution of sodium
bisulphite. Wooden partitions should receive the same treatment, and once a
week at least (or every day if possible) they should be placed in the sun
for an hour or two, care being taken that both sides of a partition are
exposed in turn. Before being placed in the latex, all wooden partitions
should be made wet on the surfaces.
Some years ago the writers had made a partition of vulcanite, which
apparently would have proved of great service but for the initial cost. The
advent of the War put the matter out of the question, but it is possible
now that such a material would be worthy of extended trial. Except in the
matter of cost, it would appear to have advantages over any substance yet
tried; and if it were possible for estates to supply their own lower grade
rubbers direct, the cost might be reduced considerably.
[Illustration: A SHEETING TANK CONTAINING COAGULUM FOR CREPE PREPARATION.
Behind wall in background are the tanks in which latex is standardized.
Note vent, to the left, through which latex flows and wooden "stopper" on
edge of tank.]
STANDARD LATEX.--Enough has been written (see Chapter VII.) to familiarise
the reader with the use of this term for the description of latex diluted
daily to a level of dry rubber content. Whatever may be the practice
elsewhere, it is now fairly general on estates in Malaya to reduce all
latices to a uniform "strength" for the preparation of sheet rubber. It is
claimed that only in this manner can uniformity of product be achieved.
The selection of a standard has been the outcome of general experience. It
has been found that if too high a standard is taken difficulties arise,
such as (1) unsatisfactory and uneven coagulation, (2) too thick a coagulum
for easy working in general, (3) too extended a period of drying and
smoke-curing, and hence too dark a colour in the finished rubber.
[Illustration: A "BATTERY" OF SHEETING TANKS (PATALING ESTATE). DILUTION
TANKS, RAISED, ON THE LEFT.]
On the other hand, too low a standard also brings trouble in its train. The
coagulum is too porous, will not stand handling, and the resultant sheet is
too thin unless an abnormal thickness of coagulum is prepared. Furthermore,
over-dilution means an increase in the number of tanks required for any
original volume of latex. This involves an increase in floor area, and
perhaps in the size of the building. The soft sheets, when rolled, may
spread to such a width as to cause the edges to be squeezed under the
cheek-blocks of the machines, etc.
For all practical purposes, whether sheets are prepared in pans or in
tanks, it has been found that the optimum results are obtained by the
adoption of a standard approximating and not exceeding 1-1/2 lbs. dry
rubber per gallon. Primarily this standard has a direct connection and
interdependence with the distance between the partitions (or between the
slots) in coagulating tanks. The distance found most practicable is 1-1/2
inches. This thickness of coagulum, when prepared from latex not exceeding
a standard of 1-1/2 lbs. dry rubber per gallon, is found to yield a very
satisfactory sheet in all respects.
It will be seen that we have two possible main factors of variation:
(_a_) Distance between partitions, causing visible differences in
thickness of coagulum.
(_b_) Dry rubber content of latex, causing differences in the density
(_e.g._, hardness or softness) of the coagulum.
The effect of variation in (_a_) will be clear. Even when latex of a
standard of 1-1/2 lbs. per gallon is employed the resulting sheet may be
either too thin or too thick.
Similarly, as already argued, the use of too low or too high a standard of
dilution (when the factor of distance between partitions is not allowed to
vary) is capable of causing much difficulty. While this is correct,
broadly, it is found in the experience of some estates that their
requirements are satisfied by a slightly lower standard than 1-1/2 lbs. per
gallon. Thus it is not uncommon to note the adoption of a standard
equivalent to 1 lb. 4 ozs. or 1 lb. 6 ozs. dry rubber per gallon.
Experience dictates, however, that for the recognised standard measurements
of modern tanks the practical limits of satisfactory density of latex lie
between 1-1/4 lbs. and 1-1/2 lbs. per gallon.
STANDARDISING INSTRUMENTS.--For standardising latex by dilution all that is
required is an instrument which will preserve a perpendicular position
while floating in latex, will be sufficiently sensitive to indicate fairly
small differences in density of latex, and has one mark on its aerial
portion accurately indicating a density corresponding to the required
standard. On scientific grounds it can be demonstrated that such an
instrument as employed in common practice would not be strictly
accurate.[6] It is not proposed, in this section of the book, to discuss
such considerations.
[6] De Vries, "Archief voor de Rubbercultuur."
Instruments of this nature are represented by the "Metrolac" (originating
from the Rubber Growers' Association) and other similar recorders. They
generally consist of a submersible bulb with a projecting stem which is
graduated. The "Metrolac" differs from others in that the bulb is of
torpedo form (thus reducing "skin friction"), and the graduations on the
stem indicate actual weight of dry rubber per gallon instead of the
ordinary specific gravity figures.
Theoretical considerations to the contrary, it is found in actual practice
in Malaya and Ceylon that, although such instruments are naturally delicate
and require careful manipulation, they are of considerable practical value
and satisfy a definite requirement. Until an instrument of greater accuracy
and equal simplicity can be discovered all estates should regard the
possession of a few "Metrolacs" as essential.
The nature of their construction and the average conditions under which
they are used (and abused) make it impossible to rely upon their accuracy
indefinitely or for any long period. It is always recommended, therefore,
that there should be at least two instruments available, one of which may
be in daily use, while the other is kept in safe custody and only employed,
say, once a week for purposes of checking the accuracy or degree of
inaccuracy of the other. This can be done with reasonable approximity by
placing both instruments in a tall vessel containing well-mixed and diluted
latex. Instruments showing a marked degree of inaccuracy should not be
preserved; but in cases of necessity "Metrolacs" from estates belonging to
company members of the Rubber Growers' Association may be sent to the
laboratories for repair and adjustment.[7]
[7] This applies to the gilt brass instruments. As the result of experiment
the Rubber Growers' Association are now introducing glass instruments.
These are necessarily more fragile, but while unbroken can be relied on to
give correct readings.
Where field coagulating stations have been instituted on estates, it is
strictly necessary that instruments should be provided in all cases; and it
should be a rule that these are tested and corrected weekly by a standard
instrument employed for that purpose only. This need was well recognised by
many estates when, during the War and the consequent shortage of supply of
"Metrolacs," a demand arose which was met in some degree by crude
instruments of local manufacture, such as that commonly known as the
"Castlefield bobber," contrived and made by the enterprising manager of the
estate of that name. The demand for the more accurate instruments can now
be met.
METHODS OF USING THE INSTRUMENTS.--The "Metrolac" was devised and
introduced by the writers on behalf of the Rubber Growers' Association, and
directions for its use were given. Tables were prepared by means of which
simple calculations for the dilution of any given latex could be made.
These did not find an extended application, inasmuch as in the majority of
cases native workers only were in charge of the processes of rubber
preparation. In point of fact, such calculations are not strictly
necessary, as the operation of standardising the latex can be done quite
simply and skilfully by a trained native. Latex as it reaches the store in
average weather from any particular division or field does not vary greatly
in density. The trained coolie or foreman, basing his practice on
experience, adds to the latex a quantity of water, and then makes a first
test with the standardising instrument. Several additions of water (with
thorough stirring) may have to be made before a test indicates that the
correct density has been obtained, but it is surprising how quickly a
skilled worker will arrive at the desired standard. Extreme or absolute
accuracy is not insisted upon or desired, as avoidable delay is to be
deprecated, and the result in any case is sufficiently exact for practical
purposes.
SKIMMING.--During the gravitation of the latex from the reception vessels
(in which the standardising of the latex is effected) to the coagulating
tanks, much surface froth is usually caused. This is best removed by means
of a thin board of a width slightly less than the breadth of the tank. The
skimmings are sometimes placed in pans and subsequently made into a second
grade of sheet rubber, or they receive treatment with a small proportion of
sodium bisulphite and eventually appear as fine pale crepe. The practice
varies usually according to the form in which the general No. 1 grade is
prepared.
On some estates a great deal of the frothing is avoided by placing in
position at the receiving end of the tank a perforated partition. This
partition may be made of wood, or of stout zinc (or aluminium) carrying ten
circular holes to the inch. Through this the latex percolates, while the
froth is retained on a small area. The froth is removed prior to the
addition of the acid. After stirring in the acid solution most estates
again skim the surface of the latex; but if the stirring has been performed
properly there should be little froth. This, when it collapses, in any case
will appear only on the upper edge of the strip of coagulum, and after
rolling should not be visible. It would appear, therefore, that the second
skimming is not necessary.
STYLE OF SHEET.--Within the last few years the custom of making plain
sheet--_i.e._, sheet having a plain surface--has gradually given place to
the preparation of ribbed sheet--_i.e._, sheet having a pattern marked on
the surface. It would probably be correct to say that plain (smooth) sheet
is now only prepared by natives or by some estates just come into bearing.
Even in the latter case there is no reason why smooth sheet should be made,
as hand machines are sold which will do all the work required. It will be
evident to anyone acquainted with rubber preparation that in the matter of
actual quality of rubber the question of smoothness or a pattern can have
no bearing on the result. One advantage claimed for ribbed sheet which may
entirely justify the preference exhibited by consumers, relates to the
question of packing. When rubber arrives at home it is frequently found to
be in an almost solid block, due to the pressure of the sheets superimposed
in the case. The smoother the surfaces of the rubber in contact the greater
the adhesion and the denser will be the mass, and consequently the greater
the difficulty in separating individual pieces. Under such circumstances it
is plain that the difficulty is diminished if the sheets have a raised
pattern on them. It is noted also that the liability to mildew-growth is
greater the smoother the surfaces of the rubber.
On these grounds the "marking" of sheet rubber is to be commended. These
reasons apart, it is really astonishing the difference made in the
appearance of the sheets by impressing upon them a ribbed pattern, and it
is highly probable that the market value of the rubber is slightly
increased. It is not our duty to attempt to reason why this simple
operation should increase the market value of sheet rubber; it is
sufficient to recognise that it is so, and that money may be thrown away by
neglecting to cater for the taste of the market. Of the patterns impressed
upon sheet rubber there is a variety, but the general style is that known
as the "spirally close-cut ribbing."
STANDARD SHEET.--Leaving for the present the question of pattern of mark,
one cannot do better by way of introduction than to reproduce the
instructions[8] given generally to estates.
[8] "Handbook on Preparation of Rubber," Rubber Growers' Association, May,
1917, p. 28.
ROLLING AND MARKING OF SHEET RUBBER.--Working with standard latex it is
found that strips of coagulum 1-1/2 inches in thickness require little
rolling to produce sheets of desirable thickness.
(1) The sheets or strips are first given a preliminary rolling with a
heavy hand-roller made of hard wood. The roller is passed once in one
direction, and once in the reverse direction.
(2) The coagulum is then passed through smooth machines twice, once
with the rolls fairly open, and once with a narrower space. It is not
found advisable to close the smooth rolls so tightly that the rubber
is made too hard.
(3) The sheets or strips are then passed once through a pair of
marking rollers. Various types of patterns are used, but the one which
appears to give the most satisfactory results is that known as the
"close-cut spiral." This produces the semblance of a small diamond
pattern on the rubber. The surface of the sheet is raised in
well-defined ridges, which appear to present the maximum drying
surface exposed to the atmosphere of the smoke-house. Thus, not only
is the appearance of the sheet rendered attractive, but also the
period of drying is reduced. Starting with standard latex and
following the procedure here described for rolling and marking, sheets
should be ready for packing in ten or eleven days. If the period is
longer, it is possible that the design or structure of the smoke-house
is at fault.
WHEN TO WORK THE COAGULUM.--Before proceeding to discuss other points the
question remains to be settled as to how long it may be necessary or
advisable to allow the coagulum to remain in the serum before rolling it.
For reasons of practical economy in factory working, it is usual to allow
sheet rubber to remain over night, and the coagulum receives attention
early next morning. During the interval (averaging about eighteen hours),
the coagulum consolidates, leaving an almost clear serum if the correct
quantity of acid has been added to the latex. Any but the very slightest
trace of milkiness in the serum indicates an insufficiency of coagulant. If
the serum is always definitely clear, there may be grounds for believing
that an excess is being used. If the quantity of coagulant has been
calculated to an average nicety, the serum should be just dubiously free
from milkiness.
The firmness gained by the coagulum on standing in the serum overnight
should enable it to be handled next morning without any marked stretching,
and in some estates the rubber is put direct through the first pair of
smooth rolls without a preliminary consolidation by means of hand-rolling.
Some estates prefer to handle the coagulum while rather softer, as it is
claimed:
(_a_) That the coagulum is easier to work, and sheets of improved
appearance can be made.
(_b_) That there is greater freedom from "bubbles."
(_c_) That the incidence of "rust" is lessened.
These claims are substantiated in practice; but in the case of the
third, it only holds provided that the rubber can be finished and
placed in the smoke-house almost as soon as the last sheet has been
machined.
In such cases all latex must reach the store comparatively early in the
day--_e.g._, before noon. Three hours is allowed for coagulation, and the
working of the rubber is then commenced. As a general rule this means that
the operations of rolling and marking must be completed, a short interval
given for dripping, weighing must be done, and the rubber placed in the
smoke-house before night falls (as a rule about 6.30 p.m.).
Unless factories dealing with a large crop are well equipped with
artificial light, such a course is not open to them; in any case it remains
true that night work should be avoided if possible. If, however, it can be
arranged without increasing the cost of production, there would appear to
be no objection to the early working of the coagulum as described above.
HAND-ROLLING.--As already indicated, some few estates do not give the
strips of coagulum any preliminary hand-rolling, as the rubber is
considered to be sufficiently firm to be handled into the first machine.
On most estates hand-rolling is found necessary, owing to the tendency of
the long strips to stretch unduly, giving badly shaped sheets. This
hand-rolling should be done carefully, and is best effected on a specially
constructed table. This consists essentially of an inch-thick hard-wood
plank about 2 inches wider, and 4 or 5 feet longer, than the strip of
coagulum. Along the edges of the plank, and at right angles to its upper
flat surface, may be fastened strips of wood about 1/2 inch square in
section, thus forming a shallow tray open at either end. These strips serve
two purposes:
(_a_) As the wooden roller is wider than the plank, they prevent the
coagulum being rolled too thin and too firm.
(_b_) They prevent the coagulum being squashed too wide, and tend to
keep the edges straight.
To avoid "thick ends" it is sometimes considered advisable to insert, at
either end of the rolling table, shallow wedges about 6 inches long, of the
same width as the table (between the edge-strips), and with the sharp end
of the wedge pointing in the direction of the length of the table. The ends
of the coagulum are drawn up and finished on these inclined planes.
These points may appear to be extreme refinements, but as long as rubber is
valued on such grounds we must endeavour to meet the system imposed upon
us.
SMOOTH-ROLLING.--It is advised that, after hand-rolling, the coagulum
should be passed through at least two machines having smooth-rolls. On some
estates three such machines are employed. The purpose of this procedure is
to reduce the thickness of the coagulum gradually. The same could be
effected, of course, on one machine; but obviously the distance between the
rolls would have to be readjusted at each operation and for each piece of
coagulum. Apart from the time thus wasted, there is the certainty, in view
of the rough adjustment of the machines, that the chances of obtaining
uniformly thick sheets would be slight.
The machines should be arranged as a battery, with the marking rolls at one
end, so that the operations are consecutive. It is erroneous to imagine
that heavy machines (such as those used in crepe preparation) are required.
Light machinery only is necessary for sheet-making; but any available heavy
smooth-roll machines in a crepeing battery may serve admirably for the
purpose.
MARKING.--Heavy machines are unnecessary for the purpose of putting a
pattern on sheet rubber. If the rubber has been properly prepared a light
pair of rolls is capable of exerting sufficient pressure to cause a good
upstanding pattern.
Rolls are cut in various designs: some with "diamond" grooves on both
rolls; some with grooves of varying width and depth encircling the
circumference of the rolls, thus creating a "stripe" effect on the rubber;
and some with diagonally-cut spiral grooves placed closely together. The
last has the greatest vogue at present, while the first has almost gone out
of favour. An objection lodged against the second design is that the edges
of the grooves sometimes cut through the rubber, so that the dried sheet
divides in strips. It would appear in such instances that either the
coagulum was too thin and soft, or that the grooves had been cut too deeply
and sharply. In any case the choice of a design is an arbitrary matter, and
should depend upon the effect produced on the rate of drying and the
general appearance.
The popular "close-cut spiral" roll is machined with varying measurements,
but the usual design has grooves 1/8 inch wide by 1/8 inch deep and 3/16
inch apart.
Many estates have a particular "brand" cut in the middle of the rolls for
purposes of identification. If this is done it is advised that the main
grooving of the rolls be carried into the "branding" strip; otherwise grip
will be lacking on this portion, and a certain amount of "cockling" of the
sheets will result.
Sheets are often seen in which the potential effect of the grooving is
reduced to a comparatively flat pattern in place of the desired ridges. The
fault is generally attributed to the shortcomings of the marking rolls.
While it is true that the grooving often deteriorates by friction-wear when
the rolls are running "free," experience generally decides that the
deficiency in the appearance of the rubber should be attributed to faulty
previous preparation rather than to the marking rolls. Sets of rolls have
been changed often without justification or an improved result. It would
always be well to be certain first that the trouble did not emanate from
the fact that the coagulum had been previously rolled so thin and hard that
the rubber could not be squeezed so as to fill the grooves. This has been
found to be a common fault, and the general effect is to delay drying in
spite of the thinness of the rubber.
Again, the trouble may have been due to an incorrect standardisation of the
latex, generally in the direction of too heavy a density (too rich a latex)
being employed. The original thickness of the coagulum would be normal, but
owing to the abnormal rubber-content the effect of passing through the
smooth rolls would be the production of a strip thicker and firmer than
ordinary. If this firmness is appreciable the resistance of the rubber to
the squeezing action of the marking rolls will result in a flat
pattern--_i.e._, the grooves cannot be filled, and the ridges are low.
It is advised that all rolls used in the preparation of sheet rubber should
be at least 18 inches wide, in order to avoid the appearance of thickened
edges which delay drying.
Working with the correct standard of dilution of latex, and following the
procedure indicated in the foregoing paragraphs, the dry sheet should not
exceed an average thickness (over ridges and depressions) of 1/8 inch.
PREPARATION FOR SMOKE-CURING.--It used to be the custom to allow sheet
rubber to air-dry first for periods varying from one to several days.
Naturally moulds were soon formed, and when the sheets were quite
smoke-cured a mass of the dead moulds could be seen, if not over the whole
sheet, at least in the corners of each diamond mark. It has been
demonstrated in practice that there is no advantage in allowing sheets to
air-dry partially before smoking. In fact, to obtain the greatest benefit
from smoke-curing, sheet rubber should be placed in the smoke-house as soon
as possible. The same effect of mould-growth may be noted if the wet sheets
are placed in a smoke-house insufficiently heated.
Other defects may arise which can be traced to faulty treatment of the
marked coagulum prior to hanging in the smoke-house and subsequent to
rolling. These will be enlarged upon in a subsequent section of the book,
and at present it will suffice to indicate the procedure which experience
directs as likely to give the best results.
When the lengths of coagulum leave the marking machine they are usually
laid in piles containing two dozen or more strips. The piles are then cut
into the required lengths, the exact length generally being determined by
the available perpendicular distance between the supports in the
smoke-house. It is necessary to remark that the piles of sheets should not
be allowed to accumulate, but should be dealt with in subsequent treatment
progressively. If for some reason this is not possible, then all piles of
sheets should be turned on edge so as to assist the draining away of the
serum or "mother-liquor," which continues to ooze from the rubber for some
time after the squeezing in the machines.
Where hot water is available the freshly cut sheets should be passed into
it as soon as possible, and given a thoroughly good swilling. The caution
must be given that the hot water should be changed very frequently and, if
possible, after every batch, say, of a hundred sheets.
The sheets should then be carried immediately to racks on which they are
hung to drip. Generally these racks are situated under cover, but there is
no reason why they should not be placed in the open air without cover or
shade. From continued experience of this practice over a period of years it
is found advantageous and to be preferred to the usual method of allowing
sheets to drip under cover.
While the sheets are fresh and loaded with internal moisture, the effect of
sun-heat upon the surface, when exposed for, say, two hours, is nil; and
the safety of the process can be guaranteed, provided the stated limit is
not exceeded to an appreciable extent.
[Illustration: THE OLD METHOD OF "DRIPPING" FRESHLY ROLLED SHEETS WITHIN
THE FACTORY.]
After dripping for an hour or so, the sheets should be placed in the
smoke-house. If it is a bright sunny day, no extra precautions need be
taken; but on cool, dull days it would be advisable to light the fires
earlier than usual, consistent with the work required to be done in the
house--_e.g._, in the removal of dry rubber. There would appear to be no
reason why the dry sheets should not be first removed, so that on dull or
wet days smoking can be commenced as soon as the wet rubber has been hung.
On a few estates where the smoke-houses are worked continuously, except for
a few hours in the morning, a portion of the building is separated by a
partition for the reception of the wet rubber. The sheets are taken
directly from the marking rolls and placed in the chamber, beneath which a
fire is started. The sheets thus drip in a warm and smoke-laden atmosphere
until next morning, when they are weighed and removed to the smoke-house
proper. It is claimed that freedom from "rust" is thus obtained.
It will be clear that in the treatment of the rubber preparatory to smoking
the whole process should be continuous, and delay should be avoided if the
best results are to be obtained.
[Illustration: THE NEWER METHOD OF HANGING IN THE OPEN AIR.]
SMOKING OF RUBBER.--The assumption may have been noted above that the sheet
is to be smoked. As far as our knowledge extends, none but small native
estates now prepare sheet rubber of any other type, with the exception of
certain patent processes. Air-dried sheets are generally made on
small-holdings, and are bought in the market chiefly for the purpose of
macerating and making into blanket crepe. We have no intention, therefore,
of discussing the possibilities or qualities of air-dried sheets, as the
output of sheet-rubber from our estates is always in smoked form. The
drying (or, properly, smoking) stage will be discussed in Chapter XI.
CHAPTER X
_PREPARATION OF CREPE RUBBER_
NO. 1, OR FINE PALE CREPE.--Considering first the preparation of the
highest grade, fine pale crepe, it must be stated that the difficulties
attached to the process are generally not sufficiently appreciated. In this
pale rubber minor blemishes are so plainly apparent that their importance
is highly exaggerated, and what would worthily escape notice in smoked
rubber assumes disproportionate prominence in pale crepes. The very fact
that such a delicate material as colourless coagulum has to be manipulated
in coarse iron rollers, with the attendant oil and grease worries, should
be sufficient to deter one from criticising too harshly the occasional
lapses of an estate struggling to give of its best to the market. At the
same time there can be no doubt that if precautions are taken to attend to
all likely sources of contamination, defects in pale crepe may be avoided
to a wonderful extent; and on some estates the observance of elementary
rules enables the preparation of the finest pale crepe to be made almost
mechanically.
STANDARDISATION OF LATEX.--The question of the standardisation of latex has
been dealt with in a general way in Chapter VII., and the reader is now
familiar with the trend of the argument in its favour. It will be
recognised that the necessity for standardisation exists to the same degree
in the correct preparation of pale crepe as in the case of smoked sheet.
Unless the dry rubber content is invariable, and the quantities of
chemicals fixed, the colour of the crepe may vary appreciably.
It may be pointed out that it is not _essential_ to adopt the same standard
of dilution as for sheet preparation. Given that latices from all fields or
divisions are fairly uniform, and of high rubber content, the standard may
be taken at a figure equivalent, for example, to 2 lbs., or 2-1/2 lbs., or
even 3 lbs. per gallon. It is wise, nevertheless, to take a lower standard
for several reasons. For instance:
(_a_) The average dry rubber content varies with climatic conditions,
position of the cut on the tree, general health of the tree, etc. On a
rainy day the dry rubber content may be lowered too greatly by
adventitious circumstances.
(_b_) Recording instruments often fail to give even approximately
correct readings in rich latex. Errors may thus be made easily.
(_c_) A fairly soft coagulum means easier working on the machines,
less labour, and proportionately cheaper costs.
[Illustration: THREE GRADES OF CREPE RUBBER.
Left to right: fine pale crepe; second quality pale crepe; compound crepe.]
It is advised, therefore, that for general purposes the same standard as
that found suitable for sheet rubber should be taken--viz., 1-1/2 lbs. dry
rubber per gallon. At all events the standard should not exceed 2 lbs. per
gallon.
COAGULATION AND COAGULANT.--Coagulation may be undertaken without any
special arrangement of tanks, and is usually effected in the ordinar
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