The preparation of plantation rubber

THE PREPARATION OF PLANTATION
RUBBER

THE PREPARATION

OF

PLANTATION RUBBER

BY

SIDNEY MORGAN, A.R.C.S.

VISITING AGEXT FOR ESTATES IX THE EAST ; FORMERLY SEXIOR SCIENTIFIC OFFICER

AND NOW HONORARY ADVISER TO THE RUBBER GROWERS' ASSOCIATION

IX 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

LIBRARY-AGRICULTURE

PRINTED IN GREAT BRITAIN bY
LILLING 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,

vi PREFACE

brokers, and particularly the rubber manufacturers in this
country and in America. My experience has been that manu-
facturers 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 pro-
moted 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 photo-
graphs 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 col-
leagues, 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 amon.g the regular quarterly

PREFACE vii

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 in-
debted 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
CHAPTER I

PLANTING

PAGE

Seeds — Seed selection — Strain improvement by bad propaga-
tion— Nurseries — Stumps — Seed at stake — Basket plants —
Preparation of land — Danger of disease — Clean clearing —
Loss of top-soil — Silt -trenches on slopes - i

CHAPTER II

FIELD MAINTENANCE

Clean weeding — Selective weeding — Loss of top-soil — Grass
ridges — Lallang eradication — Mimosa gigantea (M. invis'a)
— 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

ix

x CONTENTS

CHAPTER V

TAPPING AND COLLECTING

PAGE

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 calcula-
tion of yields per coolie — Tree-scrap, oxidation of — Pre-
vention 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 — Coagula-
tion 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-coagu-
lant, quantities for use — Formulae — Use of Formalin as anti-
coagulant— Formulae for use - - 74

CONTENTS xi

CHAPTER IX

PREPARATION OF SHEET RUBBER

PAGE

Pale (air-dried) sheets — Uniformity of product — Pans versus
tanks — The ideal tank — Modern installations — Care of tanks
— Standardised dilution of latex — Variation in dioensions
and density of coagulum — Standardising instruments —
Method of using — Skimming latex — Style of sheets — Stan-
dard 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) — Evalua-
tion 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 - no

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 record-
ing temperature — Temperatures of smoke-house — Period of
drying — Fuels for smoking — Sun-drying of sheet rubber —
Artificial driers for sheet rubber - - 132

xii CONTENTS

CHAPTER XII

SORTING, GRADING, AND PACKING

PAGE

Reducing number of grades — Reduction carried too far — R.G.A.
recommendations — Care in sorting — Choice of packing cases
— Care in assembling — Bags — Bales — Folding of crepe —
Mechanical folders — 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 — Ventila-
tion— 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 com-
bustion— 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

CONTENTS xiii

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 — Centralisa-
tion— 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 — Tacki-
ness in general — Full discussion of — Experimental reproduc-
tion— 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 — " Dcg-
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

xiv CONTENTS

PART V

GENERAL

CHAPTER XIX

CHOICE OF COAGULANT

I'AGK

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 — Hydro-
fluoric 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 — yErobic — 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. — Tests on vulcanised rubber — Prepara-
tion for testing — 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 - - II

TYPICAL YOUNG CLEARING, WITH TIMBER 15

TYPICAL YOUNG CLEARING, WITH TIMBER - 17

TYPICAL YOUNG PLANTED AREA - 2O

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 3!
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 - 4!
EFFECTS UPON RENEWED BARK OF PREVIOUS TAPPING - 44
ANOTHER EXAMPLE SHOWING THE EFFECTS OF PREVIOUS TAP-
PING - 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" 5!

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

METDOD FOR RECEIVING LATEX AND FILLING TANK - JO

RAISED VERANDAH FOR RECEPTION AND HANDLING OF LATEX 71

ANOTHER SET OF DILUTION TANKS ON RAISED VERANDAH - 72

XV

xvi LIST OF ILLUSTRATIONS

l-AGE

TWO VIEWS OF DILUTION AND MIXING TANKS 8 1

UNIT MODERN COAGULATING TANK (TWO VIEWS) - 91
ANOTHER BATTERY OF TANKS, WITH DILUTION TANKS, RAISED, ON

THE RIGHT - Q2

CLOSER VIEW OF FOREGOING - - 93
ANOTHER BATTERY OF TANKS, WITHOUT DILUTION'.; TANKS OR

MEANS OF GRAVITATING LATEX - - 95
A SHEETING TANK CONTAINING COAGULUM FOP CREPE PREPA-
RATION - 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 - III

A WASHING SHED - 1 12

DRYING GRAPH. PALE CREPE (THIN) 140

A SHIPMENT OF RUBBER, PACKED AND READY FOR TRANSPORT 155

ON ITS ROAD TO THE RAILWAY I 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 2OI
GENERAL VIEW OF DOUBLE "DEVON" SMOKE-HOUSE AND

FACTORY BUILDINGS - 2O2
VIEW OF PLATFORM OF " DEVON " SMOKE-HOUSE; DOORS OF
COMPARTMENTS OPEN, AND ONE RACK PARTIALLY WITH-
DRAWN - 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 "DEVON3' TYPE OF SMOKE-HOUSE 2O6

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 2l8

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 compara-
tive 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 prepara-
tion 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

2 PREPARATION OF PLANTATION RUBBER

be treated in a general way according to modern knowledge,
and of these it is proposed to discuss a few in the following
pages.

SEEDS. — The view is now generally held that many areas
were planted from seed which was not collected in a discrimi-

SEEDS, SHOWING VARIABLE SIZE, SHAPE, AND MARKING.

nate manner; and that probably the comparatively low yields
obtained on areas of some estates may be due to the employ-
ment 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

PLANTING 3

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.

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

FELLING LIGHT (SECONDARY) JUNGLE.

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 experimen-
ters 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

PREPARATION OF PLANTATION RUBBER

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.

Unfortunately the industry is so young that the question of
seed selection yet awaits study. The task presents certain

SEEDLING, SHOWING ROOT-SYSTEM WITH SEED
STILL ATTACHED.

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

PLANTING 5

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.

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.)

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 wrhich 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

6 PREPARATION OF PLANTATION RUBBER

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

PLANTING 7

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

LIGHT JUNGLE.

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 circum-
stances function eventually as a tap-root.

On the whole, this system of propagation receives the approval

8 PREPARATION OF PLANTATION RUBBER

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 reason-

DENSE JUNGLE.

able precautions which are not beyond the intelligence and
ability of subordinates, an extremely high percentage of
success can be attained.

Until such time as this process becomes practicable the
inception of a planted area must follow the lines usually
adopted.

PLANTING 9

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.

CLEARING READY FOR PLANTING.
Surface timber removed, but stumps remaining.

STUMPS. — At a stage, varying according to the require-
ments 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.

io PREPARATION OF PLANTATION RUBBER

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,

PLANTING it

•
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

NEW CLEARING; SLOPES " HOLED " FOR PLANTING; FLAT AREA
BEING DRAINED.

(By courtesy of manager, Membakut Estate, British North Borneo.]

are affected with Fomes lignosus (formerly known as Fames
semitostus). Such cases are directly attributable to the exist-
ence 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.

SILT CATCHMENT TRENCHES. — Granted the ultimate neces-
sity of clean clearing, it becomes necessary to take some pre-
cautions to prevent loss of soil by " wash " in young areas

12 PREPARATION OF PLANTATION RUBBER

planted on sloping land. An argument often used in extenua-
tion 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 rain-
water. These trenches are usually laid out on contour, and
do not exceed a length of 20 feet. They are usually from
1 8 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 propor-
tion 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 argu-
ment has been used that, since the habitat of Hevea Brasi-
liensis 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 arbori-
culture it could be shown that growth, development, and
yields are improved by cultivation of " wyild " 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 diffi-
culty and expense. It is the aim, therefore, of properly con-
ducted 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.

13

i4 PREPARATION OF PLANTATION RUBBER

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 experi-
ence, 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 con-
ditions, would be most inadvisable.

Nevertheless, such exceptional cases do not detract from the
wisdom of clean weeding in general. Every planter of experi-
ence 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 main-
tenance of ridges. These are built up from the debris of

FIELD MAINTENANCE 15

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 main-
tained 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-

TYPICAL YOUNG CLEARING, WITH TIMBER.
Planted " rubber-stump " in foreground.

trenches, although the latter method may be slightly more
expensive in the end.

" 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

1 6 PREPARATION OF PLANTATION RUBBER

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* on areas which one may have in view for
planting at some future date.

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

* " Eradication of Lallang," W. P. Handover, The Planter, Vol. I.,
No. i, August, 1920.

FIELD MAINTENANCE 17

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

TYPICAL YOUNG CLEARING, WITH TIMBER.

Young rubber plants in foreground. Two of these are easily
distinguishable, both with small crowns of leaves.

modern practice might be mentioned Tephrosia candiad
(Boga bean), Centrosema Plumerii, and Dolichos Hoseii
(Sarawak bean).

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.

2

1 8 PREPARATION OF PLANTATION RUBBER

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 pas1

19

20 PREPARATION OF PLANTATION RUBBER

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.

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

THINNING OF AREAS

21

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.

ANOTHER EXAMPLE OF A RECENTLY PLANTED AREA.

»fc 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

22 PREPARATION OF PLANTATION RUBBER

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:

THINNING OF AREAS

Zero ...
Above mark i
» 2

» 3
> 4

, 5

3 per cent,

6
16
42

12

o
i
o

IOO

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 Ibs. 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 Ibs. 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 Ibs. during the year, and some less.

24 PREPARATION OF PLANTATION RUBBER

In view of present information it would not be surprising to
find that a few might have been yielding upwards of 15 Ibs.
per annum. Unfortunately this information is only to be

WIDELY PLANTED YOUNG AREA, JUST READY TO BE BROUGHT
INTO TAPPING.

obtained by individual tests, and under normal estate con-
ditions the facts escape notice. Cases are known in which
out-standing individual trees have been known to yield at the
rate of 25 Ibs. and more per annum.

THINNING OF AREAS 25

FUTURE YIELDS PER TREE. — It has been shown that by selec-
tive methods based on yields, poor trees can be eliminated.
Whether by a process of seed-selection or by means of pro-

FIELD OF OLD RUBBER TREES IN WHICH THINNING HAD BEEN
DELAYED TOO LONG.

Note height and comparative lack of girth.

pagation 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

26 PREPARATION OF PLANTATION RUBBER

giving an average yield of 25 Ibs. per annum over any given
area. Yields of 1,000 Ibs. 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 opera-
tions. 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 Ibs. 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

THINNING OF AREAS 27

of several uniformly-yielding trees should be removed. In
the average sense of this consideration one must pay no atten-
tion 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 com-

28

TAPPING SYSTEMS 29

monly 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 effect-
ively 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 simul-
taneous 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 i 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-circum-
ference, 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.

30 PREPARATION OF PLANTATION RUBBER

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.

A few estates in this country still continue to tap trees by

TAPPING SYSTEMS 31

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

Two CUTS ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE.

consumption of bark without proportionate increase in yield.
For instance, if one compares the system of twro 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

32 PREPARATION OF PLANTATION RUBBER

lower cut, and that the single-cut system which excises ap-
proximately 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 experi-
ments 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 promi-
nence, 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

TAPPING SYSTEMS

33

gave yields equalling or exceeding those obtained from trees
tapped with shorter intervals.

In the Semenyih experiment the system chosen was that
which had the greatest contemporary vogue — viz., two super-

THE SINGLE CUT ox A QUARTER CIRCUMFERENCE, ON AN OLD TREE
AND ON RENEWED BARK.

imposed cuts on a quarter of the tree. The various blocks
were tapped respectively every day, every second day, and
every third day.

3

34 PREPARATION OF PLANTATION RUBBER

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 r.ppreciable 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 bole 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

TAPPING SYSTEMS

35

obtained from cuts is always greater per tapping by using the
alternate-daily system, it would appear to be plain that the

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.

one long cut on half the tree would at least equal the yield of
the single short cut tapped daily on a quarter tree.

Unfortunately no opportunity has been afforded up to the
present of definitely proving this point by prolonged experi-

36 PREPARATION OF PLANTATION RUBBER

ment 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 com-
parison 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 tappingx 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

TAPPING SYSTEMS

37

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

A V-Cux ON HALF THE CIRCUMFERENCE.

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.

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 con-
tinues, 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

38

TAPPING AND COLLECTING 39

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 irre-
concilable. 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 con-
trolled 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 attri-
buted 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

40 PREPARATION OF PLANTATION RUBBER

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 success-
ful attempts wrere 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

TAPPING AND COLLECTING

41

cups, whereas in the case of glass the point is settled by visual
examination at a comparative distance.

Glass cups are made in two patterns, one having a flat

SINGLE CUT ox TWO-FIFTHS OF CIRCUMFERENCE.

The opening cut covers two-fifths. Subsequent cuts occupy
one-fifth of circumference.

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

42 PREPARATION OF PLANTATION RUBBER

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

TAPPING AND COLLECTING 43

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 com-
paratively 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 — £.£., on old areas — it would be practically impos-
sible 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 in-
creased 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.

44 PREPARATION OF PLANTATION RUBBER

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.

EFFECTS UPON RENEWED BARK OF PREVIOUS TAPPING.
Note uneven surface and callosities.

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

TAPPING AND COLLECTING

45

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,

ANOTHER EXAMPLE SHOWING THE EFFECTS OF PREVIOUS
TAPPING.

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

46 PREPARATION OF PLANTATION RUBBER

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.

(/) 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 pre-
cautions, 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

TAPPING AND COLLECTING 47

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 i pound to 3 gallons.

(b) Of this solution each coolie is given about f 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.

48 PREPARATION OF PLANTATION RUBBER

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 commence-

i. SHOWING EFFECT OF "WINTERING."

ment of collection. The solution is made as in (a) above,
and roughly half an ordinary latex- cupful is placed in
each bucket.

COLLECTING PAILS. — All vessels intended for the transport
of latex should have a smooth and curved interior, so that

TAPPING AND COLLECTING

49

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.

2. NEW GROWTH OF YOUNG LEAF ON SAME TREE.

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 appre-
ciable increase in weight. Until such a utensil is available,
the heavily'galvanised and brass-bound milk-pails used on some

4

50 PREPARATION OF PLANTATION RUBBER

estates are as good as anything at present in vogue, providing
they are kept scrupulously clean.

The collecting pails should be kept under cover, when not in

EFFECTS OF DISEASE — "MOULDY ROT."

(a) Note on right hand the panel next in order for tapping; a
hopeless position.

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

TAPPING AND COLLECTING 51

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

EFFECTS OF DISEASE — " MOULDY ROT."

(b) The present cut badly infected; above there is no renewal
of bark.

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

52 PREPARATION OF PLANTATION RUBBER

was very markedly acid in character, and as the buckets were
not afterwards thoroughly cleansed, the latex of the following
day suffered.

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.

TAPPING AND COLLECTING 53

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

EFFECTS OF DISEASE — " MOULDY ROT."

(d) At close quarters. Note wounds due, apparently, to bad
tapping, but really caused by the disease.

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

54 PREPARATION OF PLANTATION RUBBER

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 im-
possible to set a standard rate per pound for payment by result ;

TAPPING AND COLLECTING 55

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 " Metro lac,"
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."

56 PREPARATION OF PLANTATION RUBBER

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 sub-
stances of a phenolic nature. In the course of laboratory
experiments with normal latex, it was found possible to repro-
duce 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 (i 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

TAPPING AND COLLECTING 57

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 break-
down 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.

58 PREPARATION OF PLANTATION RUBBER

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 com-
paratively small, but in actual practice it may be very appre-
ciable. 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 rain-
water 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 infor-
mation 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

59

60 PREPARATION OF PLANTATION RUBBER

be given for an estate keeping all lower grades distinctly
separate :

First-grade latex . . . . . . 75 per cent.

Cup-washings . . . . . . ^

Coagulated lump, etc. . . . . j "

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 circum-
stances, 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 dis-
covered 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

TRANSPORT OF LATEX AND COAGULUM 61

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 piossible, 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 under-
gone 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.

62 PREPARATION OF PLANTATION RUBBER

Formula for Use of Sodium Sulphite in Transport.

(a) Dissolve i 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 un-
common 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 dissatis-
faction. 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

TRANSPORT OF LATEX AND COAGULUM 63

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 diffi-
culty, 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 attri-
buted 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

64 PREPARATION OF PLANTATION RUBBER

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 coagu-
lum 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 appre-
ciably 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 con-
stantly 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

65 5

66 PREPARATION OF PLANTATION RUBBER

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 super-

RAISED VERANDAH FOR RECEPTION OF LATEX; LIKEWISE EQUIPPED
WITH FACILITIES FOR CALCULATING INDIVIDUAL DAILY
" YIELD PER COOLIE " BY SAMPLING OF LATEX.

vision. 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 responsi-
bility is thrown on the straining process.

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.

PRELIMINARY TREATMENT OF LATEX 67

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. Every-
thing 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 con-
siderable factors in determining the final quality of the rubber.
There is considerable truth in the suggestion that the coagu-
lating 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

68 PREPARATION OF PLANTATION RUBBER

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

PRELIMINARY TREATMENT OF LATEX 69

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 co-
agulated 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

70 PREPARATION OF PLANTATION RUBBER

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.

In the successful working of a tank it is necessary, in order
to obtain the best results, to standardise all latex. This can-
not 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

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.

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 prin-
ciple 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

PRELIMINARY TREATMENT OF LATEX 71

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.

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 8o-gallon cylinder is easily mounted

72 PREPARATION OF PLANTATION RUBBER

by its trunnions on a suitable iron framework which is super-
imposed on a skeleton truck.

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

ANOTHER SET OF DILUTION TANKS ON RAISED VERANDAH.

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.

PRELIMINARY TREATMENT OF LATEX 73

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. Unfor-
tunately 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 plat-
form, 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 arrange-
ment 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 dis-
cussed 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 i 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

74

COAGULATION 75

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 coagu-
lation is quickest where pure acid is employed, and slowest
where the acid is most dilute. It will also be found that, pro-
viding the quantity of acid employed was sufficient for coagu-
lation, 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 coagu-
lation 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 i part of acid in 500
parts of water. While it has been found that a i in 5 solution
can be used where the latex is very dilute (say, i part of latex
to 5 parts of water), and a i 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., i in 100, or
even i 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 i pint of acid with 20 pints of water, and i gallon of
this is necessary to coagulate 50 gallons of pure latex.

76 PREPARATION OF PLANTATION RUBBER

It is desired to use a stock solution of i 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 i gallon
of the old solution contained, and it will be necessary to add
5 gallons for every 50 gallons of pure latex. Thus:

i to 20; i gallon necessary for 50 gallons pure latex.
i 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 i 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

COAGULATION 77

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:

i 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 pro-
portion of pure acid to latex is taken as i 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 i part of pure acid, this
gives us a mixture of i to 100. For i 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 i 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 i 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

78 PREPARATION OF PLANTATION RUBBER

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 (i 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 ij Ibs. to ij Ibs. dry rubber per
gallon.

Latices of these strengths can be coagulated at a ratio of
i part pure acid to i ,200 parts of standardised latex ; and this
quantity need not be exceeded, except in cases where an appre-
ciable amount of some anti-coagulant is present in the latex.
The proportion may then be raised to i in 1,000.

If considered advisable the acid may be used in a J per cent,
solution for sheet preparation; but in any case it is advised
for the sake of uniformity that a i 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 satis-
factory to have the solution made up in approximately correct
strength at the rate of i 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 6J ozs.

COAGULATION

79

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 i 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 i 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 i : 1,200. As the strength of solution is i : 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,
yj gallons of dilute acid solution are required.

(?) A tank containing 120 gallons of latex would need 10
gallons of the i 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 i : i ,000.

If the acid solution is to be employed in i 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 i per cent.,
but it is not advised. The acid should be poured into the

8o PREPARATION OF PLANTATION RUBBER

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.

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 mani-
pulation. 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,

COAGULATION

81

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 coagu-

6

lating tank.

82 PREPARATION OF PLANTATION RUBBER

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 circum-
stances 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,

COAGULATION 83

After months of investigation into the properties of other
chemicals the writers decided that the only one which satis-
factorily answered all requirements was sodium bisulphite.
The writers make no pretension to any claim of having dis-
covered 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,*
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 intro-
duction 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 pre-
pared with sodium bisulphite, the results of our preliminary
work were published by permission of the Rubber Growers'
Association.! 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. Repre-

* Williams, International Rubber and Allied Congress, London,
1914.

t " The Employment of Sodium Bisulphite in the Preparation of
Plantation Rubber," Beadle, Stevens, and Morgan, India-rubber
Journal, August 2, 1913.

84 PREPARATION OF PLANTATION RUBBER

sentatives of manufacturers have sometimes given us to under-
stand 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.

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 un-
necessary, 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.*

Hence it follows that if in any factory uniform quantities of

* 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).

COAGULATION 85

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 ij Ibs. 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 i Ib.
to 10 gallons.

(b) Of this solution use i 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 sim-
plicity 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 neces-
sary, 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 recog-
nised 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.* It is probable that few
estates, if any, now experience trouble due to this non-observ-
ance of the rules and quantities laid down for use.

* " The Preparation of Plantation Rubber," Morgan, 1913, p. 74.

86 PREPARATION OF PLANTATION RUBBER

RESIDUAL TRACES OF SODIUM BISULPHITE. — The prolonga-
tion of the drying period was attributed to the fact that traces
of substances caused by the decomposition of sodium bisul-
phite 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 i part to 600 parts latex showed
only a trace of sulphate present; while the one prepared
i : 2,400 gave an equal quantity. Intermediate samples con-
tained 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 advan-
tages 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 :

COAGULATION 87

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 (ij Ibs. dry rubber per gallon).

The warning previously given regarding the necessity ftr
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 (form-
aldehyde) as an anti-coagulant. It must be acknowledged
that when not abused there are points in favour of its employ-
ment in preference to sodium sulphite, but these are out-
balanced by certain disadvantages. The argument may be
stated thus:

Points for : (i) 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.

88 PREPARATION OF PLANTATION RUBBER

Points against : (i) 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) i pint of formalin is diluted with 5 gallons of water.

(b) Of this solution i 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 con-
cerning 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 pre-
paration of sheet rubber always seems to demand much more
labour. As a matter of fact, although the preliminary opera-
tions 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

89

90 PREPARATION OF PLANTATION RUBBER

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 standardi-
sation 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 i foot deep.

Tanks are at present constructed either of hard timber or of
brick and cement faced with glazed tiles; both types have

PREPARATION OF SHEETJUJBBER 91

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.

92 PREPARATION OF PLANTATION RUBBER

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.

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 forth-
coming.

An even greater improvement would take the form of unit
tanks cast in glazed white-ware with the necessary slots

PREPARATION OF SHEET RUBBER

93

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 i foot deep, with slots i J inches apart, and
g 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,

CLOSER VIEW OF FOREGOING.
Note partitions in position and coagulum being removed.

and at one end a draining-hole could be made, say, i inch in
diameter.

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

94 PREPARATION OF PLANTATION RUBBER

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 construc-
tion 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 J 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
surf ace- waxed or varnished, and the treatment has been repeated
on occasions. But in course of time the surface film of water-
proof 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

PREPARATION OF SHEET RUBBER

95

" pitting " on the surface of the coagulum and enclosed bubbles
within.

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

ANOTHER BATTERY OF TANKS, WITHOUT DILUTION TANKS OR MEANS
OF GRAVITATING LATEX.

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,

96 PREPARATION OF PLANTATION RUBBER

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.

A SHEETING TANK CONTAINING COAGULUM FOR CREPE
PREPARATION.

Behind wall in background are the tanks in which latex is stan-
dardized. 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.

PREPARATION: OF SHEET RUBBER

97

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 (i) 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.

On the other hand, too low a standard also brings trouble
in its train. The coagulum is too porous, will not stand hand-
ling, and the resultant sheet is too thin unless an abnormal
thickness of coagulum is prepared. Furthermore, over-dilution

A " BATTERY " OF SHEETING TANKS (PATALING ESTATE).
DILUTION TANKS, RAISED, ON THE LEFT.

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 i| Ibs. dry rubber per gallon. Primarily this
standard has a direct connection and interdependence with

7

98 PREPARATION OF PLANTATION RUBBER

the distance between the partitions (or between the slots) in
coagulating tanks. The distance found most practicable is
1 1 inches. This thickness of coagulum, when prepared from
latex not exceeding a standard of i J Ibs. 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 ij Ibs. 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 i-|- Ibs. per gallon. Thus it
is not uncommon to note the adoption of a standard equivalent
to i Ib. 4 ozs. or i Ib. 6 ozs. dry rubber per gallon. Experience
dictates, however, that for the recognised standard measure-
ments of modern tanks the practical limits of satisfactory
density of latex lie between i J Ibs. and i-|- Ibs. 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 suffi-
ciently 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.* It is not proposed, in this section of the
book, to discuss such considerations.

Instruments of this nature are represented by the " Metro-

* De Vries, "Archiev voor de Rubbercultuur,"

PREPARATION OF SHEET RUBBER 99

lac " (originating from the Rubber Growers' Association) and
other similar recorders. They generally consist of a submers-
ible 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 mani-
pulation, 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 con-
taining 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.*

Where field coagulating stations have been instituted on
estates, it is strictly necessary that instruments should be pro-
vided 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

* 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.

ioo PREPARATION OF PLANTATION RUBBER

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," con-
trived 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 skim-
mings 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. i grade is prepared.

PREPARATION OF SHEET RUBBER 101

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 per-
formed 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

io2 PREPARATION OF PLANTATION RUBBER

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* given generally to estates.

ROLLING AND MARKING OF SHEET RUBBER. — Working with
standard latex it is found that strips of coagulum ij 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 atmo-
sphere 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.

* "Handbook on Preparation of Rubber," Rubber Growers'
Association, May, 1917, p. 28.

PREPARATION OF SHEET RUBBER 103

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 coagu-
lum 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 com-
menced. 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

104 PREPARATION OF PLANTATION RUBBER

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 coagu-
lum. Along the edges of the plank, and at right angles to its
upper flat surface, may be fastened strips of wood about | 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 advis-
able 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

PREPARATION OF SHEET RUBBER 105

effected, of course, on one machine; but obviously the distance
between the rolls would have to be readjusted at each opera-
tion and for each piece of coagulum. Apart from the time
thus wasted, there is the certainty, in view of the rough adjust-
ment 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 arbi-
trary 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
i inch wide by i inch deep and fV mcri 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

io6 PREPARATION OF PLANTATION RUBBER

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 J 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

PREPARATION, OF SHEET RUBBER 107

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 treat-
ment 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 per-
pendicular 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.

io8 PREPARATION OF PLANTATION RUBBER

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 guaran-
teed, provided the stated limit is not exceeded to an appreciable
extent.

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 OLD METHOD OF " DRIPPING " FRESHLY ROLLED SHEETS
WITHIN THE FACTORY.

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 con-
tinuously, 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

PREPARATION OF SHEET RUBBER 109

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.

SMOKING OF RUBBER. — The assumption may have been noted
above that the sheet is to be smoked. As far as our knowledge

THE NEWER METHOD OF HANGING IN THE OPEN AIR.

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, there-
fore, 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. i, OR FINE PALE CREPE. — Considering first the prepara-
tion 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 exag-
gerated, 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 coagu-
lum 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 prepara-
tion of the finest pale crepe to be made almost mechanically.

STANDARDISATION OF LATEX. — The question of the standard-
isation 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 Ibs., or 2\ Ibs., or even 3 Ibs.

no

PREPARATION OF CREPE RUBBER in

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 approxi-
mately correct readings in rich latex. Errors may thus be
made easily.

THREE GRADES OF CREPE RUBBER.

Left to right : fine pale crepe; second quality pale crepe; compound
crepe.

(c) A fairly soft coagulum means easier working on the
machines, less labour, and proportionately cheaper costs.

It is advised, therefore, that for general purposes the same
standard as that found suitable for sheet rubber should be
taken — viz., ij Ibs. dry rubber per gallon. At all events the
standard should not exceed 2 Ibs. per gallon.

COAGULATION AND COAGULANT. — Coagulation may be
undertaken without any special arrangement of tanks, and is
usually effected in the ordinary " Shanghai " glazed earthen-

ii2 PREPARATION OF PLANTATION RUBBER

ware jars containing about 45 gallons. Given reasonable care,
and a fairly fool-proof system of calculation for the quantities
of chemicals required, no difficulty need be experienced.

On a larger scale it is advised that proper reception tanks,
in which standardisation can be effected, should be installed.

A WASHING SHED.

Sheets are soaked in hot water in tanks in the background, and
then scrubbed under a spray of cold water.

Where both sheet rubber and fine crepe are being prepared,
the whole system of sheet-coagulating tanks may be employed
with considerable advantage, even to the insertion of the
partitions.

If ordinary jars are used, and the coagulum is left until the

PREPARATION pF CREPE RUBBER 113

following morning, the mass of rubber has to be cut up into
pieces of a size suitable for the machines. The knives or
saws are sometimes rusty, and the colour of the coagulum is
affected. The coolies often feed into the machines lumps
which are too large, with the result that portions are thrust
under the cheek-blocks and become stained.

When a sheet-coagulating tank is used all labour of cutting
the coagulum is obviated. The long strips are handled and
fed into the rolls easily. It may be seen, likewise, that actual
work is thus saved in machining.

QUANTITY OF COAGULANT. — For a general discussion on
the coagulant and quantities employed, the reader is referred
to Chapter VIII. It is there recommended that for latex
standardised to a level of ij Ibs. per gallon, the proportion of
pure acetic acid should be in the ratio of i : 1,200. Directions
are there given for the making of the solution, and the calcu-
lation of the quantity required for any given volume of latex.

It is pointed out that for average undiluted latex the basis of
calculation, for quantities of acetic acid required, should be
taken on the ratio i : 1,000. Where latex exceeds a dry rubber
content of 3 Ibs. per gallon, it may be necessary to increase
the quantity of acid to i : 800.

If a standard of 2 Ibs. per gallon is adopted, the formula given
for the ij Ibs. standard will not give full satisfaction, and the
quantity of acid solution must be increased slightly in order
to obtain complete coagulation. Assuming that the original
solution is prepared in i per cent, strength, the following
difference would be noted :

(a) One part pure acetic acid to 100 parts water (theoretically

99 parts).

(b) if Ibs. per gallon. 2 Ibs. per gallon.

Of the above solution use Of the above solution use

i gallon to every 12 i gallon to every 10 or

gallons of standardised n gallons of standardised

latex. latex.

It is not possible to lay down an exact figure governing all
cases, as so much depends upon the treatment undergone by

the latex before it reaches the store.

8

ii4 PREPARATION OF PLANTATION RUBBER

Some estates continue to use solutions of greater strength,
generally 5 per cent., in crepe preparation. While such
solutions may be effectively stirred in when the latex is dilute,
it is advised that for intimate mixture the solution need not be
stronger than i per cent.

In estimating the quantities of acetic acid required much
depends upon the interval which is to elapse between the
addition of acid and the time of working of the coagulum.
If the rubber is to remain until next morning, the average
formulae will be found suitable; but if it is required to work
the coagulum with an interval of less than three hours, an excess
of acid must be employed. The excess need be comparatively
small, unless the interval is much reduced. For instance, it is
the practice on some few estates to begin the machining of the
coagulum about half an hour after coagulation commences;
in which case it is usual to add from a quarter to a half of the
normal quantity in excess. It need scarcely be pointed out
that unless this procedure is strictly unavoidable it should be
discouraged on account of the waste of coagulant involved.
Incidentally, the use of strong solutions of acid under such
circumstances may lead to increased deterioration of the rolls.

COLOUR OF FINE CREPE. — We are sometimes assured that
manufacturers do not pay the attention to the question of
colour which sale conditions would lead one to believe. As
far as we are concerned, and as long as there is no direct traffic
between producer and consumer, it must be recognised that
in the vast majority of cases we are forced to concern ourselves
only with the standards set up in the markets. This, in spite
of the knowledge that, all other things being equal, the arbitrary
distinctions in colour afford no indication of the intrinsic
value of the rubber. Under present circumstances it is plain
that if paleness is demanded it has to be supplied.

Probably without exception all estates employ sodium
bisulphite as the agent for the prevention of that darkening
(oxidation) which is natural in drying rubber.

SODIUM BISULPHITE. — A formula for use of this chemical
is given in Chapter VIII., and is applicable to latex standard-
ised to 1 1 Ibs. dry rubber per gallon. If a higher standard is

PREPARATION OF CREPE RUBBER 115

chosen the quantity calculated as in (b) of that formula may
be increased slightly, and the exact requirements found by
experience. The caution must again be given that the employ-
ment of an excess of sodium bisulphite will lead to the pro-
duction of an over-pale rubber, and a prolongation of the
drying period. If thick crepes are made, an excess of the
chemical is sometimes made visible by a greyish powder
deposited on the edges of the strips of dry rubber.

It must be emphasised that the formula in Chapter VIII.
indicates the maximum quantities required for use with standard
latex. Many estates will find it expedient to use less of the
chemical; and if it is found that the desired result is not
obtained from normal proportions, attention should be directed
to the points discussed in the following paragraph.

EVALUATION AND DETERIORATION OF SODIUM BISULPHITE
AND SODIUM SULPHITE. — Sodium bisulphite and sodium
sulphite are both bought for our purpose in the form of a fine
crystalline powder, and on analysis good specimens should
contain over 90 per cent, pure substance, when packed in well-
sealed vessels.

It has often happened that shippers or local sellers, by
inadvertence, have supplied the one chemical in place of the
other — to the detriment of the rubber and the discomfiture
of managers of estates. The error, as a rule, has not been
detected for some time, and then perhaps only as a result of
complaints or enquiries reaching the laboratories. To the
layman, and certainly to the native who usually has charge of
these substances, it is not a simple matter to distinguish be-
tween them without special knowledge. There are certain
elementary tests, however, which can be applied on all estates
serving to make the distinction, but affording no information
regarding the actual quality of the chemicals. They are given
in a comparative form on page 116. Samples of doubtful
specimens may be sent to the laboratories for analysis, but
the bulk of the chemical should not be used.

During the War some very poor shipments were received,
and much trouble was caused. Under normal conditions there
can be no question that it is to the interests of chemical manu-

n6 PREPARATION OF PLANTATION RUBBER

facturers to supply the best article; and it is anticipated that
in future there should be no difficulty in procuring shipments
of a high degree of purity.

Sodium Bisulphite. Sodium Sulphite.

i. If in good condition it j i. It has no perceptible

has a powerful odour of
sulphur dioxide.*

In solution it should turn

odour.

In solution it should turn
a blue litmus-paper red. a red litmus-paper blue.

3. It exhibits a marked ten- | 3. The tendency to " cake "

dency to " cake " if the ! is less marked than in

drum is allowed to the case of the bi-

remain open. sulphite.

It will be evident that, as sodium bisulphite under normal
conditions gives off a gas when exposed to the atmosphere,
it deteriorates in quality continuously. It is the potential
presence of this gas which makes the powder effective as an
anti-oxidant and disinfectant. It is within the experience of
all accustomed to the handling of this chemical, that in addition
to the loss of gas, the powder cakes into a hard mass on ex-
posure. If only the top layer is caked, the remainder may be in
fair condition; but no caked portions should be used, as they
cannot be of good quality. They may, however, be used for
the treatment of scrap rubber, to be discussed later.

CARE OF SODIUM BISULPHITE. — The ready tendency of
sodium bisulphite to deteriorate on exposure should give
sufficient indication regarding its treatment in storage. It
should be bought only in drums (or other air-tight containers),
and should be stored in a dry place. No drum should be
opened until required, and the common practice of keeping
an open drum on the floor of the factory should be avoided.

Drums are of two sizes, generally containing J cwt. or J cwt.
respectively. It will be obvious that, although the prime cost
may be cheaper with the larger quantity, it would always be

* High-grade sodium bisulphite has very little odour, but by the
time it reaches the estate, and as a result of short exposure to the
moist atmosphere of the tropics, a little decomposition sets in and
a strong odour of sulphur dioxide gas is noticeable.

PREPARATION OF CREPE RUBBER ny

preferable to secure the smaller drums, as the loss on exposure
will be less.

Most commonly the 56 Ib. drum is purchased. It should
not be difficult to calculate the period during which the contents
will be consumed, on the basis of a maximum of i Ib. per
100 gallons of latex. A 56 Ib. drum, assuming no loss or
waste, should be sufficient to treat at least 5,600 gallons of latex
(say, 8,500 Ibs. of rubber) — if the bisulphite is of first-class
quality, and the use is applied only to the preparation of fine
pale crepe.

Where the quantity used per diem is small, it is advised that
precautions should be taken to preserve the quality of the
chemical when a drum is opened. It might be of advantage
to place the contents of the drum in smaller scaled tins, or to
have made a special container (with a closely fitting lid) into
which the powder can be placed as soon as the drum has
been opened.

MIXING SOLUTION WITH LATEX. — Emphasis has been laid, in
Chapter VIII., upon the necessity for care in the preparation
of the solution. Equal regard must be given to the mixture
of the solution with the latex.

On a few estates it used to be the practice to add the powder
to the solution of acid, with stirring. Obviously this led at least
to a great loss of efficiency, owing to the rapid escape of the
gas which was evolved.

The solution of sodium bisulphite should be poured into the
latex in as uniform a distribution as possible. The mixture
of solution and latex should be thoroughly stirred, and if only
natives are in charge a minimum period of five minutes should
be prescribed before the addition of the coagulant. A thorough
stirring should again follow the advent of the acid.

If these elementary rules are not observed faithfully, the
deficiency will most probably be manifested in the dry rubber
in the shape of streaks of varying shades of colour.

Finally it may be insisted upon that deteriorated sodium
bisulphite should not be used. In order to obtain an effect
double the quantity may be required, and the residual
salts left in the rubber on evaporation of the moisture will

n8 PREPARATION OF PLANTATION RUBBER

be responsible for prolonged drying, surface deposits, and
possibly " spot disease."

FORMER METHODS OF MAKING PALE RUBBER. — Merely as a
matter of historic interest it may be mentioned that previous to
the introduction of sodium bisulphite pale crepes were made
in comparatively small quantity by various devices, among
which the following might be quoted :

(a) Use of excessive quantities of strong acetic acid.

(b) Extreme dilution of latex in conjunction with excessive
quantities of acid.

(c) Extreme dilution in conjunction with steaming and
excess of acid.

(d) Extreme dilution of latex in conjunction with excess
of acid and subsequent heating of the coagulum in hot water.

(e) The use of excess of a mineral acid such as sulphuric acid.
(/) The skimmings and very dilute latex, coagulated with

excess of acid.

WORKING THE COAGULUM. — Description of the details of
necessary machinery for crepe-making is relegated to Sec-
tion III. of this book. Here we shall treat only of the matter
in general.

In the preparation of crepe rubber heavy machinery is
necessary, and ample engine-power must be available. The
machines should comprise three types :

(a) With rolls cut in such fashion, and run at such different
speeds, as to have a macerating effect upon the coagulum.
Such machines or rolls will be referred to as " macerators."

(b) Intermediate rolls, grooved in varying designs and geared
differentially. These reduce the thick rough crepe obtained
from the macerators into a form suitable for passing to the
rolls described in (c). They are sometimes called " crepers,"
but as this term may be applied equally to the macerating
rolls, they will be termed the " intermediate " rolls.

(c) Smooth rolls usually run at approximately even speeds
and, as their name denotes, devoid of any grooving. They
are called " smooth " rolls or " finishers."

Without such equipment it is not possible to prepare the
grade which is known as " fine pale crepe." In the common
acceptation of this term crepe of No. i quality generally
connotes fineness and paleness with a thin crepe which has a
good, smooth, and fairly well-knit texture.

PREPARATION OF CREPE RUBBER 119

It is, of course, possible to make a thick pale crepe, using
only the macerators and intermediates, but the " finish " will
be that typical of the particular grooving of the intermediate
rolls. For the preparation of crepe ordinarily, the possession
of smooth rolls is a sine qua non.

For reasons which will be explained more fully in the chapter
dealing with the defects of crepe rubber, the practice of
preparing thick crepes direct from the coagulum is now very
uncommon. Thick crepes are generally made by reworking
dry rubber, either in the form of thin crepes or from air-dried
sheets. The market for the latter in Malaya is confined almost
entirely to Singapore, where factories buy native rubber and
re- work it into thick crepe.

The bulk of the output of No. i crepe from estates is in the
form of thin " fine pale crepe." The artificial standard set up
by buyers and brokers necessitates this thin crepe being of
even texture and fairly free from small holes (" looseness ").
What difference the small holes are to make in the vulcanising
properties of the rubber is beyond our knowledge; but such
being the standard, it must be attained if the full price is to
be obtained.

In order to secure the desired effect the coagulum must be
passed consecutively through the three types of rolls, and
undergoes a varying degree of working in each.

Given the necessary equipment of machines, it is possible
to make a good specimen of thin pale crepe if the coagulum
passes through all the rolls a total of twelve times (or even less in
exceptional cases). There is no intention of suggesting that
this is possible on all estates. Clearly the number of times
the rubber passes through the rolls will depend upon the total
efficiency of the machines. This in turn involves such factors
as (a) the size of the rolls, (b) the number of machines of each
type, (c) the gearing of the pinions, (d) the speed of the drive,
etc. Again, much depends upon the nature of the coagulum
worked. A fairly soft coagulum will offer less resistance, and
conversely a dense coagulum will require more machining.

It has been shown by the writers in previous publications
that over- working of the coagulum has an effect on the vulcan-

120 PREPARATION OF PLANTATION RUBBER

isation of the rubber; and this has been confirmed by others.*
Apart from this point, it should be recognised that over- working,
beyond that necessary to produce a thin crepe of even texture,
is to be deprecated, on the ground of economy, in working.

Owing to the existing differences in equipment and speed of
drive, etc., the regular practice of any one estate may be un-
suitable for another. It remains, therefore, a matter of study
for each estate to discover the minimum number of times which
rubber should pass through the machines, consistent with the
factors indicated above. In any case it may be assumed that if
any factory cannot prepare a good crepe by passing the rubber,
say, twelve times through the rolls, there is some deficiency
in the machines, or of speed; the coagulum may be too hard, or
the rolls may be badly worn.

LOWER GRADES OF CREPE RUBBER. — Even a few years ago it
was plain that the lower grades of crepe (i.e., all grades lower
than first latex rubber) were not sufficiently appreciated in
the market. There was often a marked difference in price
between a first-grade crepe and crepe made from naturally
coagulated lump. This arose chiefly from lack of knowledge.
It has since been recognised in some measure that no reason
exists for such a wide difference in price, and more recently
the margin between even the first-grade rubber and the lowest
grade of scrap rubber has been a gradually diminishing one.
Providing sufficient care is exercised in the preparation of the
lower grades, one would expect to see but very small difference
in prices between any two grades. It is true that adequate
attention has been given to the preparation of the scrap grades
only in comparatively recent years, and it is acknowledged that
when high prices were ruling for first-grade rubbers sufficient
attention was not generally given to the subject of the prepara-
tion of the lower grades.

NATURALLY COAGULATED LUMP RUBBER. — The grade of
rubber made from the naturally coagulated lump which forms in
buckets and carts is usually of a mixed colour, due to the fact

* Bulletin No. 27, Department of Agriculture F.M.S., April, 1918,
"Preparation and Vulcanisation of Plantation Para Rubber,"
Eaton, Grantham and Day.

PREPARATION OF CREPE RUBBER 121

that the lumps oxidise very quickly. When they are allowed
to remain overnight before being machined, it can be imagined
that the colour of the dry crepe would be very dark, or would
contain very dark streaks. Such is ordinarily the case, unless
special precautions are taken.

Providing that the coagulated lump is free from bark, leaves,
and leaf-stems, and certain other precautions taken, the differ-
ence in price between coagulated-lump crepes and first-grade
crepes should be very slight. Too often, however, not sufficient
supervision is given to the coagulated-lump rubber, and it is
common to see it come into the factory containing leaves and
bark. These should be picked out before the latex is strained,
but obviously it would be better to ensure that they did not
enter the buckets in the first place.

It would seem reasonable to suppose that if some means could
be employed for preventing or checking the surface oxidation
of naturally-coagulated lump rubber, there would be a corre-
sponding improvement in the colour of the dry crepe. That
such a method is practicable has been demonstrated on many
estates. The lump when lifted out of the latex is allowed to
drain for a few minutes, and is then (without squeezing) placed
in a dilute solution of sodium bisulphite. A i per cent,
solution is sufficiently powerful. It is not to be thought for a
moment that by the use of sodium bisulphite any previous
oxidation will be counteracted; all that is claimed for the
treatment is that any further surface oxidation will be checked,
and the rubber may be allowed to remain until the next day,
for working, if it is so desired. It will probably be found that
quite a quantity of latex has been expressed from the lumps
by contraction, and acid may be added to obtain the rubber
from this. On other estates the lump rubber is worked on the
machines as it is received, and the resulting crepe is sub-
merged in a weak solution of sodium bisulphite over-night.
It is then rinsed in water and hung to drip before weighing and
placing in the drying house. Under certain conditions some
of the lump rubber darkens rapidly during transport to the store,
and any such oxidised portions must be rejected if a uniform
colour is to be expected in the crepe.

122 PREPARATION OF PLANTATION RUBBER

Following the procedure indicated above, some estates find it
possible to prepare from naturally coagulated lump rubber a
crepe which can be classed as No. i grade.

SKIMMINGS AND WASHINGS. — The skimmings of tanks, as
already shown, may be prepared sometimes as a second quality
of smoked sheet; but generally they are amalgamated with
the rinsings of cups and buckets, treated with sodium bisulphite
and acid, and made into crepe form.

The cup- washings, as they arrive at the store, represent a
very dilute latex, the rubber from which is generally of a
greyish colour.

Bucket- washings should yield a good type of pale rubber if
they are obtained properly. To obtain the maximum quantity of
good rubber the buckets should first be rinsed. A gang should
be taken, a small quantity (say a quart) of water poured into the
first bucket, and this dilute latex used progressively in all the
buckets of that gang of tappers. The result is a fair latex
which can be added to the bulk of No. i latex, provided it is free
from dirt. Where sheet rubber is being prepared, carefully
strained cup-washings or bucket-washings may be utilised
in the dilution of the latex to the required standard, thus
increasing slightly the percentage of first-grade rubber.

TREE- SCRAP. — As tree-scrap is a naturally coagulated rubber,
it should be expected to show up well in quality. This is
usually the case ; but from what has been said of the effect of
sun-heat it will be understood that if trees are not regularly
" scrapped," there is a danger that the crepes may be found
to contain tacky streaks due to the inclusion of old scrap which
has been sun-baked. In hot dry weather, on widely planted
areas tapped on alternate days, it has been noticed that scrap
remaining for two days often exhibits a resinous appearance,
and feels sticky to the touch.

If tree-scrap is to be made as a separate grade, as used to be
the general custom, care should be taken to see that it is free
from bark and dirt. On some estates where scrap-rubber is
paid for per pound collected, it is usually the rule to insist
that scrap shall be washed free from dirt and picked free of
bark. This course is to be commended, but might probably

PREPARATION OF CREPE RUBBER 123

prove impracticable to the majority of estates. Theoretically,
of course, the operation of machining should rid the scrap of
all traces of bark; but in practice it does not do so.

Some proportion of the tree-scrap is usually found to be
heavily oxidised, and naturally if a crepe of uniform colour is
to be obtained these dark scraps must be rejected, otherwise
dark streaks will be formed. Coolies should be instructed
to sort out the dark pieces before arriving at the store.

BARK- SHAVINGS. — It has been intimated in a previous section
that the method of obtaining and collecting bark-shavings
varies with the type of labour employed.

Where the scrap is removed from the edge of the bark on
each occasion before tapping, the amount of rubber to be
extracted from the dry shavings is very small — so small, in
fact, that when the price of rubber is low, it is doubtful whether
it pays to collect and work the material.

On the other hand, where trees are not " scrapped " before
tapping, the bark-shavings and tree-scrap are collected together,
and the amount of rubber derived from the mixture may be
30 to 40 per cent, upon the gross weight — depending chiefly
upon the quality of the tapping (i.e.t in this case, the
thickness of the paring). Another factor influencing this
figure would be the effect of using an anti-coagulant on
the cuts.

Bark-shavings entail such wear upon the ordinary machines
during working, especially if fairly free from rubber, that
unless the factory is equipped with a special " scrap-washer "
it is advised that this material should be sent for working to a
factory having the necessary equipment. Whenever possible,
bark-shavings should receive treatment on the day of collection .

It used to be quite common to see heaps of bark-shavings
accumulating on the floor of a factory, and generating excessive
heat. Yet these heaps were allowed to stand about for a day
or days. Is it any wonder then that tackiness was found to
develop when the rubber was dry ? It is here definitely laid
down that no heaps of bark-shavings should be accumulated
even for half a day. Tanks should be provided in which the
shavings should be submerged in water.

124 PREPARATION OF PLANTATION RUBBER

EARTH-SCRAP. — Of all grades of crepe this is the one most
liable to become tacky in transit. This tackiness to a large
extent cannot be avoided, as old pieces of earth-scrap may be
brought in amongst the bulk. Probably these old pieces have
been exposed to the sun for days, and have become quite
resinous. It would be practically impossible to go through all
earth-scrap in order to find these odd pieces, but unless this
were done one could not guarantee that the earth-rubber
would always be free from tackiness. The difficulty does not
appear, however, on estates where earth-rubber is collected
systematically at very frequent intervals.

FIBROUS MATTER IN LOW-GRADE RUBBERS. — It is some-
times found in this and other lower grade rubbers that pieces
of cloth or cotton- waste are concealed. Coolies may have
used them for cleaning cups, or the store coolies may have been
at fault. Earth-scraps especially should be examined, before
working, for such extraneous matter.

SCRAP- WASHERS. — These are heavy machines specially
devised for the treatment of lower grade rubbers. In these
the raw rubber is well masticated and freed from impurities, if
the machine functions efficiently.

There are several types of these machines, all of which are
efficient. That best known is the " Universal " washer, made
by Joseph Baker, Sons, and Perkins, Ltd. (formerly Perkins
Engineering Company). Coming into local favour during the
War, the " U.E." scrap- washer, made by the United Engineering
Company (Singapore), gives very good service. The " C.C.C."
washer, made by the Colombo Commercial Company, is suitable
for the purposes of an average estate. There are others, less
well known. Most of these machines are made in varying
sizes to meet the requirements of small, medium, or large
estates; and if funds are available, a scrap-washer should be
regarded as an essential item in the machinery of any estate
employing engine power.

The rate of output of scrap-washers will depend mainly upon
the speed at which they are driven, and when ordering the
equipment it would be advisable to state the ordinary speed of
the back-shaft, length of drive, etc. It does not follow that the

PREPARATION OF CREPE RUBBER 125

larger the rate of output, the greater is the efficiency of the
washer. The point is not as to what quantity of rubber can be
taken out per hour, but what quantity is actually freed from
impurities.

It is advisable for the superintendent to obtain a thorough
knowledge of the general construction and principles of the
particular scrap-washer employed. In the past it was not
uncommon to find superintendents innocent of the fact that
a certain type of washer possessed movable parts upon which
the efficiency of the cleansing largely depended. It was often
found that these parts, which were intended to be removed
and cleaned at intervals, had become firmly fixed and could not
be removed for inspection.

It must be recognised also that the machines are liable to
considerable damage if extraneous substances are allowed to
enter — for example, tapping-knives, stones, pieces of iron,
spouts, etc., which are sometimes present in the loose scraps
of rubber or shavings, owing to the carelessness of coolies.
Under the best regulated system, such accidents occasionally
occur, but a great deal of trouble could be avoided by having
it understood that each charge must be sorted over before
entering the washer.

Again a deal of extra work, and much wear and tear, is caused
by the abuse of the scrap-washer — e.g., in the cleansing of
earth-scrap. As this reaches the factory it often contains a
quantity of internal or adhering earth. Before entering the
washer a good proportion of the external soil could be removed
if the scraps were thrown into a tank and given a thorough
soaking and stirring. In a similar manner dry bark-
shavings, which have been allowed to accumulate, could be
softened.

In the actual working of scrap-washers instructions are
generally given by the makers. These sometimes advise the
introduction of warm water (or of steam into the cold water
supply) for an interval during the working of each charge.
Where possible, such instructions should be followed, as
by this means the individual pieces of rubber are massed
together, in the final stage, into a " sausage " form which is

i26 PREPARATION OF PLANTATION RUBBER

easy to transport and to manipulate in the ordinary crepeing
battery.

COMPOUND CREPES. — The attitude of both buyers and sellers
with regard to the types of lower grade rubbers appears to be
changing. In the past, from any one estate there might be
obtained as many as six grades of crepe below No. i. These
comprised :

(1) A pale rubber (often streaked) obtained from coagulation
of cup washings and bucket rinsings.

(2) A pale rubber (often streaked) obtained by coagulation of
the skimmings from the surface of the No. i latex.

(3) A streaked and dull rubber prepared from naturally-
coagulated clots found in cups, buckets, and latex carts.

(4) A streaked rubber prepared from scrap which had coagu-
lated upon the face of the cut bark.

(5) A brownish and streaked rubber made by maceration of
bark-shavings to which pieces of tree-scrap adhered.

(6) A dark rubber, often tacky, prepared from scrap found in
or on the ground near the base of the trees. As it is often a
matter of weeks between any two regular collections, it is
easy to understand why the dry rubber was more liable to be
" tacky " than any other grade of crepe.

It will have been evident to all who have acquaintance with
these grades, as shipped from many different estates, that
the diversity in the various shipments must have been rather
bewildering. There appeared to be a regrettable lack of
uniformity, even in the appearance of, say, a bark scrap rubber
from any two estates. When, in addition to these variations,
the further complication of condition of cleanliness is intro-
duced, one may realise the difficulty attaching to the evaluation
of these rubbers as they appeared upon the market.

Although the foregoing paragraph is written in the past
tense, it should be pointed out that within certain limits the
trouble continues to exist with respect to the output of a
great number of estates.

In the case of many, it has been realised that the manufac-
turer does not want to buy a large number of " parcels," all
differing in some respect. It is probably correct to state that
what a manufacturer requires is a big " parcel " uniform in

PREPARATION OF CREPE RUBBER 127

appearance and treatment, even though the colour may not
be so light as that of many smaller lots. This statement is
modified with the proviso that the rubber, no matter what its
colour or appearance may be, must be free from dirt, grit,
and bark.

The difficulty of making a uniform product from several
types of lower grade rubbers has been successfully solved on
several estates by the preparation of a " compound " crepe
composed of a mixture of the best lower grades in approximately
definite proportions daily. Naturally the shade of colour of
this compound crepe will depend largely upon the types of
rubber employed, but as a rule it is somewhat darker than the
highest of the types employed in the mixture. To the writers
this seems immaterial as long as the manufacturer is offered
a larger and more uniform lot which can be given uniform
treatment in vulcanisation processes. Neither would it
appear that the seller suffers any monetary loss. In point of
fact it will be found probably that the reverse is the case.
For instance, supposing it were decided to mix for a com-
pound crepe —

(a) Naturally coagulated lump rubber.

(b) Tree-scrap.

(c) Bark-shavings scrap.

The product would be darker in colour than (a) and slightly
better than (b). Let it be granted that there might be a
monetary loss on (a), it is probable that there would be a slight
gain in comparison with the usual prices obtained for (b)
and (c). Now, as a general rule, the actual percentage of crop
made into (b) is appreciably less than that made into (c) and
still less than (b) and (c) together. Apparently, therefore,
there would be a margin of profit on the whole by making a
compound crepe. It may be pointed out, on the other hand,
that there might be expended on the manufacture of this crepe
more time and labour, but as against this the labour of sorting
and grading would be simplified.

Unfortunately this process is not open to estates which do
not possess a scrap- washer. It is essential that the rubber should
be free from grit, sand, and bark particles. In the absence of a

128 PREPARATION OF PLANTATION RUBBER

scrap- washer for the cleansing of the bark-shavings, it would be
futile to attempt to make a compound crepe containing that
type of rubber, as one would run the risk of spoiling the whole.
It seems certain that in course of time a scrap-washer will be
considered as necessary a piece of machinery as an ordinary
crepeing machine in the factories of estates having sufficient
means. Until that time the preparation of compound crepes
must be the privilege only of well-equipped estates, unless
other estates can send their lower grade rubbers for treatment
in a scrap-washer to their more fortunate neighbours.

In previous publications a diminution in the number of
grades of crepe rubber has been advocated, and it is gratifying
to find that in many cases the amending grades suggested have
been improved upon. Many estates now make only three
grades of crepe — viz. :

(a) No. i. From latex coagulated in the store.

(b) No. 2. Compound.

(c) No. 3. Earth-rubber.

It will be seen that the compound crepe includes all types
between fine pale crepe and earth-rubber. Naturally one
could not safely recommend the inclusion of earth-rubber in
any compound crepe, as the risk of possible " tackiness " in the
whole would be serious. In the case of the bark-shavings
rubber to be incorporated, it is first cleaned alone in the scrap-
washer. Then all types are mixed together again in the scrap-
washer in proportions ruled by the experience of the usual
average percentages of each grade of the crop.

Besides the estates having only three grades, there are others
which make four — viz. :

(a) No. i. From latex coagulated in the store.

(b) No. 2. Compound, from cup washings, etc., skimmings,
and naturally coagulated lump.

(c) No. 3. Compound, from tree-scrap and bark-shavings
rubber.

(d) No. 4. Earth-scrap.

Other variations are possible, but their number is limited,
and they all conduce to simplification of working, and a supply
to the market of rubber having greater uniformity.

PREPARATION OF CREPE RUBBER 129

NEED FOR INCREASED CARE WITH LOWER GRADE RUBBER. —
In the ordinary procedure of estate-working there appears to be
an undesirable variety in the style of lower grade crepes. On
some estates an examination of these rubbers would appear to
suggest that there need be no expenditure of care in the prepara-
tion or the form in which it is made. This is a great mistake.
With the exception of the lowest grade (earth-rubber), it
would not be unfair to state that the quality of the rubbers on
testing should be very little inferior to the No. i product.
Often, as in the case of naturally coagulated rubbers, they are
superior in some respects to ordinary fine pale crepe. Doubt-
less manufacturers are aware of these facts, but what course is
open to them if they find the rubber spoiled for their purpose
by the presence of particles of sand, grit, or bark ? The possible
injury caused by these ingredients cannot be insisted upon too
strongly, and it must be evident that great care should be
exercised in the preparation of the lower grades of crepe.

As to the particular form of the lower grade crepe rubber,
one may apply the remarks made under the section dealing
with the best grades. It is common to find thin crepes, medium
crepes, and " blanket " crepes. More often than otherwise,
the medium and thicker crepes are prepared direct in those
forms. It follows that they are liable to attacks of " spot "
disease, which, however, is not easily visible in the lowest grades,
owing to the dark colour of the rubber. Furthermore, it is
not possible to cleanse the rubber so thoroughly if thick crepes
are made.

BLOCK RUBBER. — Few estates now prepare block rubber,
which is essentially crepe rubber pressed into blocks. In the
ordinary process the fresh coagulum is lightly rolled into thin
crepe, which is then vacuum- dried. There are slight variations
in the subsequent procedure. Sometimes the rubber as it
comes from the vacuum drier is merely allowed to remain on
racks overnight before blocking. In other instances, the
sticky rubber from the vacuum drier is passed once or twice
through wet, smooth rolls and hung to dry for some days. The
dry crepe is then folded into the pressing box or cut to suit the
size of the box. Pressure is applied for some time, and finally

9

1 3o PREPARATION OF PLANTATION RUBBER

the rubber is taken out in one homogeneous mass. Naturally
the appearance of the block depends upon the quality of the
parent crepe. Some block rubber is made up thick; other is
made in slabs about 3 inches or 4 inches in thickness. With
the latter, it should be possible, when held up to the light, to
see the shape of a hand held between it and the source of light.

It is possible that an erroneous idea of the strength of block
rubber has been formed. It should only be necessary to
point out that essentially block rubber is merely pressed crepe
rubber. It is inconceivable that the mere action of pressing
layers of crepe together would increase the physical quality
of the rubber.

The advantages which block rubber possesses are the com-
pactness of the output, its ease of packing, and a saving in
freight; but there is the disadvantage, from the consumer's
point of view, that extra labour is involved in the preparatory
work of cutting up the blocks.

SMOKED CREPE AND SHEET CLIPPINGS. — There appears to be
no certain demand for any grade of smoked crepe, and probably
all which is put into the market is really comprised of (i) clip-
pings obtained from the ends of sheets, (2) sheets which have
been malformed in machining, or (3) sheets showing the
presence of many " bubbles."

As to the first class it might be explained that through
defective rolling, thick ends or edges may be caused. These
show signs of contained moisture when the bulk of the sheet is
perfectly dry, and as undue delay would otherwise result these
moist strips are trimmed and either returned to the smoke-
house, or machined to form crepe.

Similarly a torn or otherwise badly formed sheet, when
brought from the smoke-house, may be made into crepe, rather
than it should prejudice the selling price of the bulk under
ruling conditions.

In the same manner, although " bubbles " have no influence
upon the quality of the rubber on vulcanisation, sheets thus
affected are generally made into crepe.

It cannot possibly be argued that rubber of this description
would be in any way inferior to the best smoked sheet for

PREPARATION OF CREPE RUBBER 131

manufacturing purposes, but owing to the prevailing system
of evaluation for market purposes, it is necessary to resort to
the expedients indicated above.

On some estates the rubber specified in the three classes
mentioned is not made into crepe, but cut up into small pieces
and shipped as " sheet clippings " or " sheet trimmings "-
a procedure which would appear to be justified by a steady
demand. In point of fact, the buyers are really obtaining a
first-class article (except in superficial appearance) at a reduced
price.

CHAPTER XI
DRYING OF RUBBER

AIR-DRYING OF CREPE. — It is still the prevailing custom to
air-dry crepe rubbers. A few estates, it is true, have artificial
driers installed, and in some necessary cases others will be
erected. But in the majority of cases where money has been
expended in building air- drying sheds, as long as it is only
possible to ship rubber regularly air-drying is likely to remain
in favour.

The great drawback to air-drying is that one is so dependent
upon the weather conditions. In favourable weather the
rubber dries well, but in a long period of wet weather rubber
may accumulate at an alarming rate, and the accommodation
is sometimes severely taxed. Of course, the rate of drying
under the best conditions is mainly dependent on the thickness
of the crepe, and every endeavour should be made to maintain
a thin style of preparation. If this precaution is not taken,
the rubber is liable to recurrent attacks of "spot" disease,
and one's troubles are very much augmented. This is a
disability to which rubber treated in artificial driers is not
liable. Still, air-dried rubber can be made equal, if not
superior, in appearance to pale rubbers prepared by other
processes.

For the lowest grades of crepe air-drying is always likely to
remain the only method, as it would be extremely unsafe to
submit them to heat.

It is noted in ordinary practice that the rate of drying on
different estates, for the same type of rubber, may vary widely.
Naturally the construction of the house has a great effect, and
this subject will receive attention in a subsequent chapter.

Similarly the position of the drying-shed exerts an important
influence, and the erection of the building in low- lying sur-

132

DRYING OF RUBBER 133

foundings is always calculated to prolong the drying period
appreciably. Incidentally this means that the building must
be larger than a normal rate of drying would otherwise demand.

The combination of a poor type of drying-house, a low-lying
situation, and a prolonged wet season, might render it advisable
to abandon the air- drying of high grade crepes in favour of
artificial drying.

ARTIFICIAL DRIERS FOR CREPE. — It is more common to find
artificial driers in use in Ceylon than in Malaya, possibly
because these driers have been in use in Ceylon for other
products. Some time ago the question of installing artificial
driers received the serious attention of a number of estates in
this country, chiefly on account of the incidence of fungoid and
bacterial diseases in crepe rubber. The simple treatment
for the prevention of these diseases is to get the rubber dry in
the shortest possible space of time. In most cases it is found
sufficient to roll crepe thin for air-drying in order to prevent
the appearance of coloured spots. It is found, however, that
some drying-houses are so badly planned and constructed,
that quick drying under even the best of conditions is a practical
impossibility. Cases have been known in which the disease
may disappear almost entirely during a period of freedom from
rain, only to recur as soon as wet weather sets in again. There
can be no doubt that, on the whole, the number of cases of
" spot " disease is on the decline; but equally it is certain that
a very few estates will always be liable to outbreaks as long as
drying is attempted in existing houses. For these reasons it
is a poor policy to temporise, and the only sound policy in
extreme cases would be to give up ordinary air-drying in
favour of some method of artificial drying. As regards the
majority of estates preparing pale crepe for various reasons, it
is not expected that any will instal artificial driers. Money
has been expended in elaborate buildings which certainly
do the work for which they were designed. As long, there-
fore, as the accommodation is sufficient, and regular shipments
are the rule, it is expected that ordinary air-drying will still
remain the general practice.

Of the better-known artificial driers, there are only three

134 PREPARATION OF PLANTATION RUBBER

which merit serious consideration in these pages. They are
the vacuum driers, the Colombo Commercial Company's
hot-air drier, and the Michie-Golledge process.

VACUUM DRIERS. — The vacuum drier is so well known that
only a brief description need be given. It consists of a
chamber heated by steam pipes and capable of having the
contained air and moisture withdrawn by a pump. This
description sounds very simple, and in practice the operation
of vacuum drying is really a simple one, and can well be
entrusted to an intelligent coolie under efficient supervision.
Indicators are fitted which show the vacuum pressure and the
pressure of steam in the heating pipes which travel underneath
horizontal slabs upon which trays may be placed. Still,
in spite of the apparent simplicity of the process, there would
appear to be a number of little details which, if overlooked,
prove to be factors influencing the result to a considerable
degree. Thus it is not uncommon to find complaints that
the rubber is not dry when packed. The writers have seen
rubber taken from a vacuum drier still containing a visible
quantity of moisture. One would have imagined that con-
tinuous working of the drier would give the experience necessary
to obtain dry rubber, but, apparently, such is not the case in a
number of instances. Elaborate instructions are given by the
makers, but often they are more honoured in the breach than
in the observance. Really, there are only two points to bear
in mind :

(1) That the rubber must be fairly thin.

(2) That the temperature be not allowed to rise too high.
Some makers advise 140° F. as a maximum, but no harm
results from a temperature of 150° to 160° as long as the
interval is not prolonged.*

These two points presume that the vacuum drier is true to
its name, and that one can obtain a maximum steady pressure.
The machines are so well made now that no drier should be
taken over from those responsible for its erection unless it can
show a vacuum pressure of 28 inches within fifteen minutes of

* These figures refer to temperatures recorded by thermometers
placed in the folds of the rubber.

DRYING OF RUBBER 135

starting the pump; and with the pump stopped, there should
not be a greater fall in pressure than i inch within ten minutes
after stopping the pump.

One of the most frequent sources of error is the control of
steam pressure which is responsible for the temperature of the
drier. It is quite unnecessary and unwise to maintain any
steam pressure once the drying is well under way. All that is
necessary is to heat the chamber well, with a steam pressure of
5 Ibs., before inserting the rubber. As soon as the maximum
vacuum pressure has been obtained, steam should be shut off
from the heating pipes, and it will be found that the temperature
is well maintained throughout the operation with a rise of ten
to twenty degrees at the end. If the drier is working at a
vacuum pressure of 28 inches, and if the crepe has been
prepared thin enough, the rubber should be quite dry within
two hours. Should the operation have to be extended to two and
a half hours at 28 inches vacuum pressure, it is a sign that the
crepe is too thick. On such occasions it is often noticed that
these thicker crepes are not thoroughly dry, having moist
spots enclosed in them. On re-rolling, these moist patches
become easily visible, and are a source of great annoyance,
inasmuch as they take quite a long time to dry out.

As mentioned before, the crepe for vacuum drying should be
thin. There is no necessity to give it a superfine finish, and the
presence of small holes is quite permissible, as they disappear
on subsequent re-rolling. The thin crepe may be folded loosely
to the length (or breadth) of the tray several times, but in no
other way can the drier be expected to perform its work satis-
factorily. A case was noted in which thin crepe was excel-
lently prepared, and four or five layers were rolled together
for vacuum drying. Naturally this mode of procedure does not
give the drier a fair chance, and it would be ridiculous to judge
vacuum drying on the results. After two and a half hours at a
temperature of 145° F. the rubber appeared to be only about
three parts dry, and the subsequent air-drying extended well
into a fortnight.

It is the common practice to screw up the door of the chamber
as tightly as possible. As a rule it is found in course of time

136 PREPARATION OF PLANTATION RUBBER

that the obtainable maximum vacuum pressure decreases.
This may be attributed solely to the forcible screwing up of the
door. Around the inside edges of the door are strips of rubber
compound, the function of which is to form a tight joint. Should
the door be screwed up too tightly, these strips become deformed
in course of time, and slight leaks occur. It should be pointed
out that it is only necessary to screw up the door at the beginning
of the operation. When the vacuum has been obtained, the screw
pressure may be released, as the atmospheric pressure outside
the chamber is more than ample to keep the door in a close
fitting position. This will be obvious from the fact that the
difference in pressure between the inside and the outside of
the door amounts to, say, 28 inches atmospheric pressure: — i.e.,
nearly 14 Ibs. per square foot. By slackening the screw handles,
therefore, as soon as the indicator shows the maximum working
vacuum pressure, the life of the door joints may be prolonged,
and the drier will remain efficient for a longer time.

A careful consideration of the question of temperature leads
one to the conclusion that the practice of placing a thermometer
through the roof of the chamber does not enable one to deter-
mine the temperature correctly. In the same way a thermometer
suspended behind the observation window cannot indicate
the temperature of the rubber, as in both of these positions
the thermometer must be influenced by radiation from the walls
of the chamber. The only position in which the correct tem-
perature could be indicated is between the folds of crepe.
This can be arranged easily so as to enable one to read the
temperature from the observation window.

COLOMBO COMMERCIAL COMPANY'S DRIER. — The drier of the
Colombo Commercial Company consists in principle of a
number of small chambers or units in which crepe rubber is
placed, and through which hot air is passed. As in the case of
vacuum drying, a great deal depends upon the preliminary
treatment of the rubber. If the crepe is not rolled thin enough
drying will be unduly prolonged, with a possibility that the
rubber will become tacky. The temperature usually obtained
is about 150° F., and if the rubber is thin the production of
an installation of two chambers should be at the rate of i Ib.

DRYING OF RUBBER

137

of dry rubber per minute. The usual period of drying is
under two hours. One advantage which this drier has over the
vacuum drier is that the chamber can be opened at any time
for a short period to withdraw or insert trays. The thin crepe
is folded several times, as in the case of vacuum-drying.

Figures obtained from the actual working of a drier in
Ceylon are given below:

CHAMBER i. — TEMPERATURE i6o°-i8o°F.

CHAMBER 2. —

TEMPERATURE

No. of

Drying

Weight of

Weight of

i50°-i65°F.

Tray.

Period.

Wet Rubber.

Dry Rubber.

Hrs. Mins.

Lbs.

Lbs.

i

I 22

7i

6

Worked similarly

2

I 42

7*

6

to No. i. Yielded

3

I 57

7i

6

in 2 hrs. 23 mins.

4
5

I 57

i 57

7i

7

6
5l

70^ Ibs. dry rubber,
from 87! Ibs. wet

6

i 57

72

6

rubber.

7

2 0

7f

6

8

2 0

6

9

2 II

6|

5

10

2 II

7^

6

ii

2 II

7i

6

12

2 18

7i

6

88$

7oj

It will be seen, therefore, that the drier had an output in
2 hrs. 23 mins. of 141 J Ibs., which is at the rate of i Ib. per
minute approximately.

As the rubber leaves the driers it resembles vacuum-dried
rubber in being surface-sticky. This stickiness' is only
temporary, and is got rid of by passing the crepe through wet
rolls. Opinions differ as to when this rolling should be given.
On some estates the rubber is only allowed to cool a little
before passing through the rolls; on others it is given a day
or so before rolling. The methods of rolling also differ.
In some factories the rubber has been cut to lengths before
drying, and these lengths are merely rolled together by simple
pressure. Other estates prefer to re-macerate the crepe while
still fairly warm and soft. It is probable that little harm, if any,

138 PREPARATION OF PLANTATION RUBBER

results from this re-maceration while the rubber is soft,
as it is more easily worked in this condition. The thick
rubber is then generally hung for a few days to air-dry before
packing. As most of the moisture taken up by the dry rubber
is surface moisture, three or four days is usually found ample
for air-drying.

MiCHiE-GoLLEDGE SYSTEM. — The Michie-Golledge system
comprises a process of preparation and drying. The latex is
diluted with two, three, or four volumes of water and coagulated
with acid in a vessel which is rotated with a churning motion.
In this cylinder there are curved and fixed blades. The re-
volving cylinder and its ribs force the latex against the curved
blades so as to cause an eddy in the middle of the machine.
Here the rubber coagulates and accumulates, the remaining
liquor whirling round outside the blades. It can be imagined
that with such dilute latex, the coagulum is very soft and
spongy. This soft mass is passed through a machine which
cuts it into " worms " about ^\ inch in section. These are
placed upon wire trays and dried by means of hot air. The
" worms " when dry are re-macerated and built up into medium
and thick crepes. The colour of the rubber prepared by this
process is usually very good. When treated in a Colombo
drier the " worms " usually require about two hours to dry,
so that crepe rubber may be packed at latest on the fourth
or fifth day, as in the case of vacuum-dried rubber.

RATE OF AIR-DRYING OF CREPE RUBBER. — In spite of the
facts that some estates have been making thin pale crepes for
years, and that so much has been written concerning the
preparation of this grade of rubber, one occasionally meets
with a case in which an estate seems to be unable to prepare thin
pale crepe, or if it does the period of drying is much longer
than obtains on most estates.

Again, when cases of infection by spot disease in fairly thin
crepes are submitted, it is usually found that the particular
crepes are of that type which, though fairly thin, show whitish
spots of moisture when the bulk of the rubber is nearly dry.
This type of crepe is to be noted for the excessive period of
drying in comparison with other crepes of equal thinness.

DRYING OF RUBBER 139

It has been advanced elsewhere* that a factor of the most
considerable importance in the rate of drying of crepe rubber
is the type of drying-house and its situation. This accounts
very largely for observed differences in the rate of drying of
thin crepes on different estates. Yet even where two drying-
houses may be of the same type, and the situations may be
comparable, one still observes that one thin crepe dries more
quickly than another. It has been remarked also that a thin crepe
in one old drying-house dries in a shorter period than a similar
crepe in another more modern house, although the methods
of coagulation and preparation exhibit no apparent diversity.
In all these conflicting cases allowance is made for the weather
conditions, and the observed differences seem to be inexplic-
able. It has always been the opinion of the writers that the
actual rolling of the rubber plays an important part in deter-
mining the rate of drying of crepe, apart from the question of
thinness ; and it seemed possible that this factor would account
for the discrepancies noted above, either partially or wholly.

With a view to determining to what degree the drying of
crepe rubber was hastened by the extent to which the rubber
was rolled, experiments were made. It was hoped, also, that
some idea would be gained of the particular stage in crepe
rolling which had the greatest effect upon the rate of drying.
In preparing crepe in the estate in the ordinary way the coagu-
lum is passed through three sets of rollers, and the stages
may be described as:

(1) Rough rolling.

(2) Medium rolling.

(3) Smooth rolling.

In the first the coagulum is broken down by passing through
the machines until a thick rough crepe is formed. This passes
to the intermediate rollers, where it is worked down to a medium
crepe. The rubber finally goes to the smooth running at
approximately even speeds. Passing through these a number
of times it emerges as a thin uniform crepe, free from " lumpi-

*" Preparation of Plantation Rubber," Morgan, 1913, chapters
xii. and xiii.

1 40 PREPARATION OF PLANTATION RUBBER

ness " and free from holes, which should dry in from ten to
twelve days.

In the experiment the rubber was passed through the
machines with varying frequency, the number of times in each
machine being progressively increased, while the working on
the other machines remained constant.

It was determined that the rate of drying was affected only
by the extent to which the crepe was worked in the smooth
rolls. The less often the rubber passed through these rolls,
the slower the rate of drying. Beyond a limit in the other

DRY

DRYING GRAPH. PALE CREPE (THIN).

direction, increased rolling did not reduce the period of drying.
It follows, therefore, that crepes which have a good thin finish
should dry in a minimum period.

WHEN DOES AIR-DRYING TAKE PLACE ? — Experiments*
were conducted with a view to discovering, if possible, the rate
at which crepe rubber dries, and the extent of drying during
the night under weather conditions such as prevail ordinarily
in Malaya. It is to be remembered that, during the day, most
drying-houses are fairly open and that the temperature ranges
from about 88° F. in the lower rooms to over 100° in the upper
rooms (near the roof) when the sun shines. At night, however,
there is usually a decided drop in the temperature, and unless

* Rubber Growers' Association, Malaya Local Report, No. 2, 1914.

DRYING OF RUBBER 141

it is a very clear night the air is generally saturated with mois-
ture. In addition the drying-house is closed as thoroughly
as possible, and we should expect the atmosphere of the house
to be laden with moisture from the wet and drying rubber.
It would be a just inference, therefore, that the rate of drying
during the night would be much less than the rate of drying
during the day, and the results of experiments confirm this
very fully. One was hardly prepared, however, to find that,
under certain circumstances and at a certain stage, the amount
of drying is nil; not only so, but it was found under certain
conditions that the amount of drying which took place was
negative — t.e.t the rubber weighed slightly more when taken
out in the morning than it had weighed the previous afternoon.

CREPE MAY INCREASE IN WEIGHT. — As an instance of the
kind of result obtained a graph is here given of the rate of dry-
ing of a batch of pale crepe. This was hung to dry in the top
room of a drying-house in which rubber ordinarily dries quickly.
The rubber was hung in a good position, with the bulk of
output, near a window which was open for some time during
the day. In order to restrict the day interval of drying to the
actual period in which the sun was likely to be in evidence,
the day was taken to begin at 8 a.m. and end at 4 p.m., the night
interval covering the remaining sixteen hours. Thus the night
interval was twice as long as the period of day drying. The
lengths of crepe were weighed carefully at 8 a.m. and 4 a.m.,
and the average of the several weights was plotted in a graph.

The weights are placed vertically and the duration of drying
horizontally. It will be seen that the rubber was quite dry
and fit for packing on the sixth day, as far as could be judged
in the usual way by casual inspection. Peculiarly enough at
this time it weighed slightly more than had been registered on
the fourth and fifth days, but the difference did not amount
to more than about 0*4 per cent. In examining the graph it
should be borne in mind that the steeper the slope of the curve
downwards the quicker the rate of drying, and that when the
curve takes an upward direction there is an addition of mois-
ture instead of abstraction. It will be noted that when drying
takes place the slopes more nearly approximating the vertical

142 PREPARATION OF PLANTATION RUBBER

represent the extent of day drying, and that often the night
drying is represented either by a very flat curve or even by
an upward curve which shows the addition of moisture. A
striking feature of the experiment is shown by the rapidity
with which drying takes place during the first few days and the
comparative slowness with which the remaining moisture is
got rid of. Thus, from the graph, it may be calculated that
about 80 per cent, of the total moisture content was lost in the
first two days, and over 93 per cent, in two and a half days.
Yet three days had to elapse before the remaining 7 per cent,
of total moisture was lost — i.e., before the rubber was judged
to be ready for packing. It will be seen that after this stage
had been reached the rubber alternately lost and gained in
weight, with a tendency to increase. This increase was attri-
buted to the presence of surface moisture after hanging over-
night, when the rains had become frequent. Some light is
thus shed upon a subject which has puzzled both shippers and
receivers of crepe rubber.

DIFFERENCES IN WEIGHT. — It will be obvious that if rubber
is allowed to hang after becoming dry, and is taken down,
packed, and weighed in the early morning, it will weigh more
than when it reaches a drier climate. The loss in weight
under such circumstances might amount to even i per cent.
It may seem to some an unnecessary refinement to introduce,
but it would appear from the graph that rubber should be
packed for preference in the afternoon if the weights are to be
more nearly correct.

It is extremely singular to note how quickly the curve
changes its slope after the major portion of the moisture has
evaporated, and it will be very plain that in the last stages any
decrease in weight during the day would appear to be counter-
balanced, or more than counterbalanced, by the addition of
moisture during the night. It may be pointed out, however,
that this increase in weight during the later stages of drying
of pale crepe is mainly, if not altogether, due to surface moisture.
The chief point of interest is the fact that in the case of thin
pale crepe, quite 80 per cent, of the total moisture content is
lost during the first two or three days, and that, owing to the

DRYING OF RUBBER 143

negative influence of the night atmosphere, the final drying is
delayed. It will be understood that the foregoing results
applied to thin pale crepe. Thin lower-grade crepes appeared
to dry at more uniform rates, but the differences between the
rates of drying at night and during the day were similarly
notable.

AIDS TO NORMAL AIR-DRYING. — These experiments were
undertaken in a drying- house, favourably situated for rapid
drying, in which the average period of drying for thin crepes
is nine days. It is easy to imagine that the condition of affairs
as revealed would be much exaggerated in a drying-house
situated on low- lying ground and surrounded by trees. In
extreme cases of this nature the use of large fans and heating
pipes has been advocated. It is believed that in some cases
these installations have given satisfaction, but that in others
the degree of improvement obtained has not been in economic
proportion to the outlay incurred.

SMOKE-CURING OF SHEET RUBBER. — It will have been evident
that one of the disadvantages of air-drying sheet is the incidence
of moulds. Now it is found that moulds should not develop
in smoke-curing ; and if they do, then the smoke-curing has been
insufficient or inefficient. The difference in the drying period
also is a strong argument in favour of smoke- curing, so that all-
round it is seen that there are many valuable advantages to
be gained by smoke-curing sheet in comparison with air-drying,
and no disadvantages.

The manipulation of the rubber, after it leaves the marking
rolls and preparatory to smoke-curing, has been discussed in
Chapter IX. It is sufficient only to allow adequate time for
furnace water to drip from the sheets before transferring them
to the smoke-house. As it is the general rule to roll sheet
rubber in the morning, this arrangement fits in very well. The
furnaces of the smoke-house are usually extinguished as soon
as the sun is well risen, and the rest of the day is occupied
in sorting dry sheets, etc. Towards noon the day's wet sheets
should have been admitted, and smoking may be commenced
as soon as the sun is well in the west — say, at half-past four
o'clock or earlier.

144 PREPARATION OF PLANTATION RUBBER

It used to be the custom on a few estates to smoke during
the daytime and to discontinue smoking at night. As the night-
air in Malaya is usually heavily laden with moisture, it will be
plain that such a policy was a topsy-turvy one. It is vastly
more reasonable to smoke-cure at night ; usually the heat of the
sun during the day is quite sufficient in itself to promote the
drying of rubber ; but there is no reason why smoking should
not be carried on in the daytime in wet weather, should it be
found expedient to do so.

RECORDING INSTRUMENTS. — During the night the care of the
smoke-houses is usually in the hands of natives, except for
occasional surprise visits from a European superintendent.
To all acquainted with the ways of the native it must be plain
that means must be provided for the checking of the tem-
peratures attained in the smoke-house. Ordinary thermo-
meters are quite unsuitable, and even thermometers registering
maximum and minimum temperatures are of little avail,
inasmuch as they record only the degree of heat attained at a
particular moment, and do not indicate any period during which
a particular temperature was maintained.

It is evident that something more informative is required.
There are many types of suitable recording instruments or
" pyrometers," some of which can be electrically connected,
so as to cause the ringing of a bell, placed in the superinten-
dent's office or house, on the attainment of a certain tempera-
ture. The type best known in estate practice is that named the
" Thermograph," in which a pen traces a curve or graph on
a plotted piece of paper carried by a rotating cylinder which is
actuated by clockwork. Such instruments can be purchased
through most of the local firms dealing in estate supplies.
From experience it can be asserted that, given intelligent atten-
tion, these instruments yield very satisfactory results. The
apparatus should not be placed always in one position in the
smoke-house, but should be moved frequently so as to obtain
information regarding the distribution of heat.

TEMPERATURE OF SMOKE- CURING. — In the question of tem-
perature of drying, it is well to be as strict as possible; not
that any great harm will result from a rise of 10° above that

DRYING OF RUBBER 145

recommended, but because the higher the temperature recorded
the larger the fires must have been, and consequently the more
real danger there was of the store becoming ignited. It has
been shown* that the temperature giving the maximum bene-
fit of drying and quality was found experimentally to be
rather above the temperature usually prescribed for smoke-
houses, but in the experimental work there was no danger
from fire.

The figure given in previous publications as a maximum
working temperature for smoke-houses was 110° F., but cer-
tainly the temperature may be as high as 130° if it is considered
safe to allow fires to be so arranged. One or two estates are
known to work at temperatures of 130° F. and over, in spite of
the recommendations of the writers. If those estates care to
risk it they may do so, with increased rapidity of drying;
but no responsibility can be taken for whatever may happen
in smoke-houses where the temperature is allowed to remain,
as in one case,*at 160° F. Naturally the range of temperature
is strictly limited by the properties of the substance to be
treated, and with a substance such as rubber it would be far
better to err on the side of caution than to risk damage to such
a commodity, apart from the consideration of the possible
destruction of the building.

PERIOD OF DRYING. — Considerable differences are noted in
the periods of drying on various estates; but, as there is more
than one factor influencing the results, it is not easy at first
to find why these differences should exist. Really there are
three factors :

(i) Relative thickness of rubber.

2) Extent and quality of rolling.

3) Temperature of drying.

It is presumed that the smoke-houses are identical in type
and efficiency, and that smoking is in force for the same length
of time each day. There need be no discussion of these
points ; the effect of each is so obvious. The thinner the sheet,
the quicker the rate of drying; the better the sheet has been

* " Preparation of Plantation Rubber," Morgan, 1913, chapter x.

10

146 PREPARATION OF PLANTATION RUBBER

rolled, the shorter the period of drying; the higher the tempera-
ture, the more rapid the drying.

It has been shown in Chapter IX. that the condition of the
sheet after rolling depends primarily upon the standard of
dilution of the latex and the original thickness of the coagulum.
If these factors are correctly controlled, the rolling should give
a sheet which is fairly soft and porous — i.e., it should not have
been subjected to such pressure as to make it both thin and
hard. An average sheet of rubber which has been well rolled
should be smoke-dried at a temperature of 120° F. in about
ten days. If sheets take appreciably longer to dry, then the
three foregoing factors must be examined.

On the other hand, it is often found that thin sheets made
from very dilute latex dry so quickly that they are considered to
be fully smoke-cured in from five to seven days. It frequently
happens in such cases, however, that the smoking is insufficient,
and by the time the rubber reaches home it has begun to show
signs of surface moulds. It is evident, therefore, from this
discussion that:

(1) If smoked sheet develops surface moulds within a short
period after smoking, the duration of curing has been in-
sufficient, or the quality of the smoking is at fault.

(2) The actual time taken to smoke-dry rubber may be
insufficient to smoke-cure it.

(3) The rate of drying of smoked sheet depends upon —

(a) The relative thickness of the rubber.

(b) The preliminary treatment of rolling.

(c) The temperature of the smoke-house, and

(d) The type of smoke-house used. This point will

be treated in a subsequent chapter.

FUELS FOR SMOKING. — The general idea formerly held was
that the beneficial effects of smoking were to be attributed to
the constituents of the smoke, and chiefly the creosotic sub-
stances. This is not now the opinion of the writers, who
attribute the effect largely to the temperature of drying and
constituents of the smoke other than creosotic substances.
There can be no doubt that the presence of creosotic bodies is
responsible largely for the absence of moulds and the exist-

DRYING OF RUBBER 147

ence of the typical odour, but it is becoming increasingly
known that the employment of substances rich in creosote is
not required or desirable.

Estates used to be put to considerable expense in the purchase
of " bakau " (a mangrove timber rich in creosote and creating
much heat), under the idea that it was the best material and
almost indispensable. Most estates now restrict themselves
to the consumption of timber obtained from their own areas.
Thinning-out programmes are largely responsible for the
supply, but the local authorities are much concerned regarding
future supplies; and consideration has been given in some
quarters to the question of the development of quick-growing
trees on estates with a view to safeguarding the future. This
seems to be desirable, as it is difficult to imagine that the place
of timber can be taken by any other material in the smoke-
curing of rubber. Unless some such precautions are taken
it is not difficult to predict that, in course of time, some estates
will be able to continue the preparation of smoked sheets only
at considerable expense in obtaining suitable fuel from a
distance.

It is not true that any kind of timber is suitable as a fuel to be
used in a smoke-house. All timbers are suitable, either alone
or in mixture with others, provided that the wood is not too
green.

Naturally an absolutely dead and crumbling wood will
smoulder, but does not develop sufficient smoke. A green
timber will give an acrid and moist smoke, but demands the
consumption of a certain amount of dry timber in addition if
it is to be used.

Rubber-tree prunings and sawn rubber trees obtained by
thinning-out may be used in mixture with dead wood, provided
the logs are stacked to dry in the sun for some weeks before use.
If the timber is too green, steam is formed as well as smoke, and
the sheets of rubber may have a moist surface glaze.

SUN-DRYING SHEET RUBBER. — Among the first curious sights
which impress the visitor or newcomer to this country is
the spectacle of sheet rubber hanging in the sun on native
holdings. From what one has learned of the extraordinary

148 PREPARATION OF PLANTATION RUBBER

care which must be exercised in all the processes of rubber
preparation, one fails to understand how such rubber reaches
the market without becoming tacky. That some of it does
become slightly tacky is certain, but on the whole native
rubber, though crudely prepared, is usually sound. The
native idea of giving sheet rubber a preliminary drying in the
sun is to hasten the total period of drying. That the period
is curtailed would seem to be the case, but it is open to doubt,
as the effect of sun-drying, if unduly prolonged, is to create
a thin surface film of dry rubber which retards the drying
of the rubber below the surface. Working with wet crepe
rubber, the writer found that, to all external appearances, there
was no effect upon the rubber when it was allowed to sun-dry
for four or five hours. With periods of from six to ten hours
the crepe becomes slightly sticky, chiefly on that portion
across the support. When removed to the air-drying house
this tackiness developed further, and the rubber, on the line
of support, became so weak that it stretched and broke.

Reasoning by analogy, it would appear that no apparent
harm would result to sheet rubber from sun-drying for periods
up to four or five hours. From experience (see Chapter IX.),
not the slightest ill-effect is found to result from the short
interval of preliminary drying or dripping practised on many
estates preparatory to smoke-curing.

ARTIFICIAL DRIERS FOR SHEET RUBBER. — It is understood
that when vacuum driers were first applied to the drying of
rubber it was thought possible to dry sheet rubber in this
way. The practice was found to be impossible, as the length
of time required and the temperature were responsible for
the destruction of the form of the rubber; it became tacky
and semi-liquid.

THE " CHULA " DRIER. — Although several suggestions of
devices for artificially drying sheet have been made, only one
is known to be in use at the present time. In the original form
this was used for drying other tropical products. It consists
of a large iron chamber, in which are several compartments
divided by means of baffle-plates. At one end there is a small
furnace and, by means of a fan, smoke and hot air are drawn

DRYING OF RUBBER 149

through the compartments. Owing to the temperature
attained (140° to 160° F.) sheet rubber cannot be completely
dried in the chambers, and is, as a rule, only treated in
this manner for one or two days. Drying is then completed
in an ordinary air-drying house. It is claimed that drying is
expedited, and that the rubber can be packed in ten days.

In the more recent modification, the smoke and hot air
which leave the Chula drier pass through a large room in which
may be hung either sheet or crepe rubber. It would seem
that all sources of danger have not been eliminated from the
process, as on one estate a wooden room containing rubber
was ignited by a spark which passed through the drier.

Yet another form exists in which the furnace is outside the
main building, and in the ordinary course of working only
heats a series of open pipes through which air is drawn by a
powerful fan. By means of a valve it is possible to allow
smoke from the furnace to pass into the room with the hot air
for the preparation of smoked rubber. The hot air or smoke
is distributed in the lower room by means of main and branch
pipes, and passes through an open floor to the room above.
With such an arrangement it is possible, therefore, to prepare
either air-dried or smoke-cured rubber. If the method could
be successfully applied to the drying of crepe it would be of
great assistance on some estates. There would seem to be a
difficulty in working it for the drying of sheer rubber and crepe
together, as the temperature suitable for the one is excessive
for the other. Given an efficient control over the temperature
of the hot air, the house should be successful in the drying of
crepe, provided the rubber is not hung in folds of too great
length. For smoke-curing sheet rubber the period is said to be
reduced by several days in comparison with the time occupied
in an ordinary smoke-house, but it is not clear that such a
system would have any advantage over a modern smoke-house,
in types of which rubber can be fully cured in periods ranging
from five to ten days.

CHAPTER XII
SORTING, GRADING, AND PACKING

THE question of standardising the output of our plantations is
one which has occupied attention for some years, with a not
inconsiderable degree of success.

Meanwhile opinion is growing in favour of proceeding along
the line of reducing the number of plantation grades to a
minimum. At present some confusion exists. Some estates
make up tree-scrap and bark-shavings together; one estate
puts tree-scrap, earth-scrap, and bark-shavings into one
uniform crepe ; other estates have three or more separate scrap
grades — e.g., lump-rubber and " washings," tree-scrap, earth-
scrap, and bark-shavings scrap. There is a movement on
foot at present to try to restrict plantation rubber to three
grades :

CREPES — i. First Quality Latex. — I.e., crepe made from the
true coagulum obtained from the regulated coagulation of
strained latex. This is a pale rubber, and may be prepared
satisfactorily if the directions given in preceding chapters are
followed. Naturally there must be, in all factories, some
defective rubber of this grade. For various reasons the crepe
may be of inferior colour, or is slightly contaminated with
dirt or traces of oil and grease, etc. This defective rubber
should be placed aside most rigorously and plainly marked as
" off-quality."

If a proper scheme of standardisation of latex and chemicals
is followed, there should not be any such variety in shades of
colour, such as was common in No. i crepe in the past.

Comparatively few estates in Malaya now prepare thick
(or blanket) crepes in the No. i grade, but in such cases the
same rules must be applied as govern the sorting of thin fine
pale crepes.

150

SORTING, GRADING, AND PACKING 151

2, Compound Crepe, No. i. — In this it is proposed to include
cup-coagulated lumps, coagulated lumps from transport
vessels, skimmings, bucket rinsings, cup-washings, and tree-
scrap. It has been shown in Chapter X. that strict care is
necessary to eliminate all oxidised (dark) scraps. These are
relegated to a lower grade. The possession of a " scrap-
washer " is necessary if the best results are to be obtained.

On some estates the ingredients of this compound crepe,
while fresh, are placed in a common jar or tank to which a
quantity of sodium bisulphite (i per cent, solution) and acid
are added. The resulting conglomerate mass is cut up for
working.

3. Compound Crepe, No. 2. — This grade would include the
remaining lower grades — viz., bark-shavings, scrap, and earth-
rubber scrap.

REDUCTION CARRIED TOO FAR. — However desirable it may
be to diminish the number of grades, it must be pointed out that
diminution and simplification are not necessarily synonymous
terms in this matter. It is well known that on estates where
the earth-rubber is only brought in at lengthy intervals, say of
a week, the resulting crepe is sometimes very tacky. This is
only natural, and is due to the prolonged exposure to the
sun's rays. With the improved machinery now at our disposal,
and with the increasing attention which will be given to the
lower grades in the future, it is possible to prepare from average
bark-shavings crepe free from bark, and of quite a good colour.
Where trees are not " scrapped " before tapping, there would
seem to be no objection to amalgamating the rubber obtained
from the bark-shavings with the No. i Compound crepe;
and it would be a distinct danger and possible loss if this good
rubber were to be mixed with earth rubber. The liability
of the latter to become tacky is well recognised ; and if possible
it should be maintained as a separate grade, in which it would
be permissible to mix only rubber obtained from actually
dry shavings from " scrapped " trees, or heavily-oxidised
scraps which have been rejected from other grades.

SHEETS. — Broadly there are no fine distinctions to be made at
present in the grading of smoked-sheet rubber; it is either

152 PREPARATION OF PLANTATION RUBBER

No. i, or if any so-called defect is visible the sheets must be
rejected and plainly marked as " off-quality."

Clippings (trimmings) may either be made into crepe or
shipped under their own description.

RUBBER GROWERS' ASSOCIATION'S RECOMMENDATIONS. —
Taking the foregoing arguments into full consideration, it
would seem that, strictly speaking, the number of grades
cannot be reduced to less than four at present without producing
some amount of confusion.

In its handbook,* the Rubber Growers' Association remarks :

" The fewer grades the better, and regularity of each grade
is most important.

" The grading should be as follows:

" (No. i) Fine crepe (or No. i sheet), made from the free-
or liquid latex.

" (No. 2) Clean light brown crepe, made from lumps and
skimmings.

" (No. 3) Scrap crepe, made from tree-scrap.

" (No. 4) Dark crepe, made from bark-shavings, earth
rubber, and the lower quality of scrap.

" Tacky rubber should be packed separately.

" Compound Scrap Crepe. — Estates using scrap- washers
should make a compound crepe of grades Nos. 2 and 3, which
will make one compound free from bark and specks. All rubber
intended for No. 4 should be most thoroughly washed."

Concerning these recommendations the remarks in preceding
paragraphs should be studied.

CARE IN SORTING. — Whether dealing with smoked-sheet,
pale crepe, or lower grades, the strictest care is necessary in
sorting and grading. This work must of necessity be relegated
to coolies, and they should be trained men. Instructions
must be definite, and doubtful specimens of rubber should
always be placed aside for the decision of the European superin-
tendent. Any pieces showing unmistakable signs of what
are regarded as defects should be stringently rejected. In the
case of pale crepe, when the defect is confined only to a small
area it is permissible to cut out the affected portion. Similarly
there can be no objection, in the case of smoked sheets, to

* " Preparation of Plantation Rubber," 1917.

SORTING, GRADING, AND PACKING 153

an occasional sheet being treated in this manner. On the
majority of estates these rules are observed carefully, but some
estates yet have to learn that defective pieces of rubber may not
be concealed in a bulk of otherwise good quality. Samplers
have often an uncanny knack of hitting upon the defective
specimens, and it is entirely the fault of the estate's sorters if
these pieces are submitted as being representative of the mass.

CHOICE OF CASES. — Consumers complain justly of the pre-
sence of chips, splinters, and wood-dust. It will be evident,
therefore, that whatever the type of case employed the interior
surfaces should be smooth, there should be no cracks or gaps
in the timber, and the cases should be cleaned out before using.
There remains great room for improvement in the means
and method of packing, and in spite of suggested alternatives
we are at present restricted to the use of wooden cases.

From comparisons of actual quality and fulfilment of the
requirements indicated above, there can be no question that
cases made of three-ply wood, such as the " Venesta," are in
every respect superior to the ordinary wooden cases of " Momi"
type. The consideration of cost and available supplies, of
course, enters largely into the question, and three-ply cases
are not at present so largely employed as they deserve to be.

A new type of case was recently exhibited in Singapore.
It emanates from the U.S.A. and is made of a fibrous material,
resembling in appearance a very stout cardboard. The com-
plete case when assembled consists really of two boxes, one of
which is inverted and slides down over the other. Packing is
completed by means of stout wire, which is strained by a simple
ratchet arrangement. It is claimed that from 225 to 250 Ibs.
of rubber can be contained. Other claims made amount to
the statement that the case is practically indestructible under
normal conditions of handling and shipping. A demonstra-
tion given certainly appeared to substantiate the statement
fully. Rubber packed in cases of various and average type
was allowed to fall from a height of about twenty feet. In all
instances the wooden cases of every type were either smashed
or badly burst, whereas the fibre cases were merely dented.
These cases are obtained in flat sections, which, in assembling,

154 PREPARATION OF PLANTATION RUBBER

are folded and clamped by means of copper rivets in a special
but simple machine. It was pointed out that objection might
be lodged against the use of copper for this purpose.

More recently there is announced a new packing case which
is stated to be made from low-grade rubbers, but information
is rather vague.

BAGS. — There are in local use stout canvas bags which have
the advantage of being used many times, as long as they are
waterproof and kept in good dry condition. Their employ-
ment for the conveyance of smoked-sheets would appear to
be permitted, but crepe rubbers sent in them are often reported
upon as being " massed " at the edges, and hence difficult to
" sample."

BALES. — Attempts to bale rubber for the market have been
frequent, but no success seems to have attended the efforts.
In some quarters the failure has been ascribed to prejudice
on the part of buyers, but it is the opinion of the writers
that the objections to baling are, or could be, well-founded.
Massed rubber often cannot be inspected properly, and hence
is always open to suspicion that internally there may be un-
suitable portions.

There have been several schemes put forward for winding
crepe rubber on spindles so as to form a cylindrical package
complete in itself. We have seen the process, and certainly
the method had much which appeared commendable. Apart
from other objections which might be raised, there is always the
one prominent objection mentioned in the preceding paragraph.

While baling of rubber is thus not likely to suit the general
market, there is no reason why, as in one or two instances, it
should not be practised by agreement between producer and
consumer. It is believed that " slab " rubber is shipped in
bales from Sumatra to the U.S.A.

Quite recently a proposal has been put forward to revert
to a simple form of baling for ordinary plantation rubber.
Under this scheme wooden cases are discarded, the packing
material being composed of scrap-grade crepe rubber which,
it is claimed, could be put to use by the manufacturer. An
obvious drawback would be evident if these bales happened to

SORTING, GRADING, AND PACKING 155

be exposed to direct sunlight or a continuous high temperature.
The tackiness which might supervene would make the handling
of such bales unpleasant, even if it did not affect the internal
rubber.

FOLDING FOR PACKING. — In the packing of smoked sheets
it would appear to be advisable to avoid, if possible, the folding
of any pieces, as the objection is made that such rubber is
difficult to " sample " on arrival, especially in cold weather.
Sheets should be prepared or cut to such length that they occupy
the full superficial area of the box, either singly or side by side.

A SHIPMENT OF RUBBER, PACKED AND READY FOR TRANSPORT.

The same remark applies to the packing of crepe rubbers,
except that here we deal with units of folded rubber. Crepes
are generally folded by hand, and coolies usually work to a
certain dimension by means of a standard stick. The work is
slow, but often gives employment, at a cheap rate of pay, to
women and weak coolies.

Several machines have been invented to replace this labour.
The best of these yet seen has a simple device by means of
which the length of the fold is adjustable to suit the size of

156 PREPARATION OF PLANTATION RUBBER

any packing case. It is called the " Senang " folder, and is
made by the General Engineering Company (Radcliffe) Ltd.,
Radcliffe, near Manchester.

CARE IN ASSEMBLING. — Whatever the type of case employed,
great care must be given to the assembling of parts and the
final fastening. It is not uncommon to find in the operation
of putting on the " strapping " that nails have been driven
into the rubber. Extra bands of strapping are sometimes
advised, and where these bands pass over the sides (not
edges) of the case only specially short nails should be used.

All wood should be planed, and in cases other than three-ply
should be of stout wood, not less than f inch in thickness.
All timber used should be of uniform type and thickness.

METHODS OF PACKING. — The usual method of packing crepe
is to fold the lengths to some measure of the dimensions of the
case. This is done in a haphazard fashion on some estates,
with the result that either space is lost or the packing is badly
arranged.

Some ingenuity can be displayed in the packing of sheet
rubber in order to avoid folding the sheets, which, besides
increasing the difficulty of sampling, leads to loss of space.
Endeavours are being continually made on estates to prepare
sheet of such a size as to obtain the maximum benefit of space
both in smoke-house accommodation and in packing. A few
estates employ tanks of such calculated dimensions as will
yield uniform sheets which pack flat and fill the superficial
area of the case.

In view of the contamination which sometimes characterises
the employment of wooden cases it is sometimes advised that
the interior should be lined with sheets, or pieces of crepe,
the ends of which are later folded over the top of the mass.
In this manner it is stated that contamination is confined only
to the exterior of the contents of the case.

WEIGHT OF CONTENTS. — The dimensions of average cases
are 19 inches by 19 inches by 24 inches, giving a capacity of
5 cubic feet.

In these it is possible to pack 150 Ibs. of crepe rubber and
200 Ibs. of sheet rubber (about 5 per cent, more in cases of

SORTING, GRADING, AND PACKING 157

three-ply wood). It may be noted that boxes arrive in better
condition when fully packed. The foregoing figures are not
adhered to strictly. For example, some estates find it expe-
dient to ship rubber in actual ton lots, and for this purpose pack
only 140 Ibs. of crepe per case, giving sixteen cases to the ton.
Other estates, using presses, pack more per case than the
quantities noted above. At present there does not appear
to be any definite regularity in practice.

ON ITS ROAD TO THE RAILWAY: BULLOCK-CART TRANSPORT.

In all instances it should be the invariable rule that the
rubber should be weighed before packing, and that all cases
should contain uniform nett quantities of any particular
type of rubber. Invoicing, etc., will thus be greatly facilitated.
If these practices are followed, and the rubber always weighed
on the same scales (assuming it to be perfectly dry when packed)
complaints of " short- weight " should be infrequent.

" SHORT " WEIGHTS. — In some cases the occurrence of
" short " weights on arrival at ports would appear to be
inexplicable. It often happens that the constituent parts of
wooden cases have been in stock for a considerable period.

158 PREPARATION OF PLANTATION RUBBER

If for no other reason than that indicated below, all cases, either
before or after assembling, should be thoroughly dried in the
sun. " Short " weight could be accounted for to some degree
by a lack of observance of this elementary rule, as it is most
probable that there would be a perceptible difference in weight
of the wooden case in a drier atmosphere.

(a) If rubber is weighed in the box, and the average tare of
the case deducted from the gross weight (in order to obtain
the nett weight), any loss in the weight of the timber would
appear as a deficiency of rubber at the distant port.

(b) Whether the same effect would be produced eventually
in the case of rubber which is weighed before packing will
depend upon the method of weighing at the warehouse. If
the rubber is weighed in the box, any observed deficiency
would be attributed to a loss of weight in the rubber.

PART III

MACHINERY AND BUILDINGS

CHAPTER XIII
MACHINES

THE number of manufacturers of machines for preparing
rubber would seem to be on the increase, and there can be
little doubt that this competition will result in a continued
improvement in the design of machines. It cannot be denied
that there has been room for such improvement, and it is
believed that manufacturers will display judgment in putting
only their best quality into the work. While design and finish
are very excellent in their way, it is to be regretted that in a
number of cases in the past the material of rolls has been found
to be of inferior quality. Generally, the complaint seemed
to be that the rolls were too soft, and that the " grinding " effect
wras far too great. The damage to pale rubber in such cases
is considerable, as it is impossible to keep the rolls free from
fine dark powder. The effect is generally noticed more in the
smooth rolls with which a finish is put upon the crepe.

Cases have occurred frequently in which rolls have been
returned, because of the injury caused to pale rubber, and there
can be little doubt that the life of quite a large number of rolls
is even now far too short in comparison with the expense
involved.

It is a moot point, however, in many instances how far the
quality of the rolls is actually responsible for the damage done
to the rubber. In the experience of the writers it is certain that
complaints regarding the rolls were unjustifiable, and that the
injury had been caused by carelessness in the " feeding " of the
machine. Especially in the case of smooth finishing rolls, it is

160 PREPARATION OF PLANTATION RUBBER

clear that if the rolls are allowed to run idle for more than the
briefest possible interval grinding must take place.

The complaints apply not only to the rolls themselves, but also
to the brass linings for shaft-bearings. Cases are known in
which a brass " liner " was so worn within a few weeks as to be
quite useless. If the matter ended there it would not be so bad ;
but there is always the possibility of particles of brass finding
their way into trays, and so into the rubber. The damage which
ensues to the rubber is quite irreparable. This particular defect
arising from the presence of brass will be dealt with in a later
chapter. But here again it is necessary to point out that such
wear on brass liners may be caused by the standards (ends) of
the rolls being eccentric ; and the case may be analogous to the
placing of " new wine in old bottles."

En passant it may be remarked that in any case brass liners
are not strictly necessary. White-metal alloys are in use on
rubber machines, and cast-iron bearings have been employed
satisfactorily for years.

It would be well for managers to remember, therefore, that
when machines have to be ordered, nothing but the best is
good enough, and that the difference between good machinery
and passable machinery is probably immensely greater in effect
than any saving in expenditure would warrant.

ADEQUACY OF MACHINES. — In general, the factories which
prepare sheet rubber are usually equipped with adequate
machinery. This arises from the fact that machines are neces-
sary for preparing all grades below the first, even if they are not
necessary for the making of sheet. Thus all the necessary
macerators and finishing machines are installed, but the
major part of the output is in sheet form. For the preparation
of sheet, no heavy machinery is required; all that is necessary
are light machines for rolling the sheets and expressing as much
moisture as possible. To obtain a pattern on the sheet, another
light machine may be used. It may be imagined, then, that
the work of rolling sheet rubber by power machines is small,
and that a large quantity of rubber can be worked off in a
comparatively short time. It follows, therefore, that the
preparation of the lower crepe grades can be proceeded

MACHINES 161

with at once, and that the whole work of the factory is
expedited.

The case of factories which have to prepare all first-grade
rubber in crepe form is quite different, especially when thin
rubber has to be made. The care which has to be exercised
in preparing pale crepe rubber is very great in comparison
with what is demanded by sheet rubber. The rubber has
to go first through the uneven-speed macerators, from there
to the intermediate rollers, thence to the finishing rollers.
Considerable ingenuity has to be displayed in the arrangement
of the machines, so that one section will not work faster or slower
than another. More often than not, the attempt to arrive at
such a desirable arrangement fails, owing to an insufficiency
of machines. Such a statement will probably read strangely
to the uninitiated ; but an example will make it plain. A factory
may have a battery of six machines, one only of which is a finish-
ing machine (smooth rolls). With five macerators and inter-
mediate machines working continuously, it will be more than
the work of one finishing pair of rolls to keep pace, especially
as so much more care has to be exercised in finishing than in
rough crepe-making. The obvious course to adopt is to sub-
stitute a pair of smooth rolls, writh suitable gear ratio, for a
pair of macerators or " intermediates."

If, however, the macerators and intermediates are already
fully occupied the whole of the time, any such change would be
of small benefit. What is really needed in this case is more
machinery.

It might be pertinently asked what constitutes an adequate
equipment of machines for crepe-making. The writers cannot
give a number, but have no hesitation in stating that if a factory
cannot complete its whole day's work before dark, it is inade-
quately equipped. No work should be done after dark, if
possible, as it cannot receive the supervision which crepe-
making demands. To make comparison between the number
of machines in any two factories and their respective outputs
is not sound argument, as the out-turn of two similar machines
will depend upon the speed at which the rolls travel — i.e., the
gearing between the machines and the engines. Thus, while

1 62 PREPARATION OF PLANTATION RUBBER

one machine will out-turn 40 Ibs. of crepe per hour, another
may only have an output of 30 Ibs., although the machines may
be identical in pattern. To make calculations based on a rate
per hour for any known make of machine, and to apply those
calculations to the existing machinery in any factory, in an
attempt to judge whether there is a sufficient number of
machines, would be a mistake, unless one were also supplied
with the relative speeds at which the rolls work.

Finally, on the question of adequacy of machines, it must be
pointed out that an insufficient number of machines must result
in a poor product, since all rolls have to be used for all grades.
Even with the greatest possible care it happens that pale crepe
is sometimes spoiled because it is contaminated with foreign
matter, resulting from the working of lower grades on the same
machines. This is one of the great arguments in another
direction for the installation of a scrap-washer.

In conclusion, the writers can only give their opinion that
one must not decide the question of adequacy by the number
of existing machines, but by the time taken each day in working
off the rubber, providing one can be satisfied that the best
arrangement of the existing machines has been made.

IDEAL ARRANGEMENT. — As to what this best arrangement
may be, guidance can be obtained from the results of experience
here given. It must be premised that the output of any factory
preparing fine pale crepe is limited by the output of the smooth
finishing rolls. Broadly, it will be recognised that if there
is any excess of capacity in a battery it should be found in the
smooth-roll machines. This sufficiency, or excess of capacity,
may sometimes be attained by an alteration in the gearing of
the drive of the rolls from the back-shaft, or by an addition to
the number of machines. In the former case, there are prac-
ticable limits of speed, beyond which the second alternative
measure must be adopted.

SPEED. — The usual speed at which the back-shaft travels
ranges from 60 to 70 revolutions per minute. Taking first
the macerating machines, the intermediate gearing between
the shaft and the rolls should give a driving speed of about
20 revolutions per minute on the faster-travelling roll. This

MACHINES 163

is equivalent, with a 1 5-inch diameter roll, to a peripheral
speed of about 60 to 65 feet per minute.

The intermediate and smooth rolls can be arranged to travel
more quickly, but the maximum comfortable speed for proper
feeding and control appears to be about 25 revolutions per
minute on even-speed rolls. In view of the fact that the rubber
at each successive machine becomes longer and thinner, it will
be seen that a smooth-roll machine could not cope with the
output of a macerator in the same period of time. If, therefore,
the macerator is fully occupied for the greater part of the
time, an additional smooth-roll machine must be installed,
even though the existing one has been " speeded up " to prac-
ticable limits.

For the information of the uninitiated it might be explained
that in the macerating and intermediate machines the cog-
wheels driving the two rolls are of different sizes (i.e., differen-
tially geared), as opposed to the smooth rolls on which the
cog-wheels are usually of the same size (t.e., even speed). The
idea in the one case is to exert a " working" influence upon
the rubber while it is being washed by the stream of water
coming from above; in the smooth rolls a squeezing action
only is effected.

To give an idea of the ratio of the speeds of the rolls in each
machine in a typical working battery, the following particulars
may be noted :

GEAR RATIOS.—

Machine.
i . Macerator

Differential Ratio.

02-T7

2. Intermediate (coarse grooved) . .
3. „ (fine grooved)
4. Smooth (uneven speed) . .
5. ,, (finishing)
6. „ ( „ )

o-4- -1 /

.. 32-17
. . 30-19
.. 30-19
. . 25-24
. . 25-24

It will be seen that the so-called " even-speed " smooth rolls
run at approximately the same rate.

It is advised that in all cases the gear wheels should be cut
helically. Those who have experience of the noise of some
batteries after they are slightly worn will appreciate such a
remark.

1 64 PREPARATION OF PLANTATION RUBBER

(GROOVING OF ROLLS. — Concerning the choice of grooving,
there is divergence of opinion, some managers preferring one
type, which others reject in favour of another type. Provided
any particular type can be shown to be as effective as required,
no necessity for laying down hard-and-fast rules seems to exist.

The following particulars serve to describe a battery well
known to the writers, and accustomed to produce the finest
quality of thin pale crepe and lower grades :

Machine.

Grooving.

No. of Times
Rubber passes
through.

i. Macerator

2. Intermediate . .

3-

4. Geared smooth ..
5. " Even " smooth
6.

Deep horizontal grooves ;
square-cut, y\ inch x -^ inch
x f inch spaces
Horizontal grooves; ^ inch
x jsff inch x $ inch spaces . .
Fine spiral grooves; | inch
x |- inch x £ inch spaces . .
Nil

3

2

2
I
I
I

Total . . . . I 10 times

The actual rate of output of this installation is the capacity
of the last smooth machine. This is about 180 Ibs. per hour,
while the output of the macerator is approximately double
this amount. Thus the macerator only works for about half
the time. This applies also to the two intermediate machines.
After a study of the preliminary remarks, it would not be
difficult to suggest methods for improving the condition of
affairs. It would appear that, in order to obtain a uniform
rate of working in such a battery, the relative peripheral speeds
of the several machines should be — (i),(2),and (3) 100; (4) 150;
(5) and (6) 200. The remarks on the practical limits of speed
should be borne in mind. In this case the smooth rolls
travelled at 23 revolutions per minute.

As already stated, it is not intended to lay down definitely
that, e.g., horizontal grooving alone should be cut on macerating
rolls. Some estates employ with satisfaction a deep square-

MACHINES 165

cut spiral J inch by | inch by J inch or J inch spacing; others
use a large diamond pattern. Similarly various types of groov-
ing are cut in the intermediate rolls.

It has been remarked in the chapter dealing with crepe pre-
paration that much depends upon the condition of the coagu-
lum. There is no necessity, or desirability, for having a stan-
dard higher than 2 Ibs. dry rubber per gallon, and it has been
argued that it would be better to select a standard of ij Ibs.

A BATTERY OF MACHINES.

On the left, light marking rolls for sheet rubber; on the right,
heavy machines for crepe preparation. In the middle background,
"scrap-washing "machines outside the main building.

The tougher the coagulum, the more the power required,
and the slower the rate of output of the leading machines.

In ordering machines for crepe-making, only large rolls
should be considered — e.g., rolls having a diameter of 12 inches
to 18 inches and from 15 inches to 18 inches face.

ROLLS RUNNING HOT OR " FREE." — If the rolls are found
to become hot, work on that machine should be stopped, and an

1 66 PREPARATION OF PLANTATION RUBBER

examination made, otherwise there is the possibility of the
crepe becoming sticky and " tacky " when dry.

Although comparatively cold water may be flowing upon the
rubber and the rolls, little alleviation may be noticed, inasmuch
as the source of heat lies generally at the bearing ends of the rolls.
This may be tested by placing the hand on the top of the
" standard " of the machine. The development of the heat
may be due to lack of lubrication, worn bearings, or sometimes
faulty setting-up of the machines.

Allusion has been made to the necessity for avoiding the
running " free " of rolls — i.e., in the absence of rubber. The
grinding of the rolls, when working close together, produces
a fine powder, which causes a more or less pronounced deposit
on pale crepe. When the rolls have been in action for some
time and become slightly worn, this deposit may be confined
only to the edges of the rubber.

SHEETING MACHINES. — The foregoing paragraphs have dealt
entirely with machines for crepe preparation. Concerning
machines for use in sheet-making, the ground has been mainly
covered in Chapter IX.

Where both crepe and sheet are made, it is permissible and
advantageous to use the heavy smooth rolls for the rolling
of the sheets, and it is only necessary to instal one or two light
machines for placing a pattern on the rubber.

Where a heavy battery does not exist, light machines with
smooth rolls may be employed satisfactorily. Even engine-
power is not necessary for the preparation of excellent sheets,
but the output is limited where hand-power only is employed.
Estates are known on which upwards of 1,000 Ibs of sheet
rubber are made daily with hand-power machinery in one
station. Beyond this figure, it is deemed advisable to instal
a small engine, say of 7-9 horse-power. This is ample to drive
a battery of three smooth-roll machines and two markers,
and yet have sufficient reserve to actuate a small pump for the
water supply.

LUBRICATION OF MACHINES. — It must always appear to those
inexperienced in engineering matters that existing methods
for lubricating rubber machinery are distinctly crude, when

MACHINES 167

one considers the delicacy of the material to be prepared.
Many existing machines are still lubricated with oil, which has
to be administered in generous quantities. Generally, such
machines have been so designed that the excess of oil may
find an easy passage into the tray which receives the rubber.
If not, it drops just outside the tray to the floor, and is washed
away in great gouts. Even where grease-cap lubricators are
fitted it is common to find that the excess can often be trans-
ferred from the bearings to the trays and so to the rubber.
One would have expected from the attention which is being
given to machinery for rubber estates that some improvement
in lubrication methods would have been devised.

It is probable, however, that a great deal of the disabilities
attaching to present methods of lubrication might be obviated
if closer attention were given to the actual operation of the
lubricators. Coolies should not be allowed to handle them,
and the responsibility should be placed upon a foreman or
the engine-driver.

TRAYS. — The most unsuitable and damage-causing part of
the vast majority of machines, without doubt, is the tray. On
nearly all machines the tray is wider than the effective portion
of the rolls, so that any excess of lubricant may drop into it.
On others, not only is the tray wider than the rolls, but its
edge either is in contact with the shaft of a roll or just a small
distance away. The edge of the tray is thus favourably situated
for acting as a " wipe," and the lubricant is transferred to the
inside of the tray. Considering that the effective portion of
rolls is about two-thirds of their length, it must be unnecessary
to have trays wider than the length of the rolls. For the pre-
paration of fine crepe trays are quite superfluous, and their
place can be taken by a narrow piece of board if required. If
the bed of the machines has been covered with glazed tiles,
even a piece of board is not necessary. Where trays have been
removed from the fine-crepe rolls on a number of estates, a
marked decrease in the number of spoiled pieces of rubber has
resulted.

It must be recorded that the foregoing paragraph appeared
in our 1913 publication. After a lapse of over seven years,

1 68 PREPARATION OF PLANTATION RUBBER

the remarks remain as true as when originally written. One
of us is continually meeting with cases in which the defects
are plainly attributable to the cause indicated above, and
the fault often lies with the management of estates. On most
machines the trays are not fixtures, and could be removed
if desired.

ARRANGEMENT OF MACHINES. — In considering the future
arrangement of machines, the first care should be to see that
machines and windows are to be found together.* Of all the
factory operations, rolling of rubber should be given the maxi-
mum light. At the same time it would not be advisable always
to choose a southern aspect, unless outside shades were supplied.
The best position for setting up machines, therefore, is along
a wall having a number of windows. This is extremely con-
venient also from the view of power transmission, and gives
the maximum free floor space to the factory. In setting up
machines, foresight must be displayed, otherwise one may find,
when future extensions are made, that the extra machines
may obstruct an entry or exit.

For the actual erection of machines, no labour should be
accepted without European supervision. At present there
are machines, which are practically useless owing to faulty work-
manship, and on many machines bearings run hot for no ap-
parent or explicable reason. Whether the fault lies with the
turning of the rolls or the setting of the machine cannot be
decided ; but at any rate too much care cannot be expended on
the supervision of setting up machines.

There is no reason why everything in a factory should not
be made as easy to clean as possible. For this desirable con-
dition all machines should have the beds faced with tiles. A
word of caution should be given against using marble slabs
under the machines, as they would be eroded in time by the

* Windows imply the existence of walls. Such is the conven-
tional design of factories. It may be pointed out that walls are not
necessary. The roof may be supported on pillars between which
expanded metal of large size may be placed. This fulfils all require-
ments and gives the maximum of light and air. Many new factories
have been erected to such a design.

MACHINES 169

slight amount of acid washed out of the rubber. There
would be no such objection against the use of white glazed
tiles, if they are well set.

ACCESS TO BACK OF MACHINE. — In a few factories it has
been noticed that the drainage of water from the machines
runs to the front of them. This means that the coolies
are put to unnecessary inconvenience and discomfort, and
they often suffer from sore feet. All water should drain
to the back of the machines. The necessity for seeing
that these drains are kept clear might then induce those in
charge to examine the back of the machines. It is often the
case that, while the front of the rolls and tray are kept clean,
little attempt is made to cleanse those parts which are not visible
or accessible from the front. There should be no need to
point out that any labour expended in such " front- window "
work is rendered useless by the contamination from accumu-
lations of old rubber and grease at the back of the machines.
In the course of visiting factories one of us has many times
seen great surprise exhibited by the manager or assistants on
being shown the state of affairs at the back of the machines.
There should have been no occasion for such surprise, for the
back of the machines is quite as accessible to them as to the
visitor.

In conclusion it might be said that the manager needing
advice as to the best machines cannot go far wrong in purchas-
ing any of the better-known makes, such as Shaw's, Bridge's,
Robinson's, Bertram's, Walker's, Carter's, Iddon's, etc. This
list does not include local manufacturers such as the " United
Engineers." It must not be imagined that their machines are
not recommended. As a matter of fact, their machines compare
well with those made at Home. It would be well to judge
in the final decision upon —

1. Cost.

2. The experience of those already using the machines.

3. Simplicity of parts.

4. Lubrication system.

5. Mode of adjusting rolls.

6. Fitting of trays.

170 PREPARATION OF PLANTATION RUBBER

ENGINES. — It is not intended here to discuss particular
makes of engines, or even to attempt to lay down definite
statements with regard to the type of engine. Without a
full knowledge of local circumstances, it is not possible to
recommend whether the engine shall be oil-driven, gas-driven,
or steam-driven.

Assuming a copious supply of very cheap timber, there could
be no objection to the employment of a steam-engine; but
for most estates such a choice is out of the question.

Again, in deciding between oil and gas, local economic
factors must be considered. Suction-gas plants are now made,
in which a wonderful variety of refuse can be consumed in
the production of gas, whereas ordinarily estates are restricted
to the use of either charcoal or anthracite coal. Both oil and
gas driven engines are eminently suitable for the purpose of a
rubber factory, and the results obtained on different estates
with either are often discussed in favour of one or the other.
The selection ultimately narrows itself down to one of cost of
running, in which availability of supplies becomes an essential
feature.

POWER. — No matter what type is selected, there should be
made an ample allowance for margin of power. The general
experience of estates has been that when the first portion of
the estate comes into bearing, there is a desire to avoid great
outlay, which should really have been secured in the original
capital. The result has been that as later the estate expands,
the original power unit is found to be inadequate, and a larger
engine has to be purchased. In a short while the original
engine is found to be unsuitable even as a " stand-by," in-
asmuch as it is incapable of doing more than a portion of the
work required. This means eventually that another large
engine is required. Had sufficient margin of power been
allowed originally, only two engines would have been bought,
as against the three indicated above. Without going into finer
details, it is usual to allow a rate of 10 horse-power per heavy
machine used for crepe preparation. In actual practice, when a
battery is working under full load, the power demanded is
about 6 horse-power per machine. Thus a 50 horse-power

MACHINES 171

engine running six machines and a scrap-washer is really
running with only a small margin of power, and if large pieces
of hard coagulum are placed in the washer or the macerator
there may be a sudden stoppage. Assuming an average
estate commences with only three machines for crepe-making,
on an expanding programme, allowance of power should be
made for six machines and a scrap-washer, if the purchase
of larger power units is to be avoided later.

CHAPTER XIV
FACTORIES

GENERAL CONSTRUCTION. — On the question of general con-
struction there is little to be said, except that buildings are
now being properly designed in more permanent form than
were some of the earlier buildings. On the whole there is
little fault to be found with factories in general, except in so
far as the output has outgrown the accommodation.

Most factories are now erected in iron, but there are a few
which are built of bricks. It should be premised that a factory
in which rubber is to be prepared should be as light and airy
as possible. In this respect quite a number of the older
factories are lacking, and they seem to have been designed to
exclude as much air and light as possible. Under these
circumstances, the building is always dark, there is always an
air of dampness, dirt may accumulate, and there is usually a
bad smell. Rubber prepared under these conditions is always
liable to be below the high standard which should be attained,
and the general tone of the factory is depressing.

PLENTY OF LIGHT. — The old idea that light must be excluded
is now known to be erroneous; so that in designing a factory,
provision should be made for ample light and air. It should not
be forgotten that in tropical climates, iron buildings may become
uncomfortably hot, as most of our older factories are. Usually
it will be found that the ventilation is imperfect. There is a
lack of window space, and the roof is imperfectly ventilated.
The ridge of the roof should be opened up by means of a
" jack-roof," so that the warm air rising naturally may escape
at the highest point of the building. These are defects which
should be remedied in old buildings.

As a rule no rubber remains in the factory at night-time,
except in the form of coagulum, the loss of any of which would

172

FACTORIES 173

be noted with ease. The conventional idea of enclosing the
factory with walls of galvanised sheeting, wood, or brick, is
not strictly necessary. In modern buildings these walls are
replaced by large-mesh expanded metal, thus making the
machine-room perfectly light and plentifully ventilated.
Under such conditions, dirt cannot accumulate unseen, and
the general tone of the work is raised.

THE FLOOR. — The floor should be of thick concrete, and
have a good surface layer of cement. Preparations are now
advertised for which claims are made that their employment
renders the surface of such floors waterproof and dustproof.
If these claims can be substantiated when the use is applied to
the floors of rubber factories, the employment of a preparation
of this nature should result in a considerable saving of expense
and trouble. Preferably the floor should not be flat, but should
slope slightly from the longitudinal middle of the building to
the sides on either hand. If the floor is level it usually results
in accumulation of water, the cement breaks in patches, and
the factory always appears to be dirty.

POSITION OF MACHINES. — All machines should be arranged
adjacent to and parallel with one of the long sides of the building,
and should be raised about 6 inches above the floor, so that
water may escape easily. Tanks for the reception of latex,
scrap rubber, etc., should be placed along the opposite wall
to the machines, and the intermediate length of the building
should be entirely free from fixtures. It was not uncommon in
older factories to find the engine situated in the middle of the
floor, so that what with the space occupied by the engine, and
the space rendered unavailable by the belt-drive, the real
accommodation of the factory was sadly diminished. In no
modern factory should the engines be brought into the main
room. They should always be accommodated in a special com-
partment, situated outside the wall, along the inside of which
machines are placed. In this way considerable floor space is
left available, and the machines may be worked by direct drive.
Not only so; but if a suction-gas plant is worked, there can
then be no excuse for particles of coal or charcoal dust being
found in the factory.

174 PREPARATION OF PLANTATION RUBBER

POSITION OF ENGINES. — It scarcely need be pointed out that
if the engines are placed outside the wall which is opposite
the machines, a long belt-drive would be necessitated, and
that the presence of the belt would prevent the use of end doors.
It is presumed in these arguments that two engines are to be
installed. One can hardly imagine a modern factory in full
working being equipped with only one engine, which might
possibly have an excess of power necessary to drive all the
machines . In the case of breakdown , which sometimes happens
in the best supervised factories, it would be small consolation
to know that this excess of power was present theoretically.

How MANY STOREYS. — There can be no doubt that, taking
all things into consideration, the best type of factory is that
consisting only of one floor. The factory should be quite
separate from all other buildings, and if attempts are made
to conserve ground space by putting a drying-room over the
factory, much trouble will ensue, especially if pale crepes
are to be made. In the first place, the factory is made very
much darker, and hence more difficult to keep clean;
secondly, the ventilation of the factory is seriously interfered
with; and thirdly, it is manifestly prejudicing the drying
of rubber to place it directly over a room which is always
more or less awash with water. At night such a building
would reek with a moisture-laden atmosphere, and little
drying could be expected to take place in that interval. From
actual experience it has been shown that rubber hung to
dry in such a room, situated over a damp factory, is very
liable to attacks of " spot " diseases, since the presence of
perpetual moisture is favourable to the development of these
diseases. If a double-storey building has to be worked, it will
be readily seen that no first-grade rubber should be allowed
to dry in it. The accommodation over the factory may be
restricted to the purpose of receiving lower grade rubber which
is not so liable to " spot " diseases, and possibly does not take
so long to dry as first-grade rubbers of equal thickness. It is
evident, therefore, that the erection of double-storey factories
is false economy, as separate drying-houses have to be built
eventually. This conclusion does not apply with the same

FACTORIES 175

force to factories worked in conjunction with smoke-houses for
preparing sheet rubber, but, nevertheless, such a factory should
not have another floor above the work-room.

VERANDAHS. — One of the worst features in many factories
is the necessity for coolies to bring latex into the factory.
As already mentioned, the floors of factories are usually running
with water (or should be), and it can be imagined that the
passage to and fro of scores of coolies must bring in a great
quantity of dirt. Not only so ; the very presence of the coolies
is a hindrance to the efficient working of the factory, and con-
siderable floor-space and time are wasted.

This feature in factory working is all the more annoying
because the necessity for it could so easily be obviated. All
that is necessary is the erection of a wide, open verandah out-
side the wall of the factory. Here all latex could be received
and strained, scrap-rubbers could be received and passed
through an opening into tanks placed in convenient position.
Water could be laid on in this verandah so that coolies might
wash their buckets, and the whole verandah might be enclosed
only with expanded metal so as to avoid interference with the
lighting of the factory. In this way it would be quite un-
necessary for any field coolie to enter the factory proper, and
this would facilitate cleanliness. Such an arrangement has
been discussed by the writers many times during the last
few years, but the number of estates which have made such
provision is still in the minority, and the same slipshod and
dirt-making procession of coolies continues to walk through
the factories, and the same piles of bark-shavings and scrap-
rubber continue to accumulate and ferment in a few instances.

An indication of types of verandahs is given in Chapters VII.
and IX. These are not intended to be representative of a
universal design, but may be suggestive in the planning of
others according to local conditions.

SITUATION OF TANKS.— It will be noted that these verandahs
are raised from the ground-level to a height of about 3 feet
in order that latex may be gravitated, with a slight fall, into the
coagulating tanks which are within the factory. There exists
a real necessity for this practice, inasmuch as otherwise to

176 PREPARATION OF PLANTATION RUBBER

obtain gravitation of latex (which is quicker and cheaper than
handling) the coagulating tanks would have to be either
placed on the floor or sunk beneath the level. The risk of
contamination of latex or coagulum under such circumstances
would be appreciable. Apart from this, it is advisable to
have the coagulating tanks raised to a height of between 2 and
3 feet, to secure the advantage of ease of working in the
processes of coagulation and the handling of coagulum — a not
inconsiderable factor.

In some modern designs it is proposed to place the coagulat-
ing tanks in a separate building. This would seem to be an
unnecessary refinement in a new building, if observance is
given to the suggestions made in previous paragraphs.

DESIGNS AND " LAY-OUT." — In a previous publication*
comment was made upon grievous errors in designs prepared
by those inexperienced in the requirements of the tropics.
There is little ground now for complaint, and local engineering
firms are fully capable of advising upon, and constructing,
suitable buildings.

In considering the first installation of a factory and equip-
ment one always has to weigh the question of prime cost against
the probability of future expansion of crop. If it should be
decided at first merely to cater for contemporary requirements,
the fullest consideration should be given in discussing design
of building and lay-out of machinery to the practicability of
later extension. The site should be large enough for the
eventual group of buildings, the building should be easily
capable of extension with the least cost, and the same fore-
thought should govern the lay-out of the machinery.

DRAINS. — Lastly, there is the question of drains. Generally
speaking, all factories are well provided with drains, and the
only difficulty is that of getting an adequate fall for efficient
drainage. But there is a certain amount of laxity exhibited
in the matter of providing sieves in drains. To anyone ac-
quainted with factory working, it must be apparent that quite
a lot of small pieces of rubber are washed into the drains.
This rubber should be collected at intervals during the day;
* " Preparation of Plantation Rubber," Morgan, 1913.

FACTORIES 177

but in many instances that collected is only a fraction of what
escapes. Wherever possible the drainings of a factory should
be carried as far as is practicable from the buildings by means
of cement drains. Too often these are short, and lead into
earthen drains. Even if no pieces of rubber are present,
the serum from the coagulum is subject to decomposition, the
effluvium from which is objectionable.

WATER SUPPLY. — It is essential that a good supply of water
should be available. This should be distributed by pipes all
round the building, so that a hose may be used in every part
for the thorough cleansing of the factory at intervals during
the hours of working.

Summing up, it might be said that a good factory, therefore,
should have the following features :

1. Plenty of windows, or walls of expanded metal.

2. A jack-roof in the ridge, and hence a good system of ven-
tilation.

3. Engines in compartments outside the walls of the factory.

4. Machines close to and parallel with the wall outside of
which the engines are placed.

5. Latex tanks and other fixtures along the wall opposite the
machines.

6. A long middle free space, at either end of which a large
double door should be placed in the end walls.

7. A good concrete and cement floor sloping slightly from
the middle towards each long wall.

8. An abundant water supply, and several lengths of hose.

9. The building should be of only one floor, and have ample
head room.

10. There should be an outside, open verandah upon which
latex may be received, etc. ; preferably outside the wall which
is opposite to the machines.

11. The system of drainage should be thorough, and the
drains should be adequately screened, so that all particles of
rubber may be collected.

12

CHAPTER XV
OTHER BUILDINGS

DRYING-HOUSES FOR CREPE. — It has already been shown in the
previous chapter that one type of drying- houses — viz., that over
a factory — stands condemned, except for the drying of low-grade
rubbers. Generally speaking, a great advance has been made
in the design of crepe drying- houses during recent years, and
it has been possible even to improve older ones so as to bring
them into line with the more modern buildings. Houses
for drying crepe rubber may be of one floor, two floors, or
even three floors. Doubtless those built with three floors
were designed with a view to economising the available site
for factory buildings, and as long as the ventilation is good there
can be no very great objection to them. It might be pointed
out, however, that even with the best of ventilation the air
passing successively through three layers of rubber must
be fairly saturated with moisture by the time it leaves the
building. The effect of this upon the rate of drying in the
uppermost chamber will not be so marked as it will be in the
middle floor, as the temperature of the top floor must be
many degrees higher than that of the other two rooms. It
would be expected, therefore, that the rate of drying in the
middle storey would be slower than that in either of the
other two.

In houses of two floors this objection would not have to be
met, and drying- houses of this type are successful and common.

How MANY STOREYS ? — Again nothing could be urged
against a building of two or three storeys in which the ground
floor was occupied as a packing-room, except that, by negli-
gence in not allowing wet crepe a preliminary dripping period,
water might fall upon the packed rubber below.

178

OTHER. BUILDINGS 179

As a matter of experience, such a house is, taking all into
consideration, the cheapest and most suitable type for any estate
with an increase in output. Even at the outset there should
be a separate room in which sorting and packing is undertaken.
This is conveniently the lower room of a drying-house. The
only stipulation to be made for a house with two storeys is
that the floor of the upper room should be of an open pattern,
so that the air may circulate right through the building. This
is usually and very successfully attained by laying down wide
slats of wood, with spaces of an inch or more between them.
It is not advisable to have spaces wider than ij inches,
otherwise there is a certain amount of danger to the limbs of
individuals who have to wrork or supervise in the building.
In any case, it is very convenient to have pathways of planks
running the whole length of the floor, so that the supervision
is made more convenient. If this is done, there can be no objec-
tion to the custom of suspending the rubber of a lower chamber
from the slats of the floor of the upper room. At present, in
some drying-houses, this means of suspension is used, but no
planks are laid down, and it becomes necessary to walk over
the drying rubber. This is a detail, but it is one which does
not make for the improvement of rubber, and the expenditure
of a small sum would be sufficient to rectify the matter.

From every point of view, it would be desirable to have the
floor of the packing-shed (or the packing-room in a combined
house) raised from the ground, to a height of, say, 3 feet;
or the height of a bullock-cart or motor-lorry. Not only is
ventilation improved, but there would be a great saving in
labour. Packed cases could be wheeled directly on a level
with the cart or lorry.

A great many estates favour drying- houses of one storey .
These are eminently suitable, provided that the site is suitable,
and that the relative dimensions of the house are favourable
to efficient ventilation. It is a common mistake to find build-
ings of which the breadth is out of proportion to the height.
Obviously, if the height is not considerably in excess of the
breadth, ventilation will be defective. For a single-storey
drying-house, the maximum height should bear the ratio to the

i8o PREPARATION OF PLANTATION RUBBER

breadth of 3 : 2, and in a house of this type specially long pieces
of crepe can be utilised. Naturally, in a house of two storeys,
this factor is not likely to be neglected, and if the lower room
is used for packing purposes the rate of drying should be rapid.
Again, when a single-storey building is contemplated, it is well
to make strict examination of local conditions. If the site is
low-lying and surrounded by trees it will be clear that tall
buildings are required, and that a house of more than one floor
is to be preferred. Considerations of this nature would have
prevented the erection of some dry-sheds which do not give
a satisfactory rate of drying.

VENTILATION. — No matter how many floors there may be in
a drying-house, the greatest attention should be given to the
question of ventilation. It is an elementary point in the study
of ventilation problems that the best system of natural ventila-
tion is obtained by admitting cool air near or through the floor
and providing an exit for the warmer air at the highest point
in the building. It is not often that such a rule is infringed
in the ventilation of rubber drying-houses, but several of the
older buildings erred in this respect. In a good modern house
there is a space (about 2 feet in height) all round the base of
the walls merely closed with expanded metal; this admits cool
air. An exit for warm air is provided in the ridge of the roof
by either ventilation chimneys or by a jack-roof. The latter
is preferable, as it provides for a more free and uniform escape.

In some drying-houses, besides the ridge openings, the space
along the eaves is left open. This would seem to be un-
desirable, as it provides for the entrance of outer air, which
might combat the ascending warm air and so interfere with
the natural upward currents. Provided that a jack-roof or
other suitable openings have been installed, there is, therefore,
no necessity for the existence of open spaces at the eaves, and
they probably do more harm than good.

In the tropics, on days of sunshine, there must always
be an upward current of air in well-designed houses. Tem-
peratures of 105° F. are easily recorded in the ridge space of a
building, while the temperature in the lower part of the house
may be at least 15° F. lower. On the floor of an upper room a

OTHER BUILDINGS 181

temperature of 90° F. is commonly noted, and in buildings
with three storeys the usual day temperature of the top room
is about or over 100° F. Even, therefore, when there is no
trace of a breeze, there must be a displacement of air in an
upward direction, though it may not be detected without
tests being applied.

It is often asked whether a temperature of 100° F., such as
is obtained in the upper room, is calculated to injure the quality
of the rubber. There need be no fear on this ground; the
experience of many estates goes to show not only that no harm
results, but also that the drying of the rubber is expedited.
There would seem to be no reason why crepe rubber should not
be dried at a temperature of 100° F. It must be understood,
however, that higher temperatures for crepe rubber are not
recommended, as it has been proved that the rubber is affected.
The fact becomes obvious with continued treatment at tempera-
tures much above 100° F., for the rubber stretches and breaks
across the support.

WINDOWS. — Concerning the subject of window space in a
drying-house, there has been much discussion at various times.
Years ago it was common to find windows widely open with
the sunshine streaming in. Naturally, tackiness developed
in some of the rubber, and care was then taken to keep the
windows closed. Thus the rooms were darkened and air
excluded. There followed a period in which windows were
fitted with ruby-coloured glass to keep out the actinic rays
of the sun, which were responsible for tackiness, and excess of
light, which was supposed to be responsible for the rapid
oxidation of rubber. Unless special precautions were observed
in the processes of coagulation and preparation, it was not
proved that the exclusion of light prevented or lessened the
natural oxidation of crepe rubber. Since the introduction of
sodium bisulphite for the prevention of oxidation, there has
been no cause to worry as to the possible effect of light, as no
perceptible darkening of the rubber takes place. It follows,
therefore, that no trouble need be taken to exclude light,
although the necessity for excluding direct sunshine still exists.
Windows may be left open as long as the sun does not reach

1 82 PREPARATION OF PLANTATION RUBBER

them. This can usually be arranged in a drying-house by
manipulating the windows at intervals during the day, so that
those in the shady side of a building are always open, while
those on the sunny side are always closed. If it is thought
that this manipulation cannot be entrusted with success to
the store coolies, the case may be met by having all windows
constructed on the louvre pattern, so that, although the windows
are closed all day, air and light are not excluded. Should it
be desired to retain the existing type of windows, which open
outwards, and to keep them open all day, a simple arrangement
of ruby-coloured cloth on an outstanding wooden frame may
be placed within the walls of the building, or the shutters
of the windows may be hinged at the top to open outwards.
Unless there is a pronounced breeze, or it is required to
examine the rubber closely, there is no necessity to have windows
open, except in the case of a house in which the bottom floor
is used as a packing-room. The windows of this chamber
may remain open during the day, to advantage in sorting and
packing, and also to the proper ventilation of the building.
Thus the direct rays of the sun are rendered harmless, while
air and light are allowed to enter.

HOT- Am DRYING-HOUSES . — Mention has already been made
of the existence of a system of drying in which hot air is forced
into a drying-house by means of a powerful fan. Provided
that the temperature of the hot air could be so regulated as
not to exceed 100° F., there would be merit in the system.
Such matter of regulation could be solved by having a duct in
the main air passage, through which cool air could be admitted
in such proportion as to modify the temperature of the hot air.
As the process is worked at present, the temperature attained
is often well above 100° F., and there is a danger of thin crepe
placed in this house over-night being found upon the floor
in the morning. Unless the crepe is prepared thick and cut
into fairly short lengths, it will not bear its own weight at
higher temperatures; and if it is made thick, drying is im-
practicably prolonged. It is probable that, with a temperature
of 100° F., and a steady current of air, average thin crepe would
dry in such a drying-house within six or seven days. This

OTHER BUILDINGS 183

would be an improvement upon the usual rate of drying in most
factories, although several ordinary drying- houses are known
in which thin crepe will dry naturally in that period.

SMOKE-HOUSES. — No discussion of theoretical considerations
regarding the process of smoke-curing will be attempted here.
We are concerned only with the necessity for supplying a
demand for smoke-cured sheet rubber. Broadly, the process
is akin to the smoke- curing of herrings, and the objects are
much the same — viz., (i) drying, (2) preservation — except
that while herrings are only dried partially, rubber should be
dried perfectly.

On a small scale a primitive smoke-house could be built
easily and cheaply, and such a building might be fully as
efficacious as the most elaborate and expensive installation.
In the early days of estates it was not uncommon to see tem-
porary smoke-houses constructed of wood, and roofed with
" attaps " (palm leaves). Some of the best rubber in the
market .has come from wooden buildings, but naturally the risk
of destruction by fire is considerable.

For imperative reasons it may be sometimes found necessary
to smoke rubber when the only available building is a single-
storey one. As a temporary measure, the building may be
converted into a smoke-house by placing the fires in pits sunk
deeply into the ground, and effectively screened above by iron
baffle plates. But it is not advisable that smoking be continued
in such a single-storey building, as the best effects are not
obtained, and the risk of fire is far too great.

USUAL TYPES. — At first sight it would appear that the best
type of smoke-house would be one consisting of a tall building,
covering a comparatively small superficial area, and having
a number of superimposed chambers in which the rubber could
be hung to dry. In practice there are several solid objections
which limit the height and the number of floors. Chief
among these is the question of temperature. If smoke-curing
is to be effective, a certain temperature must be attained and
maintained. To obtain such results in a house of excessive
height would be difficult, if not impossible, under normal
conditions. It would be found that the chamber immediately

1 84 PREPARATION OF PLANTATION RUBBER

above the furnace-room would be overheated if the temperature
in the upper rooms was within the desired range, etc.

Until recent years smoke-houses could be classed as belonging
to one of two types :

(1) Those having external furnaces.

(2) Those having internal furnaces.

The number of the former existing at the present time must
be very small, as it has been shown that the arrangement of
the furnace outside the house is unsatisfactory in comparison
with the other type of house. In discussing the question of
smoke-houses, therefore, it will be understood that the standard
type accepted is that having an internal furnace. In its
original form it was known as a " Kent " drier, and consisted
of a tall two-storey wooden building. The walls of the lower
chamber had the form of an inverted and truncated pyramid.
By this arrangement it was possible to obtain from a com-
paratively small fire sufficient smoke and heat to cure the
product placed in the room above. This- is the principle
upon which many smoke-houses in Malaya are designed.
On a very large scale it is not claimed that the sloping sides
of the lower chamber lead to economy in the number of fires,
but merely divert the smoke in an upward direction. It is
acknowledged that vertical lower walls are quite effective,
and it is an easier matter to fit in doors.

It may be noted that the usual type of smoke-house now in
general use consists of a building of two storeys, in the lower of
which are situated the furnaces, while rubber is hung on
racks in the upper room. Sometimes there may be a third
storey, also used as a drying (curing) chamber. As a rule the
drying-room is one long unit, as also is the furnace chamber;
but in some cases they are subdivided by vertical partitions
into smaller chambers, for ease of working and better control.
This applies with some force in the case of very long houses
standing in an open space. It is sometimes found in such
cases that at certain seasons the prevailing winds have the
effect of making drying and curing uneven in parts of the
building.

OTHER BUILDINGS 185

With these exceptions, the ordinary type of smoke-house
functions very efficiently, and is capable of drying average
sheet (from standardised latex) in a period ranging from
seven to eleven days. . Should the building not be capable of
such performance, in spite of the strict observance of all rules
laid down for the processes of preparation, then there is some
defect in ventilation or in the distribution of heat.

GENERAL VENTILATION. — The ordinary rules of ventilation
in drying-houses apply equally to a smoke-house. There
should be a slow current of air and smoke from the lowest
point to the highest point in the building.

In spite of all that has been written on this subject, it is
by no means uncommon to encounter the idea that a smoke-
house should be perfectly closed in order to get good results.
As to what must become of the (say) 25 per cent, of moisture
which the rubber contains there is no knowledge. In dozens
of cases, when complaints regarding slowrness of drying have
been investigated, it has been necessary to point out the need
for providing a rational system of ventilation.

Naturally only a slow current of air and smoke is required.
The creation of an appreciable draught would have the effect
of increasing the fuel consumption of the furnaces, raising
dust from the ash, and of causing a temperature higher than
that which is known to be desirable. It will be clear, therefore,
that if there are to be any openings at the base of the walls
they should be small in area, and should have some device by
means of which the current of air can be efficiently regulated.
In the usual case the construction of the building is not
calculated to render it air-tight, and the necessity for providing
special air inlets does not arise.

WINDOWS. — Windows are not strictly necessary, and are only
intended to be of service during the time in which coolies are
at work within the building. The operations of examining
rubber, turning sheets, removing dry rubber, cleaning racks
and floors, and putting wet rubber into position, usually occupy
some hours daily. During this interval the windows should
be widely opened if the weather is favourable, and should remain
so until the fires have been lighted. It should not be forgotten

1 86 PREPARATION OF PLANTATION RUBBER

that during the heat of the day quite an appreciable degree of
drying is possible. Advantage can be taken of this; but there
is no necessity to extend the interval unduly, and it is of
greater advantage to proceed with smoke-curing when the
work in the drying-chambers has ceased.

RACKS OF SUPPORTS. — Still referring to the usual type of
smoke-house, it may be remarked that in the upper room
bays of racks run at right angles to a central passage down the
length of the building. Narrower passages run between the
bays of the racks to facilitate ease in handling and inspection.
The wooden supports may be placed about 3 inches apart
horizontally, and 15 or 18 inches apart vertically. A full
bay of racks should contain nine or more lines of support
in each of the planes which are 15 or 18 inches apart vertically.
The number of these planes is governed only by the height of
the room, measured from the floor to eaves. The supports
should be of smooth timber, and need not exceed ij inches
square in section.

It is usual and advisable to smooth off the rectangular edges
of the supports or bars, to avoid the incidence of splinters
of wood adhering to the rubber. The bars should not be
fixtures, but may either be accommodated in slots, or may
rest between two nails,- so that it is possible to give them a
rotary motion by turning the projecting ends. This practice
is followed in smoke-houses, the idea being to move the drying
sheets slightly each day, with a view to the prevention of a
pronounced mark across the sheets.

Care should be taken to see that the vacant racks are thor-
oughly cleaned before fresh rubber is placed upon them,
otherwise a distinct dirty mark is caused across the middle of
the sheet. This mark usually cannot be removed, even by
scrubbing with water. Where this mark occurs regularly in
all sheets, attention should be turned to the openings beneath
the bays of racks, if open fire furnaces are employed. It will
generally be found that gauze of too wide mesh has been fitted.
This should be removed or covered with a finer gauze.

A more effective way of dealing with the trouble, provided
other precautions have been taken, is to have plenty of spare

OTHER BUILDINGS 187

wooden bars. It should be a rule stringently enforced that,
as soon as racks are emptied, the bars should be removed to
the factory to be cleansed thoroughly. A spare set should enter
the smoke-house with each batch of fresh rubber. The actual
number of spare sets required could be limited to a two days'
supply, and the extra cost would be recouped easily.

FLOOR OF DRYING- CHAMBER. — The floor of the chamber is
usually of planks, except that the space under each bay of
racks should be filled with expanded metal. With the use of
wood fires there is always a large amount of light ash formed,
which may find its way into the upper chamber. To counteract
this, screens of fine mesh gauze are laid over the expanded
metal. This gauze may be fitted into a movable wooden
frame, so that when it becomes necessary to clean it the whole
may be removed.

The difficulty is that with furnaces of the " open-fire " type
the rise of dust is so great that the gauze screens soon become
clogged, especially as the slight tarry matter in the smoke
condenses on the gauze, causing the dust to adhere. With
the better types of furnaces, the employment of gauze screens
is not necessary, as there should be very little rise of dust.
It is sufficient to use only expanded metal, to prevent any
displaced pieces of rubber falling into the furnace chamber.

FURNACES GENERALLY. — The crudest and dirtiest method of
fuel consumption in the preparation of smoked-sheet rubber
is that of making a fire on the ground. This is still a common
practice, and should be condemned as being both wasteful and
harmful. Under prevailing conditions coolies will, in spite of
instructions, heap up a pile of logs in order to save themselves
the trouble of stoking the fire in small quantity and at regular
intervals. A small supply of water is kept at hand with which
to quench the fire somewhat if it threatens to cause trouble.
Naturally a large quantity of fine ash is thus thrown up, and
the rubber above receives the deposit. If the coolie does not
happen to be sufficiently awake, of course a house burns
occasionally.

From this primitive type of furnace, others have been evolved.
These usually take the form of more or less shallow trucks,

1 88 PREPARATION OF PLANTATION RUBBER

the majority of which are similar in principle to the fire on the
ground, except that the container can be withdrawn from the
house for the purpose of removing the ash. Sometimes they
are even more objectionable than the ground fire, inasmuch as,
being raised above the ground level, an under-draught through
fire-bars is caused, and consumption of fuel is so much the
more rapid.

PITS. — It is clear that large fires are not desirable, and
that combustion should be slow, provided that the necessary
temperature can be maintained. The lines along which the
development of furnaces needed to extend are therefore plain!
The simplest device adopted was the digging of pits in the
ground. Sometimes these pits received the addition of an
iron truncated cone which was movable. Naturally the
combustion was slow, but sufficient heat was obtained if the
pits were large enough or in sufficient number. An objection
was that the ash had to be cleared in situ, and in the process
the earthen pits gradually increased in size. In all cases it was
necessary to suspend an iron baffle-plate above the furnaces
to distribute smoke and arrest any sparks.

" POT " FURNACES. — The next development was the employ-
ment of " pot-furnaces." These consist of iron drums,
sometimes merely resting on the ground, and sometimes
mounted on trucks for easy withdrawal. These drums radiate
sufficient heat if present in sufficient numbers, and the fuel
consumption is low. They are usually manipulated by
starting a fire in the bottom and packing in logs cut to the
necessary length. Some have no lids, while others are fitted
with perforated caps.

It was considered necessary in some instances to punch a few
small holes near the base of the drum in order to ensure a very
slight upward draught. In a few cases this perforation has
been exaggerated to the form of a hinged door. Unless this
can be closed with ease, and is closed according to instructions,
part of the object of this type of furnace is defeated; fuel con-
sumption is rapid, and the temperature is too high. In the
original form " pot-furnaces " have been found to be effective on
many estates, and are still employed with satisfaction.

OTHER BUILDINGS 189

IRON STOVES. — Working on exactly the same principle,
on some estates one finds small iron stoves in use. Sometimes
broad pipes are attached for the better distribution of the
smoke ; if this is the case it should be noted that the pipes should
have a slight downward slope, and that the " bend " at the end
should be turned downwards. In this way condensed moisture
and creosotic matter falls to the ground, and does not lodge in
the pipe. The life of the conduit is thus prolonged. Usually
such stoves are in use where the " head-room " of a smoking
chamber is insufficient for other types, or where the nature of
the site does not permit of sunken furnaces being installed.
They are of value likewise on occasions where the fuel supply
is limited to a rich timber such as mangrove-logs (" bakau "),
when it is necessary to ensure a low combustion with low cost
of fuel.

HORIZONTAL DRUM-FURNACES. — To overcome difficulties
inherent to drums or " pot-furnaces," the next development
wras that in which the drum was made to assume a horizontal
position, and adapted ingeniously to a simple system of working
from the outside of the building. Reference to the drawings
given will explain how this is effected. In the first illustration
(No. 2) it will be noted that the drum is supported upon brick
pillars, with one end projecting through the wall of the building.
At the other end a short chimney is mounted, having within it
a " damper " which is adjustable from the outside. Over this
chimney is suspended a simple baffle-plate, made from a Chinese
iron cooking-pan. The outer end of the drum is furnished
with a hinged and latched door, in which a small air-regulator
is accommodated.

In the second set of drawings (No. i) the drum is increased
in size and fitted in a special manner for incorporation with a
distinct type of building. Such a scheme was first put into
effect by Mr. R. C. Sherar, the manager of Third Mile Estate,
Seremban, F.M.S., and for ease of reference the house and
furnace will hereafter be mentioned when necessary as the
" Third Mile " type.

It will be seen that the furnace has at the farther end a door
for the removal of ash. As this, if badly fitting, may result

PREPARATION OF PLANTATION RUBBER

No. 2.
"THIRD MILE" TYPE; HORIZONTAL DRUM.

This type of furnace is suitable for adapting to existing buildings
with perpendicular lower walls.

No. i.

THIRD MILE " TYPE OF FURNACE, USED IN CONJUNCTION
WITH "THIRD MILE" SMOKE-HOUSE.

OTHER BUILDINGS 191

in too great a draught, it is well to insist upon good workman-
ship. Other adjustable air-inlets are provided, and the drum
is enclosed in a brick chamber.

RATE OF COMBUSTION. — However successful this furnace
may have proved in the hands of trained coolies, one must feel
that with such a number of air-inlets (whether accidental or
designed) there would always be present the possibility of
obtaining too rapid a combustion. In the orginal forms of
drums or pot-furnaces of various kinds, a very slow rate of
combustion was attained. Naturally a relatively larger pro-
portion of carbon remained unconsumed, and there was a small
proportion of ash. In these respects the furnaces resembled
charcoal-burners. In point of fact, some estates used this
principle for the dual purpose of smoke-curing the rubber, and
at the same time obtaining a supply of charcoal to provide
fuel for their suction-gas engines. This is a consideration
in times when managers are desirous of discovering any devices
which tend towards reduction of costs.

It will be clear that, under ordinary circumstances, the con-
dition of what remains after the combustion of the fuel gives
an indication of the rate at which the wood has burned, and this
test should apply to all furnaces. That in which there is the
most ash and the least charcoal is the one least to be desired.
In direct connection with this consideration, one must recognise
that a fire which is sunk below the level of the ground exposes
the least surface from which heat may radiate; and hence, in
order to obtain the maximum benefit of heat from a slow-
combustion furnace, it should be above ground-level, or
should have a superstructure from which the heat may be
dissipated.

Simple drum furnaces, with slow combustion, have the
further advantages that a " charge " of fuel will need no atten-
tion for possibly eight to ten hours, and practically no ash
is found to be ejected. These advantages have great practical
importance. The first minimises any disabilities arising from
neglect on the part of coolies, and the second makes for increased
cleanliness in the drying-chamber. While these advantages
would appeal to most estates, there would appear to be a further

192 PREPARATION OF PLANTATION RUBBER

advantage to small estates which have only temporary timber
smoke-houses. With a slow rate of combustion in a furnace
of this type, danger from fire is diminished considerably.

Bearing in mind the slow rate of combustion, and hence the
comparatively low temperature obtained, it will be plain that
drum furnaces should be employed in larger number than
ordinary open-hearth fires ; and the drums can be so placed as
to ensure the best possible uniform distribution of heat and
smoke.

Large furnaces are sometimes seen, with flues of brickwork.
In view of the foregoing remarks, it will be obvious that these
tend to large fires and a rapid combustion, and hence must be
classed as undesirable.

BRICK STOVES. — Developing from " drum " furnaces, another
type comes into existence. In principle it consists of an en-
closed brick furnace, with feeding door, and a low conical
dome surmounted by an adjustable cap or spark-arrester. The
rate of combustion can be influenced by a suitable movement
of the cap, which is operated by a screw. This type of furnace
has been installed on several estates by the engineering depart-
ment of Messrs. Harrisons and Crosfield, and is understood
to give satisfaction.

PATALING TYPE. — With the exception of the " Third Mile "
type already mentioned, all the furnaces described are open to
a strong objection, in that the coolies have to enter a room,
usually filled with hot smoke, in order to attend to the fires.
The mere opening of the door of the building is sufficient to
fan most fires into a blaze and to raise sparks. Apart from
these points, it is natural for coolies to avoid entering too often,
with the result that they generally stoke with the maximum
load of timber. Even should they not sleep the danger is
clearly great.

To obviate these drawbacks, furnaces which are fed from the
outside of the building were designed. There have been
various forms, but as they were first installed on Pataling Estate,
in the present form, they may be known under the description
of the Pataling type of furnace. They are eminently satis-
factory, and have a low rate of fuel consumption. They are

OTHER BUILDINGS

Dr«xunags tuft to scale

193

Brwk fur

BB

Coi\cr«te A Cenveixt
Floor

•V-f-

•

IU»i(KcUy

I J

.Iml

S«l,<m. of fur^:.
tkr^ AB

SIDE SECTIONAL ELEVATION (PATALING TYPE OF FURNACE).

PATALING TYPE OF FURNACE.

i94 PREPARATION OF PLANTATION RUBBER

very safe, and in fact, if worked with average intelligence in
supervision, can be regarded as being fool-proof. There is
practically no ejection of fine ash, and no fine-mesh screens
need be employed. They can be adapted to any building
having either vertical or sloping walls of galvanised iron.

In essential the furnace consists of a shallow pit below
ground-level, lined with brick, and having a square brick
superstructure rising 4 feet above the floor of the building.

LARGE SMOKE-HOUSE OF ORDINARY CONSTRUCTION, WITH SHIELDED
VENTILATORS PERMANENTLY OPEN.

In foreground, movable folding racks on which sheets " drip " in
the open air. This smoke-house is equipped with brick furnaces
fed from the outside (Pataling Estate).

On top of the brick walls rests a sheet of boiler-plate perforated
with small holes. The hearth being below ground-level, and
with the extra 4 feet of height above the floor, it follows that
if ash is disturbed it is confined.

From the drawings it may be seen that the pit is prolonged
to the side wall of the building, with steps leading up to the
ground-level. The top and sides of the opening are made
with galvanised sheeting, forming a kind of short tunnel in

OTHER BUILDINGS

'95

which the coolie may stand upright. The outer face of the
brick furnace forms the inner end of the tunnel, and accommo-
dates the door of the furnace. The bottom of the pit is filled
up with clay and stones almost to the level of the bottom of
the'door. This ensures a very shallow hearth, and guards against
an unduly large fire. Obviously it is not desirable or necessary
to make the hearth of fire-bars, as was done in one instance,

BRICK AND CEMENT SUPERSTRUCTURE OF FURNACE INSIDE THE
BUILDING, BUT FED FROM OUTSIDE.

On the top of the superstructurs rests a sheet of perforated boiler-
plate. The actual fire-pit is below ground-level, and to the left
may be seen parts of the sides and top of the downward approach,
from the outside, to the door of the fire-pit.

with the provision of a door below for removing the ash. This
would lead only to a strong draught being created, with a high
rate of fuel consumption.

The openings can be screened by a narrow sloping lean-to,
which serves to keep out rain, and provides shelter for the stock
of fuel and the coolie. The iron furnace-door should be well
made, with an easily worked latch; but it is not necessary that
it should be perfectly fitting. Any slight aperture will serve

196 PREPARATION OF PLANTATION RUBBER

to provide the necessary air-inlet, but in any case it should
not be more than slight.

CONSUMPTION OF FUEL. — Regarding this furnace, it may be
said in conclusion that it is more satisfactory in general working
than any other furnaces yet encountered. Obtaining infor-
mation from over sixty estates, on the question of fuel con-
sumption compared with output of rubber, it was found that,
as far as ordinary smoke-houses were concerned, the Pataling
type of furnace showed the lowest unit consumption of fuel.

GENERAL VIEW OF SHELTERS COVERING APPROACHES TO
FURNACES.

This was at the rate of slightly less than i Ib of fuel per i Ib of
thoroughly cured sheet rubber. The figure on some estates
mounted as high as \\ Ibs. of fuel per Ib. of rubber. Naturally
this factor may have been affected by failure to utilise the drying
space to its fullest capacity, but in the main the high rate of
consumption could be attributed solely to the deficiencies of
the furnaces.

FLOOR OF FURNACE- ROOM. — As a rule no attempt is made to
improve the natural earthen floor. Whether open-hearth fires,

OTHER BUILDINGS 197

truck furnaces, or drums are employed, it is usual to find a
floor with an inch or two of dust upon it. Where all endeavours
are directed in other directions towards cleanliness, it appears
strange that this should be overlooked. In contrast, houses
employing the Pataling type of furnace (or others) have concrete
and cement floors, which can be kept quite clean. Cleanli-
ness should be as zealously attempted in the smoke-house as
in other departments.

NEAR VIEW OF SHELTER.

Steps lead downwards where the wall of the smoke-house has
been removed.

ROOF. — In any type of smoke-house, the roof should fit
tightly at the eaves, and the only vent should be in or near the
roof- ridge.

In an ordinary smoke-house, the opening should take the form
either of a low jack-roof or of squat chimneys protected against
rain. If a jack-roof is chosen, it may be so low as to need no
scheme of adjustment, or otherwise adjustable swing shutters
must be provided. The chimneys may be made with such low
fitting between the cap and the body that no interior swinging
flaps are required.

198 PREPARATION OF PLANTATION RUBBER

During the operation of smoke-curing the smoke vents must
remain open to a degree which is arrived at by experience.
Failure to provide a comparatively free egress for smoke and
moisture will bring trouble in its train. After a house has been
in use for some time, it will be noted that the timber becomes
covered with a shiny tarry coating deposited by the smoke.
If the rubber remained in the house for an equal period, it
would take on the same appearance. During the interval
between the entry and the exit of the rubber some amount
of deposit does take place, and it is this mixture of creosotic
substances which plays a part in fitting the rubber to with-
stand growths of mildew which would otherwise form.

If proper smoke- vents are not provided, the moisture evapo-
rating from the sheets is unable to escape quickly enough, with
the result that a great deal condenses at night-time upon the
inner surface of the comparatively cool roof, and falls back
upon the rubber in unsightly black " drips," which leave a
distinct mark on the sheet. Even if vents are open, this may
happen during seasons of rain. The temperature of the moist
smoke in the roof-ridge may be as high as 130° to 140° F.,
while the outer atmosphere may have been cooled by rain to
70° F. Such a difference on the two surfaces of the roof must
lead to condensation within the house, with consequent
" dripping." It used to be the custom to drape sacking
material above the bays of racks in order to prevent the drops
of liquid falling upon the rubber ; but often for want of renewal
the last state was worse than the first. Modern houses have
often an inner lining, a few inches below the roof. This is
made of soft wood which receives any product of condensation
and absorbs it.

OTHER TYPES OF SMOKE-HOUSE. — So far we have confined
the arguments to smoke-houses of the usual type. There
arc others which vary in either design and method of working,
or in the material of the structure. Mention may be made
of the most prominent of these.

BRICK HOUSES. — Some houses are constructed of brick, and
may have one or two storeys above the furnace chamber. The
floors arc sometimes made of ferro-concrete, and the furnaces

OTHER BUILDINGS

199

may also be of this material. These brick houses give satisfac-
tion, but there would seem to be some difficulty in obtaining
and maintaining the desired temperature, although it is not
quite plain why this should be so. The principle of these
buildings is the same as that of the ordinary iron house, and
the suggestions made in previous paragraphs apply with
equal force.

" THIRD MILE " TYPE. — Reference has been made to the
" Third Mile " type of furnace. This is an integral part of a

CHEWING
Of ft9 1 Fu<m<\CE

" THIRD MILE " TYPE OF SMOKE-HOUSE.

smoke-house, which for clearness of distinction may be known
as the " Third Mile " type of smoke-house, the original of
which was erected on the Third Mile Estate, Seremban, F.M.S.

In essence the design consists of a building, having two
storeys for rubber-drying, and a shallow inverted pyramidal
base, ending on the ground in " Third Mile " furnace, already
described and illustrated.

It will be seen that the principles of ventilation employed are
those indicated for an ordinary house — viz., air-inlet near the

200 PREPARATION OF PLANTATION RUBBER

ground (with little draught), and smoke- vent at the roof-ridge.
The windows shown in the drawing are only for purposes of
inspection of the rubber during the day, and form no part of
the scheme of ventilation during the hours of smoking.

It is claimed that the efficiency of the house is high. Certainly
the work of attending to the furnaces is simplified, and there
should be small ground for excuse if negligence is displayed.

JACKSON HOUSE. — This was brought into notice under the
description of the " Jackson Cabinet," and it was claimed
that average sheets could be dried in a few days. It consisted
of a small house of one storey, having several tiers of racks.
Smoke and heat were generated in a small stove placed outside
the wall. A smoke vent was provided in the roof. These
cabinets had a certain vogue as part of a small unit installation,
with a fair degree of success. It is not clear, however, that
such speed in drying is required. (This point will receive
further attention in a subsequent chapter.)

" DEVON " TYPE. — In its full original design this type owes
its origin to Mr. H. E. Nixon, General Manager of the Devon
Estates, Malacca, where it forms part of unit divisional instal-
lations worked under a scheme of decentralisation.

The original units consisted of a building erected with an
iron framework covered with sheets of asbestos-slate, and a
roof of galvanised iron.

The novelty in design lies in the utilisation of external
platforms upon which the racks of bars supporting the sheets
of rubber may be drawn out of the smoking chambers, and
on which the racks are loaded and unloaded. By this device
it is possible to remove the contents of any compartment
bodily without interfering with the continuity of curing in the
other compartments. That is to say, smoking in such a house
can proceed day and night if necessary, and yet the rubber in
any part of the house can be examined, can be removed, or can
be replaced without cessation of smoking.

It will be seen from the illustrations that the house is more
or less of the same general design as the " Third Mile " type,
with the addition of external platforms. It has two storeys
for the reception of rubber; and a basal furnace-room with

OTHER BUILDINGS

2OI

sloping sides converging downwards into a pit containing a large
drum-furnace. This is mounted on a low truck, and travels
on a short length of railway.

GENERAL VIEW OF DOUBLE " DEVON " TYPE OF
SMOKE-HOUSE.

The platforms are common to both units. Building of brick with
iron roof (Batu Caves Estate).

Each of the curing-rooms is divided into four compartments
(making eight compartments in all). These are closed by
swing doors, each of which is the full width of a compartment,
and has a slight overlapping edge. Through these doors light
railways run into the house and out upon the platforms. On

202 PREPARATION OF PLANTATION RUBBER

the rails " bays " of racks run, and when fully loaded they
are easily moved. The racks were designed with a frame of
stout hard wood, but light angle-iron could be utilised.

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The chimney style of smoke-vent has an internal butterfly
flap, which is controlled by means of a wire from the outside.
In the ordinary course of smoke-curing, it is advised that this
flap should be permanently open so as to reduce the possibility

OTHER BUILDINGS

203

of internal condensation of moisture and creosotic matter.
The exact degree to which it should be open must be found
by experience.

Although reference has been made several times to
compartments, it should be understood that the chambers
are not subdivided internally by means of partitions.
There exists only the external effect of compartments in

204 PREPARATION OF PLANTATION RUBBER

the form of the eight swinging doors which allow for the
withdrawal of, or insertion of, any one unit of racks

DOUBLE " DEVON " SMOKE-HOUSE OF BRICK, WITH ROOF OF
CHINESE TILES, SHOWING LOADING PLATFORMS WITH RACKS
WITHDRAWN FROM SMOKING CHAMBERS.

Federated Engineering Co., Ltd., Kuala Lumpur.

at any time without interference with the bulk of the
rubber.

OTHER BUILDINGS 205

DETAILED DESCRIPTION. — As enquiries are often received it
is permissible to reproduce the following detailed description

SIDE VIEW OF PRECEDING PHOTOGRAPH, SHOWING EXTERNAL
ARRANGEMENT FOR STOKING FURNACES.

Federated Engineering Co., Ltd., Kuala Lumpur.

of the original house. This appeared in the Fourth Local
Report (Malaya) 1916, issued to subscribers by the Rubber
Growers' Association.

206 PREPARATION OF PLANTATION RUBBER

;< The house has a steel frame-work, 22 feet long, 16 feet
wide, and 22 feet high. Of the length, 14 feet is occupied
by the platforms, and 8 feet by the chambers. These measure-
ments can be varied. The whole of the width (16 feet) is
occupied by compartments of which one series is placed above
the other.

" Platforms. — The loading verandahs or platforms are of
ordinary * seriah ' timber.

" Compartments and Furnace Chamber. — These are enclosed
with Bell's * Poilite ' sheets, each of which measures 8 feet bv

FRONT VIEW OF DOUBLE " DEVON " TYPE OF SMOKE-HOUSE.
Glenmarie Estate: Batu Tiga Co.

4 feet by -fa inch. The sheets are affixed to the steel stanchions,
doors, etc., by galvanised bolts (i inch by J inch) which pass
through iron flats measuring 8 feet by 2 inches by g inch
(about). These iron flats hold the sheets at the edges. The
dimensions of the compartments are 8 feet by 8 feet by 4 feet.
" Racks. — These are eight in number, and measure just
under 8 feet by 8 feet by 4 feet. The capacity of each is
roughly about 450 Ibs., of dry sheet rubber. The racks are
mounted on 6-inch iron wheels, running on rails of stock size,
* T ' iron (if inches by if inches by J inch).

OTHER BUILDINGS

207

" The sheets are hung on split bamboos. To prevent jthese
projecting over the edge of the rack and catching in the doors
when the rack is moved in or out, a thin strip of wood, about
J inch high, is nailed along the sides of the rack.

" Furnace. — This is of the type that aims at slow combustion.

SIDE VIEW OF DOUBLE " DEVON " TYPE OF SMOKE-HOUSE.

Building constructed of galvanised iron. Shows door to furnace
chamber, and ventilator.

It consists of a cast-iron cylinder, 3 feet in diameter and 4 feet
high, carried on a truck made of a sheet of boiler-plate, and
mounted on small wheels, so that the whole can be moved
easily out of, and into, the furnace chamber for easy cleaning
and stoking. A , i

" The furnace chamber is a pit lined with concrete, just

2o8 PREPARATION OF PLANTATION RUBBER

wide enough to take the trolley, and about 12 feet long. The
top of the furnace, which is almost flush with the ground-level,
consists of a sheet of zinc or galvanised iron with numerous
holes about 3 inches in diameter. Over these holes are strips
of mosquito gauze, as flame and dust arresters (see note below).
There are no holes in the sides or bottom of the cylinder.

" Over the furnace is hung a baffle-plate, measuring 4 feet
by 4 feet. Above this, on the first floor-level, the bottom of
the compartments is covered with wire netting, to prevent any
rubber dropping accidentally into the furnace chamber. The
furnace chamber is fitted with an iron-frame door, swinging
on perpendicular hinges.

" Method of Stoking. — The timber used is a mixture of
jungle wood and rubber-tree wood, cut to lengths of about ij
feet. In the ordinary way the furnace is charged at 6 p.m.,
and at six-hour intervals a little more fuel is added, but a new
charge is not necessary. . During the daytime, when the heat
of the sun is sufficient to raise the temperature appreciably,
a smaller fire is maintained.

" Temperature. — There is no difficulty in maintaining a
temperature of 120° F. By continuous smoking, average sheets
prepared from standardised latex can be fully cured in five days.
This represents no hours of smoke-curing, which is at least
equal to ten days' intermittent smoking in an ordinary house.

" Capacity. — There are eight racks, each accommodating
450 Ibs. of standardised sheet rubber. The loading capacity
of the house, therefore, is 3 ,600 Ibs. As each charge is cured in
five days, the monthly output may be 21 ,000 Ibs.

" The cubic capacity is 2,048 cubic feet. As there are no gang-
ways, etc., this is fully utilised. This gives a rate of monthly
output capacity to over io| Ibs. dry rubber per cubic foot of
drying space; an excellent figure much in advance of values
obtained in the great majority of ordinary smoke-houses."*

Owing to shortage of supplies during the War, similar
buildings have been erected with frames of well-seasoned
hard wood, which was protected by strips of asbesto-slate or
galvanised iron. The latter material was also substituted in
the covering walls. Later, houses were erected of brick,
with other minor modifications. As a natural development, the

* Since the above was written, it has been found possible to
eliminate the gauze. A mild steel top has been made, perforated
with 2-inch holes. Practically no dust is ejected from the furnace,
and there are no flames.

OTHER BUILDINGS 209

latest buildings consist of two of the original houses face to
face, under a common roof, and served by common platforms.

As originally designed, the house was intended to meet the
needs of a small estate, or a division of an estate, having a
maximum output of about 20,000 Ibs. of sheet rubber per
month. The possibility of an extension of this idea has been
shown to be great.

The furnace has been described as situated in a pit. Situated
on a bank or on sloping ground, it was easy to arrange for
withdrawal of the furnace. In some cases this has not been
possible, and various modifications have been effected. The
most satisfactory yet encountered is that in which a shallow
brick pit is surmounted by an iron cone, about 4 feet in height.
This is fitted with a cap having small perforations. The fire
burns in the pit, and the heat is radiated by the cone. It
would have been more effective to have allowed greater height
in the furnace chamber, and to have employed the travelling
drum-furnace as in the original design.

In order to avoid interference in draught by a space between
the bottom of the doors of the compartments and the platform
(due to the presence of rails), the floor of the platform is laid
level with the top of the rails ; or to the bottom of the doors is
attached a swinging flap, notched for accommodating the rails
when in position.

There are in use houses of other designs, which all more or
less vary only in some modifications from the types described.
Hence they do not call for special comment. Recently a
rather distinct departure has been noted in a structure desig-
nated the " Barker " smoke-house.

BARKER PATENT. — In essential this consists of a long narrow
structure erected with an appreciable slope from one end to the
other. At the lower end is a small furnace enclosed in a brick
compartment. The smoke from this furnace travels up the
slope to the other end, at which the rubber enters. The
sheets are hung on bars which are attached to a unit frame-
work. This frame slides, by its own weight, upon timber
side supports. A sufficient number of these units occupies

14

210 PREPARATION OF PLANTATION RUBBER

the full effective length of the structure. The removal of
" stops " at the lower end enables the foremost frame to be
removed, and the succeeding frames slide into a new position.
Thus the freshly prepared sheets, entering at the higher end,
gradually and automatically move towards the furnace as the
frames of dry rubber are removed from the lower end.

Thus far only small units have been seen. It is claimed
that, properly prepared, sheet rubber can be smoke-cured in

THE NEW "BARKER" TYPE OF SMOKE-HOUSE: A SMALL UNIT.

The racks slide automatically from top to bottom on withdrawal
of the lower frames through door at front. The furnace is con-
tained in the brick compartment at the lower (front) end.

about five or six days, and it is stated that installations have
been in successful working for sufficiently long periods to
prove their efficacy. The device is better known in Java and
Sumatra than in Malaya. The capacity of a unit building is
stated to be 7,000 Ibs. per month, calculating on a six days'
cycle of working. In a more recent design provision is made
at the lower end for a water tank, into which all rubber can be
discharged in case of fire.

CHAPTER XVI

OTHER BUILDINGS (continued) AND SITUATION OF
BUILDINGS

SORTING-ROOM AND PACKING-ROOM. — It is in these depart-
ments that most factory installations are lacking. More often
than one cares to acknowledge, sorting and packing are done
under conditions which place a premium upon poor work.
As a consequence, consignments of rubber are often marred
by the inclusion of defective specimens. The result is that
shipments may be rejected when tendered against contracts,
or that allowances in price have to be made. In many instances
it would not be fair to lay the blame upon the manager or an
assistant, as it is obviously impossible for an individual to inspect
every piece of rubber. Neither would it be strictly fair in some
cases to ascribe the fault to pure carelessness on the part of
the coolies.

Often the only provision made for this important work is the
lower room of a drying-shed, which may also contain hanging
rubber. Under these circumstances, space is cramped, and
the light often poor. Small defects may pass unnoticed, and
the general surroundings do not conduce to keen work.

Where, for economic reasons, the sorting and packing opera-
tions are conducted in the drying-shed, there should be ample
space free from hanging rubber, and it should not be possible
for wet rubber placed in the upper room to drip upon the dry
rubber below or upon packed cases. There should be plenty
of light, and for this reason windows should be ample. Usually
the window-frames are fitted with wooden shutters, which
are preferably hung on horizontal hinges from the top of the
frame. By this device it is not necessary to close all windows
during a shower of rain, and rubber may be stacked near a
window with reasonable chance that direct sunlight will not
be allowed to fall upon it.

211

212 PREPARATION OF PLANTATION RUBBER

In dealing with smoked sheet, it is advised that the rubber
to be examined should be placed upon tables facing the windows,
so that each piece may be scrutinised in a strong light.

Crepe rubber also is best examined in a strong light, but
preferably with one's back towards the source of light or at an
angle to it. For this work coolies usually are most efficient
when sitting on the floor.

It will be clear from the foregoing remarks that the best
conditions would be secured in a separate building especially
constructed. A single room would be all that is required;
at one end sorting could be undertaken, while packing could
be done at the other end. No hanging rubber should be
allowed in the room.

The floor should be of hard timber, and raised from the
ground, to the height approximately of a bullock-cart or motor-
lorry, as the case may be. The boxes of rubber could thus be
transported by small hand-trucks on a level with the transport
vehicle, reducing labour to the mimimum.

The ventilation of the building should be good, especially
if cases of rubber are to be stored therein; and the entire
structure should be weather-proof.

STORE-ROOMS FOR RUBBER AND STORAGE. — The question
of storage of rubber in factory buildings has always possessed
importance, but has demanded increased consideration recently.

From experience in this country, it is clear that cement floors
for store-rooms or packing-sheds are the least suitable. They
are often visibly damp, especially in the early morning. To
allow rubber, packed or unpacked, to remain upon a cement
floor in the tropics, is to court trouble from moulds, external
or internal . If the employment of a cement floor is unavoidable,
the rubber and boxes should be raised on wooden supports,
giving a clearance of at least 3 or 4 inches, and there should be
clear ventilation space between tiers of boxes.

Experience indicates that the best type of floor is that already
advised for sorting and packing rooms — i.e., a good hard timber
floor raised at least 3 feet above ground-level. Apart from the
advantage in labour specified in the previous paragraphs, this
provision of ample ventilation space below the floor is a great

SITUATION OF BUILDINGS 213

consideration in the preservation of the timber. Raised store-
rooms become essential in low-lying districts which are at all
subject to flooding, yet the writer has seen many boxes of rubber
damaged by flood-water entering a packing-room situated on
the level.

The question has often been raised recently as to the length
of the period during which rubber may be safely stored in this
country. The answer can be only supplied by experience, of
which up to the present we have none possible of being classed
as reliable. Whatever storage may have been done in the past
has been influenced greatly by the unsuitability of the storage
accommodation, and the fact that often the rubber was not
prepared with a view to prolonged storage.

While the market demand was strong, rubber was being
shipped and passed into circulation, at a rate which did not
demand investigation of the subject of local storage. In the
year 1918 conditions were such as to bring the matter into pro-
minence, and we were able to tender advice on the lines given
in this chapter. The necessity passed, but has again arisen.

Our experience goes to prove that if rubber is properly
prepared and thoroughly dried before packing, it will remain
in good condition for a period of a year or more in this country.
How much beyond a year it may be kept remains to be deter-
mined. The assumption of " proper preparation " leaves great
room for reservations.

In the case of crepe rubbers, there is no great difficulty, pro-
vided that the recognised methods and formulae are employed,
and that the rubber is packed only when perfectly dry. Under
those conditions, the higher grades of crepe remain apparently
unaffected on storing. Any appreciable deterioration may be
attributed to defective preparation or external causes, such as
accidental damage by water.

The prolonged storage of lower grade rubbers is attended by
more risk, especially in the case of the lowest grade (earth-
scrap) from estates which neglect the practice of regular and
frequent collection of the raw product. The same reservation
applies to crepes made from tree-scrap which is not collected
daily. In these types of crepe rubber " tackiness " may be

PREPARATION OF PLANTATION RUBBER

initially present only in small degree, but the final damage may
be immensely greater by close contact of the folded rubber
during prolonged storage.

When we come to discuss the possibility of storage of smoked
sheets, the difficulties become immensely greater. We have
yet no reliable experience as to the keeping properties of this
grade when properly prepared, fully cured, correctly packed,
and stored under the best of local conditions. It is understood,
of course, that in the qualification by the term " local " con-
ditions, we assume it to be more difficult to store rubber
generally in Malaya than in a temperate climate. The average
temperature and humidity of the atmosphere are here much
more favourable to the development of mould growths than
would be the case, say, in Great Britain.

In discussing this question, as far as it refers to the preserva-
tion by storing of smoked sheet rubber, it is not fair to draw
conclusions as to the likely behaviour of packed rubber from
data based upon observation of loose specimens. We have
samples of smoked sheets prepared in 1910, and these, super-
ficially, appear to have remained unchanged. No mould is
present and, as far as intermittent observation enables us to
judge, moulds have never been incident. Whether such rubber
would have been preserved in this condition had it formed part
of a packed case, is a point upon which we have no experience ;
neither can we give any opinion. It seems true, however,
that loose specimens " keep " better than bulk samples of the
same preparation.

It cannot be argued that the present good condition of these
old specimens may be due to correct preparation. In those
days methods and formulae were rather haphazard, especially
in view of the fact that the daily variability of dry rubber
content of latices was not then recognised.

One would rather submit the factor of adequate smoke-
curing as the chief influence in the superficial preservation of
smoked sheets. Ten or eleven years ago it was considered
advisable to allow the rubber to remain in the smoke-house for
a period extending well beyond that necessary for ordinary
drying. As a result, very dark rubber was produced, which

SITUATION OF BUILDINGS 215

was thoroughly impregnated with the products of wood com-
bustion. There would seem to be little doubt that this
procedure was responsible for the prolonged freedom from
mould growths.

Market standards have varied to some degree since, with a
tendency to prefer a paler product than that in vogue, say,
six or seven years ago. Moreover, standardised methods of
preparation have been introduced, with the result that sheets
of a desirably high standard can be produced in from ten to
fourteen days, when smoke-curing is conducted only during
night hours. Some estates are equipped with smoke-houses
which, by continuity of working day and night, provide smoke-
dried rubber in from five to six days; but the actual hours of
smoke-curing are approximately equal to those of the ordinary
type of house.

This tendency towards the production of sheets paler in
colour than the old standard is probably largely responsible in
the present for the commonly observed incidence of surface
moulds on stored smoked sheets, and also for some complaints of
<f under-curing," where the term specifically refers to a failure
to dry and cure the rubber thoroughly. Boxes of smoked sheets,
which had been stored for varying periods up to five months,
were recently inspected, and, in the majority of instances,
surface moulds were found to be plentiful. In all cases it
was observed that the trouble was intensified where boxes of
rubber were stored in contact with cement floors.

This " under-curing " is not a question solely of the duration
of smoke-drying, although probably the modern practice of
curtailing the period has exerted a great influence. To make
this clear, it may be stated that, given two batches of uniformly
prepared wet sheets, it would be possible to smoke-cure them
for equal periods in different houses, so as to produce one batch
very much paler in colour than the other, although the total
hours of actual smoke-curing would be identical. In order to
produce such effects, all that is necessary is to employ different
timbers for fuel or different types of furnaces. In the one case
there would be produced heat and very little smoke, while in
the other the necessary heat would be obtained plus plenty

2i 6 PREPARATION OF PLANTATION RUBBER

of smoke. The best results naturally are obtained by the
employment of the happy medium, and if smoked sheets have
to be stored, the ordinary period of smoke-curing should be
prolonged to an interval consistent with the capacity of the
smoke-house.

All precautions taken in preparation and curing can be
nullified, as already indicated, by unsuitable storage conditions.

TOOL-SHEDS AND STORE- ROOMS. — In some factories it is
the rule to see lime, cement, spare rolls, sieves, and a general
heterogeneous assortment occupying part of the rubber-drying
rooms. The inconvenience is often great; and it certainly
seems that these stores and tools are of sufficient value to be
accommodated in suitable buildings.

SITUATION OF FACTORY BUILDINGS. — There can be no doubt
that a great deal of the " spot " disease trouble, and the general
slowness of drying, can be attributed in many factories to the
unsuitability of the site chosen. Probably the idea which
actuated those responsible for the choice of site generally was
proximity to a water supply. This would account for the fact
that a number of factories are situated in valleys or near
swamps. More often than not, also, the actual clear space is
very limited, and rubber trees grow close up to the walls of
the buildings. Under such circumstances, it is difficult to
see how these buildings can be anything but dark and damp,
and it is not difficult to understand the slow rate of drying.
In a few cases the sites chosen proved to be so unsuitable that
the estates were confronted with a very serious problem, the
solution to which was, either the erection of another complete
set of buildings in a more suitable spot or the installation of
artificial driers.

It must be laid down as an axiom that the first essential in a
suitable site is that water may be brought to it easily, but, as
already indicated, this does not mean that the buildings need
be placed in actual proximity to the water-supply. The mistakes
made by pioneers in this work are not likely to be repeated,
and it is common now to note well-designed and comprehensive
schemes in which the water is pumped to a reservoir placed at a
suitable elevation, whence the supply is gravitated to bungalows,

SITUATION OF BUILDINGS 217

coolie lines, and the factory. The importance of securing a
plentiful supply of good water for factory purposes cannot
be exaggerated, and it is a point which is only thoroughly
appreciated on estates where smoke-sheet rubber has to be
prepared.

The second essential, but of equal importance, is that there
shall be an ample open space on which the sun may shine all
day. There must be no trees too near the buildings, and there
should be no adjacent swamps. Preferably, the site should be
on a raised position, so that it will be impossible for surround-
ing trees to cut off sunshine, even when they are fully grown.
From such an arrangement it will follow that the factory will
be light and airy, and the drying - houses will receive the
maximum of benefit to drying from direct sunshine on the roof
and walls. There can be little doubt that these considerations
play a most important part in determining the rate of drying
of the rubber, and where comparisons are made between the
rates of drying in various drying-houses all these factors enter
into the question and contribute to the total result. Presum-
ing that the thin crepes made in two factories are equal in thick-
ness, it is not uncommon to find that in a drying-house, situated
in a wide open space, the period of drying may be as low as
six or seven days ; while in another drying-house, situated near
a swamp and surrounded by trees, the period may be as high
as eighteen days to twenty-one days. The figures quoted are
not fictitious, but are facts actually noted in the course of the
writers' experience.

A great deal also depends upon the exact position of buildings.
Thus, to obtain the maximum of light in a factory, it will be
obviously beneficial to erect it with the long sides running east
and west, so that the windows face the north and south, and
the large end doors face the east and west respectively. At
first sight it would appear that the best position for the machines
would be on the north side of the building where no sun can
enter; but a moment's consideration shows that the south
side would give the best results. By the time the sun has come
round to the south, it is usually high in the heavens, and the
direct sunshine does not fall very far into the room. Even

2i 8 PREPARATION OF PLANTATION RUBBER

should it play upon the machines for an hour or two during the
day, no harm could result to the rubber which was being worked,
as no piece would remain there a sufficiently long time to be
injured in the slightest degree. Placed in this position, the
maximum benefit of light would be obtained, whereas if the
length of the building ran east and west, the machines would
have only either the morning or afternoon light.

While it is advisable to erect a factory running east and west,
the drying-houses should run north and south. In this position
the maximum wall area will be exposed to the sun during the
day, and it will be possible to manipulate the windows of the

\D FACTORY »/

LiJ

SUGGESTED ARRANGEMENT OF BUILDING.

drying-rooms so that those along one side are open, and it will
never be necessary to close all the windows at any time of the
day. Thus the windows facing east will be closed, and those
facing west will be open until after midday; then vice versa.
With such an arrangement a more uniform temperature may
be obtained than by any other arrangement of the buildings.
If the building ran east and west, the windows on the north
side could remain open all day, while those facing south would
have to remain closed practically all day. The south side
of the house would be heated by the sun, while the north side
would remain cool, and the rates of drying would be corres-
pondingly unequal. The total wall area heated by the sun at

SITUATION OF BUILDINGS 219

any time of the day would be less in this position than if the
house ran north and south.

Similarly, to obtain the best drying effect during the daytime
in a smoke-house the building should run north and south. By
this means the temperature will be maintained to the maximum
possible by sun heat, and the rate of drying will correspond.

References to Sketch Plan.

Drying-house No. 2 should be of two storeys, and unless a
separate sorting and packing room is to be built, No. i should
also have two floors (see previous notes on packing-rooms).

In the factory —

V shows the position of the verandah, which may be quite
open and only divided from the inner room by

S, a wall composed of very strong expanded metal, which
allows light and air to enter the factory.

T,T are the glazed tile tanks for the reception of latex,
scrap rubbers, and bark-shavings.

M shows the position of the machines on the south side
of the factory, with the direction of extensions, and

E,E the compartments in which the engines are bedded.
In these positions it is possible to obtain direct drive to the
machines.

D,D are large double swing or sliding doors (the latter for
preference always). These, while suiting transport of rubber,
provide also for a free draught of air.

If possible the scrap-washing machine should be placed
outside the wall of the factory, and tanks for the recep-
tion of scrap rubbers may then be situated in convenient
proximity.

Economy of labour is obtained by grouping all factory
buildings as closely as possible, but it should be borne in mind
that smoke-houses should be regarded as a possible source of
danger from fire. This point has a practical bearing upon
rates of insurance, and it is essential that the smoke-house
should be situated at a minimum of 50 feet from any other
building or group of buildings. In this connection, also, it

220 PREPARATION OF PLANTATION RUBBER

may be noted, as being of further practical interest, that, in
the insurance of smoke-houses, preferential rates are given to
those having a good type of slow-combustion furnace.

CHOOSING A FACTORY SITE. — Sufficient has been written to
make it clear that the choice of a site for factory buildings is
a matter demanding weighty consideration. Much, of course,
depends upon the planted area, and the rate at which it comes
into bearing. Under certain circumstances which will be
obvious, it is permissible to instal first a group of buildings of
a temporary nature only, the future site and permanent build-
ings to be chosen later when the main portion of the estate
comes into bearing. Often, however, one finds that, from lack
of forethought, the estate has been committed to considerable
expense in the establishment of equipment, which later is proved
to be unfavourably situated with regard to the majority of the
area in ultimate bearing. In such case, transport of latex is
fraught with difficulties and may be expensive.

In the instance of an estate which will gradually come into
bearing, it is not easy to decide whether a temporary installation
shall first be provided, or whether, in anticipation of future
demands, a complete equipment shall be erected. So much
depends upon the financial aspect of the question, and upon
the rate at which areas will come into bearing. As far as is
possible, the best policy would be that of a compromise under
which the site would suit later requirements, and the factory
would be so planned as to be capable of future easy extensions
both of buildings and machinery.

It is not possible to lay down any definite data as regards
requirements based on acreage, or to make comparisons
between any two estates of similar acreage. The important
factors determining such requirements are:

(a) Area.

(b) Shape of the estate.

(<:) Topography of the estate.
(d) Available supplies of water.

Naturally the ideal site for factory buildings would lie in a
central position, given other favourable conditions.

SITUATION OF BUILDINGS 221

CENTRALISATION OR DECENTRALISATION. — It is the experience
of a number of estates that, all other conditions being favourable,
there is a limit beyond which the centralisation of factory work
leads to an unwieldy position. We are not here concerned
with the few extremely large estates running into tens of thou-
sands of acres. In those cases the total area would be divided
into economic sections. The argument there would resolve
itself into a discussion on the size of an economic section.
This, in turn, would be dependent upon the type of main pro-
duct, involving the question of transport of latex or coagulum,
and the possible provision of batteries of heavy machinery.

The differentiation between the transport of latex and coagu-
lum, respectively, is a most important one, and has a powerful
influence in determination of the maximum of centralisation
possible. Whereas properly prepared coagulum may be safely
transported by bullock-cart, light-railway, or motor vehicle
for many miles, latex, on the other hand, demands very careful
treatment. Anti-coagulants may be employed to preserve
fluidity, but only within certain limits. Even under these
conditions, other factors (chiefly climatic) exert an influence
which renders the transport of latex for any distance a matter
of anxiety.

It will be plain, therefore, that the limits of centralisation
of factory work are much narrower for the preparation of sheet
rubber than is the case when crepe rubber is to be made. In
actual experience the preparation of a high standard and a
high percentage of smoked sheet is attended with considerable
difficulty in those cases where the factory processes have been
ultra-centralised. Apart from the difficulties inherent to the
transport of latex in a state of good preservation, there is the
added difficulty of dealing quickly with large volumes of latex
brought from various quarters. None of these should be
allowed to remain standing if the best results are to be secured ;
but obviously there must at times be some congestion. Even
on a small scale it is often found that the latest batches of latex
are unfit for the preparation of good sheet rubber, and the
trouble may be easily exaggerated when \vorking on a large
scale.

222 PREPARATION OF PLANTATION RUBBER

The centralisation of work on crepe preparation, therefore,
is limited only to a comparatively slight degree by distance
of transport, and in the main only by the size of the necessary
equipment of machinery and drying accommodation.

The successful preparation of sheet rubber is, on the contrary,
governed chiefly by the factor of transport. With this con-
sideration in view, several large estates, preparing sheet rubber
as the chief grade, have found it necessary to decentralise the
factory work, with very satisfactory results. Outlying sections
are given uniform and complete equipments of necessary
buildings on a small scale, and hand-driven light machines.
Uniform coagulating tanks are installed, and the methods and
quantities of chemicals employed are carefully standardised.
Experience has shown that often the best sheet rubber coming
to the market has been prepared on small estates ; and the same
applies to the product of these decentralised stations on large
estates. There is no a priori reason why the product from one
station should differ in the smallest particular from that of
another, apart from minor fluctuations which are due to vari-
able weather conditions affecting the latex. If the contrary is
found to be the case, it indicates failure on the part of the
person responsible to follow the regular rules and methods.

In the natural scheme of development of a large estate, it
would be necessary, of course, to have a comparatively small
centrally situated factory, equipped with power and heavy
machinery for working scrap rubbers in the preparation of
crepe grades below No. i in quality. As the yield per acre
increases, or the area in bearing expands, it would be advisable
later to increase the size of the central factory and buildings
so as to permit of the preparation of a proportion of the crop
in the form of No. i crepe rubber, in order to be able to comply
with prevailing .market demands under which preferential
rates fluctuate between pale crepe and smoked sheet.

PART IV
THE FINISHED RUBBER

CHAPTER XVII
DEFECTS IN CREPE RUBBERS

GENERAL STYLE OF FINISH. — Broadly, there is no single and
definite- style of finish, but on the whole it may be stated that
the greater proportion of crepe rubbers are prepared in a thin
form and with a close-knit texture or finish.

Very little thick or blanket crepe is now made on estates in
Malaya, so that beyond the mention of that type little need be
written. A fair amount of blanket crepe is sold in the Singa-
pore market, but it should generally be regarded as re-made
rubber — i.e., it may have been prepared from thin crepes, or
from native pale sheets, in local rubber- washing factories.
In appearance these crepes have a rough finish, and vary in
colour according to the crude material employed.

The general preference of the market at present is for a thin,
smooth-finished crepe, with a close-knitted surface — i.e., free
from what is described as " laciness." What effect this
looseness of finish can possibly have upon the quality of the
rubber is not understood, but the standard type set up by the
market must be comparatively free from small holes.

Under existing conditions governing the sale and purchase
of rubber, various " standards " are set up. These really have
no bearing upon the intrinsic qualities of the rubber, and are
concerned almost entirely with superficial attributes. They are
necessary in the absence of any proper scheme of evaluation
for the establishment of certain standards of comparison, which
imply that the rubber is apparently clean, free from certain
recognised defects, and has been carefully prepared — as far

223

224 PREPARATION OF PLANTATION RUBBER

as can be determined by a superficial examination. Thus the
question of " finish " has attained disproportionate importance,
but must be respected when preparing rubber for sale.

Under ordinary conditions, thin crepe rubber, as it leaves the
finishing machines, has what may be termed " deckled " edges.
On many estates, in order to comply with market conditions,
the edges of the wet crepe are trimmed, and the trimmings
re-made into lengths of crepe. This is done under the impres-
sion that the market price is influenced by the evenness of the
edges of crepe rubbers.

Again, it sometimes happens that, owing to " wear" of the
rolls, the finished dry crepe may show a faint but distinct
pattern of mark — a diamond or a horizontal bar. Since these
are not accepted under the " standard " comparisons, rubber
exhibiting these characteristics does not obtain the top market
price. In other words, these innocent and innocuous marks
are regarded as defects and penalised accordingly.

Enough has been written to show how very important
becomes the question of finish. It will be acknowledged
that the superficial qualities demanded in the " standard "
market type can be reproduced by any estate having adequate
machinery and ample facilities for drying and handling the
rubber.

Methods of preparation and formulae for the employment of
chemicals are so well laid down that, up to the stage of machin-
ing, no difficulty need be encountered. But the standard type
of finish in the dry crepes cannot be obtained unless the estate
factory is fully equipped with the three types of rolls necessary
— i.e., macerators, intermediate crepers, and smooth finishing-
rolls. This subject has received full discussion in Chapter XIII.,
and is here only mentioned with the view of emphasising the
point that no estate can be blamed for a lack of " finish " in
crepe rubbers if the equipment of machinery is inadequate
or in poor condition.

If, on the other hand, the factory has ample machinery for
requirements, and a good finish cannot be obtained on the
thin crepe, then it is time the rolls were attended to and changed,
or that the ratios of the driving pinions were altered.

DEFECTS IN CREPE RUBBERS 225

DIRTY EDGES. — It seems to be almost impossible to keep old
machines clean, and it is equally difficult to keep the edges of
crepe free from oil and dirt. Usually these dark edges are to be
found on crepe which is rather wide, and it will be noticed that
where wide crepe is made, unless special precautions are taken,
the edges of the rubber often pass under the edges of the hopper
and so pick up dirt and oil. On most machines it is a great
mistake to attempt the preparation of wide crepe ; nothing but
narrow crepe must be made. To obtain this it is necessary
to decrease the width of the hopper placed above the rolls.
This can easily be effected by blocks of heavy hard wood, cut to
shape and fastened in position.

Sometimes the dark edges of crepe are due to another cause.
Rolls may be gradually worn in the middle, so that to obtain
a good finish it becomes increasingly necessary to tighten up
the screws which regulate the distance between the rolls.
It thus happens that just at, and beyond, the edges of the
rubber the rolls grind upon each other, and fine particles of
iron and graphite are transferred to the rubber. In such a case
it is evident that either the rolls must be " turned " or that
a new pair of rolls must be substituted.

IRON-STAINS. — One of the causes of iron-stain on rubber has
been mentioned in the preceding paragraph. This particular
kind of iron-stain must not be confounded with rust-stain,
and gives a dark dirty colour. It results from the grinding
together of the rolls, and is usually noticed in the finishing of
fine pale crepe. For this operation it is necessary to screw
up the rolls tightly, and it will be plain that, whenever the rolls
are vacant of rubber, there is a tendency for them to grind
upon each other, thus setting free fine particles of iron and
graphite. In order to avoid this, one must be careful to see
that between the working of each length of fine crepe the rolls
should be occupied with another piece of rubber, which may
be kept for the purpose. In some factories this trouble
apparently does not exist, while in others the amount of wear
on the rolls is surprisingly great, and the damage done to
the rubber is excessive. The only way in which this difference
can be accounted for is that there must be a great difference in

15

226 PREPARATION OF PLANTATION RUBBER

the quality of the roll material. Some rolls seem to be exces-
sively soft, and from these contamination by iron-stain is
great. For this reason rolls are sometimes rejected, and there
would appear to be an objection to any but chilled steel rolls
for the final stage of finishing crepe rubbers.

RUST- STAINS. — Rust-stains, on the other hand, throw the
responsibility entirely upon the labour and supervision of the
factory. Rust is formed upon the rolls when they are at rest,
and any one passing pale rubber between the rolls before they
have been thoroughly cleaned is guilty of culpable negligence.
Even when apparently clean, a piece of lower grade rubber
should be passed through the rolls several times so as to
remove any slight trace of rust remaining.

Rust-stains have also been caused in a few cases by the
large knives which are used to cut up lumps of coagulum,
or by allowing freshly coagulated rubber to come into contact
with iron vessels in the factory.

A similar appearance has been traced in a few instances to
contamination of the coagulum in transit by the dust of the
reddish rock (laterite) employed in localities for road-making.

OIL-MARKS. — The origin of oil-marks in crepe has already
been described in Chapter XIII. The whole question resolves
itself into one of cleanliness, moderation in lubrication, and
supervision. The machines should be inspected every day,
and once a week rolls may be swabbed down with a 10 per cent,
solution of caustic soda applied by means of a piece of cloth
fastened round the end of a stick. Immediately after this
operation water should be turned on and the rolls set in motion,
so that all traces of caustic soda are thoroughly removed. If
possible, lubrication by oil should be substituted by grease
lubrication through screw caps.

Particular attention should be paid to the back of the
machines. None but the individual in charge of engines
should be allowed to lubricate the machines, and he should
be held responsible for any excess of lubricant.

As a rule oil-marks are restricted to the edges or the proximity
of the edges of crepe, but sometimes the streak is to be found
in the middle of the length. In such a ca.se, it is almost certain

DEFECTS IN CREPE RUBBERS 227

that the oil or grease has been picked up by the rubber in the
tray. It sometimes happens, if the " liners " of the bearings
are eccentrically worn, that a few drops of dirty oil or a particle
of grease are squirted out to some distance. These usually
find a resting-place in the tray, and the contamination may
then appear in any part of the rubber.

It will be clear, therefore, that all trays beneath machines
should be examined as the probable source of danger from
contamination by oil and dirt. If the trays are as wide as or
wider than the effective portion of the rolls, they should be
discarded. In their place (except sometimes in the case of
the macerating machine) all that is necessary is a movable piece
of board, in width not less than from 4 to 6 inches shorter than
the width of the rolls. Any oil or grease ejected from the bear-
ings will thus be allowed to fall clear of the board ; and defects
due to oil streaks, etc., will be very much diminished, if not
entirely obviated.

This point in connection with the damage possible by the
existence of wide trays is commended to the notice of manu-
facturers of machines for plantations, as it is common to find
that trays are made which contravene the rule prescribed by
experience. In fact, trays on some machines have been so
designed as to act as " traps " for all dirty matter exuding from
the bearings. Not only so; they are sometimes made of such
a shape and height that oil or grease lodging upon the edges
act as a " wipe " to the rolls, thus increasing the possibility
of contamination. Until this defect was investigated, it was
common to note continued contamination of pale crepes in spite
of all precautions taken in cleaning the rolls at frequent inter-
vals. The trouble due to this cause is intensified when the
same machines are employed for the preparation of scrap-
rubber crepes and No. i crepe. Small pieces of scrap find
their way towards the bearings and lodge on the edges of the
trays. Unless a thorough inspection is made before proceeding
with the working of the No. i (pale) grade, contamination may
be continuous.

DIRT. — Streaks due to the presence of dirt (as apart from oil
or grease contamination, or that due to pieces of oxidised scrap)

228 PREPARATION OF PLANTATION RUBBER

are unusual, and when they do appear their origin seems to be
somewhat of a mystery. It could scarcely be advanced that
the dirt was picked up on the machines, as it is difficult to ima-
gine where such dirt could come from. In one or two instances
there has been fairly clear evidence that the dirt was contained
in the coagulum, and the only explanation fitting the case is
that it fell into the latex after straining and during the course
of coagulation. On cutting open lumps of coagulum brought
in from the field division, it has sometimes been noticed that
dirt is included, and the foregoing explanation is the only
reasonable one. How it was possible for dirt to get into the
latex must be left for explanation to those better acquainted
with the conditions under which the latex was coagulated.

HOLES. — On some estates it would seem impossible, with the
existing machines, to make really good crepe. The complaint
is that, if thin crepe is attempted, it is invariably found to be
" full of holes"; and as, apparently, the presence or absence
of small holes in crepe rubber is a factor which influences
buyers, this defect must be avoided at all costs. Why this
matter of small holes in thin crepe should weigh so heavily
with buyers is a matter which the writers are not in a position
to explain. As a matter of fact, the presence of small holes is
most generally an indication that the rubber has received the
minimum amount of working on the rolls consistent with good
washing. Further working would only be undertaken with
the idea of so consolidating the rubber as to get rid of holes in
order to meet the market scheme of valuation.

This is usually achieved by making a very thin crepe and
rolling together two lengths when wet. The resulting crepe
may be slightly thicker than ordinary, and the method employed
may be usually detected by the appearance of the edges unless
these are trimmed.

GREENISH AND TACKY STREAKS. — Occasionally one meets
cases in which pale crepe exhibits streaks varying in colour
from a decided green to an almost black in which the greenish
tinge is scarcely perceptible. Experience indicates that these
streaks are much more dangerous than they appear super-
ficially, inasmuch as they contain traces of brass from the

DEFECTS IN CREPE RUBBERS 229

" liners " of the bearings. The presence of the copper in
brass is responsible for a gradual disintegration of the rubber,
commonly recognised as " tackiness." In fact, copper may be
said to be a " poison " to rubber, and every effort should be
made to avoid possible sources of contamination. The effect
may be proved easily and perceptibly by fastening together
several pieces of crepe rubber by means of a brass " paper-
fastener." In course of time a salt of copper, green in colour,
will be formed, and it will be found that the portions of rubber
in contact with the fastener have " perished " and become
tacky.

This contamination of crepe rubber may take place in two
ways :

(1) By the ejection of actual particles of brass from the
bearings of machines, due to eccentric grinding of the
" standards " of the rolls upon the brass " bushes." These
particles are carried by exuded oil or grease into trays, and
thence to the rubber.

(2) By the action of an acid lubricant upon the brass, with
the formation of a metallic soap which has a decided green
colour, unless obscured by the dark colour of the oil or grease.
It is transferred to the crepe rubber in the manner indicated
above.

The inevitable effect, apart from the superficial defect, is
incipient tackiness. The extent to which this may develop
will depend upon the amount of the copper compound present,
but it should be remembered that an exceedingly small trace
is capable of causing a disproportionately large amount of
damage. This effect is further magnified if the " tacky " piece
of rubber is packed in close contact with previously unaffected
rubber.

When the defect is discovered, the affected portions should bo
cut out, and the cuttings should be burned. To mix them
with the lowest scrap grades, as may be done thoughtlessly,
is only inviting further trouble.

Besides the source of danger already indicated, it may be
found, but far less frequently, that contamination may arise
from the presence in the rubber of small pieces of the brass
mesh which is generally used for straining latex.

230 PREPARATION OF PLANTATION RUBBER

The view appears to be held in some quarters that these
tacky streaks and patches in crepe rubber may arise from
contamination with oil or grease alone. This does not agree
with our experience. An experiment was made to test the
point using fresh oil and grease drawn from drums in stock,
specimens of the same lubricants to which traces of a copper
salt were added, and samples of lubricants taken from the
bearings of several machines . The treated pieces of rubber were
placed in contact with untreated pieces of crepe which served as
" blanks."

Notes were made at intervals extending over a period of two
years. The conclusions arrived at were :

(1) Although there was surface discoloration, no tackiness
had been caused by fresh (unadulterated) lubricant; neither
were the " blanks " affected.

(2) In the majority of specimens upon which had been
smeared a small streak of lubricant taken from the bearings
of machines, tackiness had supervened, and had developed
likewise in the contact " blanks."

(3) In all cases where a trace of copper salt had been used to
adulterate the fresh lubricant, tackiness was to be noted in
the course of a short period (a week upwards) after the rubber
was dry. Development was slow, but progressive, over the
full period of experiment, and the " blanks " in contact were
affected. The degree of affection was determined by the
proportion of copper salt employed. In the worst cases the
affected strip of rubber had deteriorated and disintegrated to
such a degree as to cause a distinct longitudinal gap, the edges
of which appeared to consist of a moist gummy substance of a
deep syrup colour. The adjacent blanks in some cases ex-
hibited a similar appearance in lesser degree, or were merely
affected by a characteristic brownish stain.

These observations regarding the possibility of damage to
crepe rubbers from the existence of brass " liners " or " bushes "
in the bearings of the machines lead to the natural query as
to whether the use of brass is necessary. Experience shows
that it is not necessary. Machines in use for years have been
running with plain bearings of iron or other metallic sub-
stances. Satisfaction is obtained without the use of brass.
COTTON AND OTHER FIBRE. — One of the most frequent

DEFECTS IN CREPE RUBBERS 231

complaints made against low grade crepes is the presence of
fibre — generally classed in a wholesale fashion as " cotton-
waste."

It is true that some years ago most of the complaints were
genuine in referring the cause to cotton- waste. The defect
arose chiefly owing to the careless use of this material in the
factory. Lumps of waste when discarded were often thrown
to the ground, and became mixed with the heaps of scrap
rubber and bark-shavings awaiting attention. The fault was
one of sheer negligence, and nothing can be advanced in ex-
tenuation. Even when the soiled waste was thrown into the
external drains, it often returned to the factory mixed up
with the scraps of rubber recovered by means of the drain-
screens.

As far as the complaint concerns itself with cotton-waste
only, the remedy is plain, and lies in the power of the manage-
ment by reason of the ability to restrict the use of " waste "
only to the engine-drivers and mechanics.

In the vast majority of cases, however, the defect arises from
circumstances beyond the direct control of the factory, and
under conditions which make it difficult to check the evil.
Although against instructions, and for the purpose of fulfilling
other orders, some coolies persist in using pieces of cloth for
cleaning cups . In course of time , unless the practice is detected ,
this cloth becomes coated with rubber. Careless coolies throw
it away, when it may be collected by the individuals who
gather earth-scrap ; or it may be brought into the factory in the
tappers' scrap-bag.

Cases have been known in which the fibrous matter observed
in the dry crepe rubber was of such a nature as to indicate that
the source might be attributed to leaf-stalks which had passed
through the scrap-washer. It is an easy matter to condemn
the sorting as being careless, but it is another matter to instil
into the mind of factory coolies such a respect for easy and sane
precautions that the practice of them will be continued when
the eye of the supervisor is not fixed upon the workers.

It will be clear that contamination by fibrous matter should
be limited practically to the lowest grades of rubber.

232 PREPARATION OF PLANTATION RUBBER

The appearance of cotton-waste in high-grade crepes must
be most unusual, and the writers have not yet seen a case in a
drying-house. That it does occur, however, seems to be evi-
dent from brokers' reports. It is extremely difficult to imagine
how the waste enters the rubber. One possible explanation
is that a coolie may have been cleaning the rolls surreptitiously
with waste, which may have passed later into the rolls together
with rubber. Another explanation was offered in one factory
by the observed fact that coolies engaged in cutting up coagu-
lum, ready for passing into the machines, kept a wad of waste
for the purpose of keeping the knife-blade clean. This may
have found its way into the rolls. It must be recorded that in
the course of many years of experience no case has been seen
in any drying-house of contamination of the higher grades of
crepe by fibrous matter.

BARK AND GRIT. — With ordinary machines and the usual

process of working, it would seem impossible to wash and

macerate some of the scrap rubbers sufficiently to free them

entirely from bark. This applies specially to the grade of

rubber prepared from bark-shavings. Specimens have been

handled in which it was practically impossible to detect bark,

but in such instances the amount of working necessary would be

such as to interfere seriously with the regular working of the

factory. Even with the employment of special scrap-washing

machines, complaints of the presence of bark in dry crepe have

been received, but it is certain that this mode of operation

reduces the quantity of bark to a minimum. While fully

realising that the amount of working it is possible to give in

proportion to the existing machinery and the output per day

is limited, it must be recognised that the working of lower grades

of rubber is usually insufficient, and that where possible it is

the duty of estates to pay more attention to these lower grades.

A considerable improvement in this direction has been noticed

of recent years. It is not uncommon to encounter managers

who fail to appreciate that complaints regarding the presence

of bark in the lower grades are founded on legitimate grounds,

and that they are not frivolous objections put forward for the

purpose of depressing the price of the article. The sooner such

DEFECTS IN CREPE RUBBERS 233

an idea is jettisoned the better. There would appear to be a
good future demand for the lower grades, and it is only natural
that consumers will be willing to pay the best price only for an
article which is clean.

The same arguments apply to the complaints regarding the
presence of sand and grit. The quantity of the latter found
in low-grade crepes from some estates is surprisingly high.
Its presence can often be shown by the simple device of spread-
ing a piece of crepe over the upturned and hollowed palm of
one hand, while striking the rubber with the other hand.

The incidence of bark in higher grades of crepe may be due
to inadvertence or to gross negligence. In the former class
one might put those occasions on which pieces of bark are em-
bedded in lumps of naturally coagulated rubber. A piece of
bark-shaving may fall unnoticed into latex and be partially
responsible for the coagulation which takes place. This piece
of coagulated lump may be massed with others, and hence,
unless each small piece is cut up, the bark is not perceived.
Or again, by some unknown means, a piece of shaving may drop
into a jar of latex, and so become embedded in the coagulum.
Sometimes this becomes evident on cutting up the rubber,
but it is quite as likely to pass unseen. On the whole, the
presence of bark in first-grade rubber is most unusual, and
should be seen before the rubber is packed.

In the class due to negligence may be included cases in which
careless coolies place the cup upon the ground before tapping.
Pieces of shavings fall into the cup, and coolies are too lazy to
pick them out. More often than not coagulation in the cup is
caused. As it is impossible for the European staff to supervise
each individual tree tapped, some cases must continue to pass
unheeded. Sometimes bark-shavings are brought in with the
latex, and if a broken sieve is being used, these, with other im-
purities, pass into the jar, and are embedded in the coagulated
rubber. This must be classified as negligence, for no manager
would willingly allow the use of a broken sieve. Again,
naturally coagulated lump rubber on arrival at the factory some-
times contains evident pieces of bark, leaves, and stems of leaves.
For lack of supervision the average coolie would not think of

234 PREPARATION OF PLANTATION RUBBER

picking out these obvious impurities, and would pass the whole
mass into the machines.

OXIDATION STREAKS. — Since the introduction of sodium
bisulphite defects due to streaks, caused by portions of the coagu-
lum becoming oxidised, have practically ceased to exist. In the
usual course, and without the use of an antiseptic agent, the
freshly coagulated rubber has a surface darkened by oxidation.
Unless this dark surface were carefully cut off, there would
result a crepe containing dark streaks caused by the mixture
of the oxidised surface portion with the bulk of the paler
coagulum. The presence of oxidation streaks in No. i crepes,
now being made, would imply either that no anti-oxidant sub-
stance was in use, or that the quantity necessary to prevent this
surface oxidation is exceedingly small. Although the price
obtained would appear to be influenced by the presence of
oxidation streaks, no evidence can be obtained that the actual
quality of the rubber suffers to the same degree as does the
appearance — i.e., there is no evidence to-show that a pale rubber,
in which surface oxidation has been inhibited, is intrinsically
superior to one in which slight natural oxidation has been
incident.

" YELLOW LATEX " STREAKS. — This appearance of " yellow-
latex " streaks in not common, and may be accounted for by
incomplete mixture of two different latices. It is a fact of
common observation that, when a new portion of bark is
being tapped for the first time, there is a distinct yellow tinge
in the latex excluded. As tapping progresses, this colour
vanishes ; usually it may persist for a period varying from two
weeks to more than a month. Should this latex be poured into
ordinary latex without thorough mixing, it is sometimes found
that, when the crepe rubber is dry, there are distinct yellow
streaks. It should be remembered that, as the rubber content
of the latex from first tappings is high, this latex is lighter
than latex which is more dilute, so that the mixed latices must
be well stirred with a broad paddle to obtain intimate mixture.
It would be much better to keep yellow latex apart, and coagu-
late it separately, if at all possible. In such case the resultant
crepe may be of a distinct canary yellow in tint.

DEFECTS IN CREPE RUBBERS 235

In scrap-crepes of the higher grade this distinct yellow colour
is often visible in streaks which indicate the presence of
tree-scrap, etc., obtained from recently opened tapping areas.

BISULPHITE STREAKS. — These, again, -arise from defective
mixing. In the dry rubber it is seen that there are streaks of
colourless rubber in a general mass, which may be of varying
shades of yellow; or, a length of exceedingly pale rubber is
apparently streaked in patches with a darker shade of colour.
A solution of sodium bisulphite is heavier than latex, and there
would be a tendency, therefore, for the chemical to sink in
the large mixing jar. Unless stirring is thorough it is possible
that portions of the latex would not be in contact with sodium
bisulphite while others receive more than a fair share. Espe-
cially would this effect be seen where coagulation takes place
quickly, and experience bears out the truth of the suggestion.
Another factor which has some bearing on the point is the
strength of solution in which sodium bisulphite is used. In
the ordinary course of working, the acid coagulant is added
immediately after sodium bisulphite has been stirred in.
Should a strong solution of the bisulphite be used, and if coagu-
lation takes place quickly, it is easy to see that the possibilities
of obtaining a uniform and intimate mixture are small. Prob-
ably in no factory is the sodium bisulphite now added to latex
in powder form, but it has been found that if care is not taken
to see that all the bisulphite has dissolved before the solution
is added to latex streaks may result in the dry rubber. The
undissolved particles sink to the bottom of the coagulating jar
or tank, and there slowly dissolve, forming local strong solu-
tions. The effect upon the rubber in the vicinity of these
strong solutions is much more marked than in the bulk of the
coagulum, and hence lighter streaks or patches appear in the dry
rubber. In spite of apparently complete mixture by good
stirring, it will be seen that it is possible, therefore, to have
failed in this direction if any undissolved powder remains in the
solution of sodium bisulphite.

" SPOT " DISEASE. — Few managers of estates preparing pale
crepe rubbers are unacquainted with this defect. It is mani-
fested by the appearance of small coloured spots varying in

23 6 PREPARATION OF PLANTATION RUBBER

density (i.e., number to a unit area) and differing in hue. The
most common colours are black and orange, but " spots "
of brick-red, yellow, violet and ruby and green tints have been
noted, the last named very seldom. Sometimes in place of
definite " spots," or colonies, the colour is spread over practi-
cally the whole surface of the rubber as a " flush."

These coloured spots, or " flushes," indicate infection by
minute fungi, which are present in the latex prior to coagulation.
The infection of the latex takes place in the field by means of
spores, which are only visible with a microscope.

It is not feasible to discuss any method of preventing this
infection of latex by air-borne spores, as the eventual preventive
measures are so simple. But it may be believed that under
ordinary weather conditions most latices are infected before
reaching the factory. It is likewise true that even fine pale
crepes shipped in perfect condition may contain possibilities
of trouble in the form of " dormant " spores, the development
of which may commence and continue if favourable conditions
arise.

The subject of " ' Spot ' Diseases " has been treated fully in
previous publications,* and it is not proposed here to enter
into any lengthy discussion.

If any reader is desirous of producing the defect experimen-
tally, all that is necessary is to prepare a piece of crepe rubber
of rather more than ordinary thickness, roll it up while wet,
and place aside for some days.

This experiment reproduces the conditions favourable for
the development of the spores, and spots of various colours
may result. It will be clear that the chief factor influencing the
result is the continued presence of plenty of moisture.

This condition may be created inadvertently in the course
of factory practice, if piles of crepe rubber are allowed to
remain for any appreciable period before hanging to dry.
For this reason batches of wet crepe should always be placed

* "Preparation of Plantation Rubber," Sidney Morgan, 1913.
" Spotting of Plantation Rubber," Keith Bancroft, 1913; Bulletin
No. 16, F.M.S. Department of Agriculture. " Spotting of Prepared
Plantation Rubber," A. Sharpies, 1914; Bulletin No. 19, F.M.S.
Department of Agriculture.

DEFECTS IN CREPE RUBBERS 237

THREE SPECIMENS OF FINE PALE CREPE SUFFERING FROM
" SPOT " DISEASE.

238 PREPARATION OF PLANTATION RUBBER

on edge, to allow free drainage of surface moisture, if the rubber
cannot be taken at once to the drying-sheds.

The condition also is provided if the thickness of the crepe
is excessive. In some factories, having no smooth-roll finishing
machines, the crepes may have a distinct raised pattern upon
them. It is usual to note that if " spot " disease appears in such
crepes, it is incident to much greater degree in the thicker
portions of the rubber — i.e., upon the raised pattern.

The direct connection between the rate of drying and the
appearance of coloured spots or flushes is thus established, and
it only remains to adopt precautionary measures which will
lead to an avoidance of delay (i) between machining and
hanging, (2) in drying.

It is indicated, therefore, that, if spot disease is to be avoided,
the prime consideration is the preparation of a thin crepe which
will dry quickly under average conditions. It may sometimes
happen that even very thin crepes will sometimes be found
affected on some estates. In such instances, it will be found
that the design or situation of the drying-house is at fault, and
that specially favourable conditions for the development of
the fungi have been created by excessively wet weather.
Should the trouble persist in spite of the preparation of the
thinnest crepe, it would be advisable either to abandon this
form of No. i product or to consider the installation of artificial
aids to drying.

We have not yet encountered any case in which it was found
necessary to treat the latex with an antiseptic or disinfectant
substance for the prevention of " spot " disease. There appears
to be an idea held in some quarters that sodium bisulphite
may be so employed as a fungicide. This does not agree with
our experience , which is confirmed by Sharpies (Bulletin No .19,
F.M.S. Department of Agriculture).

In 1913 experiments with chinosol were undertaken at the
Pataling Laboratory of the Rubber Growers' Association, and
an account of the method of treatment was given in a printed
report issued to subscribers. Dr. P. Arens,* of the Malang

* "Guide to the Preparation of Rubber," Arens, 1918; Com-
munications from the Experimental Station (Malang, Java).

DEFECTS IN CREPE RUBBERS 239

Experimental Station (Java), has also recommended the use
of chinosol. The substance is expensive, but is effective
in very small quantity. On the whole, given average condi-
tions in factory practice, such aids should not be necessary,
and where keen supervision is not available may lead to other
difficulties.

It has already been remarked that it is possible for " spot "
disease to develop in dry rubber which previously gave no
evidence of the presence of fungi. The condition necessary
to such an occurrence is supplied by the presence of moisture.
Thus, to state instances which are by no means uncommon,
if a box of rubber is allowed to remain exposed to rain, or is
damaged by flood-water, or by sea-water during transit, or
(sometimes) if the rubber is packed in a damp case, the crepe
on arrival at its destination may be found to be affected to a
degree dependent upon the extent of wetting and the duration
of the wetting period.

No means are known by which these coloured spots, due to
the growth of chromogenic organisms, can be removed from the
rubber. Naturally, although they may be present in the darker
lower grades of crepe, they are not so easily visible as in pale
crepe. It follows, therefore, that every possible precautionary
measure must be taken when pale crepe has to be prepared.

We are often asked whether it is possible for an infected piece
of rubber to affect sound rubber hanging in the same building ;
and whether, in case of " spot " disease appearing, it is necessary
to disinfect the drying-house.

In a general sense, the answer to both queries is in the nega-
tive. It has not been proved possible to transmit the disease
from one piece of crepe to another, except by the closest possible
contact and in the presence of an abundance of moisture.

A dry crepe, even when in close contact with an infected
dry specimen, has not been found to be affected.

Unless, therefore, pieces of rubber are pressed together,
under favourable conditions as to moisture, there has been
observed no transfer of disease.

Similarly it has not been found that the presence of spotted
rubber in one part of the drying-house has been responsible for

240 PREPARATION OF PLANTATION RUBBER

an outbreak of disease in another part of the same building.
Furthermore, after the removal of diseased rubber from the
drying-shed, freshly prepared rubber may be hung on the same
supports without becoming affected, and without any inter-
mediate treatment of the wooden bars, providing the crepe is
thin and weather conditions are good. In our experience,
no case has been observed in which the disease has been com-
municated to freshly prepared rubber by reason of the previous
presence of affected rubber. In our opinion, therefore, any
scheme for disinfecting the interior of a drying-house, as a
preventive measure against the spread of " spot " disease,
is unnecessary.

All other things being equal, it is plain that much will depend,
as to the incidence of coloured spots, upon the design and
situation of the drying-house. Sufficient has been written in
previous chapters to indicate the importance of these points
as affecting the rate of drying, upon which hinges the possi-
bility of the appearance of " spot " disease.

In conclusion, the chief points in any discussion of this sub-
ject may be summarised thus:

1. No coagulum should be left without working for longer
than the ordinary period. Otherwise, the prevailing conditions
are very favourable for the development of the disease.

2. Thin crepe only should be made. The quicker the rate
of drying the less possibility is there of the coloured spots
appearing.

3. Crepe should never be allowed to remain folded over-
night, and batches of folded wet crepe should be placed on
edge to drain off surface moisture. The rubber should be hung
to dry as soon as possible.

4. Several species of fungi causing coloured spots have been
recognised, and it has been proved conclusively that it is possible
to infect latex and also fresh coagulum.

5. As far as our present knowledge goes, it appears that
infection takes place. chiefly, if not entirely, by means of the
latex in the field- vessels. It may take place during transport
also, or even during coagulation.

6. While it is certain that infection can be caused by contact,
it has not yet been shown that infection of the finished wet
rubber takes place in the drying-houses by means of air-borne
spores — at least, under ordinary drying conditions.

DEFECTS IN CREPE RUBBERS 241

7. There is reason to believe that no further infection takes
place once the rubber is well into the drying stage, and that dry
rubber is not infected even by contact. From this one might
infer that, as long as rubber remains dry, infection cannot take
place during the voyage to the port of consignment.

8. Coloured spots do not appear until the rubber is about
half dry, because that period is necessary for the development
of the fungus to that stage in its life-history when it excretes
colouring matter. The fungus in its earlier and colourless
stage may have been present from the time the latex entered the
cup.

9. The natural habitat of the fungi would appear to be de-
caying vegetable matter in the field.

10. Finally, if it is found impossible to be rid of fungoid-
spot disease after having exercised all care and observed all
known precautions, nothing remains but to supersede the
ordinary drying process by some system of quick drying, such
as the vacuum-drying process or a hot-air draught system,
in which the rubber dries so quickly that any possibility of
appearance of " spots " is entirely removed.

SURFACE MOULDS OR MILDEWS ON CREPE RUBBER. — Defects
of this nature are most uncommon in the higher grades of crepe
rubber, but cases of affection in the lower grades are not rare.

It will be evident from all previous discussions that the
incidence of these moulds must be due to an extremely slow rate
of drying. The necessary conditions would be supplied by
one or more of the following causes :

(a) Making the crepe too thick.

(b) Hanging the crepe in a badly ventilated or badly situated
building.

(c) Occasionally by abnormally wet weather.

(d) Allowing piles of crepe to remain too long before hanging.

(e) Using excessive quantities of deteriorated sodium bi-
sulphite. In short, any factor contributing towards a retarded
rate of drying may be responsible for the appearance of
surface mildews. The last mentioned cause is of not infrequent
occurrence. Knowing the chemical to be of poor quality,
relatively more is used to produce the desired anti-oxidant
effect. Unless the rubber is particularly well washed on the
rolls, there remains within it a residue of sodium bisulphate,
an oxidation product of the bisulphite. This is hygroscopic
to some degree — i.e.t it takes up moisture from the atmosphere.

16

242 PREPARATION OF PLANTATION RUBBER

Hence drying is delayed, and even should mildews not develop
the chemical may sometimes be seen on the surface of the
rubber as a whitish " bloom."

The enumeration of the possible causes of mildews on crepe
rubber is sufficient to indicate the necessary precautions to be
taken, and the discussion will not be extended further.

TACKINESS IN RUBBER. — •" Tackiness " is a term used to
denote a deterioration of rubber which renders it sticky, and,
beyond this, implies that some physical and chemical change
in the nature of the substance has taken place. In fact, it is
no longer " rubber," but an oxidation product containing much
resinous matter. It does not behave as rubber, and hence
its value is much depreciated.

With modern ideas of erection of factories to guard against
the introduction of direct sunlight, it was hoped that this defect
had practically ceased to exist. In one grade of rubber it would
be expected that tackiness would continue to appear. Earth-
rubber, often exposed to direct sunlight for a week, would
naturally become tacky, and this tackiness cannot be avoided
unless the earth-scrap is to be collected more frequently. But
in many cases even the higher grades of rubber show signs of
tackiness. Experiments have been carried out at various times
and in various places to determine the cause of tackiness. For
some time the theory of bacterial origin was in favour, but none
of the experimental results was convincing. Bacteria may be
present in tacky rubber; but, on the other hand, many cases of
bacteria in rubber have been observed in which there was no
tackiness. Experiments were made by one of us some years
ago with a view to testing the bacterial theory by inoculating
latex with small pieces of tacky rubber. In opposition to the
results which were stated to have been obtained, there was no
spread of tackiness. Other investigators have obtained similar
results. One writer proposed to explain tackiness as caused
by excess of moisture. This perfectly simple explanation un-
fortunately displays only a profound ignorance of the subject,
and does not take into account the fact that tackiness is incident
in rubber after dryness has been reached. It need not be
pointed out to planters in Malaya that wet sheets of rubber

DEFECTS IN CREPE RUBBERS 243

are often exposed to direct sunlight by workers of native
holdings, with no resulting harm as long as plenty of moisture
is present in the rubber.

TACKINESS THE RESULT OF A SLOW PROCESS OF CHANGE. — As
stated above, tackiness does not appear until the rubber is
dry, and even then it is to be noted that it is possible for tacki-
ness to appear in rubber arriving in London, which showed
no indications of tackiness when packed for shipment.

TACKINESS CAUSED BY TRACES OF COPPER SALTS. — Spence,
as the result of investigations, has pointed out that none of the
various theories put forward to account for tackiness — viz.,
the action of bacteria, premature putrefaction, oxidation,
excess of moisture, the action of enzymes, etc. — have any
basis in scientific proof, and believes that the cause of tackiness
cannot be directly attributed to bacteria. It has been stated
that the only known way of causing rubber to become tacky
is to expose it to sunlight or heat. While agreeing that in the
ordinary way this statement is correct as far as one rules out the
employment of chemical substances, it must be pointed out
that tackiness of the worst degree may be caused by the presence
of traces of copper or copper salts. This point has already
been touched upon in a preceding paragraph dealing with the
defect of " green streaks " in pale crepe rubber.

In the course of laboratory experiments tackiness has often
been induced by the use of traces of copper salts. The rate
at which tackiness is induced appears to be dependent upon
the amount of copper salt used, but once it begins, the rubber
molecule is very rapidly broken down, and resins are formed.
As the formation of resins is accompanied by the inclusion of
oxygen in the chemical constitution, it would be expected
that dry rubber becoming tacky should increase in weight.
This is found to be the case, and to give an idea of how this
weight increases with the progress of tackiness, the results
below may be studied.

It will be seen that the maximum quantity of copper sulphate
used amounted to 0*025 Per cent- (approx.) upon the weight
of latex taken. Now it is highly probable that only a fraction
of this quantity was retained in the rubber on coagulation,

244 PREPARATION OF PLANTATION RUBBER

the remainder being in solution in the serum. Furthermore,
as the rubber was well washed and worked down to thin crepe,
the total quantity of copper salt remaining in the dry crepe must
have been exceedingly small. Yet the effect is most marked and
should impress upon all managers the necessity for guarding
against any possible contamination caused by brass or copper.

Weight of Rubber.

-Si

•fc,

|

Amount of Copper Salt.

After

Further

Further

Percent-

«

When

Interval

Interval

Interval

age in In-

0)

Dry.

of Four

of Seven

of Three

crease in

Weeks.

Weeks.

Weeks.

Weight.

Grms.

Grms

Grms.

Grms.

I

o'O2 grms. copper sulphate,

per 100 c.c. latex

430

441

482

488

I3-5

2

Ditto

428

439

481

486

I3-55

3

o-o i grms. copper sulphate, \
per 100 c.c. latex. .
o-o i grms. copper acetate, j

962

987

i°35

1036

7'7

per 100 c.c. latex . . J

4

0-025 grms. copper sulphate,

per 100 c.c. latex. .

502

513

558

560

H'5

In view of the effect thus produced by the addition of traces
to latex of a copper salt, and the observed effect on rubber of
contact with copper salts, one may imagine the result produced
some years ago when on an estate smoked sheets were washed
with a solution of copper sulphate as a remedy for surface
moulds !

With the exception of this chemical action we know of no
other means by which tackiness is produced, beyond those of
direct sunshine and heat. Cases governed by these two causes
are common on estates. They are confined chiefly to the lowest
grades of scrap rubber, when the component raw materials
have been exposed to the sun for a period before being brought
to the factory.

It is now comparatively rare to find cases of tackiness in the
higher grades of crepe, and when they occur, one may look
for evidence of gross carelessness in the admission of direct
sunshine. Usually this means the failure of some individual
to regulate window shutters according to the position of the

DEFECTS IN CREPE RUBBERS 245

sun in the sky. More rarely does it happen that tackiness may
have been induced by placing thin crepe rubber too near the
iron roof of the drying-shed.

Regarding the question as to whether tackiness may be com-
municated by direct contact, opinion appears to be divided.
It has been stated that sound rubber left in contact with tacky
specimens was found to be unaffected after two years. On the
other hand, it is claimed that tackiness has been induced in a
sound rubber by infecting it with small pieces which were
tacky. In a preliminary article on the effect of copper and
copper salts upon pieces of dried and sound crepe* it was
noted, after one year, that tackiness had been communicated
from the treated portion to the " blank " in contact. There
is sufficient evidence to warrant the injunction that tacky
rubber should be excluded from contact with sound rubber.
If shipped it should be packed separately.

Compounds have been put upon the market which assumedly
claim to be cures for tackiness. These are merely palliatives,
consisting of starch, talc, or chalk powders, which counteract
stickiness.

No CURE FOR TACKINESS. — At the present stage of our
knowledge, there appears to be no cure for tackiness. Neither
do we see the necessity for a cure when the phenomenon may
be avoided by taking simple precautions, which may be briefly
summarised thus :

(1) Any permanent openings through which it is possible
for direct sunlight to enter, whether large or small, should
either be totally closed or provided with some substance which
cuts off the direct effect of the sunlight — e.g., ruby glass or
ruby glazed cloth.

(2) Rubber should under no circumstances be placed near
any source of heat.

(3) No rubber should be hung in a drying-room in such a
position adjacent to a window or door that it is possible for
sunshine to reach it, even should coolies neglect to obey rules.

(4) Instruments or vessels of copper or brass should not
be used where acids are employed.

* Report I., 1916 (Sidney Morgan), Rubber Growers' Association
(Malaya).

246 PREPARATION OF PLANTATION RUBBER

LACK OF UNIFORMITY IN COLOUR. — The complaint is far
less real than it was a few years ago. The introduction by
the Rubber Growers' Association of the " Metrolac " led to
uniform dilution of latices varying in rubber content. Pre-
viously the only known method of obtaining uniformity in colour
and appearance was that by which latices from all fields were
mixed together in bulk. Even so the uniformity applied only
to the one bulking operation, and any other day's results might
show considerable variation from the first standard.

This does not take into account any observed differences in
shade of colour attributable to natural oxidation which might
vary in intensity from day to day. The introduction of sodium
bisulphite as an anti-oxidant exerted a great influence upon the
colour of pale crepes generally ; but considerable variation would
still have been notable but for the adoption of the scheme for
uniform dilution, in addition to the use of small quantities
of anti-oxidant.

On most estates it is now possible, with slight exceptions due
to abnormal conditions, so to treat the latex that the pale
crepes prepared on any one day differ in no perceptible degree
from the product of any other day. Where this is not the
case it must be suspected that there has been some carelessness
in manipulating the latex or the chemicals. Attention has been
drawn to the fact that there may be exceptional cases, when the
determining factors lie beyond the control of factory processes —
e.g., heavy rains causing over-dilution of latex, the yielding of
" yellow " latex from newly opened areas, etc. But on the
whole there is now no reason why the general average product
from any estate should not be uniform in colour and appearance.
Furthermore, it should be possible for large groups of estates,
by the adoption of uniform methods, to produce similar rubber
from all the plantations. Moreover, apart from some dif-
ferences caused by factors which still need determination,
the total product in a general sense should not only be
uniform in appearance but uniform in physical and chemical
properties.

BLOCK RUBBER. — This mode of preparation is employed only
in comparatively few instances. The block is prepared from

DEFECTS IN CREPE RUBBERS 247

crepe rubber, which has been dried either in a hot-air drier
or in a vacuum chamber.

There is another type of block which is made by placing layers
of dry crepe under considerable pressure. This is not the
true type of block, and the layers are quite distinct — i.e., they
do not amalgamate. Usually this pressed rubber consists of
lower grades of crepe, and it should not be popular, inasmuch
as it leaves too wide an opportunity for the inclusion of dirt,
bark particles, and other impurities, which cannot be seen
generally on account of the protective colour of the rubber.

In the true type of block, the layers are in a plastic condition,
due to heat, when they leave the drying-chamber; and being
immediately submitted to great pressure the result is a homo-
geneous mass in which the layers disappear by amalgamation.
Only the best grade of crepe is employed, and given the absence
of defects in the layers there should be no complaint regarding
the final block.

Prepared in slabs which are three or four inches in thickness,
the product is easily handled, and should be sufficiently trans-
lucent to make it possible to distinguish the shape of the hand
when held between the block and the light. This is not possible
when blocks are made of greater thickness.

The only complaints which it should be possible to lodge
against block rubbers are:

(a) The inclusion of dirt and other matter.

(b) The use of layers of crepe which have some defect.

(c) The inclusion of air-bubbles.

The remedy for (a) and (b) lies in the hands of the factory
superintendent. The last ground of complaint is dependent
upon the style of preparation of the original layers of crepe.

When layers of crepe are placed one upon the other, and sub-
mitted to great pressure, it is natural to suppose that air would
be contained in spaces, and would be unable to escape. To
guard against this, it would seem necessary to prepare the crepe
thin and with a fairly good surface finish.

It must be obvious to all acquainted with the processes
involved in the preparation of block rubber, that no possibility

248 PREPARATION OF PLANTATION RUBBER

exists for the presence of air-bells actually enclosed in thin
crepe. When the vacuum-dried crepe is folded preparatory
to the blocking process it is apparent that between the layers
there must always be a considerable volume of air, a small
proportion of which is bound to be retained owing to the nature
of the surface of crepe rubber.

That this has always been true of the preparation of block
rubber cannot be denied. It is possible, of course, for one type
of block to show the presence of air-bells more than another
type, the proportion of air enclosed in blocking depending
upon the nature of the crepe of which the block is composed.
A block built up of layers of smooth, fine crepe would be ex-
pected to contain less air-bells than a block composed of layers
of a rough crepe.

Block rubber has been seen which was free from air-bells,
but this was the thin variety of block prepared for show
purposes with far greater care, probably, than would be
expended in commerical preparations.

CHAPTER XVIII
DEFECTS IN SHEET RUBBER

BEFORE proceeding to deal with defects in the rubber as it is
put upon the market a brief account will be given of faults
which may be noted in the preparatory stages.

MILKY RESIDUE OR SERUM. — If the serum is not clear after
the ordinary period allowed for coagulation, it indicates one of
the following possible causes:

(a) Failure to obtain complete mixture by thorough stirring.

(b) Insufficiency of acid solution. This may be real or
indirectly due to the presence of an excess of anti-coagulant
such as formalin or sodium sulphite.

(c) In cases where other coagulants than acetic or formic
acids have been employed the failure may be due to an excess
of, or an unsuitable, coagulant — e.g., hydrochloric acid.

COLOURED SURFACE BLOTCHES AND UNPLEASANT ODOUR.—
Sometimes the surface of the coagulum exhibits yellowish or
bluish streaks and patches. It will be found generally that
the yellowish colour is possessed by a slimy substance, of
offensive odour, which may be scraped from the surface.
Either insufficient acid has been used, or the mixing of latex
and coagulant has been at fault.

DARK DISCOLORATION OF THE RUBBER. — This may be stated
to be a natural process when fresh rubber is exposed to the
atmosphere. It is usually described as " oxidation," and it
will be noted to be absent, or to occur to less degree, on those
portions of the rubber which are protected from the atmosphere
by being below the surface of the remaining liquid. This
surface change may be prevented (see Chapters VIII. and IX.)
by the use of small quantities of sodium sulphite (for prefer-
ence) or bisulphite.

SOFT COAGULUM, SPONGY UNDER-SURFACE, TEARING OF
COAGULUM. — If the whole mass of coagulum is too soft, while

249

250 PREPARATION OF PLANTATION RUBBER

coagulation appears to be complete, over-dilution of the latex
has occurred. This may apply also to the case in which the
under-surface only is spongy and soft. If coagulating-tanks
are employed, the upper edge may be comparatively hard,
while the lower is soft and weak. Often the spongy portion
may adhere to the partitions. This prevents the natural
rise of the coagulum, due to retraction, as the mass " sets."
The pull between the free upper portion and the adhering
lower edge causes splitting and tearing of the coagulum, with
marked porosity (spongy appearance). The two factors to
receive attention are the standard of dilution and the condition
of the surfaces of the partitions. If these have minute cracks
into which latex can penetrate, and in which coagulation takes
place, the boards should be discarded. Given the conditions
indicated above, the tearing and splitting of rubber in coagulat-
ing tanks is sometimes augmented by the practice of flooding
the tanks when coagulation is judged to be complete. The
surface water finds its way downwards between strips of coagu-
lum and the partitions, thus increasing the upward tension
between the free and adhering portions. The main idea
governing the practice of flooding the tanks is to prevent
" oxidation " (darkening) of the upper edges. If a small
quantity of sodium sulphite is employed as an anti-oxidant
and to retard coagulation, it is not necessary to flood tanks.

" PITTING " OF SURFACES. — In pan coagulation this " pitted "
appearance is usually limited to the under-surface, while coagu-
lum prepared in tanks may exhibit the defect on both faces.
The existence of these numerous " pits," or small depressions,
points to the presence of bubbles of gas which have been un-
able to escape freely. As the formation and retention of gas-
bubbles is not a normal occurrence in coagulation, we are led
to infer that some special conditions must have arisen. These
may be supplied by one or more of the following contributory
causes :

(a) The latex had begun to " sour " before arrival at the
factory or while waiting to be treated. This premature coagu-
lation is usually checked or diminished by the employment of
anti-coagulants (see Chapters VIII. and IX.). It is generally

DEFECTS IN SHEET RUBBER 251

accompanied by the appearance of enclosed gas-bubbles in
the dry rubber.

(b) There may have been a slight insufficiency of coagulant,
or the admixture was not thorough, thus allowing a slow putre-
factive change to take place in the incompletely coagulated areas.

(c) The wooden partitions may not have been effectively
cleansed. The existence of a thin slime, of bacterial origin,
is sometimes noted. This is accountable for putrefactive
effects in the surfaces of the coagulum, or in the serum, giving
rise to the formation of gases. If these cannot escape freely,
by reason of adhesion between the coagulum and the partitions,
" pitting " occurs.

THICKENED ENDS OR EDGES, AFTER ROLLING. — As a rule
these defects may be ascribed to the employment of too rich
a latex, or faulty manipulation. Even if the standard of
dilution should be correct it sometimes happens that, in the
preliminary rolling of a long strip of rubber, coolies begin
in the middle, rolling with a forward pressure and tension
towards the ends of the strip. This is generally not so much
the fault of the coolie as being due to the lack of proper facilities
for preliminary rolling. The table should be about 3 feet in
height, so that ease of working is obtained merely by natural
pressure due to the position in which the worker stands. The
use of a heavy wooden roller would contribute towards this
result, inasmuch as it obviates the use of force, and the pressure
is almost entirely in a vertical direction.

MIS-SHAPEN SHEETS. — It is sometimes noted that sheets may
be wider and thicker at the ends than in the middle. Manipu-
lation alone, as indicated above, is not solely responsible.
The primary cause is to be traced to over- dilution of latex,
giving a very soft coagulum which responds too readily to
tension and pressure. Faulty treatment in rolling exaggerates
the tendency for the strip of sheet to become narrow and thin
in the middle, wider and thicker at the ends.

THICKENED PATCHES, TORN SHEETS, " DOG-EARS," CREASES.

—These elementary defects are all due to careless working.

While occasional errors cannot be avoided, there is no real

excuse for the continuance of trouble to any degree, under

average supervision.

Thickened patches are often caused in conjunction with torn

252 PREPARATION OF PLANTATION RUBBER

sheets, and the trouble may be ascribed to faulty practice in
allowing too heavy a pile of wet strips to accumulate before
machining. Or a comparatively small pile may have been
transported some distance. It is difficult to separate the strip,
and occasionally the separation is only effected at the expense
of two sheets, one of which is torn and the other has a portion
of the first strip adhering to it.

" Dog-ears " due to the folding over of corners of the sheets,
and creases due to the rumpling of the coagulum, are generally
the result of haste and lack of average care. Machine coolies,
more often than not, will not be at any pains to straighten out
folds before passing the coagulum through the rolls.

GREASINESS BEFORE SMOKING. — Under ordinary methods of
working this should never be encountered. It may be taken
to show that the machined rubber has been allowed to remain,
either hanging or in piles, far too long before entering the
smoke-house. The appearance is most marked if the rubber
has remained in a cool and moist atmosphere — e.g., if it has
been hanging over-night in a closed and badly-ventilated factory.
In a marked degree this is to be observed in the preparation of
air-dried sheets, unless they are exposed, when freshly prepared,
to the action of the sun for a period. This period, in the case
of rubber prepared on native small-holdings, generally extends
over several days — until the sheets are more than half dry.

In the preparation of smoked sheet, the greasy appearance
and the cause outlined contribute to a defect which is eventually
described as " stretching rusty."

SURFACE BLEMISHES. — The coagulum, during coagulation
and subsequently, can be contaminated in various ways. In
most cases a little intelligence or increased care would prevent
the occurrence of these defects.

When the coagulum remains over-night, in the absence of a
cover, it is not uncommon to note the presence of dirt (from the
roof above, or blown in from the outside), the droppings of mice
and rats, flies and small insects. In theory these should be
seen and removed by the factory hands. In practice, except
while under immediate supervision, the extraneous matter is
often rolled into the soft coagulum.

DEFECTS IN SHEET RUBBER 253

A fairly common cause of this surface contamination is the
exhaust from the power-unit ; generally the worst offender is a
steam-engine. Grit and smuts continually find their way into
the factory, alighting on the tables, in the latex, in the water,
and on the freshly prepared rubber. They are rolled into the
soft rubber and lead to marked depreciation in the selling value.
The radical remedy seems obvious, but is often beset with
many difficulties not unconnected with financial considerations.

Other superficial blemishes, such as those due to the presence
of rust marks, oil or grease patches, etc., are self-explanatory,
if a little thought is brought to bear upon them ; and it is not
proposed here to discuss such defects more fully.

Having now dealt with certain defects which are visible
in wet rubber, we come to the discussion of others which are
only perceptible either during or after the drying period. As
far as is known no plantations of any size now prepare sheets
other than in the form of smoke-dried rubber, with the exception
of a few which make a special form of thick and partially air-
dried product known as " slab " rubber.

It is not proposed, therefore, to treat in any detail with air-
dried sheet rubber. Certain obvious defects are common to
both air-dried and smoke-cured sheets, and these will be first
discussed.

UNEVENNESS OF APPEARANCE. — This lack of uniformity may
refer either to size or colour, or to both. Apart from any
other contributory causes, this variation is due, in pan sheet,
to a neglect to standardise the dilution of all latices, or to lack
of uniformity in the quantity of standardised latex placed in
each receptacle.

Where tanks are employed all sheets from the same tank
should be of the same size before rolling, and any subsequent
disparity in thickness and length must be attributed to some
alteration in the width of the gap between the rolls of the
machines.

Unless all latices are standardised by means of an instrument,
it is of course probable that the content of one tank may be
found to differ from that of another.

254 PREPARATION OF PLANTATION RUBBER

In a general sense, whether air-dried or smoke-cured sheets
are considered, a thin strip will dry more quickly than a thick
one, and should be paler in colour when viewed by transmitted
light — i.e., when the rubber is held between the eye and the
source of light.

It is necessary, therefore, to guard against the possibility of
variations in thickness caused by faulty manipulation. The
distance between the squeezing rolls (smooth) and between
the marking rolls (patterned) should be adjusted and should
remain set until the conclusion of work. In a factory having
nothing beyond average requirements in equipment of machines
it should not be necessary to have to interrupt the work of the
smooth rolls or " markers " by having to make adjustments.
This is, however, inevitable if there is only one smooth-roll
machine, as it is always desirable to reduce the thickness of
the coagulum by at least two stages through even-speed smooth
rolls. In some factories there are three light power-driven
smooth-roll machines, the gaps between pairs of rolls being
set so as to obtain a gradual thinning effect upon the fresh
coagulum, which is then passed once between patterned rolls.
With such equipment it is found possible, in some cases, to
omit the preliminary hand-rolling, and the strips of coagulum
from the tank are passed direct through rolls set with a wide gap .
This work demands much care, as it is necessary to avoid any
distortion of the coagulum which may be caused by its own
weight and length".

VARIATION DUE TO OXIDATION. — The subject of oxidation
has been mentioned in the opening paragraphs of this chapter.
It will have been learned that oxidation is a natural process,
and that it may be prevented by the employment of anti-oxi-
dants such as the sulphite or bisulphite of soda. In earlier
days it was sometimes prevented by steeping the thin rubber
in very hot water.

In the absence of an anti-oxidant the degree of oxidation may
vary daily and in different batches of latex on any one day, so
that there is always the possibility of a lack of uniformity due
to oxidation effects. This would be more evident in air- dried
sheets than in smoke-cured rubber, as in the latter case the

DEFECTS IN SHEET RUBBER 255

darkening of the surface would be masked by the colour induced
by the smoke-drying process.

To obviate this variation anti-oxidants are used on most
estates, but the accidental or misinformed abuse of these
chemicals may lead to further lack of uniformity. Hence it
is necessary to follow carefully the formulae prescribed by
experience.

COLOUR OF SMOKED SHEETS. — It may be of interest to note
that the effect known as oxidation is attributed to the presence
of micro-organisms called enzymes (ferments) in the latex. It
can also be produced artificially in various ways — e.g., by the
use of the crude product of wood-distillation (pyroligneous
acid) as a coagulant, or by the addition to the latex of small
quantities of a phenol such as carbolic acid. It is thus possible
to prepare in sheet form a rubber which has the appearance of
having been smoke-cured, although it may never have been in
a smoke-house.

It will be clear, therefore, that apart from other causes, the
colour of the cured sheets may be influenced by oxidation of
the fresh coagulation, and by the constituents of the smoke.
It follows that the smoke from timbers which are richer than
others in certain chemical bodies set free by combustion
will produce a rubber darker in colour.

There is thus no real connection between colour and period
of cure, although in a general sense the longer the interval
the darker the colour.

Similarly it is now plain that when anti-oxidants are employed
in excess the paleness of the rubber is in no degree truly indi-
cative of the period during which the rubber has been smoke-
cured.

The influence of the effect of the hypsical condition of the
wet rubber upon the final colour must be thoroughly grasped .
One may take two sheets of apparently the same thickness,
and smoke-cure them in juxtaposition \vithin the same house,
only to find that one dries much more rapidly than the other.
As a consequence, the first, when fully cured, will be of a medium
golden brown colour; while the other, owing to protracted
smoking, will be dark. Evidently there must be some distinct

256 PREPARATION OF PLANTATION RUBBER

difference between the two in physical condition prior to the
smoking. Here the factor involved is the rubber-content of
the latex. Given two pieces of coagulum of identical thick-
ness, but prepared from latices of different dry rubber content,
it will be obvious that to reduce them to similar thickness, more
pressure will be necessary in one case — i.e., that piece of coagu-
lum will be much more dense (more consolidated) — while the
other will be comparatively soft and porous. Into the latter
warm smoke can penetrate much more easily, and the internal
moisture can escape more rapidly. The full cure may be made,
say, within twelve days, while the tougher sheet may demand
up to twenty days.

To attain uniformity in colour, therefore, the following
points must be studied and controlled as far as is possible :

(a) Uniform dilution of all latices.

(b) Uniform dimensions of coagulating receptacles.

(c) Uniform volumes of standardised latex.

(d) Uniform quality and quantities of chemicals.

(e) Uniform methods of manipulating the coagulum.

(/) Uniform conditions of fuel and accommodation during
smoke-curing.

SURFACE GLOSS. — In the choice of fuel there is room for con-
trol if one has good timber available. This point opens up a
discussion on the vexed question of " over-smoking," as the
term is sometimes applied to a pronounced dry glossy appear-
ance of the surface of sheets.

Three main factors are involved:

(1) The nature of the fuel.

(2) The ratio between furnace capacity and the capacity of
the smoke-house.

(3) The rate of combustion.

Obviously any fuel which yields an excessive quantity of tarry
matter or creosotic substance would conduce to the formation
of a heavy glaze on the rubber. Such fuel, therefore, should at
most only be employed as the smaller portion in a mixture with
" dead "timber.

It is impossible to lay down any general rules for the guid-
ance of estates, as the timber available varies so widely in
nature. Experience must be the only guide, and it should not

DEFECTS IN SHEET RUBBER 257

be difficult to obviate the defect. Even so, there must be minor
differences between the results obtained on estates, so that it
is not possible to make strict estimations of the smoke-curing
period by an examination of the surface appearance of rubber,
even under the best of conditions. Some estates find that
the rubber has a distinct gloss in ten days, while others may
smoke-cure for twice that period without difficulty. Evidently,
therefore, the question of available fuel is of prime importance.
It may be remarked that very satisfactory results are always
obtained from the use of fairly dry timber obtained from thinned
rubber trees, mixed with the " dead " timber of old logs and
stumps found on the estates.

Obviously if a smoke-house has a superabundance of furnaces,
producing more heat and smoke than is required, glazing will
result. The point is tested by the average temperature main-
tained and the average rate of drying. The result of a high
temperature would be the possibility of volatile tarry matter
being driven in excess to the upper chamber. That this
effect is eventually produced even at optimal temperatures
is evident from an examination of the wood-work within the
upper room.

It is clear, also, that the rate of combustion exerts an influence.
In a general sense a rapid consumption of fuel would augment
the quantity of tarry matter passing into the upper chamber
over any given period, and the possibility of glazing would
be increased.

On the other hand, it is possible that a surface glaze might
be formed if the temperature were uniformly too low, especially
if the rubber were rather thick. The rate of drying would be
so slow, that if a timber rich in tarry matter were employed,
the rubber might be exceedingly glossy.

In order to guard against the appearance of a heavy glaze,
then, the following points must be observed:

1 . The fuel must be carefully selected by experience.

2. The sheets must not be thick. No sheets should be
thicker than J inch measured in average section across the ribs.

3. The temperature must not be too high. An average
working temperature of 120° to 125° F. should be ample.

258 PREPARATION OF PLANTATION RUBBER

4. If the sheets are fairly thick, a low average temperature
should be avoided. No lower average than 110° F. should be
allowed.

DULL, BLACK SURFACE. — This is the opposite of the previous
case, and generally is accompanied by a fairly heavy darkening
of the surface due to " oxidation " effects. The fuel used is too
" dead," and needs the addition of some substance containing
a fair amount of creosotic matter. The appearance of the
rubber does not justify the assumption that it has been over-
smoked. As a matter of fact, this type of rubber often becomes
affected by mildew fairly rapidly, thus showing that the
smoking has been inefficient.

It may happen that an estate is in the habit of using a fuel
which gives even to a thin sheet a heavy glaze in a compara-
tively brief period. The general custom is to soak such sheets
in cold water, and then to scrub the surfaces, sometimes using
soap, in order to cleanse the rubber and free it from the glaze.
This operation may be done too well, in which case the rubber
will have a dull appearance, and may be rather more liable to
develop surface mildew after a time.

MOIST GLAZE, GREASINESS OF SURFACE. — This describes the
condition of sheet rubber when taken from the smoke-house.
Sometimes the greasiness does not develop until the rubber
has been out of the smoke-house for a day or two.

As far as experience shows at present it may be due to two
causes :

(a) The use of an excess of sodium bisulphite or sodium
sulphite. The use of sodium bisulphite is not recommended
generally for sheet-making. It may cause the rubber to be too

?ale in colour, and the abuse of it may delay the drying unduly,
n the latter case, a trace of the salt may remain within the
rubber or upon the surface. If so, as the substance remaining
is fairly hygroscopic, it will take up moisture from the atmos-
phere and may cause the surface of the sheets to have a moist
and shiny appearance. The moist surface deposit comes away
upon the hand when the sheets are touched, and is difficult
to remove entirely. On some estates a very small quantity of
the bisulphite is employed, as it is found to be of service in the
prevention of bubbles, but in unskilled hands the method is open
to abuse, and is, therefore, not recommended for general use.

DEFECTS IN SHEET RUBBER 259

A large number of estates now use sodium sulphite in very
small quantities as an anti-coagulant and a preservative for latex
in the field. The abuse of this very useful substance carries
its own penalty. The substance is hygroscopic ; and if an ex-
cess is present the drying period will be protracted, and the
sheets will have a very moist surface film.

It may be found sometimes that only some of the sheets are
affected. This indicates that, whereas uniform quantities of a
solution of sodium sulphite have been served out in all fields,
the proportion may have been excessive in the case of fields
giving a latex of comparatively low rubber content. What suits
the latex from old trees may be excessive probably for the latex
of younger trees. This is not an infallible rule, as in the case
of older fields in which immature bark is being tapped, it is
to be noted that the dry rubber content of latex may be less
than that of latex obtained from younger trees.

This type of moist glaze is not easy to remove. Ordinary
surface washing had but a temporary effect, and the trouble
recurs. The only way of dealing with the difficulty is to soak
the sheets for days in running water (or in successive changes
of water) and to re-smoke until dry.

(b) The second type of moist glaze is not so difficult to deal
with, and may be removed as a rule by washing the sheets when
the rubber is otherwise apparently dry.

It appears to be mainly a matter of unsuitable fuel for smoking
and of failure to provide adequate ventilation. A large number
of estates have been " thinning-out " or are doing so systemati-
cally. The logs thus obtained are often used as fuel in the
very green stage. The smoke thus generated must be moist,
and if the building is entirely closed, this moisture must be
deposited eventually upon the rubber and racks. Some estates
have surmounted the difficulty by opening up the roof-ridge
slightly so as to allow the moisture to escape with some of the
smoke; but if the logs from rubber- trees are to be used, they
should be stacked in the sun for some time. Even then,
preferably, they should not be used alone. A judicious
admixture of dead and rotting jungle- timber appears to give
very satisfactory results.

VIRGIN SPOTS AND PATCHES. — If the description really
indicates the defect it simply means that portions of the sheets
are not dry. When cut they exhibit the typical whitish, opaque
appearance described as " virgin." It is doubtful whether
any rubber put upon the market as No. i product nowadays

26o PREPARATION OF PLANTATION RUBBER

can have this complaint levelled at it. In the extreme case
if points to gross negligence on the part of the packer.

Sometimes what are taken to be small spots of " virgin "
are really patches of tiny air or gas bubbles. The point can
be easily determined by cutting through the patch and examin-
ing the cut edges.

SURFACE MOULDS OR MILDEW. — During the last two years,
complaints regarding the incidence of " mouldy rubber " (t.e.t
relating chiefly to the presence of mildews on the surface)
have become increasingly common.

To judge by the comments of producers, who as a rule never
again see their rubber after it leaves the estate, one would infer
that the defect is imaginary, and that the complaints are made
solely with a view to repudiation of contracts or the general
cheapening of an article of commerce. They can often point
out, with a certain amount of truth, that there has been no
change in the methods of preparation or curing, and that
previously there were no complaints.

It is forgotten, however, that in former years the smaller
output of rubber was taken into consumption more rapidly than
of recent years. That is to say, the interval between smoke -
curing and the employment of the rubber in the manufacture
of goods did not demand such a long period of storage. Hence
the effects of smoke-curing are now more likely to vanish.

Going still further back in the history of plantation rubber,
we can point to the time when smoked sheets were allowed,
or had, to remain in the curing-sheds for very extended periods.
Loose specimens of rubber prepared during that decade still
exhibit no signs of mildew growth.

In later years a demand arose for sheets paler in colour than
the old type, and in order to meet that demand, a change had
to be made in methods. This led to a system of working
whereby it was possible to smoke-dry sheets thoroughly in
from twelve to fourteen days. This interval was further
reduced on many estates, until some were producing rubber
which appeared to satisfy all requirements after only five or
six days' curing. % This does not refer to the case of estates
having smoke-houses of " continuous- working " type, but to

DEFECTS IN SHEET RUBBER 261

those on which smoking was confined practically to the hours
of night. Under former conditions of rate of production
and consumption, this short period of smoke-curing would
possibly have been ample; but even this is very doubtful, as
often the rubber would not stand the relatively short journey
from the estate to Singapore without mildew-growth being
incipient. We have often received specimens of rubber sent
from estates for criticism, and have noted that within a compara-
tively brief period mildew was to be seen.

The whole matter resolves itself into a question of thorough
efficiency of smoking. This is not dependent on duration of
smoking alone, but involves other factors, such as the kind of fuel
employed, the rate of combustion of fuel, the average tempera-
ture sustained, the ventilation of the smoke-house, and the
situation of the building. Other occasional contributory
factors are contemporary adverse climatic conditions and the
possible abuse of an anti- coagulant such as sodium sulphite.

It has been shown that after a time, given suitable conditions
involving the presence of moisture, moulds may appear on sheets
which were apparently fully smoke-cured, and that under the
same conditions other and older samples were unaffected. It
is argued that the latter sheets had evidently been smoked
more efficiently than the others. Hence it is fair to assume
that, except under very special conditions, which do not apply
to the ordinary procedure in the shipping, storage, and sale of
rubber, moulds will not develop upon sheets which have been
properly smoked. The term " properly smoked " signifies
efficient smoking for all practical purposes under ordinary
procedure, and implies or includes all the advantageous factors
which have been discussed or alluded to in preceding para-
graphs.

Without discussing in wearisome detail conditions which
may give rise to the incidence of mildew on properly smoked
rubber, it may be pointed out that the following are favourable
to the growth of moulds :

(a) Storing sheets in a damp place before packing.

(b) Packing sheets in wooden cases which ^ire not thoroughly
dry.

262 PREPARATION OF PLANTATION RUBBER

(c) Piling up cases of rubber in a badly ventilated store-room.

(d) Placing the cases on a cement floor.

(e) Wetting of cases by sea-water or by rain during trans-
port, etc.

BLACK STREAKS, SPOTS OR PATCHES. — The origin of these is
not difficult to trace. They are caused by drippings from the
roof, and contain condensation products from smoke plus
moisture. The ventilation of the roof-ridge should receive
attention, and if the trouble persists it will be necessary to
place some absorbent screen below the sloping roof. Sack-
cloth is sometimes used, but leads to a worse state of affairs
unless changed frequently. In most modern smoke-houses
having an iron roof there is an inner lining of soft timber.

There scarcely seems a necessity to discuss the case in which
an iron roof has become perforated by the action of smoke.
The remedy is too obvious to describe.

WHITISH OR GREY STREAKS. — This is a very uncommon
defect, and is generally to be traced to a building in which fairly
new galvanised sheets have been employed. The zinc surface
becomes oxidised, and the whitish powder which is formed
" flakes," or is carried away by drops of moisture condensing
on the surface of the iron sheets.

RUST. — Sometimes if a sheet is stretched forcibly and
allowed to retract quickly, the hitherto clear surface will be
seen to be marred by a " rusty " deposit. The rubber is then
described as " stretching rusty," and its value is depreciated.

This defect has caused more trouble during recent years than
any other. It is not proposed here to argue the question as
to whether the presence of this film, which appears when some
rubbers are stretched, is detrimental to the physical qualities
of the product on vulcanisation. With the mere statement of
opinion that it could do no apparent harm, we may pass to the
aspect of the case as it affects the buyer and consumer. If
one were to judge by the attention drawn to the appearance of
smoke sheet-rubber after it has been stretched and allowed to
retract, one would imagine the defect to be of comparatively
sudden and recent incidence. This is not so. The peculiarity
must have existed for years, and perhaps became more marked

DEFECTS IN SHEET RUBBER 263

as so many estates abandoned the former common practice
of allowing varying quantities of water to be placed in the
collecting cups. As the substances which cause the defect to
be visible are partially soluble in water, it would follow that
when working with the very dilute latices which were charac-
teristic of the earlier years of the plantation industry, the remain-
ing liquid in the pan after coagulation would contain an appre-
ciable quantity of soluble substances which would otherwise
have been retained in the coagulum.

Conversely, the richer the latex, the greater the percentage
of protein matter retained in the coagulum. In the case of
very rich latex, it must be within the knowledge of every
manager that the quantity of remaining liquid in the pans
would be almost nil. We may assume that the greater part
of these soluble proteins would be enclosed in the structure of
the rubber, but as the fresh coagulum must retain a quantity
of liquid amounting to from 60 to 70 per cent, by weight
(we are now referring to rich latices), it follows that some of
the soluble protein matter must be removed when the coagulum
is placed under pressure. Even after the pressure is released
more of the contained liquid will exude from the surface of the
rubber; and from experience it is easy to imagine that this
exudation, becoming progressively feebler, will continue until
the rubber begins to dry. Then, with the evaporation of the
surface moisture, the protein matter, either in original form
or as a degradation product, remains on the surface of the
rubber as a thin, solid film or crust. As drying continues,
the interior moisture escaping through the pores of the rubber
evaporates, leaving behind the substances hitherto held in
solution. Should, however, the sheet be thick and/or the
temperature of drying low, the rubber may dry first on the
outside, forming a thin skin of dry rubber, which delays
further drying indefinitely.

It will be seen, therefore, that sheets which have been
prepared from rich latex or from too deep a layer of compara-
tively dilute latex will have a surface film of dry protein matter.
Moreover, these sheets will be slow in drying, and in all
probability will have a surface gloss and a dark colour. Hence

264 PREPARATION OF PLANTATION RUBBER

it is not difficult to understand that some brokers regarded
the presence of the so-called " rust " as an indication of over-
smoking.

To show that this is not so, and further that the presence
of rust has nothing whatever to do with smoke-curing, it may
be stated that the presence of this protein film may be seen on
unsmoked sheets which have been prepared from rich latex, from
too deep a layer of more dilute latex, or from some thick
sheets which have been rolled only very lightly. In fact, the
presence of the protein film was noted on unsmoked sheet in
1910, when it was seen to resemble a thin yellowish glaze
which could be scraped off with a pen-knife. Later, sufficient
of this substance was removed from some very thick air-dried
sheets, or thin slabs, to fill a small test-tube.

When the sheets were bent or twisted, the apparent surface
of the rubber (i.e., the protein glaze) cracked in all directions.
In the case of sheets prepared from less rich latex, the surface
film naturally is extremely thin, and no cracking is observed.

If the fresh sheets are placed in a smoke-house, the drying
film will take up colour from the constituents of the smoke, and
it will be invisible. Somewhat analogous to the instance of a
transparent glass giving a visible and opaque powder when
crushed, so the transparent film on stretching breaks up into
a visible powder which is lighter in colour than the rubber on
which it is superimposed.

It will be noted that since the introduction of standard
methods of preparation, involving uniform dilution of latex,
say, to a content of i-J or ij Ibs. dry rubber per gallon, com-
plaints as to " rust " have decreased considerably.

It is to be further noted as a peculiar fact that while two
estates may be apparently working on identical lines, both as
regards manipulation of latex and subsequent treatment of the
coagulum, the rubber of the one may always be free from rust,
while that of the other is often, if not always, condemned for
the alleged defect. Obviously, in such a case, there must be
an initial difference between the two latices as regards the
percentage of proteins present; or there must be some small
unrecognised difference at some stage of working.

DEFECTS IN SHEET RUBBER 265

It will now be clear that " rust " is caused by a film of matter
which is formed on the surface of the pressed coagulum,
being there deposited by the exudations from within the
rubber and through the pores. It is, therefore, necessary to
avoid any conditions which will favour the formation of this
deposit — e.g., allowing sheets to remain too long in a moist
atmosphere before placing in the smoke-house.

At present there would seem to be only two methods which
are successful in the prevention of a " rusty " appearance in the
dry rubber. Singularly enough, the two methods appear to be
directly opposed in principle. They are :

A. THE HOT- WATER TREATMENT. — This method has been
in constant use on estates which have old trees giving rich
latices. These latices are always diluted to a uniform standard
daily. Some estates which formerly suffered from the defect
now experience no difficulty, and in other instances, where
no complaint has yet been received, the treatment has been
followed consistently.

(1) After the sheets have been through the marking rolls,
it is the general custom to allow them to drip for about three
hours. This interval is really excessive for the mere draining
away of the surface water, but as a rule it is just sufficient to
allow a portion of the liquid retained in the rubber to exude.
It has been shown that this liquid may contain some protein
matter in solution. Sometimes in the case of thick sheets
which have been subjected to pressure so much of this matter is
exuded as to form a thin surface slime which is distinctly
evident to the touch. If the sheets are allowed to hang over-
night, the presence of the exuded matter may be detected
also by its odour.

(2) Obviously, any method which will remove this surface
film should be of great benefit. It is found that the best
results are obtained by allowing sheets to drip for about two
hours, and then placing them in hot water for five or ten minutes.
The water should be hot as the hand can conveniently bear,
and it need hardly be pointed out that the same water should
not be used for the whole day's output. For preference there
should be three or four vessels, each capable of holding a fair
proportion of the total number of sheets, and frequent changes
of hot water.

(3) After remaining in the hot water for the period men-
tioned, the sheets are removed singly, each one being surface
washed or swilled as it is taken out.

266 PREPARATION OF PLANTATION RUBBER

(4) It is important to see that the sheets are now well washed or
scrubbed under running cold water, or in frequent changes of
water. The reason for this procedure is plain. If the sheets
are merely hung again to drip after removing from the hot
water, some moisture is bound to remain on the surface of the
sheet. As this surface moisture contains some protein matter
in solution, it is evident that, as the water evaporates, the solid
protein is again deposited on the surface of the rubber. This
would explain why some estates were unsuccessful with the
hot- water treatment. It is not essential that the running
water should be cold; it may be conveniently lukewarm if
drawn from the cooling tanks of the engines. But it is essential
for the best results that there should be running water, so that
the substance in solution is carried away. If the sheets are
merely washed in a large vessel, which has been filled with
clean water, it must be obvious that, by the time some scores
of sheets have been washed, the protein matter in solution on
the surface of the sheets has been transferred to the washing
water, so that the later sheets of the batch are liable to show
the defect again on drying.

B. The second method is much more simple, and entails
no extra labour such as is demanded by the first method. A
successful issue, however, is rather more uncertain, and the
method appears to give the best results with sheet-rubber
prepared on young estates or from more dilute latex.

In this method, the sheets after rolling are allowed to drip
for a very short interval, so that the surface water is mainly
removed. The sheets are then placed in the smoke-house,
and smoking is commenced at once. In some cases where the
defect had appeared continuously for a long period, it was
found to vanish entirely as soon as the method was adopted ;
but when tried on some of the older estates, the results were
very doubtful, and a return was made to the hot- water treat-
ment.

The explanation of the action which takes place is rather
obscure, but two theories may be advanced.

(a) It may be assumed that the interval given for dripping
is too brief to allow for the exudation of the internal moisture
containing dissolved protein matter.

In such case, the rubber is still in a highly porous condition,
and it might be advanced that the heat of the smoke may help
to maintain that condition. Thus the contained liquid might
evaporate so quickly as to leave behind the dissolved substances
in the minute cellular structure of the rubber. In other words,
instead of the internal moisture exuding slowly to the surface

DEFECTS IN SHEET RUBBER 267

in liquid form, it may leave the rubber, even in the first stages,
in an evaporated condition, just as it does in the subsequent
stages of drying. Thus no dissolved protein matter would be
brought to the surface of the sheet and be deposited there.

(b) The other theory also demands the first assumption pro-
pounded in the preceding theory, but subsequently perhaps is
less feasible as it assumes a chemical action of which we have
no definite knowledge.

The idea is that as the rubber is in a porous condition, and
is placed quickly in an atmosphere of smoke, the heat may
maintain that condition to such a degree, that some constituents
of the smoke may enter the rubber and cause the precipitation
in situ of the protein matter held in solution by the contained
water or other liquid. The contained liquid would be water
which has in solution possibly a very slight trace of the coagu-
lant employed, of sugars, of protein matter, and of inorganic
salts. Of these the substances which would evaporate \vould
be probably the water and the coagulant in most cases. If a
salt had been used as a coagulant, the dissolved trace would be
deposited within the rubber in this case, whereas if a rich latex
had been employed or a thicker sheet made from more dilute
latex, some of the salt would be brought to the surface and there
deposited together with the protein matter. This has actually
been experienced in practice, and it has been possible to remove
minute crystals from the edges of the rubber so prepared.

It will be evident that in order for either theory to contain
an element of probability, the rubber must be soft (porous)
when placed in the smoke-house, and must also be fairly thin.
It is observed in all cases where the method has been success-
fully employed that both these conditions are generally fulfilled
— at all events the rubber is fairly thin. When thicker sheets
are made, either from rich latex or from a deeper layer of
comparatively dilute latex, the method is not uniformly suc-
cessful.

OTHER VIEWS ON " RUST " CAUSATION. — Later experimental
work on " rust " formation by Hellendoorn* leads to the
observation that " rustiness " is caused, not actually by the
deposition of original serum-substances, but by the decom-
position thereof, under the action of aerobic micro-organisms.

* "The Cause of Rustiness in Sheet-Rubber," H. J. Hellendoorn.
Archief voor de Rubbercultuur, October, 1919 (Communication from
the Central Rubber Station, Buitenzorg, Java).

268 PREPARATION OF PLANTATION RUBBER

Without going into a full discussion of the subject, the follow-
ing points noted in the experimental work may be quoted :

1. Rustiness could apparently be produced at any time
merely by keeping freshly rolled sheets for periods varying
from twenty-four to forty- eight hours in a moist atmosphere.

2. Sheets placed immediately in a temperature of, say, 110°
to 130° F. never showed " rust"; but if air-dried at ordinary
room temperature, " rust " might appear.

3. " Rust " can be prevented by soaking freshly prepared
sheets in dilute solutions of disinfectants — e.g., formalin, sodium
bisulphite, or chinosol.

If subsequently the sheets are hung for any length of time
in a moist atmosphere, the protective effect of the disinfectant
gradually vanishes and " rustiness " may be produced.

The same disinfecting effect may be obtained by the use of
steam or hot water. It was found that there was less liability
to the formation of " rust " when sheets were immersed in
water at a temperature of 95° to 120° F., whilst steeping at
140° F. gave complete freedom.

4. It was shown that the micro-organisms which cause
decomposition of the serum-products flourish only in the
presence of air — i.e., they are aerobic in character. It is not
uncommon to find, therefore, that " rust " may be incident
only on those parts of a sheet which have been exposed for
some time to air and moisture before being placed in a warm
smoke-room.

5. The optimal temperature for development of the par-
ticular organisms appeared to be about 100° F., in a moist
atmosphere.

6. Soaking the sheets in water (except the short immersion
in hot water, which we recommend), even for a period extending
over a week, does not hinder the formation of " rust."

7. Rustiness may be prevented by placing the sheets in a
sufficiently warmed smoke-house as long as there is adequate
ventilation and a moist atmosphere does not persist.

The simplest means of prevention is to soak the sheets
first for a short period in water, and then to hang them to
drip for a few hours in a well- ventilated place, outside the
factory and under cover.*

It will be gathered that, although there may be a slight dif-
ference between our previous views and those advanced by

* We advise and practise hanging sheets in the open, without
shade or cover.

DEFECTS IN SHEET RUBBER 269

Hellendoorn as to the exact cause of formation of the " rusty "
film, the general conclusions are identical with those given by
us in preceding paragraphs and previously advised in the
Malayan reports of the Rubber Growers' Association.

BUBBLES. — The presence of bubbles in sheet-rubber has
for years been the bane of some managers' existence, and the
bone of contention between sellers and buyers. Taking the
argument down to bed-rock, producers urge that the presence
of bubbles has no influence upon the ultimate quality of the
rubber on vulcanisation. They assert that the alleged defect
is merely a peg upon which to hang an unreal grievance,
serving the purpose of the buyer under the existing conditions
of sale. All this may be true, but as long as the present system
continues, it must be recognised that " kicking against the
pricks " is a futile recreation.

The sympathy of the writers is certainly on the side of the
producers, inasmuch as they realise how extremely difficult,
and even impossible at times, it is for the most careful individual
to prepare sheet-rubber free from this blemish.

Much has been written, and many have been the discussions,
on this vexed subject; and it is recognised that sometimes, in
spite of all precautions, there may suddenly be an incidence
of bubbles in rubber which is ordinarily free from them.
It must be allowed that climatic conditions and physiological
variations affecting the metabolic functions of the trees exert
an influence which is difficult at times to combat, and often
beyond human control.

The contributory causes are many and varied. It should
be premised that, although the defect is described as " air-
bubbles," it is seldom that the appellation is strictly correct.
Rarely do the bubbles contain air. In the vast majority of
cases they contain gases in minute quantity. These gases
may be considered to arise, broadly, from some decomposition
of substances (other than rubber), contained either in the
coagulum or in the serum. In a general way, if this decom-
position is evidenced by an unpleasant odour, it is described
under the term of " putrefaction." We are not concerned here
with the question as to how far such decomposition may be

270 PREPARATION OF PLANTATION RUBBER

ascribed to a purely chemical action, or to the indirect result
of the presence of certain bacteria or other micro-organisms.
Suffice it to state that, at least as far as field operations influence
the result, the decomposition is generally to be attributed to
the work of micro-organisms. Conditions favourable to the
incidence and development of these are to be found when
absolute cleanliness in all details is not aimed at.

With this preamble we may proceed to classify possible
causes of the formation of bubbles into two groups :

(a) Those originating in field operations.

(b) Others which may arise after the arrival of the latex
at the factory.

IN THE FIELD. — Decomposition may be caused by:

(1) Spouts, buckets, and cups being dirty. Regular
cleaning is necessary. If the buckets are allowed to be taken
to the lines by tappers, trouble may ensue. Within the
writers' experience it has been shown that an otherwise baffling
case of premature flocculation of latex was traced to the
presence of acid substances in the buckets, which had been
used by coolies for preparing their food.

(2) Delay in commencing work. This means similar delay
in collecting the latex which is exposed to greater heat than
under ordinary circumstances.

(3) Exposure to the sun's rays. The heating of the latex
may provide improved conditions favourable to the develop-
ment and action of micro-organisms.

(4) Allowing latex to stand too long before collection.
This usually is the result of giving tappers too great a task.

(5) The addition of water to the latex, either purposely or
accidentally, in the form of rain. The water may be slightly
acid in character, or it may carry micro-organisms from the
bark into the latex.

(6) Tapping trees at too great a height. The latex generally
has an abnormal distance to travel before reaching the cup.

(7) Sometimes the latex from old trees, or from trees after
wintering (just prior to full renewal of leaf), contains more than
the usual proportion of substances (e.g., sugars), which are
capable of effecting flocculation or coagulation.

(8) Too great a distance for transport. The trouble arising
from this cause is likely to be much increased if the journey
has to be made over bad roads. In such case the physical

DEFECTS IN SHEET RUBBER 271

action augments the effect likely to be produced by long
standing.

The foregoing do not include all possible causes, but serve to
indicate the directions from which trouble may be mainly
anticipated. It will be plain that any latex which exhibits
symptoms of premature coagulation (or minute flocculation)
should be regarded as a potential source of bubbles in sheet-
rubber.

It will be equally obvious that the employment in the field
of any harmless substance of an anti-coagulant nature is to be
encouraged. This point is discussed in detail in Chapter V.

IN THE FACTORY. — As a general rule it may be understood
that the mischief has been done before the latex is handled at
the factory. Sometimes it is perceptible from the peculiar
appearance of the latex, and in such case the batch should
not be used for the preparation of sheet-rubber. Often it is
found that only the last to arrive at the store is visibly affected.
This should not be mixed with other apparently normal latex,
as it is capable of acting as a " leaven " to the bulk.

Contributory factors in the store are :

(1) Lack of cleanliness of utensils, particularly of coagulating
dishes or tanks.

The trouble becomes acute sometimes where wooden
tanks are employed. Unless the tank and the partitions are
thoroughly and regularly cleansed, the wood may become
coated with a bacterial slime, which is capable of causing
what may be termed " fermentation " of the latex layers in
contact.

The tank should be thoroughly cleaned occasionally with
a weak (5 per cent.) solution of sodium bisulphite. The
partitions should be scrubbed and placed in the sun twice or
three times a week.

(2) Allowing latex to stand too long before treatment. This
point needs no further expansion.

(3) The use of a latex of too high a rubber content. Such
latices are difficult to handle in order to secure uniform mixture
with the coagulant.

(4) The use of too concentrated a solution of coagulant.
In conjunction with (3) there may be a rapid and irregular
coagulation, giving rise not only to decomposition in parts

272 PREPARATION OF PLANTATION RUBBER

(and subsequent formation of gas), but also to the formation
of true " air-bubbles " by inclusion of air during stirring.

(5) The use of insufficient coagulant. Coagulation is slow
and incomplete.

(6) Defective straining and skimming. Small flocculated
particles of rubber may pass, or be rubbed through, the
strainer. If allowed to remain, they act as local points of
danger.

(7) The proximity of the coagulating latex to some source of
heat, or exposure to sunlight.

(8) Any delay of drying in the preliminary stages, either
before or after the rubber enters the smoke-house.

BLISTERS. — This description aptly fits the case in which
sheet-rubber in the smoke-house exhibits large bubbles of
gas which distend the surface of the rubber. When subjected
to pressure, small " balloons " are formed, which burst with
a perceptible report. It was formerly the belief that this
defect was occasioned solely by an abnormally high temperature.
That such is not the case can be shown by the experience of
estates which have had only the rubber of a particular day or
short period affected under normal factory conditions.

At the same time it is not disputed that the heat of the smoke-
house exerts an influence (causing expansion and distension),
but it is advanced that the gases had begun to form before the
rubber entered the house.

The view held is that decomposition had supervened or was
taking place — probably from one or more of the causes enu-
merated in the preceding paragraphs. The heat of the smoke-
house only serves to exaggerate the effect. It is acknowledged
that the degree of decomposition must be initially greater than
in the ordinary incidence of " bubbles."

Beyond this point we are not in a position to put forward
any definite supposition as to the apparently haphazard occur-
rence of the phenomenon.

It is to be noted, fortunately, that the defect is comparatively
rare, and seldom appears on estates which employ an anti-
coagulant in the field. While we have examined persistent
cases, one of which led to a temporary discontinuance of the
preparation of smoked sheet rubber, we have not yet been able

DEFECTS IN SHEET RUBBER 273

to arrive at any satisfactory idea of the exact conditions govern-
ing the incidence of " blisters." Our investigations only lead
us to two observations :

(a) That blisters have appeared on the rubber of some
estates after wintering, and during the period of new leaf-
development.

(b) That the defect has been noted on other estates during
a period when there were frequent but not heavy rains, and
when there was a comparatively low average temperature.

In either case, as the factors are beyond human control,
it would be expected that without any change being made in
estate procedure, the trouble would vanish as mysteriously
as it appeared. This is our experience; but as showing the
possible intensive effect of a high temperature in the smoke-
house, it may be remarked that very infrequently, in a batch of
sheets exhibiting ordinary bubbles, a few hanging directly
above the furnaces show signs of a slight blistering effect.

" SPOT " DISEASE IN SHEET RUBBER. — That " spot " disease
may appear in air-dried sheets was evident at the beginning of
the outbreak in the spring of 1911. The first cases noticed
took the form of pink and bluish " blushes " spreading over
the whole of the sheets. Later, fungoid spots began to appear.
These mainly took the form of red or black blotches, and were
very unsightly. As " spot " disease cannot develop in smoked
rubber, the obvious and simple course to adopt was to smoke-
cure the sheets. When it is stated that " spots " do not develop
in smoke-cured rubber, it is understood that the smoke-curing
must be efficient and must commence as soon as the rubber
has been rolled, and the surface water has drained away. If
the sheets are allowed to air-dry for a few days, the disease may
develop, and then smoke-curing will not get rid of the coloured
patches. The operation of smoke-curing will not get rid of the
coloured patches. The operation of smoke-curing may tone
down the colour, but the spots would still remain evident.

SUPPORT MARKS. — It frequently occurs that one sees across
the middle of smoked sheets a wide mark. This is where the
wooden support in the smoking-chamber has been. As a rule,
even in the most careful cases a faint mark may always be seen,

18

274 PREPARATION OF PLANTATION RUBBER

but in many instances this mark is exaggerated to such an
extent as to point to lack of care on the part of the store super-
vision. If bays of racks remain empty over-night, they may
possibly become covered with a light sprinkling of fine wood-
ash and tarry deposit. Wet rubber placed upon these racks
will pick up and retain the impurities, and more often than not
they cannot be washed out. It is incumbent upon the manager
to see that empty racks are thoroughly cleansed before placing
wet rubber upon them. The better plan is to arrange that the
bars can be removed easily from sockets. There should be
in stock sufficient " spares " for, say, two days' rubber. When
the dry rubber is removed, the bars should likewise be taken
away, to be cleansed and kept in the factory until again re-
quired. This will ensure that fresh rubber always rests upon
a clean support.

On some estates, in order to guard against a pronounced
" bar-mark," sheets are moved and turned daily.

In other smoke-houses the upper surface of the bar is
chiselled in concave form, so as to admit of the passage of
smoke below the surface resting on the bar.

STICKINESS. — This is not to be confounded with " tacki-
ness," from which the rubber does not recover. Stickiness is
only temporary, and may be remedied. As a general rule, it
is due to packing sheets, which have not a good raised " rib-
bing," and which may have been coated with light tarry deposits
(see Glaze). This surface film may be removed by washing
the sheets, or scrubbing them, with cold water. Usually a
further two days' air- drying will make the rubber fit for packing ;
and if the smoke-curing has been efficient, there should be no
need to anticipate trouble from mildew. Some estates adopt
this practice daily with success, as a form of insurance against
complaints of surface deposits.

RIBBING, SURFACE PATTERN. — While we know that the passing
of sheets of rubber between rolls, causing a particular raised
pattern to appear, has no effect upon the actual quality of the
rubber, there is a great deal of practical advantage gained.

The practice ensures an increase of superficial area which is
an aid in drying, improves the appearance of the rubber for

DEFECTS IN SHEET RUBBER 275

selling purposes, and is of distinct advantage in enabling the
rubber when packed to travel in better condition. Sheets do
not become so closely packed ; sampling and general handling
are easier on delivery.

As long as the plane surfaces are sufficiently and regularly
distorted, there would seem to be no limits to the type of
pattern or " mark " which may be placed upon the rubber.
But in actual practice the variety is small. The most popular
type of " ribbing " is that best described as a small diamond
effect, produced by a pair of rolls cut with closely placed
narrow grooves running spirally. The spirals travel in the same
direction on both rolls, producing close-cut ribbing running
in opposite directions on the surfaces of the sheet. On sheets
of standard thickness, the result approaches a diamond effect.

A few other patterns are employed, notably that producing
longitudinal stripes of varying thickness. On the whole, the
type of pattern would seem to be immaterial, if the points already
indicated are achieved.

It is seldom one encounters a case nowadays in which the
" marking " is unsuitable, but a few estates may be using an
old type of patterned roll on which the full diamond grooving
is cut. As this appears on both sides of the sheet of rubber,
and as the ribbing does not coincide, a blurred effect is seen
when the sheet is viewed against the light.

THICK ENDS, " SHEET CLIPPINGS." — It rarely happens,
even with good equipment and average supervision, that the
preparation of smoked sheet is unaccompanied by slight defects.
For instance, in spite of rules and regulations regarding mani-
pulation of the coagulum, it is not uncommon to find that some
sheets, after rolling, have slightly thickened ends. In the
ordinary course of events these might delay drying considerably.
It is the practice on some estates to cut off these thickened ends
while the rubber is still wet. The pieces are then machined
into crepe form, but as no sodium bisulphite may have been
used, the resulting rubber cannot be classed as No. i Standard
Crepe.

The other alternative is to trim the ends when the bulk of
the rubber is thoroughly smoke-dried. The moisture con-

276 PREPARATION OF PLANTATION RUBBER

taining portions are then returned to the smoke-house until
dry, and are subsequently packed without further treatment as
"smoked-sheet clippings." It will be plain that, except in
the particularity of form, these clippings differ in no degree
from the original sheets; and, owing to extra smoke-curing,
may arrive in even better condition. One must be prepared,
however, to find that a slightly lower price is offered . Whether
the price obtained would be comparable with that commanded
by the crepe made from wet sheet slipping would depend
upon general ruling market conditions, and the degree of care
exercised in guarding against the inclusion of any inferior
pieces of rubber. In ordinary factory practice, there could be
no room for abuse under the latter clause.

OTHER INFREQUENT DEFECTS. — This chapter will be closed
with a reference to other small defects which, although infre-
quent, cannot be classed as minor complaints. In point of
fact, when they occur, they assume an importance, in the eyes
of the consumer, which is not, perhaps, sufficiently appreciated
by producers.

DIRT. — Trouble from this source should be absent, but care-
lessness on the part of packing coolies may be responsible for
occasional complaints. How the dirt is incident may remain
a mystery, but it has been noted that sheets have at times been
thrown upon a cement floor. A certain amount of loose dust
may thus adhere to the rubber.

ASH. — The source of this surface deposit scarcely needs
indication. Where open-hearth furnaces are employed, and
the wire-mesh floor screens are not perfectly sound, fine ash
may find its way into the upper chamber. If this trouble is
persistent in spite of precautions, the sheets should be surface-
washed and air-dried before packing.

BARK. — Complaints of the presence of particles of bark in
sheet rubber used to be fairly frequent, but are now less
common. The trouble may be traced to the use of defective
straining sieves when the latex is being handled.

SPLINTERS. — The use of packing-cases of unplaned soft
timber is responsible for complaints of this nature on delivery.
Without here discussing the larger question of the ideal packing

DEFECTS IN SHEET RUBBER 277

case, it is sufficient to emphasise that the interior surfaces of
wooden chests should be planed. The cases are often so
damaged in transit, that splinters of wood may be found
throughout the contents. The device adopted on some estates
may go far to prevent this. The cases are first lined with loose
sheets, and finally other sheets are arranged to overlap at the
top of the case. The bulk is thus enclosed in a wrapping of
sheets, and any splinters or other deleterious substances are
confined to the surface of the mass.

PART V
GENERAL

CHAPTER XIX
CHOICE OF COAGULANT

ALMOST without exception, the agent employed in the co-
agulation of plantation (Heved) rubber is acetic acid, or in
some cases formic acid. Under ordinary trade conditions
supplies are always obtainable at reasonable prices, but during
the recent War the question of possible substitutes was brought
greatly to the fore. Fortunately the subject of coagulation
and coagulants had been previously studied to such effect in
laboratory practice, that there would have been small difficulty
in prescribing agents other than acetic acid in cases of expe-
diency. As far as our knowledge extends, all the possible
substances which have the power of coagulating latex have
been tested. They include mineral acids, organic acids,
compounds known chemically under the general term of
" salts," alcohols, sugars, etc.

The heading of this chapter must be seen to " beg the
question," inasmuch as it leads to the assumption that a
coagulant (in the popular sense) is necessary to secure coagula-
tion. In point of fact, methods are sometimes employed which
depend upon no artificial coagulant to produce the desired
effect. To these methods reference will be made later.

In this section it is proposed to describe briefly the more
important agents which are used, or might be used, in effecting
coagulation. In the class of those which are not in common
use some could be used as expedients, while others are only of

scientific interest.

278

CHOICE OF COAGULANT 279

ACETIC ACID. — There is no need to enter into a discussion of
the merits of this agent. In practice it remains the cheapest
and safest coagulant known at present.

FORMIC ACID. — This agent is equally as safe to use as acetic
acid, and as easy to handle. Bulk for bulk its coagulative power
is higher than that of acetic acid. Its pre-war shipping price,
when taken in conjunction with its coagulative power, was
slightly below that of acetic acid, but local prices put the
balance in favour of the latter. If prevailing costs put it on
terms of parity with acetic acid, there would appear to be no
reason why formic acid should not have a widely-extended
use on plantations.

CITRIC ACID, TARTARIC ACID. — The acids of the extracted
juices of most tropical fruits consist, to a large degree, of citric
or tartaric acids. These can be used in place of acetic acid
as satisfactory coagulants in case of emergency ; but the questions
of availability of supplies and of costs preclude their more
general adoption.

OXALIC ACID. — This is a satisfactory coagulant as far as
observed effect is concerned. It produces a rubber paler than
ordinary coagulants (without the use of sodium bisulphite),
as it has the nature of an anti-oxidant.

It would not be a safe agent in the hands of coolies, as it is
classed as a poison.

SULPHURIC ACID. — During the War, in a period of shortage
of acetic acid and of high prices, this agent was used with
success on some estates.

It scarcely need be remarked that it is a dangerous substance
to handle, and that its employment must be accompanied by
close European supervision.

At prevailing prices during the War it was very much cheaper
than acetic acid, and even at the present reduced cost of the
latter the advantage still lies writh sulphuric acid.

It must be emphasised, however, that the abuse of this agent
to any but the slightest degree is harmful to the resultant
rubber. Hence its use would be sanctioned only in the absence
of the commoner, and much safer, coagulants.

In view of the possible incidence of such an emergency,

28o PREPARATION OF PLANTATION RUBBER

the following notes are given. It is impressed that strict ad-
herence to the rules must be given.

HANDLING SULPHURIC ACID. — (a) Always use glass or glazed
earthenware vessels.

(b) Pour slowly and avoid splashing. Drops finding their way
to clothing or other fibrous material will destroy it locally; and
if thrown upon any part of the body may cause painful burns.

(c) When diluting this agent always remember to pour the
acid into the water (i.e., the lesser into the greater), and never
vice versa. Pour the acid carefully and slowly down the side
of the vessel, and stir well.

(d) Should strong acid be spilled, do not throw water upon
it. A supply of sand or dry earth should be kept close at hand.
Throw this upon the acid.

STORING SULPHURIC ACID. — (a) Jars or cases should be
handled as seldom, and as carefully, as possible. If the acid
is contained in a case, the top should be plainly indicated.

(b) Stocks should be stored in a detached building which
should not be damp. Jars or cases should not stand on a
wooden floor if possible.

(c) See (d) above.

BUYING SULPHURIC ACID. — (a) Commercial acid of specific
gravity 1*84 is the best of its kind. It contains impurities
which are non-injurious to rubber preparation.

(b) It is always advisable, if possible, to buy the acid in
small jars containing not more than 100 Ibs. each. Smaller
jars, with a content not exceeding 50 Ibs., would be preferable.

(c) If the acid is bought in jars, it should be stipulated that
the stoppers be covered with a plaster head, and that the
containing crate or case should have prominent labels or
marks indicating the top of the case.

FORMULA FOR USE OF SULPHURIC ACID. — It will be understood
that as this formula has been calculated for working with latex,
having a consistency of i J Ibs. dry rubber per gallon, it applies
in a strict degree only to such latex. In other cases, where the
dilution of the latex is not known, the formula will serve as a basis
for experiment until the correct quantity has been discovered.

(Sulphuric acid of specific gravity 1*84.)

CHOICE OF COAGULANT 281

NOTE. — The directions must be followed carefully, and
glass measuring vessels should be used if procurable.

(a) Measure out i pint of strong acid, and pour it carefully
and slowly down the inner surface of a jar containing 20 gallons
of water. Do not pour it directly into the water.

The heavy acid will sink to the bottom of the jar, and a good
mixture must be obtained by stirring well.

(b) Of this solution (which is approximately i per cent, by
weight), use i gallon to 20 gallons of latex.

Readers are doubtless now well aware of the corrosive
action of strong sulphuric acid, and we scarcely need point out
that even the dilute acid should not be kept in contact with
the usual iron vessels found in factories. The mixing of
solutions should be done in one of the glazed earthenware
jars commonly in use.

The formula given above works out at approximately i part
strong acid to 2,000 parts of latex (of dry rubber content i J Ibs.
per gallon). The formula for using acetic acid with the same
latex works out at about i : i ,200. It will be apparent, therefore,
that relatively sulphuric acid is a more powerful coagulant
than acetic acid. In terms of dry rubber obtained from latex
of the consistency indicated above —

i Ib. sulphuric acid will produce 300 Ibs. dry rubber,
i Ib. acetic acid will produce 180 Ibs. dry rubber.

With both acids selling at the same rate, sulphuric acid
would be more economical in use; when its cost is less than
that of acetic acid, which is the normal condition, the economic
advantage in favour of sulphuric acid is augmented still
further.

It may be found that the standard formula for sulphuric
acid will not always give a perfectly clear remaining serum,
even though an attempt is made daily to work to a uniform
consistency for all latices. It is inevitable that the manipulation
of the latices should be slightly in error on occasions, or that
a small mistake might occur in preparing the solution of acid.
Hence a clear remaining serum after coagulation may be
secured less often than a slightly turbid serum. This is as it
should be. The minimum quantity of acid may be adjusted

282 PREPARATION OF PLANTATION RUBBER

so closely as to give such results. If a clear serum is obtained
always, that should be an indication of continual excess of
coagulant. Naturally, if a milky serum is always obtained,
the reverse is the case.

As a last word on the subject, it may again be emphasised
that the use of sulphuric acid is not advised, except in an
emergency; and that the greatest possible care must be exer-
cised in the observance of the strict formula for use.

HYDROCHLORIC ACID, NITRIC ACID. — -These mineral acids
would prove more expensive than sulphuric acid. In addition
they are much more uncertain in action. For example, the
use of a certain excess of hydrochloric acid would not hasten
coagulation, but would prevent it. Above all their effect, in
excess, is deleterious to the rubber.

HYDROFLUORIC ACID. — This has a strong corrosive action
on porcelain or glass. Hence it has to be contained in bottles
of gutta-percha or lead. It is mentioned here merely because
some years ago it found a use as a coagulant, chiefly in Ceylon.
It was sold in the form of a 10 per cent, solution under the
name of " Purub," and was the subject of a patent.

It is effective as a coagulant, and has also an anti-oxidant
action, which was its chief recommendation when cheap and
harmless anti-oxidants were not commonly known. It is
comparatively expensive, and, as indicated above, difficult to
handle and store. In short, it has nothing to commend it,
in comparison with acetic or formic acids.

ALUM. — This substance has been used for years by native
rubber producers as a coagulant. It fulfils the desired purpose,
and its popularity was maintained because of the ease with
which it could be stored and handled. Unfortunately, this
facility often led to the use of an excess, and native sheets
were often criticised as being brittle. Investigations have
shown that alum, even in minimum proportions, has an appre-
ciably harmful effect upon the quality of the rubber prepared
by its use as a coagulating agent. Its employment by native
rubber producers has now been largely superseded by acetic
acid in some form.

PYROLIGNEOUS ACID. — This is otherwise known under the

CHOICE OF COAGULANT 283

names of " crude acetic acid " and " crude wood vinegar."
Owing to the shortage of acetic acid during the War, attention
was directed towards the possibility of making an effective
coagulant locally by what is termed the " dry distillation of
wood " — t.e.y the wood is not burned but heated in a retort.
The enquiries could be placed in two classes :

1. Those which aimed at making the pure, strong acid of
commerce.

2. Those which sought information concerning a crude
coagulant (pyroligneous acid) on estates.

Regarding the first class, we can do no better than reproduce
our remarks published in the April local report of the Rubber
Growers' Association for 1916 — with the reservation that,
on account of a threatened shortage of timber, a local scheme
might not now be feasible :

" Probably the most common enquiry encountered since
the rise in the price of acetic acid is concerned with the possi-
bility of making acetic acid in this country. It may be stated
that the proposition is a feasible one, even on a fairly large
scale. We have the essentials necessary for such a scheme in:

" i. A good supply of suitable timbers, the most valuable of
which, possibly, is mangrove timber, locally known as * bakau.'
Other suitable timbers are known, but as far as preliminary
experiments show mangrove timber gives the best yield.
At present this timber is in great demand as a fuel for steam
plants, but with the extension of the local coal industry the
timber may become cheaper.

"2. There would appear to be less valuable timber which
would be suitable for heating the retorts. Or, local coal might
be used.

"3. Supplies of lime at reasonable rates are available, as the
limestone formation in the peninsula is quite considerable in
extent.

"4. Supplies of sulphuric acid are available from Japan,
Australia, Burma, etc., even at the present time, although
naturally rates are higher than normal. Under ordinary con-
ditions, supplies from England and parts of Europe would
be much cheaper than at current rates.

" For the benefit of many readers perhaps a brief and non-
technical description of the preparation of acetic acid would

284 PREPARATION OF PLANTATION RUBBER

not be amiss, and would explain the necessity for the essentials
indicated above. In brief, the process is as follows:

" (a) A suitable timber is heated in a closed retort. This
is termed ' dry distillation,' and results eventually in the
carbonisation of the wood — i.e., charcoal is obtained in the
retort.

" (b) Tar, vapours and gases are distilled over during the
carbonisation of the wood. These liquors and gases pass
through condensers. The gases pass away, while the condensed
liquors separate out into (i) wood tar, (2) a watery liquor called
pyroligneous acid or crude wood vinegar.

" (c) The pyroligneous acid is separated from the tar, and
again distilled to obtain the acetic acid present.

" (d) This crude acid is steam-heated with milk of lime, which
fixes the acid, forming calcium acetate (or acetate of lime).

" (e) Eventually the calcium acetate is taken out in the form of
a thick paste, which is spread to dry. When dry this ' grey
acetate ' is the main source of all glacial acetic acid now made.

" (/) The acetic acid is released from the ' acetate of lime '
by the action of sulphuric acid. It is then distilled several
times, and under various conditions, in order to increase its
strength. In the past copper tubes were used for this purpose,
but owing to the fact that traces of copper were found to be
injurious to rubber, some works instal tubes of glazed earthen-
ware for the distillation.

Such is the process in outline, and it will be seen that no pro-
posal to manufacture glacial acetic acid on an estate could be
considered feasible, although it would not present any great
difficulty on a large scale and under skilled direction. Further-
more, the cost of the plant would be far too great for any estate."

Although it is clear that pure acetic acid is beyond the scope
of an estate, crude pyroligneous acid has been produced on a
varying scale in this country and in Ceylon. In the latter
country some success was obtained by the distillation of
coconut shells with comparatively inexpensive plant. In this
country, wood-distillation was practised on a few estates,
but improved facilities for obtaining pure acetic led to a
termination of the experiments, although sufficient crude acid
could then be made at a reasonable cost.

The pyroligneous acid obtained is generally clear, after
filtration, and of a dark brown colour. It has a peculiar odour

CHOICE OF COAGULANT 285

reminiscent of smoked sheet-rubber, or of creosotic substances
in general.

Its acid content depends chiefly upon:

(a) The kind of timber heated in the retort.

(b) The efficiency of the apparatus.

(c) Condition of the timber as to moisture.

(d) The temperature employed, and rate of working.

(e) The point at which distillation ceases (i.e., the duration of
interval between commencement of heating and cessation of
collection).

Samples received from estates for testing purposes were found
to contain equivalents varying from 2 per cent, to 10 per cent,
of acetic acid.

They were all suitable coagulants when used in quantity
calculated from the discovered acidity, but produced rubber
darker than ordinary wrhen air-dried. This effect was not of
much importance in the preparation of smoked sheets, but to
produce a pale crepe it was necessary to employ sodium
bisulphite as an anti-oxidant.

This darkening in colour is to be ascribed to the presence of
traces of phenols,* which are stated to exert an effect upon the
rubber during and after vulcanisation. f This subject will be
discussed in another section.

With this provision the crude pyroligneous acid which
can be produced on estates, could be employed as a coagulant
until such time as the price of glacial acetic acid was so low
as to make the production of the crude acid non-profitable.
This point would be determined from a knowledge of the cost
of production per gallon, and the percentage of acetic acid per
unit. For example, if the cost of production (including cost
of timber for distillation, cost of fuel for heating the retort,
cost of labour, etc.) was 60 cents per gallon of crude acid
containing 9 per cent, of acetic acid, that would be equivalent
approximately to buying glacial acetic acid at $30 per demi-
john of 44 Ibs.

* Whitby, Journal Soc. Chem. Industry, vol. xxxv., No. 9, 1916.

t See also " Preparation and Vulcanisation of Plantation Rubber "
(Eaton, Grantham, and Day), Bulletin No. 27, F.M.S. Department of
Agriculture, April, 1918.

286 PREPARATION OF PLANTATION RUBBER

SMOKED WATER. — A weak solution of pyroligneous acid
may also be obtained by passing smoke through water. With
this object in view, a machine was designed by the Federated
Engineering Company of Kuala Lumpur. In this the principle
of retorting was not employed. Smoke was produced by
ordinary combustion in a compartment of the apparatus, and
was drawn through water by the action of a high-speed fan
worked by hand. A solution, equivalent in effect to a 2 per cent,
solution of acetic acid, could be obtained at a comparatively
cheaper cost than crude pyroligneous acid produced by dry
distillation as it was then being practised. This was chiefly
because of the wasteful methods of fuel combustion, in the
latter process, in the heating of the retort.

CHINESE VINEGAR. — This agent was found to be a satisfactory
coagulant, and, a priori, there is no reason why it should not be
suitable, as it is essentially a dilute solution of acetic acid.

The qualities sold were generally colourless, and were
probably the result of acetic fermentation of rice.

Samples tested showed a varying content of acetic acid,
ranging roughly from 3 per cent, to 8 per cent. ; but on this basis
of valuation it was found generally that the price bore no
relation to the degree of efficiency.

It was advanced not only that the vinegar was an efficient
substitute for glacial acetic acid, but that it was also cheaper.
This latter claim was proved to have no foundation in fact, even
at the high price of acetic acid prevailing during the period of
stress. It is not likely, therefore, that vinegar can displace acetic
acid, except as an expedient.

SULPHUROUS ACID. — The anti-oxidant effect of sodium
bisulphite and sodium sulphite is due to the liberation of the
gas, sulphur dioxide. This gas dissolves easily in water, form-
ing an acid solution called sulphurous acid.

This acid solution is an effective coagulant in fairly small
quantity. Not only so, but it produces, in addition, the anti-
oxidant effect noted in the employment of sodium bisulphite.
It is thus possible to produce rubber varying in shade of
paleness by means of a single solution.

In the event of sulphurous acid being used, it would be

CHOICE OF COAGULANT 287

necessary to import cylinders of sulphur dioxide from which
the solution could be prepared in factories each day. There
would be no insurmountable difficulty in this, as it is only
necessary to pass the gas through a series of closed vessels
containing water. Enough solution could be prepared at one
time for three or four days, but preferably the solutions should
be as fresh as possible. Altogether there would seem to be
possibilities in the use of sulphurous acid for preparing pale
crepe rubbers, providing the cost is within comparable limits
with the commoner coagulants at present in use, and that no
adverse effect on the rubber can be shown to result. If the
cost did not exceed the combined cost of acetic acid and sodium
bisulphite, the employment of sulphurous acid solution might be
worthy of consideration. There is one drawback to the use of
sulphurous acid solution, and that lies in the proximity of the
limits of the quantities necessary for coagulation and that which
is in excess, and prevents coagulation. Thus, with ordinary
field latex having about 20 per cent, dry rubber content, the
minimum necessary for coagulation per 100 c.c. of latex is
about 8 c.c. of a i per cent, solution. The maximum quantity
possible for use is about 15 c.c. of a i per cent, solution, so that
great care would have to be exercised in avoiding an excess of
coagulant, otherwise coagulation would be effectually prevented.

It is believed that the preparation of rubber by this method
is the subject of a patent secured by Messrs. Boake, Roberts, and
Co.. London.

SUGARS. — Coagulation may be effected by the addition of
small quantities of sugars.* These are assumed to be effective
by fermentative conversion into lactic and acetic acids. The
presence of lactic acid is supposed to have a twofold effect :

(a) As a direct coagulant.

(b) In its action upon certain organisms which, in the
ordinary course of events, would delay or prevent coagulation.
Although work on an experimental scale has been done, as

* " Preparation and Vulcanisation of Plantation Para Rubber "
(Eaton, Grantham, and Day), Bulletin No. 27, F.M.S. Department of
Agriculture; Gorter and Swart, Bulletin No. 6, West Java Expt.
Station.

288 PREPARATION OF PLANTATION RUBBER

far as we know no practical application has been made of the
employment of sugars as coagulating agents.

VARIOUS SALTS. — Of experimental interest only it may be
recorded that coagulation has been effected by means of various
chemical " salts " — e.g., calcium chloride, barium chloride,
magnesium chloride, sodium chloride, aluminium sulphate,
magnesium sulphate, sodium sulphate, etc. None of these
has been found to have any practical application, except,
perhaps, calcium chloride, which is used in small quantity as
an accelerating agent in a special process of anaerobic coagu-
lation, which will receive mention in the following chapter.

At one period during the War and the dearth of acetic acid,
it was found that there were available in England large supplies
of the acid sulphate of sodium (sodium hydrogen sulphate),
which proved to be an effective coagulant. Experimental
work gave satisfactory results, but no practical application
resulted when supplies of acetic acid were again obtainable.

VARIOUS PROPRIETARY COMPOUNDS. — We have seen many
proprietary coagulants advertised and pass into the limbo of
forgotten things. They can generally be divided into two
classes. The first embraces those founded upon a woefully
incomplete knowledge of requirements. The second covers
those which meet requirements, but for which exaggerated
claims are made and excessive prices charged.

As as instance of a substance which fell under both classifi-
cations might be mentioned the case of " Coagulatex." Pre-
tentious claims were made, and it was emphasised that the
liquid contained no vegetable acids. Acetic and formic acids
might be quoted as examples of vegetable acids, and as these
have been shown to be the most satisfactory coagulants now
employed one fails to imagine where lay the value of the
guarantee given by the advertisers of " Coagulatex."

On analysis the liquid was found to consist mainly of sul-
phuric acid, against the indiscriminate use of which warnings
have been given. Thus it was a dangerous substance for
common use.

Furthermore, comparing the value with its sulphuric acid
content, it was found that the price required for " Coagula-

CHOICE OF COAGULANT 289

tex " was roughly four times the contemporary cost of commer-
cial sulphuric acid in the Federated Malay States.

Those in charge of estates should realise, therefore, that no
proprietary coagulants should be adopted until a proper
report of tests, and a comparative valuation, has been obtained
from one of the research laboratories.

CARBONIC ACID GAS, CARBON DIOXIDE. — Now of only scien-
tific interest, it may be noted that some years ago great claims
were made for the use of carbon dioxide gas as a coagulant.
In actual practice we were unable to effect coagulation by pass-
ing the dry gas into latex. It was suggested that the original
investigators were misled by failure to secure a dry and clean
gas. It would appear that probably the gas was prepared by
the action of hydrochloric acid upon marble or limestone.
Unless intervening " washers " and " driers " were used, the
liberated gas, when passed into latex, would carry with it traces
of hydrochloric acid, which would effect coagulation.

ALCOHOL. — In the cheap form of methylated spirit, alcohol
has been employed by us as a speedy coagulant for many years.
Latex run slowly into alcohol coagulates instantaneously. The
method has been in common laboratory use.

The employment of Alcohol has also been made the part-
subject of a patent process of coagulation, to which reference
will be made in the succeeding chapter.

VEGETABLE EXTRACTS. — At various times experimental work
has been directed towards the use of liquids of purely vegetable
origin, such as the juices of tropical fruits, and of a waste pro-
duct of tropical industry — the so-called " milk " (or water)
of ripe coconuts.

In the former class there is usually a natural acidity, but in
coconut water the acidity is chiefly the result of fermentation
of the carbohydrate (sugar) constituents.

These substances were all found to effect a more or less
satisfactory coagulation, but it is unlikely that they would be
suitable for practical application on a large scale.

As being more directly related to the subject of coagulation
in general than to coagulants in particular, a discussion of
several special processes will be relegated to the ensuing chapter.

19

CHAPTER XX
SPECIAL METHODS OF PREPARATION

EVERY year appears to bring forth some new ideas in the mode
of rubber preparation. Some of them are based in principle
upon the oldest known method — i.e., the native Brazilian process
of making " Hard Para." Others strike a new note, and in a
few cases the claims put forward are substantially confirmed
by results. In other instances the claims are too pretentious,
and discredit may be brought upon schemes which, although
lacking in comparative success, are yet commendable for the
ingenuity manifested.

To the present not one of these new methods has been able
to compete to any marked degree in general practice with the
established methods of ordinary preparation. A few continue
to find local application, but most have either been abandoned
or are gradually falling into desuetude.

We do not propose to discuss in fine detail all the various
claims made on behalf of these special processes, or to enter
into controversies. The aim is to present to the reader an
outline embodying the main principles and advantages claimed.

DA COSTA PROCESS. — Briefly, this was a method by which
coagulation was effected with smoke. The smoke was
generated by the combustion of wood in a special compartment,
and was forced into latex by means of a jet of steam. It was
really only applied to the preparation of coagulum intended
for crepe form. The exact degree of coagulation effected
was uncertain, and the. final colour of the rubber precluded it
from being classed as a modern No. i product.

" BYRNE CURING " PROCESS. — This is a process for treating
coagulum obtained by ordinary methods.

2 go

SPECIAL METHODS OF PREPARATION 291

It was the subject of a patent obtained by Messrs. E. J. and
F. A. Byrne, and at one time had a considerable vogue on
estates. The chief claim advanced was that the rubber pro-
duced was in all respects equal to Fine Hard Para, and could
be shipped while still moist without detriment to the physical
qualities.

The principle of the process was the treatment of coagulum,
in either sheet or thick crepe form, with vapours produced by
the volatilisation of two special fluids. This treatment was
undertaken in comparatively small wooden sheds, in which
the coagulum was placed. The " smoke " was conducted into
the curing sheds from furnaces outside the building. The
sheds were covered externally with " felt " material to pre-
vent leakage of the vapours, and a very dense smoke was
obtained.

The furnaces were specially designed, and consisted essen-
tially of a " hot-plate " heated by a powerful kerosene blast-
flame. On top of the machine were two reservoirs controlled
by taps. In these were placed the special fluids which were
released in definite proportion. The composition of the
fluids was not divulged, but it is assumed that the principal
ingredients were (a) wood tar products, (b) crude pyroligneous
or acetic acid. The mixture of these, dropping on the hot plate
at the correct temperature, spontaneously volatilised, to form
dense whitish fumes, having an intense and not disagreeable
odour of wood combustion. A duct led from the back of the
machine into the curing- shed, where the vapours were dis-
tributed through perforations in the pipe.

The coagulum usually remained under treatment in the shed
for three to four hours, and then was removed for ordinary
air- dry ing. When taken from the curing- shed it had a pinkish
colour, which later developed into a dark brown by a natural
process of oxidation. The exterior of the rubber, on shipment,
resembled the appearance of smoked sheets ; while the interior,
on cutting, was seen to be still white. As packed for shipping,
the rubber contained from 10 to 15 per cent, of original
moisture, for the usual sheet form, and even more when " slab "
rubber was prepared.

292 PREPARATION OF PLANTATION RUBBER

Originally either crepe or sheet rubber was made, but later
the preparation of the crepe form was displaced largely by
" slab " rubber. These " slabs " were really very thick
sheets, which had been subject to only slight pressure.

Still later the preparation of the " slab " form was displaced
by " loaf " rubber. This form was built up by winding
together ordinary thin sheets which had been subject to the
" cure." Only slight tension was needed, during the operation
of winding, to cause close adhesion of the component wet
layers, and the final result was a " loaf " or roll dark in colour,
and apparently dry when examined superficially. On being
cut, even after an interval of months, the middle portion was
still so moist as to be quite white.

In course of time it was discovered that all the claims made
for the process could not be substantiated, and for various
reasons (which need not be detailed) most of the estates which
had adopted the scheme reverted to ordinary methods of
preparation. At the time of writing few, if any, continue to
work the process. It appears to be agreed, as the result of
investigations, that in no degree does the process yield advan-
tage over ordinary methods.

FREEZING PROCESS. — A patent was secured a few years ago
to cover a process whereby coagulation was effected by
refrigeration.

Latex remained for several hours in the refrigerating chambers
of an ordinary ice-making plant. The resulting solid mass,
on being thawed, yielded a coagulum appearing in no way to
differ from that obtained by ordinary methods of coagulation.

Provided the process exerted no influence for good or evil
upon the quality of the resulting dry rubber, the value of it
would appear to depend upon the relative cost of working, plus
considerations of capital expenditure and depreciation on the
plant. At the present time it would be difficult to imagine
that the cost of preparation alone would compare favourably
with that sustained by ordinary coagulative methods.

Furthermore, beyond the expensive refrigerating plant, the
usual machinery of a factory would still be required if the
ordinary market demands are to be met.

SPECIAL METHODS OF PREPARATION 293

Finally, it has not been found* that any advantage in the final
physical qualities of the rubber is obtained by the employment
of this process.

WICKHAM PROCESS. — This process, invented by Sir Henry
Wickham, aimed at the production of a rubber resembling
Fine Hard Para. The principle employed was that underlying
the preparation of the best rubber in Brazil — viz., coagulation of
superimposed thin layers of latex by the action of smoke and
heat.

In essential the machine employed consisted of a rotating
drum into which latex and smoke entered. The result was
the formation of thin " skins " of rubber which, coagulating
in situ, formed a mass corresponding to " Fine Hard."

That the rubber was fully satisfactory as to quality is
acknowledged, but economically and in practical utility the
process was unsuccessful, the rate of output being so low.

DERRY PROCESS. — The invention of Mr. R. Deny, late of
the Singapore Botanic Gardens, this in principle resembled the
Wickham and other processes. It aimed at a mechanical
imitation of the native method of producing Fine Hard Para.

In place of the rotating drum, an endless belt was used. This
travelled over pulleys, more or less horizontally placed. The
upper of these could be raised to varying height above the
level of the other, and likewise could be so adjusted as to
tighten the belt.

The under layer of the belt impinged, in its travel, upon the
surface of a layer of latex contained in a shallow tray. The
belt was operated by hand-power, and the height of the latex
trays was adjustable.

The trays of latex were situated at the lower end of the
machine \vhich lay outside the smoking-chamber. It will be
understood that the vastly major part of the total length of belt
was always within the chamber.

Smoke was generated by combustion of wood in an external
structure, was brought into the chamber by a wide duct, and

* " Preparation and Vulcanisation of Plantation Rubber " (Eaton,
Grantham, and Day), Bulletin No. 27, F.M.S. Department of Agri-
culture.

294 PREPARATION OF PLANTATION RUBBER

was then distributed below the belt by means of perforated
pipes.

The thin film of latex picked up by the belt was coagulated
partly by the action of smoke constituents by evaporation due
to heat. Assuming (i) that the belt was of adequate length,
(2) that the rate of travel was not excessive, (3) that the latex
was not too dilute, (4) that the temperature of the smoke
was sufficiently high, (5) that the smoke was sufficiently dense
and not too damp — then the process should be a continuous one.

It will be clear that success could only be obtained by a
careful adjustment of all these factors. The latex must, neces-
sarily, be of a fairly rich consistency (at least 2| Ibs. dry rubber
per gallon), but unfortunately there is considerable difficulty
in maintaining such latex in a state of fluidity for the period
demanded by this process, without loss of latex. Naturally, the
addition of an anti-coagulant would retard the rate of output
of the machine to a marked degree.

The layer of rubber thus formed on the belt was stripped off ,
and hung for further air-drying, as it still contained a fair
percentage of moisture.

As a really practicable method for treating plantation latex,
the process failed by reason of its low rate of output over a
given interval. This alone was sufficient to condemn it, apart
from the facts (i) that it was not shown to be a cheaper method
than coagulation by acetic acid, (2) that the resulting rubber was
not proved to be of superior intrinsic value to rubber prepared
by ordinary methods.

SPONTANEOUS COAGULATION. — All readers will be aware
of the phenomenon of the curdling or souring of milk. The
behaviour of Hevea latex, under certain conditions, may be taken
to be analogous. Difficulty is experienced in maintaining
fluidity — a difficulty which appears to vary in great degree
according to locality, nature of soil, age of trees, the relative
demand made upon the trees by the system of tapping employed ,
etc.

It is sometimes found, before the latex reaches the store, that
it may exhibit one of various stages of premature (spontaneous)
coagulation:

SPECIAL METHODS OF PREPARATION 295

(a) To all appearances it may be quite fluid, but a close
examination shows it to consist mainly of a serum containing
very minute particles of rubber in suspension (microscopic
coagulation).

(b) In a later stage these, particles coalesce to form larger
" flocks " (macroscopic coagulation).

(c) The whole, or practically the whole, of the latex may have
coagulated, forming one mass of rubber with a milky residual
serum.

Passing from this aspect of the question, it may be noted as
peculiar facts that :

(1) A shallow layer of latex is less likely to coagulate spon-
taneously (i.e., without the addition of a coagulant) than a
deeper volume.

(2) The shallow layer, and also the surface of the deeper
volume (where exposed to air), on standing will be found to
develop a superficial film of finely coagulated particles, yellowish
in colour, and having an offensive odour due to decomposition
of protein matter.

(3) While this partial coagulation is confined only to the
surface of a shallow layer of latex, it will be found that below
the surface film of the deeper volume a much more definite
coagulation has taken place. The coagulation will be practically
complete, and the coagulum, apart from a spongy appearance,
is normal in character. This coagulum is free from the
offensive odour noted above.

(4) On testing the surface film of both the shallow layer and
the deeper volume, it will be found to be alkaline in character;
whilst the lower liquid surrounding the main portion of the
coagulum in the deeper volume of latex is of an acid nature.

These observed facts are sufficient to indicate that there are
apparently two distinct types of spontaneous coagulation, and that
the latter takes place particularly where the latex is more or
less out of contact with the atmosphere. We may, therefore,
differentiate thus:

(a) In contact with air (aerobic): incomplete spontaneous
coagulation, accompanied by yellowish slime, offensive in
odour and alkaline in character.

(b) Out of contact with air (Anaerobic) : Practically or wholly
complete. There is no offensive odour under normal condi-
tions and the serum is acid in character.

296 PREPARATION OF PLANTATION RUBBER

It is concluded* that there are present in latex, on collection
in the field, two types of organisms. Those which work in
contact with air (aerobic) show a tendency to prevent coagulation
and to form an alkaline yellow slime on the surface of the
latex. The others, which work in the absence of air (anaerobic) ,
may, under favourable conditions, cause complete coagulation
unaccompanied by any decomposition or offensive odour
within a normal period. If air is rigidly excluded, the coagulum
obtained is quite satisfactory for all purposes.

This type of coagulation, without the employment of a
chemical coagulant, and under anaerobic conditions, was the
subject of a patent granted in 1914 to Messrs. Maude, Crosse
and others. The process has been in use on Cicely Estate
(Perak) for some years. With subsequent slight modifications
the apparatus consisted in essential of a tank with a loose cover.
The flanges of the cover were sufficiently long to dip into a
water-seal surrounding the tank. Thus the cover may rise
and fall without an inrush of air.

Coagulation, in fact, can be effected thus in any kind of air-
tight receptacle; and experimentally the reader can obtain a
satisfactory result by filling completely with latex the bottle
which has a loose stopper.

Under the patent held the coagulum may be prepared either
for crepe-making, or for sheets by a modification of the tank.

The crepe when dry does not have the bright appearance
of the ordinary " Fine Pale " standard prepared with the aid
of the anti-oxidant sodium bisulphite.

Unfortunately the addition of this substance to the latex in
normal proportions is not possible under anaerobic conditions,
as it is found to prevent coagulation, probably owing to its
sterilising effect upon the anaerobic organisms.

To prevent the oxidation of the rubber in actual practice,
the freshly prepared crepe is soaked in a solution of sodium

* "Preparation and Vulcanisation of Plantation Rubber " (Eaton,
Grantham, and Day), Bulletin No. 27, F.M.S. Department of Agri-
culture, 1918; "Dc la Coagulation naturelle du Latex d'Hevea
Brasilicnsis " (Denier and Vernct), Comptes Rendus I' Academic des
Sciences, No. 3, July, 1917.

SPECIAL METHODS OF PREPARATION 297

bisulphite before hanging to dry. The resulting colour of
the rubber is quite good.

It was shown by Eaton and Grantham that anaerobic coagu-
lation is slightly uncertain in action. Owing probably to
variations in the composition of the latices, or to the extent
of infection by organisms, coagulation may one day be complete
and on other days less satisfactory.

They found further that, by the addition of small quantities
of sugars, coagulation under both aerobic and anaerobic con-
ditions was improved. The conclusion formed was that the
addition of sugars created a medium favourable to the develop-
ment of anaerobic organisms and unfavourable to those which
cause decomposition of the natural nitrogenous constituents
of latex.

This \vork was confirmed by Gorter and Swart,* who attri-
buted the action to the conversion of sugar to lactic, acetic,
and succinic acids by fermentation.

Denier and Vernet, whose work has already been mentioned,
studied the presence of the organisms in latex, and succeeded
in isolating one which, under anaerobic conditions, effects
coagulation within twenty-four hours. Sometimes to produce
complete coagulation it was found necessary to employ small
quantities of sugars — e.g., i gramme per litre of latex (i : i ,000) .

It is to be noted also that the addition of small quantities
of soluble calcium (lime) salts to latex has much the same
effect as the employment of sugars. Recent investigations!
showed that the addition of 0*5 to i gramme of calcium chloride
per litre of latex caused complete coagulation in closed vessels
within twenty-four hours, a result agreeing with the findings
of Barrowcliff.

On page 308 of the same publication, experiments on the
effect of sugars are described, in connection with aerobic
coagulation. Observations from a further set of experiments
tended to indicate a direct connection between the effects of
tapping and spontaneous coagulation. It is suggested that

* Gorter and Swart, Bulletin No. 6, West Java Station.
t "Archief voor de Rubbercultuur," Nederlands Indies, 1920,
4> 273.

298 PREPARATION OF PLANTATION RUBBER

heavy tapping causes a diminution in the latex of those sub-
stances which act in some way as accelerating agents in
coagulation — e.g., sugars. The smaller the proportion of these
substances, the slower and less complete is natural (spontaneous)
coagulation.

ILCKEN-DOWN PROCESS. — This process is the subject of
patents granted in 1915 to Messrs. Ilcken and Down. It has
been in fair prominence, and has been tried experimentally
on several estates and in public demonstration.

It is a coagulating process, and, in the original specification,
employed as agents a mixture of alcohol (in the form of methy-
lated spirit) and benzene (petrol), or alcohol with petrol and
coal-tar naphtha. The mixture was injected in the form of a
fine spray into the latex, contained in a tank specially fitted
with paddles.

Later modifications covered the addition of a small quantity of
glycerine; or, failing supplies of that substance, coconut oil.

Many advantages are claimed for the process, but most of
them cannot be substantiated. The two chief claims are:

1 . The production of a uniform standard of rubber.

2. The obtainment from a unit volume of latex of a greater
weight of rubber than can be obtained from an equal volume
of the same latex by ordinary coagulation with acetic acid. It
is to be inferred that the agents employed have the power of
adding to the coagulum some of the substances which usually
remain in solution in the clear serum.

Regarding the first of these claims, it has been shown* that
the rubber is not uniform in its behaviour on vulcanisation,
and that its variability is similar to that of rubber prepared by
other processes.

The second claim has been the subject of much controversy.
Experiments made on estates under the supervision of, or
in the absence of, the patentees have given conflicting results.
When varying factors have been eliminated, the general
conclusion was that no increase in weight of rubber was
obtained.

* " Preparation and Vulcanisation of Plantation Rubber "
(Eaton, Grantham,-and Day), Bulletin No. 27, F.M.S. Department
of Agriculture, 1918.

SPECIAL METHODS OF PREPARATION 299

Private laboratory investigations led to a similar verdict, and
Eaton* records a confirmatory finding. More recently the
claims made for the process were investigated in Javaf under
varying conditions. Three series of experiments were made:

(1) During the rainy monsoon and at a height of 1,800 feet.

(2) During the dry monsoon on a low-country estate.

(3) In the experimental gardens at Buitenzorg during bright
sunny weather and the most favourable conditions.

The agents used were (a) a mixture of alcohol and fusel oil,
(b) alcohol and petrol (benzene).

In these experiments no advantage in weight of rubber was
obtained by the Ilcken-Down process, and it would thus appear
that the principal claim fails to be substantiated.

The general composition of the rubber was approximately
the same as ordinary crepe obtained from undiluted latex.
The rubber on vulcanisation was found to be normal in
behaviour, and was similar to the controls.

The coagulum ordinarily is affected by oxidation, and does
not produce a fine pale crepe. To remedy this defect the
freshly prepared crepe is soaked in a solution of sodium
bisulphite and sulphuric acid.

It may be noted that in the recent experiments coagulation
was effected in vacuum in a specially designed wooden tank.
From a study of the previous section on " Spontaneous
Coagulation," the reader will perceive that results equal to
those obtained by the Ilcken-Down process can be obtained
without the necessity of using such agents as alcohol, petrol, or
fusel oil.

SLAB RUBBER. — This type of preparation has been the
subject of much discussion of recent years. There is nothing
really special in the mode of preparation, and in its original
form " slab " rubber is only a thick sheet which may be
obtained by coagulation with acetic acid or other agents.

The coagulum, when removed from the serum, is subjected
to comparatively slight pressure, and the " slab " thus made is

* Ibid.

t " Archief voor de Rubbercultuur " (De Vries and Spoon), Central
Rubber Station, Java, May, 1921.

300 PREPARATION OF PLANTATION RUBBER

either placed to air-dry at once, or may be subject to treatment
in other liquids before drying.

The rubber is not allowed to remain until wholly dry, but is
shipped while still containing an appreciable percentage of
enclosed moisture.

It is claimed* that the production of " slab " rubber by
standardised methods eliminates to a great degree the varia-
bility which at present characterises plantation rubber, and
that a fast-curing medium is obtained. These claims will be
discussed in later chapters dealing with the vulcanisation of
rubber, and demand no notice in this section.

From the producers' point of view, it may be noted that the
preparation of slab rubber is a simple process, but not alto-
gether as pleasant probably as might be desired, when under-
taken in crude form.

The appearance of the partially dry slabs is unattractive,
but that does not signify if the quality of the vulcanised
product satisfies requirements.

For the average producer, the difficulty lies in having to meet
the demands of the general market. Even, therefore, if one
assumes that the intrinsic qualities of slab rubber are all that
the claims advance, it would be necessary for the producer to
be assured of definite and regular sales.

At present it would probably be fair to state that practically
all the " slab " rubber being prepared is produced by those
who are also consumers. They are thus in the enviable
position of being able to satisfy their requirements as to the
mode of preparation. Until such time, therefore, as there
exists a regular demand for " slab " rubber in the general
market, the vast majority of estates must proceed on ordinary
lines of preparation,

* "Preparation and Vulcanisation of Plantation Rubber"
(Eaton, Grantham, and Day), Bulletin No. 27, F.M.S. Department
of Agriculture, 1918.

PART VI
VULCANISATION

(By DR. H. P. STEVENS)

CHAPTER XXI

INTRODUCTORY DEALING WITH TREATMENT
AND VULCANISATION

IN the foregoing chapters the methods of treating latex,
coagulating, rolling and curing, or drying, have been des-
cribed in great detail. These details will give the reader some
idea of the precautions taken, and procedure necessary to
produce rubber which will be acceptable to the market.
The expressions " inferior rubber," " defective crepe,"
" poor quality sheets," etc., are frequently met with, but these
expressions must not be taken to indicate any defect in the
rubber for manufacturing purposes, but merely that the rubber
is defective for selling purposes — that is to say, being unsightly,
it will not fetch the full market price.

Raw rubber, as produced on the plantations, is almost in-
variably subjected to the process of vulcanisation in the pro-
duction of manufactured rubber articles as we know them.
Previous to the advent of plantation rubber, the raw material
was purchased by the manufacturer in a moist and impure
condition; frequently the rubber was adulterated with sand,
dirt, and even small stones. Consequently it was the invariable
practice of the rubber manufacturer to wash the raw rubber
and convert it into crepe, which was then hung and air- dried
before use. The effect on the rubber, if of high grade, was more
severe than the washing and crepeing process on the plantation,
because the rubber was not a soft coagulum but generally

301

302 PREPARATION OF PLANTATION RUBBER

dried on the surface and semi-hard. The power required
was considerable, and the resulting crepe was consequently
softer and more susceptible to heat than plantation first latex
crepe. Much of the " wild " rubber was soft and tacky and
inferior to " earth-scrap."

Vulcanising in its simplest aspect consists in mixing the
rubber with sulphur and heating the product under regulated
conditions. The effect of heat on the inferior grades of " wild "
rubber is very marked. A soft, sticky, and resinous material
is transformed into a relatively tough and elastic product.
The effect of vulcanising on the better grades is less marked,
but immediately apparent. On the other hand, the effect of
vulcanising is least apparent on first latex plantation grades,
because in these we have a raw rubber prepared in a manner
best suited to retain its natural characteristics.

The need of vulcanising in the process of manufacturing
rubber goods became an axiom in pre-plantation days, and
it is only quite recently that attempts have been made to
utilise raw rubber directly, without vulcanisation, particularly
for shoe soles. For this purpose a thick dense crepe has been
found satisfactory. Smoked sheet rubber is not generally
suitable, apparently owing to its microphysical structure. It is
possible that the process of rolling in the making of dense crepe
compacts the rubber particles, yielding a harder and more
resilient product. The rolling must not be carried too far, or the
" working " of the rubber will approximate to a preliminary
mastication, and the product will be weakened.

The utilisation of crepe rubber directly has not yet been
sufficiently tested to enable a definite conclusion to be reached
as to its future scope, but it is obvious that for use in a raw state
some modification in preparation may be advantageous. The
present method — e.g., coagulation, with acetic acid — does not
yield the hardest and toughest rubber.

Hardness and toughness are actual drawbacks in the utilisa-
tion of rubber which is required for vulcanising. When the
output of plantation rubber began to increase and to displace
the inferior wild soits, manufacturers complained of the in-
creased power consumption of their machines. The power

TREATMENT AND VULCANISATION 303

was required mainly to " break down " or " mill " the rubber
preliminary to the mixing with sulphur and other ingredients.
It is obvious that a material such as raw rubber cannot be
mixed with powders such as sulphur with a pestle and mortar,
or in any simple form of mixing machine. This difficulty was
overcome by the earlier experimenters by immersing the rubber
in a bath of molten sulphur. The latter was gradually absorbed
and " dissolved " in the rubber, and the heat of the bath
caused the dissolved sulphur to combine with the rubber to
produce vulcanised rubber. The limitations of such a process
are apparent. Thus the vulcanised rubber retains the form in
which it was originally shaped. Moreover, other ingredients,
such as mineral matters, cannot be dissolved or absorbed by
the rubber in this manner. The method eventually adopted
consisted in " breaking down," " milling," or " masticating "
the rubber by passing it continuously between differentially
geared steam-heated rollers. By this means a high-grade rubber
is converted into a soft, plastic mass, which will " take up "
sulphur, mineral matter, and other ingredients as desired.
The mixing operation may be carried through on the same
roller machine as was used for breaking down the rubber, or
separate machines of other designs may be adopted. Details
of the process will be found in books dealing with rubber
manufacturing.* It will suffice here to explain that when
rubber is kneaded between two hot rollers moving at different
speeds the rubber forms a continuous band around the slower
moving roller, and if the distance between the rollers be adjusted
the excess of rubber held back fcy the nip of the rollers will
form a " bank " or moving wedge-shaped mass on the top of the
nip. This closes the space between the rollers, so that sulphur
and powder placed on the rubber pass round towards the nip,
and are there driven into the rubber. In this manner it is easy
to mix, say, 10 per cent, of sulphur into the rubber without
a single particle falling through. In technical mixes where
large quantities of powders require to be mixed there is always
some caking, and part of the powder falls between the rollers

* For instance, " India-Rubber and its Manufacture," by H. L.
Terry.

304 PREPARATION OF PLANTATION RUBBER

into a tray underneath. This is swept up with a broom and
put back on to the rollers, the process being repeated until the
whole of the ingredients have been incorporated.

From this description it follows that, preliminary to mixing,
it is necessary to thoroughly masticate or " plasticise " the raw
rubber. Much of the " wild " rubber was of so inferior a
quality that it very readily broke down, and but little mastica-
tion was necessary. It was soft and resinous, and readily took
up the powders which were to be mixed with it. The better
grades of wild rubber, such as Fine Para, were more difficult
to break down, but not so difficult as most plantation rubber,
because they had already received a preliminary " working "
in the process of washing and crepeing, and we have already
explained that such treatment takes more power than the crepe -
ing of the soft moist coagulum on the plantations. The amount
of " working " or " plasticising " produced in the rubber is
connected with the power expended ; the greater the expendi-
ture of power, caeteris paribus, the greater the working effect
on the rubber. Although the manufacturers possessed a rela-
tively soft rubber in the form of washed Fine Para, it was cus-
tomary in most cases to employ this rubber in conjunction with
washed lower grades to produce a soft plastic material for
further treatment. Now, however, the manufacturer has
little else but plantation to deal with, and most of it more diffi-
cult to break down than washed Para crepe. This is the reason
why a hard, tough rubber is no longer a desideratum with
manufacturers, although originally taken as an indication of
good quality. For the majority of purposes they want some-
thing which will break down easily. Hence if a rubber could
be produced answering to these requirements, without loss of
vulcanising quality, it would be preferred.

Having incorporated sulphur and other ingredients, the
plastic mass is sheeted and run between layers of calico to pre-
vent the superimposed sheets from adhering. From this
"calendered sheet" the article, whatever it may be, is built
up. The calender rollers are heated so as to keep the rubber
compound plastic. There is a limit to the thickness of the
sheet which can be produced. It is a difficult operation to

TREATMENT AND VULCANISATION 305

perform satisfactorily so as to yield a smooth surface and a
sheet free from enclosed air. When cool the rubber hardens
and is readily handled. The object to be manufactured is
then built up from the calendered sheet. Thus in the manu-
facture of a motor tyre the tread is built up on the casing
or carcase by laying the sheets on the canvas and rolling these
with a hand or power operated roller, so that they adhere firmly,
the first layer to the canvas of the casing and subsequent
layers to one another. This rough description will suffice
to illustrate how important it is that the rubber when mixed
should be plastic enough to give a smooth sheet, and to allow
the sheet to be manipulated in building up the article in process
of manufacture. The testing of rubber in regard to its plas-
ticity and power to absorb finely divided mineral matter will
be discussed in a later chapter. We may* however, point
out here, that the mineral matter is not generally added as an
adulterant, but because of certain specific properties it confers
on the product.

To proceed with our outline of vulcanisation, we have now
arrived at the stage at which the goods are built up and ready
for vulcanising. For this purpose they are generally enclosed
in some manner, either in metal moulds bolted together, or
tightly wrapped in cloth, as, e.g., in the manufacture of inner
tubes, hose, etc. In the latter case, you can detect the cloth
mark on the finished product. Sometimes the rubber is
spewed — that is, driven out of a barrel by means of an endless
screw revolving in it. In this way rubber tubing, perambulator
tyres, and such articles, may be made. More recently even
tyre treads and the shaped rubber for band tyres (heavy solid
tyres) have been extruded in this manner, for the process is
much cheaper than building up a tyre from calendered sheet,
and then cutting the mass to shape by hand. But for spewing
the rubber mass must be very soft and plastic; this condition
is not obtainable unless the raw rubber originally used can be
made thoroughly plastic without damage. Nor can it be
effected with a rubber mass containing much finely divided
mineral matter, as this hardens the mixture.

For other purposes the rubber is swollen in a solvent, such as

20

3o6 PREPARATION OF PLANTATION RUBBER

coal-tar naphtha, and subsequently masticated; the soft dough
is then shaped or spread on cloth, and vulcanised after allowing
the solvent to evaporate. Here, again, the properties of the raw
rubber are of immense importance. Thus, the more plastic
the dough, the less solvent required, and the less there is to
drive off before vulcanising. The plasticity of the dough will
depend on the plasticity of the raw rubber, and so forth. It is
evident that the physical properties of the raw rubber are of
great importance. They directly affect the manufacturing
operations up to the vulcanising stage, and indirectly affect
the results obtained on vulcanising.

The actual vulcanising consists of heating the mass of mixed
rubber for a definite time and at a definite temperature, each
" heat " being chosen to suit the particular mixture. These
data are arrived at empirically — that is, by trying a number of
" heats " and choosing that which appears the most suitable.
The suitability will depend on the nature of the article, the
service to which it is to be put, and the time it is intended to
last. All vulcanised rubber goods, whatever the process, have
a limited life or period during which they can be relied on to
give useful service. After a time, vulcanised rubber tends to
harden, cracks appear on the surface when the article is bent
or stretched, and eventually the rubber becomes rotten and
" perished." This tendency varies with the quality of the
original raw rubber and the conditions of vulcanising. Before
plantation rubber was available, the manufacturers were
dependent on inferior wild grades for a great part of their
output, and, consequently, the goods made from these inferior
rubbers never showed very good mechanical properties and
soon deteriorated. The severest critics of plantation rubber
have admitted the advantages to the manufacturers of the
replacement of the lower wild grades by plantation rubber.*
But even the best grades give a vulcanised product which

* See Williams, "The Rubber Industry," 1914, p. 284. It must
also be remembered that the inferior wild grades were derived from
latices often containing a large proportion of " resinous " matter,
and which could not yield a really high grade of vulcanised rubber
whatever the care and skill employed in preparation.

TREATMENT AND VULCANISATION 307

rapidly deteriorates if the vulcanisation is carried too far.
This results from too long heating, or too high a temperature,
and the product is termed " overvulcanised " or " overcured."*
The appearance of the product is deceptive, as the physical
properties are remarkably good if the overvulcanising is not
more than 50 to 100 per cent, in excess of the normal cure.
Only in the case of very much overvulcanised rubber do we
obtain a product which is brittle from the beginning.

The degree of vulcanising will vary with the type of article
to be produced, and where a long life is desired, the tendency
will be to " undervulcanise "; but if the best mechanical
properties are desired, the tendency will be towards " over-
vulcanising," or, more correctly, " fully " vulcanising. These
considerations are aptly illustrated by reference to pneumatic
tyres. The inner tube need not possess high tensile strength,
provided that it is easily distensible, for the reason that, during
use, it is protected by the casing of the tyre proper, which
confines and supports it against the air-pressure applied.
Inner tubes are therefore cured to give a long life without
developing the maximal physical properties. On the other
hand, the casing and tread of the tyre are required to with-
stand severe mechanical conditions — particularly the constant
flexing of the cover, and the abrasion of the road surface. Tyres
are not stored for any long period, and, when put into service,
have a limited period of useful life. Consequently it is needful
to develop maximal mechanical properties, and vulcanisation
is therefore carried further than in the manufacture of inner
tubes.

The rate of cure is controlled by a number of factors in
addition to the period and temperature of vulcanisation, in
particular by the proportion and nature of the other ingredients,
especially sulphur and accelerators, and also by the rubber
itself. The main complaint as regards plantation rubber is

* The terms " curing " and " vulcanising " are generally em-
ployed as if synonymous. Twiss has suggested that the former
be applied in regard to a change in physical properties, and the latter
to the chemical change whereby sulphur is combined with the rubber.
The term " curing " is also applied to the process of preparation of
raw rubber. This must be kept in mind so as to avoid confusion.

3o8 PREPARATION OF PLANTATION RUBBER

that it varies excessively in this respect. This matter will not
be discussed here, but is only introduced in order to explain
the importance of a constant rate of vulcanising to the manu-
facturer. Plantation rubber should, therefore, be prepared
so as to be as uniform as possible in this respect, and the earlier
part of this book gives full details of the precautions advised,
and in many cases adopted on the plantations. Unfortunately,
it is impossible to secure uniformity of methods among all
producers, even when they are Europeans, to say nothing of the
native producers, who account for perhaps one-third of the
output. Hence the importance of branding the rubber when-
ever possible, so that the manufacturer may identify the rubber
he purchases. If found satisfactory, he can then secure further
supplies from the same estate.

CHAPTER XXII
TESTING OF PLANTATION RUBBER

THIS subject may be subdivided into (a) Tests on the raw
rubber ; (b) tests on the vulcanised rubber.

The tests on the raw rubber may be carried out (i) on the
sample of sheet and crepe as received. For this purpose the
rubber rs cut into a strip, which is clamped between grips and
gradually stretched to breaking-point. The ring testing
machine can be adapted for this purpose by replacing the
rollers with clamps. As the thickness of the samples to be
tested will vary, it is advisable to cut the strips of such a width
that the cross-sectional area of all test pieces is the same —
say, 40 sq. mm. The method is applicable to both sheet
and crepe rubber. (2) Tests may be made as to the behaviour
of the rubber during milling or mastication. Small batches
are milled under uniform conditions, preferably in an enclosed
masticator such as Baker and Perkins supply. The power
taken (as measured by the current taken to drive the motor
actuating the machine) and the time are recorded. A further
test may be applied to the milled or masticated rubber, to
ascertain the amount and the time taken to incorporate a
finely divided mineral matter, such as carbon black, zinc
oxide, or one of the refined clays.* The results are not very
exact, and the difference in plasticity and dryness noted are
usually less than found when working with full-sized machines
in the factory. (3) The rubber, either raw or masticated, may
be " dissolved " in a " solvent," such as benzene, and the
viscosity of the " solution " measured. Generally speaking,
the less viscous the solution, the more plastic the rubber.

The testing of vulcanised rubber has been treated in such

* Bulletin Rubber Growers' Association, January, 1921, p. 43;
August, 1921, p. 340.

309

3io PREPARATION OF PLANTATION RUBBER

detail in the recent works of Whitby* and De Vriesf that a
few special points only will be dealt with here. The prepara-
tion of samples for testing involves first the sheeting of the
mixture of rubber, sulphur, and other ingredients, if any. The
sheets may be i to 2 mm. thick. They are soft and adherent,
and must be kept between layers of calico to prevent adhesion.
A sheet of rubber is then built up by laying three or four sheets
evenly upon one another, and pressing together to form a
sheet 5 mm. thick. The thick sheet is then roughly cut to
shape and vulcanised in a mould by heating in steam under
pressure. From the vulcanised sheet so obtained the rings
for testing are cut (45 mm. internal diameter. 5 mm. face,
and 4 mm. thick). Rings obtained in this manner will not
vary in diameter or thickness (reckoned as sections of a tube),
as these are controlled by the size of the punch, but will vary a
little in the face, as this is controlled by the thickness of the
sheet, which depends on the completeness with which the mould
is closed. More recently smaller moulds have been adopted,
one mould for each ring, and an annular space for moisture to
develop a pressure during vulcanising and prevent porosity.
The moulds are vulcanised in an oil bath, or oven of some
description, in which a constant temperature is maintained.
I have adopted for some years a third method. The principle
is that used in the factory for making annular-shaped rubber
articles, such as washers, rings, elastic bands, etc. An alu-
minium mandrel, 45 mm. external diameter, is taken, and the
thin rubber sheet is wrapped round this, so as to build up a
tube about 4 mm. thick, the surplus rubber is cut off, and the
edge bevelled with a wet knife. The manipulation will vary
somewhat with the type of compound to be treated; thus, in
some cases, it is sufficient to well roll the tube with a hand
roller to secure adhesion. In other cases it is better to wipe
the sheet of compound with a rubber solvent previous to
rolling. In the latter case time must be given for the solvent
to evaporate before vulcanising. The tube is next tightly
wrapped in wet cloth, and is then ready for the vulcaniser.

* " Plantation Rubber and the Testing of Rubber."
t "Estate Rubber."

TESTING OF PLANTATION RUBBER 3n

Or the tube may be enclosed in moulds which form an outer
circular shell and take the place of the cloth, but for most
purposes, and in particular for the rubber - sulphur mixing
usually employed, it is sufficient to use cloth to obtain even
and regular tubes. The tube, after vulcanising, is slipped on
to a wooden mandrel and cut into rings on a lathe. Of these
rings the internal diameter is constant, for this is formed on
the mandrel, also the face, which can be cut accurately in the
lathe, but the external diameter, and consequently the thickness,
may vary a little.

It appears, therefore, that all methods result in rings of
approximately the correct size, and it is usual to check, and, if
necessary, make an allowance for variation in dimensions.
It is not possible to do this, even approximately, with soft
rubbers, as the rubber gives under the pressure of the micro-
meter. No doubt a photographic method would give more
accurate results, but would take too long. I have found that
a very close approximation is obtainable by weighing the rings
as the specific gravity of the standard rubber mix is known.
It is not necessary to weigh each ring, but the whole five or
ten taken for testing may be weighed together.

The next point that arises is the choice of a formula for the
test mix. Practically all the work to date has been carried out
on mixtures of rubber with 7 to 10 per cent, of sulphur. For
some purposes — e.g., detecting variation in rate of cure — this
mixing is satisfactory, but for other purposes it is not. Nor
is the behaviour of a rubber-sulphur mixing a sure guide to the
behaviour of one containing other ingredients, such as litharge.
Thus, two samples vulcanised satisfactorily when mixed with
sulphur only, but one of them gave unsatisfactory results in
the presence of litharge. It has long been recognised that
mineral ingredients may modify the product when vulcanised,
but the modification is not necessarily uniform. Consequently,
tests should also be made, when practicable, with vulcanised
rubber containing other ingredients in addition to sulphur.

As regards physical tests on the vulcanised products, these
usually involve determination of breaking load and elongation
at rupture (usually recorded as final length — that is, including

3i2 PREPARATION OF PLANTATION RUBBER

the original length reckoned either as unity or as 100 units).
Simultaneously a load-stretch curve is recorded on an auto-
graphic attachment. The type of curve varies with (i) state
of cure, or degree to which the rubber is vulcanised ; (2) propor-
tion of sulphur and/or other ingredients; (3) specific nature of
the rubber used. The last factor is almost negligible compared
with the two former — at any rate for average quality rubber.
As (2) is kept constant for any batch of tests, or even for every
test, it follows that the load-stretch curve is mainly dependent
on the state of cure, and the degree of vulcanising may be
measured by comparing either the elongation produced at a
given load or the load produced at a given elongation. Either
set of figures is readily determined by measuring up the load-
stretch diagram.

The peculiar type of the curves has long been a subject of
comment and speculation. Special properties have been attri-
buted to the " slope " or inclination of the upper and approxi-
mately straight portion of the curve. According to the writer's
investigations, the " slope " is largely dependent on the degree
of vulcanisation, so that it is difficult to " place " as an index
of the specific nature of a rubber.* Moreover, it has recently
been shown that the peculiar type of curve given by vulcanised
rubber is the result of plotting the load against the sectional
area of the unstretched test piece, whereas this area decreases
progressively as the test piece stretches. If this decrease be
allowed for, the curve obtained is an equilateral hyperbola. f
Preliminary experiments with rubber compounded with large
proportions of finely divided mineral matter, such as carbon
black, show that the load-stretch curves obtained autographically
are likewise reducible to equilateral hyperbolae.

* Bulletin R.G.A., October, 1921, p. 397.

f Hatschek Journal Soc. Chem. Ind. 1921; Trans., p. 251.

CHAPTER XXIII
THE PROPERTIES OF RUBBER

THIS section, like the last, is divisible into two subsections.
The first deals with raw rubber, the second with vulcanised
rubber.

We have already explained that, until recently, rubber was not
used in the un vulcanised condition, but that the excellent
physical properties of plantation rubber have made this
possible. It is interesting to compare the physical properties
of raw rubber with that vulcanised with sulphur. A compact
sample of crepe as received from the East will give breaking
strain of over 30 kilos per sq. cm. and over 300 per cent, elon-
gation. When mixed with sulphur and vulcanised, a breaking
strain of 150 kilos and elongation of 1,000 per cent, are not
unusual. It is possible that crepe rubber would give higher
figures if it could be prepared in the form of a compact ring,
as used for tests on vulcanised rubber. In any case, the
figures for vulcanised rubber are much in excess of those
for raw crepe rubber. It must also be remembered that a
breaking strain of 150 kilos is not permanent with vulcanised
rubber, for reasons which will be explained later.* To obtain
a reasonably permanent vulcanised product, the vulcanisation
would not be carried further than to give a figure of 100 kilos.
On the other hand, raw rubber is remarkable on account of its
great permanency, although subject to some physical changes
at ordinary atmospheric temperatures. Tensile tests, although
valuable, do not tell us all about the physical properties of a
sample of rubber. Abrasion tests, or tests designed to measure
resistance to wear and tear, would be more valuable, but, un-
fortunately, these properties do not lend themselves to simple
* Journal Soc. Chem. Ind., 1916, p. 872.
313

314 PREPARATION OF PLANTATION RUBBER

tests. There are grounds for believing that raw rubber is
superior in some respects to fully vulcanised rubber, if prepared
without the addition of finely divided mineral substances which
exert a toughening effect.

Sheet rubber gives results in some ways inferior to compact
crepe rubber when subjected to physical tests. Tensile
strength seldom exceeds 15 kilos, but the elongation is usually
higher — up to 600 or 700 per cent. That is to say, it stretches
more, but breaks more easily. If, however, we take into con-
sideration the diminution in sectional area of the test piece
during stretching, it will be seen that crepe and sheet rubber
have compensating properties.

As this matter of sectional area reduction during stretching
is important, both for raw and vulcanised rubber, it may be
briefly referred to here. When rubber is stretched, the volume
does not appreciably alter — at any rate, as regards uncom-
pounded rubber. Hence the reduction of sectional area on
stretching bears a simple relationship to the amount of stretch-
ing. If we double the length of the test piece, we halve the
sectional area ; if we treble the length, we reduce it to one-third,
and so forth. Hence, if we multiply the breaking strain by the
final length (i.e., length at break, taking the original length =i),
we obtain a figure, the " tensile product," which embodies both
breaking strain and stretching capacity. In effect it gives us
the breaking strain calculated on the sectional area at the
moment of rupture of the test piece. Adopting this formula,
we obtain for crepe —

Tensile Final Length — i.e., Tensile

Strength. Elongation + 1. Product.

30 x 4 120

and for smoked sheet

15 x 8 120

The difference in properties between crepe and sheet may
probably be attributed to the heavier rolling of the crepe,
which compacts the rubber. But if the crepe is rolled too much ,
the tensile strength falls, and there is no increased elongation
to compensate. For the same reason, crepe which has been

THE PROPERTIES OF RUBBER 315

rerolled in this country is inferior to crepe as received direct
from the plantation. At the most it is permissible to unite
two or three layers of thin crepe to a thicker one by a single
passage through even speed rollers, if the physical properties
of the original rubber are to be conserved.*

Attempts to prepare crepe for use in a raw state, by rerolling
uneven or irregular surfaced crepe in this country, only result
in a rubber with inferior physical properties. Nor can sheet be
rerolled to give crepe of good physical properties. The power
required to break down the sheet and the heat developed,
even on cold rollers, are an indication of physical properties
destroyed. For subsequent 'vulcanisation this is not a matter
of importance, because the vulcanising process restores to the
rubber the properties which are lost in the process of rolling
and milling or mastication.

Raw rubber has been used to some extent for proofing
purposes, as for the manufacture of material for hoods of
motor-cars. In this case no attempt is made to preserve the
physical properties. The rubber is masticated, mixed, taken
up with solvent and spread on the cloth exactly as if it were to
be vulcanised.

VULCANISED RUBBER. — We have already explained that the
properties of vulcanised rubber are dependent, to some extent,
on the specific nature of the raw rubber, or what De Vries
terms the " inner qualities." That is to say, differences appear
on vulcanising which are not apparent from the tests made on
the raw rubber. Indeed, no investigation or analysis of the
raw rubber can enable one to foresee exactly how the rubber
will behave on vulcanisation. This illustrates the deficiency
in our knowledge of vulcanisation. When dealing with soft,
resinous, or decomposed rubbers, it is safe to anticipate a weak
vulcanised product ; but when we come to deal with a number
of samples of " standard " crepe or sheet — i.e., sheet or crepe
passing a certain standard of appearance — it is found that
differences in vulcanising properties cannot be foreseen. This
matter is, however, not so great a drawback as might be imagined,
for reasonably well prepared consignments of standard crepe or
* Bulletin R.G.A., February, 1922, p. 64.

3i6 PREPARATION OF PLANTATION RUBBER

sheet differ but little from one another, and the difference is
mainly in the ease with which they break down, or the rate or
speed with which they vulcanise, and not with the properties
of the vulcanised product. Many of the plantation scrap grades
are equal to or nearly equal to " standard " ; but some of these,
as also the rubber produced by native holders, show appreciable
variation, and are the source of most of the complaints which
emanate from manufacturers. We shall consider in turn the
different grades and the effect of the usual surface defects,
such as mould, spots, etc.

CREPE RUBBER. — Oil marks and tackiness are the most
serious defects from the manufacturing standpoint. In the first
part of this book we have shown that damage caused by the
so-called oil marks is not due to the oil, but to traces of copper
from the bearings of the machines. There are several metallic
compounds which cause deterioration of rubber both raw and
vulcanised, but copper is the most deadly, and rubber showing
signs of deterioration is rightly rejected by the manufacturers.

The only other defect of crepe rubber which has any bearing
on its use in manufacture is mould. Crepe rubber very seldom
shows the ordinary surface moulds not uncommon in sheet-
rubber. There are, however, microscopic growths which
cause the development of coloured spots referred to in detail
in the earlier part of this book. The rubber hydrocarbon itself
does not appear to be affected by the moulds, but some of the
serum constituents are altered, with the result that the rubber
vulcanises more slowly than it otherwise would do. For this
reason, crepe rubber with coloured spots may give rise to
trouble in the factory.

SHEET RUBBER. — The commonest defect is mould.* This is
usually of a light surf ace type, easily brushed off, and numbers of
vulcanising tests failed to trace any reduction in rate of vulcan-
ising or other defect due to this. In spite, however, of the
harmlessness of light surface moulds, they are looked upon
with suspicion by the manufacturer. Occasionally samples
of smoked sheet are offered contaminated with a " heavy " type

* Bulletin R.G.A., February, 1921, p. 97; April, 1921, p. IQO; June,
1921, p. 243; November, 1921, p. 472.

THE PROPERTIES OF RUBBER 317

of mould. The sheet feels damp and " heavy " or flabby,
and contains an excess of moisture; sometimes a moist exu-
dation is noticeable on the surface, and " virgin " patches are
present. Such sheet vulcanises more slowly than F.A.Q.
samples, but does not necessarily show other defects after
washing and drying.

" Stretching rusty," as already explained, is due to a dry
film on the surface of the sheet, and according to a recent
investigation, this film consists, not of serum substances, but
of a microscopic mould growth, which presumably grows on
the serum substances. A sample of sheet which stretches
rusty gives the rubber a " dry " appearance, and for a long
time manufacturers mistook the surface film for resin. On
the assumption that such rubber was " resinous " they rejected
it, and to this day it is regarded as a defect, although it has no
influence on the vulcanising properties of the rubber.

It is hardly necessary to point out that defective appearance,
such as is due to thickened edges, faint markings, bubbles, and
so forth, have no effect on the vulcanising properties of the
rubber. They only point to some irregularity or carelessness
in preparation. The only justification for distinguishing
between rubber of good and bad appearance is that the former
bears the impress of careful preparation, and is therefore more
likely to be uniform in rate of vulcanising.

Similar considerations apply to the colour of smoked sheet,
which may vary from a pale yellow-brown, through various
shades of red-brown to dark brown. There are various factors
affecting the colour, but the buyer can see but one — viz., the
" degree " of smoking — and the rubber, from his point of view,
may be undersmoked or oversmoked. No doubt the degree
of smoking affects the vulcanising properties, but to a less
extent than was at one time imagined. In a recent paper*
it has been shown that the average breaking strain and rate of
cure of a number of samples of smoked sheets were practically
the same for light as for dark sheets.

VARIATION IN PHYSICAL PROPERTIES. — A very large number
of tests on vulcanised specimens of plantation rubber have been
* Bulletin R.G.A., December, 1921, p. 521.

3i8 PREPARATION OF PLANTATION RUBBER

carried out. The rubber was almost invariably mixed with
7 to 10 per cent, of sulphur, and no other ingredient, and
vulcanised to give the maximal breaking load. Unfortunately,
this determination is subject to a very appreciable experimental
error, so that a large number of determinations are necessary to
give a reliable figure. It is quite impracticable to make a
large number of determinations in routine testing, on account
of the labour involved. It is usual to make five, or possibly
ten, determinations, although some investigators have been
content with two. It is generally conceded that any excep-
tionally low figures should be ignored, as probably caused by
some flaw or irregularity in the test piece. On the other hand,
a study of actual determinations shows an occasional exces-
sively high figure, and it is questioned whether this also should
be left out of account. Others ignore all except the highest
figure, and take this to represent the true breaking strain.
As a consequence, the figures published by different workers
show considerable variation. De Vries has analysed a large
number of the figures obtained in systematic examination of
estate samples, and has constructed curves to illustrate the
results.* It is open to question how far the variations shown
are attributable to experimental error. The figures show,
however, that the variation in breaking strain is relatively
small, and not very different for crepe and sheet rubber. In
our opinion, undue importance should not be attached to very
high or exceptionally high figures for breaking strain, which
are occasionally met with. Provided the figure does not fall
much below the average, the sample may be regarded as
satisfactory. It is very seldom that any sample of first latex
estate rubber does not show satisfactory figures.

THE RATE OF CURE OR RATE OF VULCANISATION is subject
to more exact measurement, whether this be based on the
physical or the chemical properties of the rubber. If the
testing machine be provided, as is usual, with an autographic
attachment, the position of the curves traced on the recording
paper gives a measurement of the rate of cure. These load-
stretch curves, to which reference has already been made,

* " Estate Rubber," p. 466.

THE PROPERTIES OF RUBBER 319

take up a definite position in accordance with the physical
properties ; it is only the length of the curve, or the point where
it terminates (which gives the breaking strain and elongation
at break), which is largely fortuitous.

As a measure of rate of cure we may take the actual measure-
ments made on the record.* It is convenient to measure the
elongation produced by a load of 130 kilos per sq. cm., as all
fully vulcanised rings of soft rubber should give higher breaking
load figures. For less cured or weaker samples a lower figure
may be taken, such as 60 kilos. We have found that when
fully vulcanised to give the maximal breaking strain, the elonga-
tion at a load of 130 kilos is in the neighbourhood of 850 per
cent, (final length 950 per cent.). This applies to ordinary
samples of estate rubber under the conditions of testing
indicated above. If, however, the proportion of sulphur be
considerably reduced, or mineral ingredients in a fine state
of division be added to the mixing, or accelerators, whether
organic or inorganic, be employed, the above relationship no
longer holds. Nor does it hold with regard to plantation
rubber prepared in an exceptional manner, as, for instance,
matured coagulum or " slab."

There is a second method of determining the rate of cure — •
namely, by analysing a vulcanisate produced under standard
conditions, and determining the amount of sulphur which has
entered into chemical combination with the rubber. For this
purpose the weighed sample is cut thin or creped thin, and
exhaustively extracted with acetone to remove any " free "
sulphur — that is, sulphur not in combination with the rubber.
The sulphur remaining is then determined and calculated as
a percentage of the raw rubber contained in the sample taken.
This gives the so-called coefficient of vulcanisation.

If we compare the coefficient with the time of cure at a
constant temperature for an ordinary sample of plantation
rubber, they are found to be approximately proportional, so
long as the sulphur is in sufficient excess." The amount of
combined sulphur is, therefore, an index of the time vul-
canisation has been in progress (under standard conditions of
* Bulletin R.G.A., June, 1921, p. 246.

320 PREPARATION OF PLANTATION RUBBER

temperature, etc.), and, therefore, the coefficient is a measure
of the rate of cure.

The change in position of the load-stretch curve is not
directly proportional to the time of heating, and it therefore
follows that it is also not directly proportional to the coefficient.
For ordinary samples of crepe and sheet the relationship is,
however, not very far removed from proportionality. This
applies particularly to sheet rubber. The relationship is readily
seen on plotting one against the other and tracing the curves.
For sheet we get an almost straight line ; for crepe there is
some curvature.* For ordinary estate samples of sheet and
crepe rubber the maximal breaking strain is obtained when the
coefficient reaches approximately five units, so that this corre-
sponds to the elongation of 850 per cent, at a load of 130 kilos.

Either physical or chemical methods may, therefore, be used
for determining the rate of cure of ordinary sheet or crepe
rubber, but great care must be taken when interpreting the
results obtained with rubber prepared in an unusual manner.
The rate of cure may be expressed in terms of the time taken
to vulcanise the rubber at a constant temperature (in our case
138° C.), so as to give an elongation of 850 per cent, at a load
of 130 kilos, or to give a coefficient of five units. The higher
the figure so obtained, the slower curing the rubber. To
express the results more directly as rate of cure, we have adopted
the plan of taking an average crepe rubber, calling the rate of
cure 100 units, and expressing the rate of cure of other samples
in these terms. Thus, a sample which gave a coefficient of
four only, in the time taken by the standard to give a coefficient
of five, would have a rate of cure four-fifths of the standard,
that is, 80; or if a sample takes only two hours to give an elon-
gation of 850 per cent., whereas the standard takes three hours,
the rate of cure of the sample will be f of standard or i5O.f

As stated, the coefficient is approximately directly propor-
tional to the time of cure ; it is also independent of the propor-
tion of sulphur, if. in fair excess, and in the presence of inert
ingredients. It is also independent of the amount of masti-

* Bulletin R.G.A., June, 1921, p. 246, October, 1921, p. 398.
t Journal Soc. Chem. Ind., 1918, p. 280.

THE PROPERTIES OF RUBBER 321

cation giv^n to the original raw rubber, however great. On
the other hand, the position of the load-stretch curve is variously
modified by these factors — in some respects, therefore, the
coefficient is a more reliable index. However, the coefficient
is influenced by accelerators, so that here also great care must
be exercised when interpreting results. For the purpose of
detecting variations in rate of cure, it is best to choose a mixing
which is particularly sensitive. In the first place, there must
be an ample excess of sulphur; and in the second place, no
ingredient should be added which will complicate the load-
stretch curves, and no accelerators should be present which
may possibly tend to obscure the vulcanising properties of
the rubber itself. It has been found, therefore, that the best
mixing to use consists of rubber with an excess of sulphur — say ,
in the proportion 9 : i without other ingredients. The rate of
cure of a specimen of plantation rubber is attributed to the
presence of certain natural vulcanising catalysts, because it is
found that carefully purified raw rubber (that is, with the
resinous and nitrogenous constituents removed) vulcanises
very slowly or hardly at all, but that on replacing the extracted
matter the rate of vulcanising is restored. The natural catalysts
contained in the extracted matter are influenced to a varying
degree by some of the common ingredients of manufactured
rubber articles. This applies particularly to litharge (oxide
of lead), to which reference has already been made. Thus,
acetone extraction of raw rubber to remove resinous matter has
but little effect on the vulcanising properties of a mixture of
rubber and sulphur. But if litharge be a constituent, it is
found that acetone-extracted rubber will hardly vulcanise at all.
From this, it follows that a rubber giving a low acetone extract
may be found to vulcanise exceptionally slowly in a mixing con-
taining litharge, whereas it shows no such defect when com-
pounded with sulphur only.* Litharge is used to a very large
extent, as it has a balancing effect in a rubber compound — that
is to say, it allows of appreciable variation in vulcanising condi-
tions, without corresponding alteration in the state of cure.f

* Journal Soc. Chem. Ind., 1916, p. £74.
f Ibid., 1915, p 524.

21

322 PREPARATION OF PLANTATION RUBBER

INFLUENCE OF VARIOUS FACTORS IN RAW RUBBER PREPARA-
TION ON THE " RATE OF CURE," OR " RATE OF VULCANISATION."
— As the capacity of a rubber for vulcanisation depends on the
presence of small quantities of accessory substances in the
serum which act as catalysts, the rate of vulcanisation (or
curing) will depend on the nature and quantity of such sub-
stances present in the rubber. A very small quantity of these
substances has a considerable influence on rate of vulcanising,
and as the substances are difficult to isolate and identify, our
knowledge of their formation and chemical nature is not as
definite as is desirable. Substances have been isolated having
the characteristics of " simpler bases." Bodies of this class
are formed by putrefaction of organic matter, and can be
separated in much larger quantity from coagulated latex, which
has been allowed to putrefy before working up than from
such which has been worked up without giving time for an
appreciable amount of putrefaction to take place. Further,
rubber from putrefied coagulum vulcanised much faster than
that ordinarily prepared, so that we are justified in connecting
the putrefaction bases with the rate of vulcanisation. More-
over, it has been shown that any treatment of the latex or
coagulum which inhibits the development of putrefactive
organisms also prevents the rubber vulcanising as fast as would
otherwise have been the case.* Also, the crude bases isolated
from fast vulcanising rubber have the power of increasing
the rate of vulcanisation when added to ordinary slow vulcan-
ising rubber. f

On the other hand, there are one or two facts which are
difficult although not impossible to fit in with theory. Thus,
although the putrefaction bases are very easily soluble in water
and acetone, they cannot be removed by washing on the creping
rollers, or by acetone extraction. This may be due to the power
of colloidal substances to retain other crystalloidal substances,
such as the bases, which, in consequence, cannot be washed out.
A parallel case is the retention of small quantities of water

* Eaton and Co-workers: See Bulletin No. 27, F.M.S. Department
of Agriculture.

t Journal Soc. Chem. Ind., 1917, p. 365.

THE PROPERTIES OF RUBBER 323

soluble substances in the soil . Also , the theory does not explain
why rubber obtained by evaporation of latex at relatively high
temperatures is fast vulcanising, although the possibility of
putrefaction is excluded.

As regards practical results, it follows that the rate of vul-
canisation (or cure) of a sample of rubber will depend on the
time allowed to elapse between the collection of the latex and
treatment till the rubber is dry, as also on atmospheric condi-
tions. Thus, slow drying will result in an increased rate of
cure, for it gives an opportunity for putrefactive organisms to
play a part. The results will, however, be influenced by the
extent to which the rubber was washed previous to hanging,
and so forth. Smoking is an antiseptic process and will,
therefore, tend to inhibit the action of micro-organisms and
produce a slower vulcanising rubber. On the other hand,
sheet contains more serum than crepe, so that there is more
food material for growth of micro-organisms. The net result
is to give a rubber (sheet) which usually vulcanises a little
faster than crepe.

Among other factors controlling the rate of cure, special
mention should be made of the nature and amount of coagu-
lants. Weak " organic " acids, such as acetic, lactic, tartaric,
etc., used in the minimal proportions (i to 1,200 of standard-
ised latex in the case of acetic acid), give the fastest vulcanising
rubber; "strong" mineral acids, such as sulphuric acid, even
when used in the minimal proportions (i to 2,000), yield slower
vulcanising rubber. Acid salts, such as alum, are intermediate
in effect. Increased proportions of coagulant cause a reduction
in rate of vulcanising with all coagulants, and the effect is
least noticeable in crepe rubber, intermediate in sheet rubber,
and most pronounced in " slab " rubber (discussed below).*

OTHER TYPES OF PLANTATION RUBBER. — We have up to now
confined our attention to ordinary thin air-dried crepe and
smoked sheet, as almost all plantation rubber is now marketed
in one or other of these two forms. There are, however, other
types, to which reference has been made. Of these, the most

* Bulletin R.G.A., July, 1919, p. 39; September, 1920, p. 343;
November, 1920, p. 433; October, 1921, p. 393; March, 1922, p. 134.

324 PREPARATION OF PLANTATION RUBBER

important is the thick blanket crepe, made chiefly in Ceylon
by rolling together thin crepe, which has been artificially dried
(Colombo drier or vacuum drier) . The heat of the driers causes
a surface stickiness, which is got rid of by rolling several thin
layers together to give one thick one. This rubber vulcanises
at about the same rate as ordinary thin crepe, for the relatively
high temperature of drying does not appear to influence the
rate of cure. The rubber is generally softer than air-dried
crepe, and is easily "let down" in naphtha; it is, therefore,
suitable for some solution work. Generally speaking, the
properties of blanket crepe do not differ materially from ordinary
thin crepe. Another type of rubber seldom met with is
matured slab or crepe, prepared from it. This type of rubber
is being made in small quantities on one or two estates, who
supply direct to the manufacturer. The method of prepara-
tion has already been described. It is unsuitable for sale in
the open market, as it contains a variable amount of moisture,
has the various surface defects such as slime, mould, and "rust,"
and there is the additional disadvantage that it is not easy to
judge of its cleanliness or freedom from coarse impurities by
inspection. If the slab rubber be creped and air-dried on the
spot, the product is of satisfactory appearance, except that it
is of low colour and may be streaked. As the crepe so pro-
duced vulcanises almost as fast as the original slab, the crepe
embodies all the advantages of a fast curing rubber with few
of the disadvantages of the slab itself. We have made experi-
ments from time to time, and found that by a judicious use of
sodium bisulphite it is possible to produce a fast vulcanising
crepe rubber sufficiently even and light in colour to satisfy
the Standards Committee.

A fast curing raw rubber is not necessarily a desirable type
for all manufacturing purposes. In the vulcanising of large
masses of rubber, a slower rather than a faster vulcanising rubber
may be desirable, so as to give ample time for the heat to pene-
trate and spread evenly throughout the mass. But for many
purposes a fast curing rubber enables a larger output to be
obtained, so that artificial organic accelerators are coming
more and more into use. The addition of such accelerators

THE PROPERTIES OF RUBBER 325

might be obviated, if a suitable fast curing rubber were available,
but it is essential that such rubber should be uniform. It is
just in this respect that slab rubber or crepe made therefrom
is found to be deficient.* The rate of cure depends on the func-
tions of wild bacteria, which are naturally sensitive to changes
of conditions, such as temperature, etc. The coagulated
rubber depends on chance circumstances for infection, and, as
a natural result, the activity of the bacteria and the nature and
amounts of active vulcanising agent produced will vary and
be difficult to control. Consequently, the rate of cure of slab
rubber shows considerably greater variation than ordinary
crepe or sheet. f This, in our opinion, is the main difficulty
of utilising " slab/' or crepe prepared from it. Experience
in other industries, using micro-organisms, has shown that
the only method of control has been to replace the wild growths
by cultures of some particular strain, as, for instance, in yeasts
for brewing. To control the rate of cure of slab, it might be
possible to use a special culture for the purpose.

Other less usual methods of preparation, referred to in the
earlier part of this book, do not call for particular mention, as
the properties of the rubber do not differ much from ordinary
sheet or crepe. It is mainly a matter of variation in rate of cure.

This short account of the vulcanising properties of plantation
rubber would not be complete without a reference to Fine Hard
Para, the premier rubber of the Amazon. This rubber has
come to be regarded as the standard high-grade product with
which plantation rubber may be compared, and many manu-
facturers are still of the opinion that it is unsurpassed by any
plantation product. Yet, when subjected to the ordinary
vulcanising tests, we find that samples of Fine Hard Para give
figures very similar to average plantation rubber; indeed, it is
not difficult to find specimens of plantation rubber which give
appreciably higher figures on testing. It is claimed, how-
ever, that Fine Para is more uniform than plantation rubber,
and can be relied on always to give the same results. Yet
tests on a series of Fine Hard Para specimens gave variations in

* Bulletin R.G.A., January, 1920, p. 6; January, 1921, p. 47.
•f Ibid., January, 1920, p. 68.

326 PREPARATION OF PLANTATION RUBBER

rate of cure similar to those found for plantation. Some figures
were published, which tended to show that the variation was
smaller for Fine Para, but it turned out that each of the samples
taken for examination consisted actually of a number of slices
cut from different balls, so that greater uniformity was not un-
expected . * The superiority of Fine Para is , therefore , somewhat
of a mystery. It is probable that some manufacturers prefer
to use it because they feel safer with it, and know actually
how it wrill behave from long experience. In one respect
Fine Para is possibly superior to most plantation rubber — that
is, for the preparation of raw rubber solution for sticking the
seams of waterproof garments, and for similar purposes. The
method of preparation may well influence the strength of the
raw rubber when used for this purpose. Plantation rubber
has been prepared in the same manner as Brazilian Para, in
particular on an estate in Java. The product resembles Bra-
zilian Para in appearance. Vulcanising tests gave satisfactory
figures, but, as already stated, this would not serve to show that
the rubber was equal to Brazilian Para from the manufacturer's
standpoint.

* Bulletin R.G.A., September, 1920, p. 347.

INDEX

ACETIC acid, 74, 279

Acid, acetic, 74, 279

-— , carbonic, gas, 289

— , formic, 279

— , hydrochloric, 282

— , hydrofluoric, 282

— , mixing, with latex, 79

— , nitric, 282

— . oxalic, 279

— , pyroligneous, 282

— , quantity of, 76

— , sulphuric, 279, 286

Acids for coagulation, effect of, on

rate of cure, 323
— , quantities necessary for modern

requirements, 78
Air-drying, aids to normal, 143
— , of crepe, rate of, 138
— , progress of, 140
Alcohol, coagulation with, 289
Alum, coagulation with, 282
Anti-coagulant for transport, 61
Anti-coagulants, 46
Artificial driers, 133, 148
Ash on sheet, 276
Assembling cases for shipment, 1 56

Bags for packing, 1 54
Bakau, 147
Bales for packing, 1 54
Bark in crepe, 232

shavings, 56, 123

sheet, 276

Bases in vulcanised rubber, 322
Basket plants, 10
Blanket crepe, properties of, 324
Blemishes of surface, 252
Blister in sheet, 272
Block rubber, 129, 246
Breaking down of rubber, 304
— load of test piece, 311
Bubbles in sheet, 269
Buildings, 159
Bulking latex, 69
Byrne curing process, 270

Calendered sheet, 304
Carbon dioxide, 289
Carbonic acid gas, 289
Cases, choice of, for packing, 153

Catalysts, natural, in rubber, 312

— , vulcanising, 312

Centralisation of factories, 221

Chinese vinegar, 286

Chinosol, 238

" Chula " drier, 148

Clippings, sheet, 275

Coagulant, 1 1 1

— , choice of, 74, 278

— , quantity of, 113

Coagulation, 74, ! 1 1

— centres, 62

— , premature, 46
— , spontaneous, 294.

— with alcohol 289

sugars, 287

various salts, 288

Coagulum, soft, 249

— , spongy undersurface of, 249

— , tearing of, 249

— , transport of, 59,63

— , working of, 103

Coefficient of vulcanisation, 319

Collecting latex, 38

— pails, 48

Collection, advantages of early, 60
Combustion, rate of, in smoke

house, 191
Compound crepes, 126

No. i, 151

No. 2, 151

Contents of cases, weight of. 1 56
Copper salts, cause of tackiness,

243

Cotton fibre in crepe, 230
Creosotic substances, 146
Crepe, air-drying of, 132

— bark in, 232

— bearing of defects in, on manu-
facture, 316

— bisulphite streaks in, 235

— colour of fine, 1 14

— dirt in, 227

— dirty edges of, 225

— drying houses for, 178

— fibre in, 230

— general style of finish, 223

— grades of, 150

— greenish, tacky streaks in, 228

— iron stains on, 225

327

328 PREPARATION OF PLANTATION RUBBER

Crepe, No. i fine pale, no

— , oil marks on, 226

— , oxidation streaks in, 234

— , rate of air-drying of, 138

— , rust stains on, 226

— , smoked, 130

— , surface moulds on, 241

— , weight increased in drying
house, 141

— , yellow latex streaks in, 234

— rubber, defects in 223

, lower grades of, 120

preparation of, no

, tensile strength of, 313

Cups, cleaning, 40

— , water in, 44

Cure, rate of, 318

Curing, 307

I

Da Costa process, 290

Decentralisation of factories 221

Defects of sheet, infrequent, 276

Derry process, 293

Designs and " layout " of tanks, i
176

Dirt in sheet, 276

Discoloration of rubber, dark, 249

Drains for tanks, 1 76

Drier, Colombo Commercial Com-
pany's, 136

Driers, artificial — for crepe rubber, !

, for sheet rubber, 148

— , " Chula," 148

— , vacuum, 134

Drum furnaces, horizontal, 189

Drying chamber, floor of, 187

, arrangements of, 1 86

— houses for crepe. 178

, hot air, 1 82

, ventilation of, 185

, windows of, 185

— of rubber, 132
— , period of, 145

— , rate of, effect on rate of cure, 323 i

Earth scrap, 124

— , collection of 58
Edges, thickened, after rolling, 251
Elongation of test piece, 31 1
Ends, thickened, after rolling, 251
Engines. 170
— , position of, 174

Factories, 172

— , centralisation of, 221

— , decentralisation of, 221

— , number of floors, 174, 178

— , ventilation of , 180

— , windows of, 181

Factory buildings, situation of, 216

— , choosing site for, 220

— , ideal arrangement of, 162

— operation, 65

Fibre cotton, in crepe, 230
Field maintenance, 13
Fine hard Para properties of, 325
First latex and other grades, per-
centage of, 59
Floor of drying chamber, 187

— factories, 173

— furnace room, 196
Formaline, 87
Formic acid, 74, 279
Formula for test mix, 3 1 1
Freezing (coagulation) process, 293
Fuel, consumption of, 196

Fuels for smoking, 146
Furnace room, floor of , 196

, Petaling type of, 192

Furnaces, horizontal drum, 189
— , " pot," 188

Germination, 6

Grades, number of, 151

Grading, 150

Grafting, 8

Grass squares, 14

Greasiness before smoking, 252

— of surface, 258
Grit in crepe, 232

Hand rolling sheets, 104
Hevea Brasiliensis, i
Hot air drying houses, 182
Hydrochloric acid, 282
Hydrofluoric acid, 282

Ilcken-Down process, 298
Instruments, method of using, 100
— , recording, 144
— , standardising, 98

Lallang, eradication of, 1 5
Latex, bulking, 69

— cups, choice of, 40

— , decomposition of, in the field,
270

— , first and other grades, percen-
tage of, 59

— , first quality, 150

— , mixing acid with, 79

— , mixing sodium bisulphite solu-
tion with, 117

— , preliminary treatment of, 65

— , reception of, at the store, 6 5

— , standard, 96

— , standardisation of, 69, no

— , straining, 67

— , transport of, 59

INDEX

329

Light, importance of, in factories,
172

Litharge, 312

Load stretch curve, 312, 319, 320,
321

Low grade rubbers, fibrous matter
in, 124

Lower grade rubber, care in manu-
facture, 129

Lubrication of machines, 166

Lump rubber, naturally coagulated,
120

Machinery, 159
Machines, access to, 169

— adequacy of, 160
arrangement of, 168
lubrication of, 166
position of, 173
sheeting, 166
speed of, 162

Mangrove, 147
Marking sheets, 105
Metrolac, 98, 100
Michie-Golledge system, 138
Mildew on surface, 260
Milky residue on serum, 249
Mixing acid with latex, 79
Moist glaze of surface, 258
Mould on surface, 260
Moulds, surface, on crepe, 241

Natural catalysts, 312
Nitric acid, 282
Nurseries, 9

Overcured, 307
Overvulcanised, 306
Oxalic acid, 279
Oxidation, prevention of, 56
— , variation due to, 254

Packing, 150
— , bags for, 1 54
— , bales for, 1 54

— cases, choice of, 153
— , folding for, 155

— , methods of, 156

— rooms, 211

Pale crepe, No. i fine, no
— rubber, former methods of mak-
ing, 118

— sheet, 89
Patches, 259, 260
— , virgin, 259
Payment by result, 5 3
Perished rubber, 306

Physical properties of rubber,

variation of, 317
Pits for smoke houses, 1 88

Pitting of surface, 250
Plantation rubber, testing of, 309
Planting, i

Plasticising of rubber, 304
Plasticity of plantation rubber, 309
" Pot " furnaces, 188
Power units, 170
Premature coagulation, 46
Preparation, special methods of,

290
Pyroligneous acid, 282

Racks, 1 86

Rate of cure, 307

Raw rubber, physical properties

of, 313

, tests on, 309

, uses of, 315

Recommendations, Rubber

Growers' Association, 152
Recording instruments, 144
Ribbing of sheet, 274
Rolling, 251
Rolls, grooving of, 164

— running hot, 165
" free," 165

Roof of smoke house, 197
Rubber, drying of , 132
Rubber Growers' Association, Re-
commendations, 152
Rubber, properties of , 3 1 3
— , smoking, 109
Rust, cause of, 267

— on sheet, 262

— , treatment to prevent, 265

Scrap washers, 57, 124
Screw plug, unsatisfactory, 73
Seed at stake, 10
Seeds, 2
Selection, 5
Senang folder, 156
Serum, milky residue on, 249
Sheet, ash on, 276
— , bark in, 276

— , bearing of defects on, in manu-
facture, 316
— , blisters in, 272
— , bubbles in, 269
— , clippings, 130, 275
— , creases in. 251
— , dirt in, 276
— , " dog ears," 251
— -, grades of, 151
— , infrequent defects of, 276
— , pale, 89
— , ribbing of, 274

— rubber, artificial driers for, 148
, defects in, 249

, preparation of, 89

330 PREPARATION OF PLANTATION RUBBER

Sheet rubber, rolling and marking
of, 102

•, tensile strength of, 3 1 3

— , rust on, 262

— , splinters in, 276

— , stickiness in, 274

— , style of, 101

— , support marks on, 273

— , surface pattern of, 274

— , thick ends of, 275

Sheeting machines, 166

Sheets, mis-shapen, 251

— , thickened patches in, 2 5 1

— , torn, 251

— , unevenness of appearance, 253

Short weights, 1 5 7

Skimming, 100

Skimmings, 122

Slab rubber, 299

, properties of, 324

Slope, 312

Smoke curing of sheet rubber, 143

, temperature of, 144

— , houses, 183

, Barker patent, 209

, Devon type, 200

, iron stoves for, 189

, Jackson type, 200

of brick, 198

rate of combustion in, 192

, roof of, 197

— , " Third Mile " type, 199

— , types of, 198
Smoked crepe, 1 30

— sheets, colour of, 255

— water for coagulation, 286
Smoking, effect on rate of cure, 323
— , greasiness before, 252

— rubber, 109

Smooth rolling of sheets, 104

Sodium bisulphite, 8o; 114

, abuse of, 85

, care of, 116

-, deterioration of, 115

, evaluation of , 1 1 5

, making a solution of, 85

— , quantity of, 84

— , residual traces of, 86

solution, mixing, with latex,

117

— sulphite, 86

, deterioration of, 115

, evaluation of, 115

Sorting, 150, 152

— rooms, 2 1 T
Spewing, 305
Splinters in sheet, 276
Spontaneous coagulation, 294
Spot disease, 235

in sheet rubber, 273

Spots, 259, 262
— , virgin, 259
Standard latex, 96

— sheet, 1 02

Standardising instruments, 98
Stickiness in sheet, 274

Stock solution, method of making,

Storage of rubber, 212, 216
Stoves, iron, for smoke houses, 189
Straining latex, 67
Streaks, 262
Stumps, 9

Sugars, coagulation with, 287
Sulphuric acid, 280, 286
— , buying, 280

, formula for use of, 280

, storing, 280

Sun-drying sheet rubber, 147
Support marks on sheet, 273
Surface blotches, coloured, 249
— -, dull or black, 258

— pattern of sheet, 274

Tackiness, cause of, 243

— , copper salts cause of, 243

— in rubber, 242
Tanks, 90

— , care of, 94

— , designs and " layout," 176

— , drains for, 1 76

— ; installation of, 93

— , situation of, 1 7 c

— , water-supply for, 177

Tapping, 38

— , former systems of, 29

— knives, 38

— systems, 38
Tartaric acid, 279
Tensile product, 314
Test mix, formula for, 311

— pieces, making of, 310
Testing of plantation rubber, 307
Thick ends of sheet, 275
Thinning, 19

Timber for smoking, 147
Tool sheds, 216
Transport, 60

— by coolie, 62

— of coagulum, 59, 63

— of latex, 59
Trays, 167

Treatment of rubber in the factory,
301

— to prevent rust, 265
Tree scrap, 55, 122
, care of, 56

— , oxidation of, 56
j Trees per acre, 26
j Trenches, silt catchment, 1 1

INDEX

Uniformity, 90

— in colour, lack of, 246

Vacuum driers, 134
Variation due to oxidation, 254
Vegetable extracts, 289
Ventilation of drying houses, 185

— factories, 180
Verandas, 175
Virgin spots, 258

Viscosity of rubber solution, 309
Vulcanisation, 301
— , rate of, 318
Vulcanised rubber, 318
— - — , tests on, 309

Vulcanising, 307

— catalysts, 312
— , " heat," 306

Washers, scrap, 57, 124
Washings, 122
Water-supply for tanks, 1 77
Weeding, clean, 1 3
Weights, " short," 157
Wickham process, 293
Windows of drying houses, 185

— factories, 181
Working of rubber, 304

Yields, 23, 25

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