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diff --git a/35510-h/35510-h.htm b/35510-h/35510-h.htm new file mode 100644 index 0000000..1d80428 --- /dev/null +++ b/35510-h/35510-h.htm @@ -0,0 +1,17033 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> + +<html xmlns="http://www.w3.org/1999/xhtml"> + <head> + <meta http-equiv="content-type" content="text/html; charset=iso-8859-1" /> + <title> + The Project Gutenberg eBook of The Preparation of Plantation Rubber, by Sidney Morgan, A.R.C.S. + </title> + <style type="text/css"> + + .bbox {border: solid 2px; background: #999966; margin-left:25%; margin-right: 25%;} + .bb {border-bottom: solid 1px;} + .blockquot {margin-left: 5%; margin-right: 5%; font-size: .9em;} + body {margin-left: 10%; margin-right: 10%;} + .br {border-right: solid 1px;} + .bt {border-top: solid 1px;} + .caption {text-align: center;} + .capt350 {margin-left: 35%; margin-right: 35%; text-align: justify;} + .capt500 {margin-left: 25%; margin-right: 25%; text-align: justify;} + .center {text-align: center;} + .denom {vertical-align: text-bottom; font-size: .7em;} + .enum {vertical-align: text-top; font-size: .7em;} + .figcenter {margin: auto; text-align: center;} + .footnote {margin-left: 10%; margin-right: 10%; font-size: 0.8em; background-color: #CCFFCC;} + .footnote .label {position: absolute; right: 84%; text-align: right; vertical-align: middle;} + .fnanchor {vertical-align: baseline; font-size: .8em; vertical-align: top; text-decoration: none;} + .fsize80 {font-size: .8em;} + .fsize100 {font-size: 1em;} + .fsize110 {font-size: 1.1em;} + .fsize125 {font-size: 1.25em;} + h1,h2,h3,h4 {text-align: center; clear: both;} + hr {width: 33%; margin-top: 2em; margin-bottom: 2em; margin-left: auto; margin-right: auto; clear: both;} + hr.c05 {width: 5%; margin-top: 1em; margin-bottom: 1em;} + hr.c25 {width: 25%; margin-top: 1em; margin-bottom: 1em;} + p {margin-top: .75em; text-align: justify; margin-bottom: .75em;} + .pagenum {position: absolute; left: 92%; font-size: smaller; text-align: right; color: gray;} + .smcap {font-variant: small-caps;} + .ssfont {font-family: sans-serif; font-size: 1.05em; font-weight: bold; font-style: normal;} + table {margin-left: auto; margin-right: auto; margin-top: 1em; margin-bottom: 1em; border-collapse: collapse;} + table.loi {margin-left: 15%; margin-right: 15%; padding: 1em;} + table.toc {margin-left: 10%; margin-right: 10%; padding: 1em;} + td.bottom {vertical-align: bottom;} + td.center {text-align: center;} + td.ind {text-indent: -1em;} + td.just {text-align: justify;} + td.left {text-align: left; padding-left: .5em; vertical-align: top;} + td.leftbot {text-align: left; vertical-align: bottom;} + td.padl {padding-left: 2.5em;} + td.padr {padding-right: 2.5em;} + td.right {text-align: right; vertical-align: top;} + td.rightbot {text-align: right; vertical-align: bottom;} + td.top {vertical-align: top;} + + </style> + </head> +<body> + + +<pre> + +Project Gutenberg's The Preparation of Plantation Rubber, by Sidney Morgan + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Preparation of Plantation Rubber + +Author: Sidney Morgan + +Contributor: Henry P. Stevens + +Release Date: March 7, 2011 [EBook #35510] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK RUBBER *** + + + + +Produced by Chris Curnow, Harry Lamé, Robin Curnow and +the Online Distributed Proofreading Team at +http://www.pgdp.net + + + + + + +</pre> + + +<h2>THE PREPARATION OF PLANTATION<br /> +RUBBER</h2> + +<hr class="c25" /> + + +<h1>THE PREPARATION</h1> +<h3>OF</h3> +<h1>PLANTATION RUBBER</h1> +<h4>BY</h4> +<h3>SIDNEY MORGAN, A.R.C.S.</h3> + +<p class="center">VISITING AGENT FOR ESTATES IN THE EAST; FORMERLY SENIOR SCIENTIFIC OFFICER<br /> +AND NOW HONORARY ADVISER TO THE RUBBER GROWERS’ ASSOCIATION<br /> +IN MALAYA</p> + +<h3>WITH A PREFACE AND A CHAPTER ON VULCANIZATION</h3> +<h4>BY</h4> +<h3>HENRY P. STEVENS, M.A. (<span class="smcap">Oxon.</span>,) <span class="smcap">Ph.D.</span>, F.I.C.</h3> +<p class="center">CONSULTING CHEMIST TO THE RUBBER GROWERS’ ASSOCIATION IN LONDON</p> + + +<h4>CONSTABLE & CO. LTD.<br /> +LONDON : BOMBAY : SYDNEY<br /> +1922</h4> + +<hr class="c25" /> + +<p class="center">PRINTED IN GREAT BRITAIN BY<br /> +BILLING AND SONS, LTD., GUILDFORD AND ESHER</p> + +<hr class="c25" /> + +<p class='pagenum'><a name="Page_v" id="Page_v">[v]</a></p> + + +<h2><a name="Ch0" id="Ch0"></a>PREFACE</h2> + + +<p>Mr. Sidney Morgan’s work on Plantation Rubber in the +East is so well known that he hardly needs introduction.</p> + +<p>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.</p> + +<p>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 +<span class='pagenum'><a name="Page_vi" id="Page_vi">[vi]</a></span>indirectly connected with the industry, such as importers, +brokers, and particularly the rubber manufacturers in this +country and in America. My experience has been that manufacturers +as a whole have but a vague idea as to the methods +employed in the preparation of plantation rubber, and this +work provides them with the opportunity of obtaining an +insight into the actual operations on the estates. It is most +desirable that a closer bond should unite the plantation and +manufacturing rubber industries. Such a result is best promoted +by a better understanding of the problems with which +each is confronted. Perhaps I may go so far as to suggest +that some leading scientific officer in the employment of one of +the large manufacturing concerns may take in hand a book +which will give the planters the equivalent of information in +regard to the manufacturing industry which the planters are +now offering to the manufacturers.</p> + +<p>The photographs in the earlier part of the book will give the +layman some conception of the enormous amount of labour +that must be expended in the opening up, planting, trenching, +and weeding the plantations which have replaced the virgin +jungle. The authors are indebted for most of these photographs +to Mr. H. Sutcliffe, one of the mycologists of the +Rubber Growers’ Association. The pictures of spotless +coagulating tanks and tiled verandahs regularly hosed down +will indicate the cleanliness necessary for the preparation of +the beautifully clean sheet and crepe rubber which became +available with the advent of plantation rubber. These results +are largely due to the work of Sidney Morgan and his colleagues, +on whom the planters have relied for technical +guidance and advice.</p> + +<p>As regards my own contribution this is confined to a general +outline of the subject. I have, therefore, omitted reference +to a number of matters which would have been dealt with in +detail had space permitted. The information given is based +on researches on vulcanisation carried out for the Rubber +Growers’ Association by the writer over a period of nine or +ten years. It was not found practicable to give detailed +references in all cases. The reports on which the conclusions +are based will, however, be found among the regular quarterly<span class='pagenum'><a name="Page_vii" id="Page_vii">[vii]</a></span> +reports made by the writer for the Association up to June, 1919. +Subsequent reports have been published in the Monthly +Bulletin of the Rubber Growers’ Association. We are indebted +to the Association for permission to publish details +from these reports, and also for the use made of numerous +earlier reports published both in London and in the East.</p> + +<hr class="c25" /> +<p class='pagenum'><a name="Page_ix" id="Page_ix">[ix]</a></p> + +<h2>CONTENTS</h2> + +<table class="toc" summary="ToC"> + +<tr> +<td colspan="2" class="center fsize125"><a href="#Part1">PART I</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Part1"><i>FIELD OPERATIONS</i></a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch1">CHAPTER I</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch1">PLANTING</a></td> +</tr> + +<tr> +<td> </td> +<td class="right fsize80">PAGE</td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec1_1">Seeds</a>—<a href="#Sec1_2">Seed selection</a>—<a href="#Sec1_3">Strain improvement +by bad propagation</a>—<a href="#Sec1_4">Nurseries</a>—<a href="#Sec1_5">Stumps</a>—<a href="#Sec1_6">Seed at +stake</a>—<a href="#Sec1_7">Basket plants</a>—<a href="#Sec1_8">Preparation of land</a>—<a href="#Sec1_9">Danger of +disease</a>—<a href="#Sec1_10">Clean clearing</a>—<a href="#Sec1_11">Loss of top-soil</a>—<a href="#Sec1_12">Silt-trenches +on slopes</a></td> +<td class="rightbot"><a href="#Page_1">1</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch2">CHAPTER II</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch2">FIELD MAINTENANCE</a></td> +</tr> + + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec2_1">Clean weeding</a>—<a href="#Sec2_2">Selective weeding</a>—<a href="#Sec2_3">Loss of +top-soil</a>—<a href="#Sec2_4">Grass ridges</a>—<a href="#Sec2_5">Lallang eradication</a>—<a href="#Sec2_6"><i>Mimosa +gigantea</i> (<i>M. invisa</i>)</a>—<a href="#Sec2_7">Green cover-plants</a>—<a href="#Sec2_8">Connection between weeding, +soil conservation, and soil improvement</a></td> +<td class="rightbot"><a href="#Page_13">13</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch3">CHAPTER III</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch3">THINNING OF AREAS</a></td> +</tr> + + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec3_1">Original planting per acre</a>—<a href="#Sec3_2">Ultimate stand per acre</a>—<a +href="#Sec3_3">Close-planting <i>versus</i> wide-planting</a>—<a href="#Sec3_4">When to commence thinning operations</a>—<a +href="#Sec3_5">How to select in preliminary rounds</a>—<a href="#Sec3_6">Later selections based on yields of +individuals</a>—<a href="#Sec3_7">Yields per tree, present and future</a>—<a href="#Sec3_8">Trees per acre</a></td> +<td class="rightbot"><a href="#Page_19">19</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch4">CHAPTER IV</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch4">TAPPING SYSTEMS</a></td> +</tr> + + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec4_1">Former methods</a>—<a href="#Sec4_2">Former systems</a>—<a href="#Sec4_3">Tendency +to reduce number of tapping cuts and frequency of tapping</a>—<a href="#Sec4_4">Period allowed for bark-renewal</a>—<a +href="#Sec4_5">Modern systems</a>—<a href="#Sec4_6">Superimposed cuts</a>—<a href="#Sec4_7">Single cuts, +etc.</a>—<a href="#Sec4_8">Tapping experiments</a>—<a href="#Sec4_9">R.G.A. experiment</a>—<a +href="#Sec4_10">Alternate-daily <i>versus</i> daily tapping</a></td> +<td class="rightbot"><a href="#Page_28">28</a></td> +</tr> + +<tr> +<td colspan="2"> <span class='pagenum'><a name="Page_x" id="Page_x">[x]</a></span></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch5">CHAPTER V</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch5">TAPPING AND COLLECTING</a></td> +</tr> + + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec5_1">Tapping knives</a>—<a href="#Sec5_2">Personal equation in use of knives</a>—<a +href="#Sec5_3">Choice of latex cups</a>—<a href="#Sec5_4">Cleaning of cups</a>—<a href="#Sec5_5">Water in cups</a>—<a +href="#Sec5_6">Premature (spontaneous) coagulation</a>—<a href="#Sec5_7">Prevention of spontaneous coagulation</a>—<a +href="#Sec5_8">The use of anti-coagulants in the field</a>—<a href="#Sec5_9">Collecting pails</a>—<a href="#Sec5_10">Payment +by result</a>—<a href="#Sec5_11">Methods for calculation of yields per coolie</a>—<a href="#Sec5_12">Tree-scrap, oxidation +of</a>—<a href="#Sec5_13">Prevention of oxidation</a>—<a href="#Sec5_15">Bark-shavings</a>—<a href="#Sec5_16">Collection +and storage of shavings</a>—<a href="#Sec5_17">Treatment of shavings</a>—<a href="#Sec5_18">Collection of earth-scrap</a></td> +<td class="rightbot"><a href="#Page_38">38</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch6">CHAPTER VI</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch6">TRANSPORT OF LATEX AND COAGULUM</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec6_1">Percentages of “first” latex and other grades</a>—<a href="#Sec6_2">Early +collection of latex</a>—<a href="#Sec6_3">Transport, nature of</a>—<a href="#Sec6_4">Light railways</a>—<a +href="#Sec6_5">Motor-lorries</a>—<a href="#Sec6_6">Bullock-carts</a>—<a href="#Sec6_7">Care of transport vessels</a>—<a +href="#Sec6_8">Use of an anti-coagulant during transport</a>—<a href="#Sec6_9">Transport by coolie</a>—<a +href="#Sec6_10">Coagulation centres (stations)</a>—<a href="#Sec6_11">Transport of coagulum</a></td> +<td class="rightbot"><a href="#Page_59">59</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize125"><a href="#Part2">PART II</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Part2"><i>FACTORY OPERATIONS</i></a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch7">CHAPTER VII</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch7">PRELIMINARY TREATMENT OF LATEX</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec7_1">Reception at store</a>—<a href="#Sec7_2">Receptacles</a>—<a +href="#Sec7_3">Jars</a>—<a href="#Sec7_4">Tanks</a>—<a href="#Sec7_5">Necessity for close supervision</a>—<a +href="#Sec7_6">Need for utmost cleanliness</a>—<a href="#Sec7_7">Straining of latex</a>—<a +href="#Sec7_8">Strainers</a>—<a href="#Sec7_9">Facilitation of straining</a>—<a href="#Sec7_10">Bulking of latex</a>—<a +href="#Sec7_11">Standardised dilution of latex</a>—<a href="#Sec7_12">Facilities for receiving and handling latex</a>—<a +href="#Sec7_13">Reception verandahs</a>—<a href="#Sec7_14">Receiving vessels</a>—<a href="#Sec7_15">Types of +installations</a></td> +<td class="rightbot"><a href="#Page_65">65</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch8">CHAPTER VIII</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch8">COAGULATION</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec8_1">Choice of coagulant</a>—<a href="#Sec8_2">Strength of acid solution</a>—<a +href="#Sec8_3">Making stock solution</a>—<a href="#Sec8_4">Quantity for use</a>—<a href="#Sec8_5">Quantities under modern +requirements</a>—<a href="#Sec8_6">Care in mixing</a>—<a href="#Sec8_7">Method of mixing with latex</a>—<a +href="#Sec8_8">Use of sodium bisulphite as an anti-oxidant</a>—<a href="#Sec8_9">Quantities for use</a>— +<a href="#Sec8_10">Formulæ</a>—<a href="#Sec8_11">Abuse of the chemical</a>—<a href="#Sec8_12">Residual traces in the +dry rubber</a>—<a href="#Sec8_13">Use of sodium sulphite as an anti-coagulant, quantities for use</a>—<a +href="#Sec8_14">Formulæ</a>—<a href="#Sec8_15">Use of Formalin as anti-coagulant</a>—<a href="#Sec8_16">Formulæ +for use</a></td> +<td class="rightbot"><a href="#Page_74">74</a></td> +</tr> + +<tr> +<td colspan="2"> <span class='pagenum'><a name="Page_xi" id="Page_xi">[xi]</a></span></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch9">CHAPTER IX</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch9">PREPARATION OF SHEET RUBBER</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec9_1">Pale (air-dried) sheets</a>—<a href="#Sec9_2">Uniformity of product</a>—<a +href="#Sec9_3">Pans <i>versus</i> tanks</a>—<a href="#Sec9_4">The ideal tank</a>—<a href="#Sec9_5">Modern +installations</a>—<a href="#Sec9_6">Care of tanks</a>—<a href="#Sec9_7">Standardised dilution of latex</a>—<a +href="#Sec9_8">Variation in dimensions and density of coagulum</a>—<a href="#Sec9_9">Standardising instruments</a>—<a +href="#Sec9_10">Method of using</a>—<a href="#Sec9_11">Skimming latex</a>—<a href="#Sec9_12">Style of sheets</a>—<a +href="#Sec9_13">Standard sheets</a>—<a href="#Sec9_14">Rolling and marking</a>—<a href="#Sec9_15">When to work the +coagulum</a>—<a href="#Sec9_16">Hand-rolling</a>—<a href="#Sec9_17">Power smooth-rolling</a>—<a href="#Sec9_18">Marking +rolls</a>—<a href="#Sec9_19">Preparation for smoke-curing</a>—<a href="#Sec9_20">Caution against accumulation of wet +sheets</a>—<a href="#Sec9_21">Hot-water treatment</a>—<a href="#Sec9_22">Dripping in the open air</a>—<a +href="#Sec9_23">When to place in smoke-house</a></td> +<td class="rightbot"><a href="#Page_89">89</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch10">CHAPTER X</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch10">PREPARATION OF CREPE RUBBER</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec10_1">First consideration, fine pale crepe</a>—<a href="#Sec10_2">Standardised dilution of +latex</a>—<a href="#Sec10_3">Coagulation and coagulant</a>—<a href="#Sec10_4">Quantities of coagulant</a>—<a +href="#Sec10_5">Colour of rubber</a>—<a href="#Sec10_6">Sodium bisulphite (use of)</a>—<a href="#Sec10_7">Evaluation and +deterioration of the bisulphite and sulphite of sodium</a>—<a href="#Sec10_8">To distinguish between these two +chemicals</a>—<a href="#Sec10_9">Care of sodium bisulphite</a>—<a href="#Sec10_10">Mixing solution with latex</a>—<a +href="#Sec10_11">Former methods of making pale rubber</a>—<a href="#Sec10_12">Working the coagulum</a>—<a +href="#Sec10_13">Lower grades of crepe</a>—<a href="#Sec10_14">Naturally coagulated lump</a>—<a href="#Sec10_15">Skimmings +and washings</a>—<a href="#Sec10_16">Tree-scrap</a>—<a href="#Sec10_17">Bark-shavings</a>—<a +href="#Sec10_18">Earth-scrap</a>—<a href="#Sec10_19">Fibrous matter in low-grade rubbers</a>—<a +href="#Sec10_20">Scrap-washers</a>—<a href="#Sec10_21">Compound crepes</a>—<a href="#Sec10_22">Increased care with lower +grades</a>—<a href="#Sec10_23">Block rubber from crepe</a>—<a href="#Sec10_24">Smoked crepe <i>versus</i> sheet +clippings</a></td> +<td class="rightbot"><a href="#Page_110">110</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch11">CHAPTER XI</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch11">DRYING OF RUBBER</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec11_1">Air-drying of crepes</a>—<a href="#Sec11_2">Artificial driers for crepes</a>—<a +href="#Sec11_3">Vacuum drying</a>—<a href="#Sec11_4">Hot-air driers</a>—<a href="#Sec11_5">Michie-Golledge system</a>—<a +href="#Sec11_6">Rate of air-drying</a>—<a href="#Sec11_7">When drying takes place</a>—<a href="#Sec11_8">Increase in weight of +drying crepe</a>—<a href="#Sec11_9">Differences in weight</a>—<a href="#Sec11_10">Aids to normal drying</a>—<a +href="#Sec11_11">Smoke-curing of sheet rubber</a>—<a href="#Sec11_12">Instruments for recording temperature</a>—<a +href="#Sec11_13">Temperatures of smoke-house</a>—<a href="#Sec11_14">Period of drying</a>—<a href="#Sec11_15">Fuels for +smoking</a>—<a href="#Sec11_16">Sun-drying of sheet rubber</a>—<a href="#Sec11_17">Artificial driers for sheet rubber</a></td> +<td class="rightbot"><a href="#Page_132">132</a></td> +</tr> + +<tr> +<td colspan="2"> <span class='pagenum'><a name="Page_xii" id="Page_xii">[xii]</a></span></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch12">CHAPTER XII</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch12">SORTING, GRADING, AND PACKING</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec12_1">Reducing number of grades</a>—<a href="#Sec12_2">Reduction carried too far</a>—<a +href="#Sec12_3">R.G.A. recommendations</a>—<a href="#Sec12_4">Care in sorting</a>—<a href="#Sec12_5">Choice of packing +cases</a>—<a href="#Sec12_7">Bags</a>—<a href="#Sec12_8">Bales</a>—<a href="#Sec12_9">Folding of crepe</a>—<a +href="#Sec12_10">Mechanical folders</a>—<a href="#Sec12_6">Care in assembling</a>—<a href="#Sec12_11">Methods of +packing</a>—<a href="#Sec12_12">Weight of contents</a>—<a href="#Sec12_13">Short weights</a></td> +<td class="rightbot"><a href="#Page_150">150</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize125"><a href="#Part3">PART III</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Part3"><i>MACHINERY AND BUILDINGS</i></a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch13">CHAPTER XIII</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch13">MACHINES</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec13_1">Quality of metal in rolls</a>—<a href="#Sec13_2">Nature of roll-bearings</a>—<a +href="#Sec13_3">Brass liners</a>—<a href="#Sec13_4">Liners of alloy or of cast-iron</a>—<a href="#Sec13_5">Adequacy of +machines</a>—<a href="#Sec13_6">Arrangement of battery</a>—<a href="#Sec13_7">Speed of machines</a>—<a +href="#Sec13_8">Gear ratios</a>—<a href="#Sec13_9">Grooving of rolls</a>—<a href="#Sec13_10">Heating of rolls</a>—<a +href="#Sec13_11">Sheeting machines</a>—<a href="#Sec13_12">Lubrication</a>—<a href="#Sec13_13">Trays</a>—<a +href="#Sec13_14">Position of battery</a>—<a href="#Sec13_15">Drainage of battery</a>—<a href="#Sec13_16">Access to back of +machines</a>—<a href="#Sec13_17">Engines</a>—<a href="#Sec13_18">Power</a></td> +<td class="rightbot"><a href="#Page_159">159</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch14">CHAPTER XIV</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch14">FACTORIES</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec14_1">General construction</a>—<a href="#Sec14_2">Plenty of light</a>—<a +href="#Sec14_3">Floors</a>—<a href="#Sec14_4">Drainage of</a>—<a href="#Sec14_5">How many storeys</a>—<a +href="#Sec14_6">Verandahs</a>—<a href="#Sec14_7">Tanks, situation of</a>—<a href="#Sec14_8">Designs and lay-out</a>—<a +href="#Sec14_9">Drains</a>—<a href="#Sec14_10">Water supply</a></td> +<td class="rightbot"><a href="#Page_172">172</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch15">CHAPTER XV</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch15">OTHER BUILDINGS</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec15_1">Drying-houses for crepe rubber</a>—<a href="#Sec15_2">How many storeys</a>—<a +href="#Sec15_3">Ventilation</a>—<a href="#Sec15_4">Windows</a>—<a href="#Sec15_5">Effect of light</a>—<a +href="#Sec15_6">Effect of direct sun-rays</a>—<a href="#Sec15_7">Hot-air houses</a>—<a +href="#Sec15_8">Smoke-houses</a>—<a href="#Sec15_9">Various types</a>—<a href="#Sec15_10">Ordinary smoke-houses</a>—<a +href="#Sec15_11">General ventilation</a>—<a href="#Sec15_12">Windows</a>—<a href="#Sec15_13">Racks of supports</a>—<a +href="#Sec15_14">Floors</a>—<a href="#Sec15_15">Furnaces in general</a>—<a href="#Sec15_16">Pit-fires</a>—<a +href="#Sec15_17">Pot-fires</a>—<a href="#Sec15_18">Iron stoves</a>—<a href="#Sec15_19">Horizontal drum-furnaces</a>—<a +href="#Sec15_20">Rate of combustion</a>—<a href="#Sec15_21">Brick stoves</a>—<a href="#Sec15_22">Pataling type +of</a>—<a href="#Sec15_23">Consumption of fuel</a>—<a href="#Sec15_24">Floor of furnace room</a>—<a +href="#Sec15_25">Roof</a>—<a href="#Sec15_25a">Brick built houses</a>—<a href="#Sec15_26">“Third Mile” +type</a>—<a href="#Sec15_27">Jackson cabinet</a>—<a href="#Sec15_28">Devon type</a>—<a href="#Sec15_29">Detailed +description of</a>—<a href="#Sec15_30">Barker patent design</a></td> +<td class="rightbot"><a href="#Page_178">178</a></td> +</tr> + +<tr> +<td colspan="2"> <span class='pagenum'><a name="Page_xiii" id="Page_xiii">[xiii]</a></span></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch16">CHAPTER XVI</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch16">OTHER BUILDINGS (<i>continued</i>), AND SITUATION OF BUILDINGS</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec16_1">Sorting-room</a>—<a href="#Sec16_2">Packing room</a>—<a href="#Sec16_3">Store +rooms</a>—<a href="#Sec16_4">Storage of rubber</a>—<a href="#Sec16_5">Need for special accommodation</a>—<a +href="#Sec16_6">Floor of store room</a>—<a href="#Sec16_7">Local conditions</a>—<a href="#Sec16_8">Temperature and +humidity</a>—<a href="#Sec16_9">Incidence of moulds</a>—<a href="#Sec16_10">Effect upon smoked sheets</a>—<a +href="#Sec16_11">Tool-sheds and stores</a>—<a href="#Sec16_12">Situation of buildings</a>—<a href="#Sec16_13">Position with +respect to points of the compass</a>—<a href="#Sec16_14">Choosing a factory site</a>—<a +href="#Sec16_15">Centralisation</a>—<a href="#Sec16_16">Decentralisation</a></td> +<td class="rightbot"><a href="#Page_211">211</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize125"><a href="#Part4">PART IV</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Part4"><i>THE FINISHED RUBBER</i></a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch17">CHAPTER XVII</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch17">DEFECTS IN CREPE RUBBERS</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec17_1">General style of finish</a>—<a href="#Sec17_2">Dirty edges</a>—<a +href="#Sec17_3">Iron-stains</a>—<a href="#Sec17_4">Rust-stains</a>—<a href="#Sec17_5">Oil-marks</a>—<a +href="#Sec17_6">Trays</a>—<a href="#Sec17_7">Dirt</a>—<a href="#Sec17_8">Holes</a>—<a href="#Sec17_9">Greenish and +tacky streaks</a>—<a href="#Sec17_10">Not due to oil <i>per se</i></a>—<a href="#Sec17_11">Tackiness and copper</a>—<a +href="#Sec17_12">Cotton and other fibre</a>—<a href="#Sec17_13">Bark and grit</a>—<a href="#Sec17_14">Sand</a>—<a +href="#Sec17_15">Oxidation streaks</a>—<a href="#Sec17_16">Yellow streaks</a>—<a href="#Sec17_17">Bisulphite +streaks</a>—<a href="#Sec17_18">Spot disease</a>—<a href="#Sec17_19">Cause of</a>—<a href="#Sec17_20">Influence of rate +of drying</a>—<a href="#Sec17_21">Percentage of moisture</a>—<a href="#Sec17_22">Humidity of atmosphere</a>—<a +href="#Sec17_23">Prevention of disease</a>—<a href="#Sec17_24">Infection by contact</a>—<a href="#Sec17_25">Outbreak of +dormant spores</a>—<a href="#Sec17_26">Rules to be observed</a>—<a href="#Sec17_27">Surface moulds or mildew</a>—<a +href="#Sec17_28">Tackiness in general</a>—<a href="#Sec17_29">Full discussion of</a>—<a href="#Sec17_30">Experimental +reproduction</a>—<a href="#Sec17_31">Lack of uniformity in colour</a>—<a href="#Sec17_32">Defects in block rubber</a></td> +<td class="rightbot"><a href="#Page_223">223</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch18">CHAPTER XVIII</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch18">DEFECTS IN SHEET RUBBER</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec18_1">Defective coagulation</a>—<a href="#Sec18_2">Coloured surface blotches</a>—<a +href="#Sec18_3">General darkening of surface</a>—<a href="#Sec18_4">Soft coagulum</a>—<a href="#Sec18_5">Spongy +underface</a>—<a href="#Sec18_6">Tearing</a>—<a href="#Sec18_7">“Pitting” of surface</a>—<a +href="#Sec18_8">Thick ends or edges</a>—<a href="#Sec18_9">Mis-shapen sheets</a>—<a href="#Sec18_10">Thick patches</a>—<a +href="#Sec18_11">Torn sheets</a>—<a href="#Sec18_12">“Dog-ears”</a>—<a href="#Sec18_13">Creases</a>—<a +href="#Sec18_14">Greasiness of surface before smoking</a>—<a href="#Sec18_15">Surface blemishes</a>—<a href="#Sec18_16">Uneven +appearance</a>—<a href="#Sec18_17">Variation due to oxidation</a>—<a href="#Sec18_18">Colour when dry</a>—<a +href="#Sec18_19">Surface gloss</a>—<a href="#Sec18_20">Dull surface</a>—<a href="#Sec18_21">Moist glaze and +greasiness</a>—<a href="#Sec18_22">Virgin spots</a>—<a href="#Sec18_23">Surface moulds or mildew</a>—<a +href="#Sec18_24">Black streaks or spots</a>—<a href="#Sec18_25">White or grey streaks</a>—<a href="#Sec18_26">Rust</a>—<a +href="#Sec18_27">Theories on formation of</a>—<a href="#Sec18_28">Prevention of</a>—<a href="#Sec18_29">Two +methods</a>—<a href="#Sec18_30">Other views on causation</a>—<a href="#Sec18_31">Bubbles</a>—<a href="#Sec18_32">Causes +of formation</a>—<a href="#Sec18_33">In the field</a>—<a href="#Sec18_34">In the factory</a>—<a +href="#Sec18_35">Blisters</a>—<a href="#Sec18_36">“Spot” disease in sheet rubber</a>—<a href="#Sec18_37">Support +marks</a>—<a href="#Sec18_38">Stickiness</a>—<a href="#Sec18_39">Surface pattern</a>—<a href="#Sec18_40">Sheet +clippings</a>—<a href="#Sec18_41">Other infrequent defects</a>—<a href="#Sec18_42">Dirt</a>—<a +href="#Sec18_43">Ash</a>—<a href="#Sec18_44">Bark</a>—<a href="#Sec18_45">Splinters</a></td> +<td class="rightbot"><a href="#Page_249">249</a></td> +</tr> + +<tr> +<td colspan="2"> <span class='pagenum'><a name="Page_xiv" id="Page_xiv">[xiv]</a></span></td> +</tr> + +<tr> +<td colspan="2" class="center fsize125"><a href="#Part5">PART V</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Part5"><i>GENERAL</i></a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch19">CHAPTER XIX</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch19">CHOICE OF COAGULANT</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec19_1">Acetic acid in general use</a>—<a href="#Sec19_2">Is a coagulant necessary?</a>—<a +href="#Sec19_3">Acetic acid</a>—<a href="#Sec19_4">Formic acid</a>—<a href="#Sec19_5">Citric acid</a>—<a +href="#Sec19_6">Tartaric acid</a>—<a href="#Sec19_7">Oxalic acid</a>—<a href="#Sec19_8">Sulphuric acid</a>—<a +href="#Sec19_9">Hydrochloric and nitric acids</a>—<a href="#Sec19_10">Hydrofluoric acid</a>—<a +href="#Sec19_11">Alum</a>—<a href="#Sec19_12">Pyroligneous acid</a>—<a href="#Sec19_13">Smoked water</a>—<a +href="#Sec19_14">Chinese vinegar</a>—<a href="#Sec19_15">Sulphurous acid</a>—<a href="#Sec19_16">Sugars</a>—<a +href="#Sec19_17">Various salts</a>—<a href="#Sec19_18">Proprietary compounds</a>—<a href="#Sec19_19">Carbonic acid +gas</a>—<a href="#Sec19_20">Alcohol</a>—<a href="#Sec19_21">Vegetable extracts</a></td> +<td class="rightbot"><a href="#Page_278">278</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch20">CHAPTER XX</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch20">SPECIAL METHODS OF PREPARATION</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec20_1">Da Costa process</a>—<a href="#Sec20_2">Byrne curing process</a>—<a +href="#Sec20_3">Freezing process</a>—<a href="#Sec20_4">Wickham process</a>—<a href="#Sec20_5">Derry process</a>—<a +href="#Sec20_6">Spontaneous coagulation</a>—<a href="#Sec20_7">Definition of</a>—<a href="#Sec20_8">Discussion of +types</a>—<a href="#Sec20_9">Ærobic</a>—<a href="#Sec20_10">Anærobic</a>—<a +href="#Sec20_11">Organisms</a>—<a href="#Sec20_12">Maude-Crosse patent</a>—<a href="#Sec20_13">Method of operation</a>—<a +href="#Sec20_14">Accelerating action of sugars</a>—<a href="#Sec20_15">Accelerating action of soluble calcium salts</a>—<a +href="#Sec20_16">Ilcken-Down process</a>—<a href="#Sec20_17">Slab rubber</a></td> +<td class="rightbot"><a href="#Page_290">290</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize125"><a href="#Part6">PART VI</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Part6"><i>VULCANISATION</i></a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch21">CHAPTER XXI</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch21">INTRODUCTORY DEALING WITH TREATMENT AND VULCANISATION</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec21_1">Wild rubber contrasted with plantation rubber</a>—<a href="#Sec21_2">Milling and +mixing</a>—<a href="#Sec21_3">Preparation for vulcanising</a>—<a href="#Sec21_4">Vulcanising</a></td> +<td class="rightbot"><a href="#Page_301">301</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch22">CHAPTER XXII</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch22">TESTING OF PLANTATION RUBBER</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec22_1">Tests on raw rubber</a>—<a href="#Sec22_2">Breaking strain</a>—<a +href="#Sec22_3">Behaviour of rubber during milling, etc.</a>—<a href="#Sec22_5">Preparation for testing</a>—<a +href="#Sec22_4">Tests on vulcanised rubber</a>—<a href="#Sec22_6">Choice of a formula</a>—<a href="#Sec22_7">Physical +tests</a></td> +<td class="rightbot"><a href="#Page_309">309</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch23">CHAPTER XXIII</a></td> +</tr> + +<tr> +<td colspan="2" class="center fsize110"><a href="#Ch23">THE PROPERTIES OF RUBBER</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><a href="#Sec23_1">Raw rubber</a>—<a href="#Sec23_2">Physical tests</a>—<a href="#Sec23_3">Vulcanised +rubber</a>—<a href="#Sec23_4">“Inner qualities” of raw rubber</a>—<a href="#Sec23_5">Defects of crepe and +sheet</a>—<a href="#Sec23_6">Variation in physical properties</a>—<a href="#Sec23_7">Rate of cure</a>—<a +href="#Sec23_8">Influence of various factors in raw rubber on rate of cure</a>—<a href="#Sec23_9">Other types of plantation +rubber</a>—<a href="#Sec23_10">Fine para</a></td> +<td class="rightbot"><a href="#Page_313">313</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="just ind"><span class="smcap"><a href="#INDEX">Index</a></span></td> +<td class="rightbot"><a href="#Page_327">327</a></td> +</tr> + +</table> + +<p class='pagenum'><a name="Page_xv" id="Page_xv">[xv]</a></p> + +<hr class="c25" /> +<h2>LIST OF ILLUSTRATIONS</h2> + +<table class="loi" summary="List of Illustrations"> + +<tr> +<td colspan="2" class="right fsize80">PAGE</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig1">SEEDS, SHOWING VARIABLE SIZE, SHAPE, AND MARKING</a></td> +<td class="rightbot">2</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig2">FELLING LIGHT (SECONDARY) JUNGLE</a></td> +<td class="rightbot">3</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig3">SEEDLING, SHOWING ROOT-SYSTEM WITH SEED STILL ATTACHED</a></td> +<td class="rightbot">4</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig4">NEW CLEARING</a></td> +<td class="rightbot">5</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig5">TYPICAL YOUNG CLEARING, AGED ABOUT THREE YEARS, PLANTED ON VIRGIN SOIL. ORIGINAL JUNGLE TIMBER SLOWLY ROTTING</a></td> +<td class="rightbot">6</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig6">LIGHT JUNGLE</a></td> +<td class="rightbot">7</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig7">DENSE JUNGLE</a></td> +<td class="rightbot">8</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig8">CLEARING READY FOR PLANTING</a></td> +<td class="rightbot">9</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig9">NEW CLEARING: SLOPES “HOLED” FOR PLANTING; FLAT AREA BEING DRAINED</a></td> +<td class="rightbot">11</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig10">TYPICAL YOUNG CLEARING, WITH TIMBER</a></td> +<td class="rightbot">15</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig11">TYPICAL YOUNG CLEARING, WITH TIMBER</a></td> +<td class="rightbot">17</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig12">TYPICAL YOUNG PLANTED AREA</a></td> +<td class="rightbot">20</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig13">ANOTHER EXAMPLE OF A RECENTLY PLANTED AREA</a></td> +<td class="rightbot">21</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig14">WIDELY PLANTED YOUNG AREA, JUST READY TO BE BROUGHT INTO TAPPING</a></td> +<td class="rightbot">24</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig15">FIELD OF OLD RUBBER TREES IN WHICH THINNING HAD BEEN DELAYED TOO LONG</a></td> +<td class="rightbot">25</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig16">TWO CUTS ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE</a></td> +<td class="rightbot">31</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig17">THE SINGLE CUT ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE AND ON RENEWED BARK</a></td> +<td class="rightbot">33</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig18">SINGLE CUT ON HALF CIRCUMFERENCE (HALF-SPIRAL)</a></td> +<td class="rightbot">35</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig19">A <span class="ssfont">V</span>-CUT ON HALF THE CIRCUMFERENCE</a></td> +<td class="rightbot">37</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig20">SINGLE CUT ON TWO-FIFTHS OF CIRCUMFERENCE</a></td> +<td class="rightbot">41</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig21">EFFECTS UPON RENEWED BARK OF PREVIOUS TAPPING</a></td> +<td class="rightbot">44</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig22">ANOTHER EXAMPLE SHOWING THE EFFECTS OF PREVIOUS TAPPING</a></td> +<td class="rightbot">45</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig23">1. SHOWING EFFECT OF “WINTERING”</a></td> +<td class="rightbot">48</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig24">2. NEW GROWTH OF YOUNG LEAF ON SAME TREE</a></td> +<td class="rightbot">49</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig25">EFFECTS OF DISEASE—“MOULDY ROT”</a></td> +<td class="rightbot">50</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig26">EFFECTS OF DISEASE—“MOULDY ROT”</a></td> +<td class="rightbot">51</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig27">EFFECTS OF DISEASE—“MOULDY ROT”</a></td> +<td class="rightbot">52</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig28">EFFECTS OF DISEASE—“MOULDY ROT”</a></td> +<td class="rightbot">53</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig29">RAISED VERANDAH FOR RECEPTION OF LATEX; LIKEWISE EQUIPPED WITH FACILITIES FOR CALCULATING INDIVIDUAL +DAILY “YIELD PER COOLIE“BY SAMPLING OF LATEX</a></td> +<td class="rightbot">66</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig30">END-SECTION SKETCH OF VERANDAH, ETC., SHOWING A GOOD METHOD FOR +RECEIVING LATEX AND FILLING TANK</a></td> +<td class="rightbot">70</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig31">RAISED VERANDAH FOR RECEPTION AND HANDLING OF LATEX</a></td> +<td class="rightbot">71</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig32">ANOTHER SET OF DILUTION TANKS ON RAISED VERANDAH</a></td> +<td class="rightbot">72</td> +</tr> + +<tr> +<td class="left ind"><span class='pagenum'><a name="Page_xvi" id="Page_xvi">[xvi]</a></span><a href="#Fig33">TWO VIEWS OF +DILUTION AND MIXING TANKS</a></td> +<td class="rightbot">81</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig34">UNIT MODERN COAGULATING TANK (TWO VIEWS)</a></td> +<td class="rightbot">91</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig35">ANOTHER BATTERY OF TANKS, WITH DILUTION TANKS, RAISED, ON THE RIGHT</a></td> +<td class="rightbot">92</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig36">CLOSER VIEW OF FOREGOING</a></td> +<td class="rightbot">93</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig37">ANOTHER BATTERY OF TANKS, WITHOUT DILUTION TANKS OR MEANS OF GRAVITATING LATEX</a></td> +<td class="rightbot">95</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig38">A SHEETING TANK CONTAINING COAGULUM FOR CREPE PREPARATION</a></td> +<td class="rightbot">96</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig39">A “BATTERY” OF SHEETING TANKS (PATALING ESTATE). +DILUTION TANKS, RAISED, ON THE LEFT</a></td> +<td class="rightbot">97</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig40">THE OLD METHOD OF “DRIPPING” FRESHLY ROLLED SHEETS WITHIN THE FACTORY</a></td> +<td class="rightbot">108</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig41">THE NEWER METHOD OF HANGING IN THE OPEN AIR</a></td> +<td class="rightbot">109</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig42">THREE GRADES OF CREPE RUBBER</a></td> +<td class="rightbot">111</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig43">A WASHING SHED</a></td> +<td class="rightbot">112</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig44">DRYING GRAPH. PALE CREPE (THIN)</a></td> +<td class="rightbot">140</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig45">A SHIPMENT OF RUBBER, PACKED AND READY FOR TRANSPORT</a></td> +<td class="rightbot">155</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig46">ON ITS ROAD TO THE RAILWAY: BULLOCK-CART TRANSPORT</a></td> +<td class="rightbot">157</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig47">A BATTERY OF MACHINES</a></td> +<td class="rightbot">165</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig48">“THIRD MILE” TYPE; HORIZONTAL DRUM</a></td> +<td class="rightbot">190</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig49">“THIRD MILE” TYPE OF FURNACE, USED IN CONJUNCTION WITH “THIRD MILE” +SMOKE-HOUSE</a></td> +<td class="rightbot">190</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig50">SIDE SECTIONAL ELEVATION (PATALING TYPE OF FURNACE)</a></td> +<td class="rightbot">193</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig51">PATALING TYPE OF FURNACE</a></td> +<td class="rightbot">193</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig52">LARGE SMOKE-HOUSE OF ORDINARY CONSTRUCTION, WITH SHIELDED VENTILATORS PERMANENTLY OPEN</a></td> +<td class="rightbot">194</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig53">BRICK AND CEMENT SUPERSTRUCTURE OF FURNACE INSIDE THE BUILDING, BUT FED FROM OUTSIDE</a></td> +<td class="rightbot">195</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig54">GENERAL VIEW OF SHELTERS COVERING APPROACHES TO FURNACES</a></td> +<td class="rightbot">196</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig55">NEAR VIEW OF SHELTER</a></td> +<td class="rightbot">197</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig56">“THIRD MILE” TYPE OF SMOKE-HOUSE</a></td> +<td class="rightbot">199</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig57">GENERAL VIEW OF DOUBLE “DEVON” TYPE OF SMOKE-HOUSE</a></td> +<td class="rightbot">201</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig58">GENERAL VIEW OF DOUBLE “DEVON” SMOKE-HOUSE AND FACTORY BUILDINGS</a></td> +<td class="rightbot">202</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig59">VIEW OF PLATFORM OF “DEVON” SMOKE-HOUSE; +DOORS OF COMPARTMENTS OPEN, AND ONE RACK PARTIALLY WITHDRAWN</a></td> +<td class="rightbot">203</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig60">DOUBLE “DEVON” SMOKE-HOUSE OF BRICK, +WITH ROOF OF CHINESE TILES, SHOWING LOADING PLATFORMS WITH RACKS WITHDRAWN FROM SMOKING CHAMBERS</a></td> +<td class="rightbot">204</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig61">SIDE-VIEW OF PRECEDING PHOTOGRAPH, SHOWING EXTERNAL ARRANGEMENT FOR STOKING FURNACES</a></td> +<td class="rightbot">205</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig62">FRONT VIEW OF DOUBLE “DEVON” TYPE OF SMOKE-HOUSE</a></td> +<td class="rightbot">206</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig63">SIDE-VIEW OF DOUBLE “DEVON” TYPE OF SMOKE-HOUSE</a></td> +<td class="rightbot">207</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig64">THE NEW “BARKER” TYPE OF SMOKE-HOUSE: A SMALL UNIT</a></td> +<td class="rightbot">210</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig65">SUGGESTED ARRANGEMENT OF BUILDING</a></td> +<td class="rightbot">218</td> +</tr> + +<tr> +<td class="left ind"><a href="#Fig66">THREE SPECIMENS OF FINE PALE CREPE SUFFERING FROM “SPOT” DISEASE</a></td> +<td class="rightbot">237</td> +</tr> + +</table> + +<p class='pagenum'><a name="Page_1" id="Page_1">[1]</a></p> + +<hr class="c25" /> +<h1>THE PREPARATION<br /> +OF PLANTATION RUBBER</h1> + +<h2><a name="Part1" id="Part1"></a>PART I</h2> + +<h3>FIELD OPERATIONS</h3> + +<h2><a name="Ch1" id="Ch1"></a>CHAPTER I</h2> + +<h3><i>PLANTING</i></h3> + + +<p>To criticise the methods of the pioneer planters of <i>Hevea +Brasiliensis</i> presents no difficulty in the light of present comparative +knowledge, and to be “wise after the event” is a failing +which is not confined to those interested in modern planting +methods. Looking at the matter broadly, however, it must +be acknowledged that the pioneers, wrong though they may have +been on some points, did remarkably well, considering that +there existed no real knowledge on the subject and that the +methods employed were perforce of an empirical nature. +Although we know a little more concerning the scientific +aspects of rubber planting, the sum total of that knowledge +does not justify any drastic criticism of the methods employed +by our predecessors. In fact, although we may be of opinion +that on general lines there is little now to be learned regarding +the planting of <i>Hevea Brasiliensis</i>, 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.</p> + +<p>The main theme of the present volume is that of the preparation +of rubber for the market. Hence it is not proposed to +deal in detail with the work attaching to the opening and +development of rubber estates. For this the reader is referred +to the literature dealing specifically with rubber planting. +Certain points in connection with planting may advantageously<span class='pagenum'><a name="Page_2" id="Page_2">[2]</a></span> +be treated in a general way according to modern knowledge, +and of these it is proposed to discuss a few in the following +pages.</p> + +<div class="figcenter"><a name="Fig1" id="Fig1"></a><img src="images/illo019.jpg" alt="Seeds, showing Variable Size, Shape, and Marking" /> +<p class="caption"><span class="smcap">Seeds, showing Variable Size, Shape, and Marking.</span></p></div> + +<p><span class="smcap"><a name="Sec1_1" id="Sec1_1"></a>Seeds.</span>—The view is now generally held that many areas +were planted from seed which was not collected in a discriminate +manner; and that probably the comparatively low yields +obtained on areas of some estates may be due to the employment +of seed from a poor strain. To be able to decide whether +such explanation fits the case demands a full knowledge of +all the possible factors governing the question of yields. It +may, or may not, be a fact that seed from a poor strain is wholly<span class='pagenum'><a name="Page_3" id="Page_3">[3]</a></span> +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.</p> + +<div class="figcenter"><a name="Fig2" id="Fig2"></a><img src="images/illo020.jpg" alt="Felling Light (Secondary) Jungle" /> +<p class="caption"><span class="smcap">Felling Light (Secondary) Jungle.</span></p></div> + +<p>The recognition of these principles as applied to the planting +of <i>H. Brasiliensis</i> has focussed recent attention upon the +desirability of planting nurseries with seeds obtained from those +trees which are known to be good producers of latex of normal +consistency. It does not follow that the tree of most rapid +growth and development is necessarily the best yielder; such +is often not the case. In the matter of selection, therefore, one +has to take other standards than that of size; and the issue is +narrowed chiefly to a consideration of the yields of latex given +by individual trees. It has been found by various experimenters +that there is no necessity to proceed to such a refinement +as the determination of the actual weight of rubber yielded. +The dry rubber content of latices from the same trees is found<span class='pagenum'><a name="Page_4" id="Page_4">[4]</a></span> +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.</p> + +<div class="figcenter"><a name="Fig3" id="Fig3"></a><img src="images/illo021.jpg" alt="Seedling, showing Root-System with Seed +still Attached" /> +<p class="caption"><span class="smcap">Seedling, showing Root-System with Seed<br />still Attached.</span></p></div> + +<p>Unfortunately the industry is so young that the question of +seed selection yet awaits study. The task presents certain +practical difficulties, and would be by no means so easy to +control as in the case of seed selection from other plants. It +will be obvious that several generations of trees raised from +selected seed would have to be under observation before any +sound deductions could be made from statistics obtained in +the course of the work. Thus the problem of seed-selection<span class='pagenum'><a name="Page_5" id="Page_5">[5]</a></span> +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.</p> + +<div class="figcenter"><a name="Fig4" id="Fig4"></a><img src="images/illo022.jpg" alt="New Clearing" /> +<p class="caption"><span class="smcap">New Clearing.</span></p> +<p class="capt500">In the middle distance, felled trees awaiting burning; in the +foreground, a flat and wet area with main drainage outlined. +(<i>By courtesy of the manager of Membakut Estate, British North +Borneo.</i>)</p></div> + +<div class="figcenter"><a name="Fig5" id="Fig5"></a><img src="images/illo023.jpg" alt="Typical Young Clearing, Aged about Three Years, planted on +Virgin Soil" /> +<p class="caption"><span class="smcap">Typical Young Clearing, Aged about Three Years, planted on Virgin Soil.<br /> +Original Jungle Timber slowly Rotting.</span></p></div> + +<p><span class="smcap"><a name="Sec1_2" id="Sec1_2"></a><a name="Sec1_3" id="Sec1_3"></a>Selection.</span>—It +is possible, however, that the question of +strain improvement will be solved in another manner than +that of successive breeding from the seeds of high-yielding +trees. Such investigatory work is now occupying the attention +of scientific organisations in the East, and credit is due to the +stations in Java which have begun experimental work in this +direction. In brief, the scheme may be outlined as follows. +Trees known to be uniformly good yielders are kept under<span class='pagenum'><a name="Page_6" id="Page_6">[6]</a></span> +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<span class='pagenum'><a name="Page_7" id="Page_7">[7]</a></span> +same strain as the parent high-yielding trees. It is possible to +go a step farther, and by certain processes induce a new root +system to grow above the existing roots, which are then removed. +One is then able to guarantee that the roots, stem, and branches +will be of the original high-yielding strain. An objection +sometimes made against the third operation of inducing +a new root system is that the original tap-root is removed and +that the subsequent system consists only of laterals. Against +this argument may be quoted the observed fact that in actual +development any one of the laterals may under such circumstances +function eventually as a tap-root.</p> + +<div class="figcenter"><a name="Fig6" id="Fig6"></a><img src="images/illo024.jpg" alt="Light Jungle" /> +<p class="caption"><span class="smcap">Light Jungle.</span></p></div> + +<p>On the whole, this system of propagation receives the approval<span class='pagenum'><a name="Page_8" id="Page_8">[8]</a></span> +of investigators, and removes the objections which may be +advanced against the development of a scheme entirely founded +upon successive breedings from selected seed. The course of +the investigations, also, are thereby shortened considerably. +Care must be exercised in the work of obtaining and grafting +the buds, but it has now been proved that by exercising reasonable +precautions which are not beyond the intelligence and +ability of subordinates, an extremely high percentage of +success can be attained.</p> + +<div class="figcenter"><a name="Fig7" id="Fig7"></a><img src="images/illo025.jpg" alt="Dense Jungle" /> +<p class="caption"><span class="smcap">Dense Jungle.</span></p></div> + +<p>Until such time as this process becomes practicable the +inception of a planted area must follow the lines usually +adopted.</p> + +<p><span class='pagenum'><a name="Page_9" id="Page_9">[9]</a></span><span class="smcap"><a +name="Sec1_4" id="Sec1_4"></a>Nurseries.</span>—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.</p> + +<div class="figcenter"><a name="Fig8" id="Fig8"></a><img src="images/illo026.jpg" alt="Clearing Ready for Planting" /> +<p class="caption"><span class="smcap">Clearing Ready for Planting.</span></p> +<p class="center">Surface timber removed, but stumps remaining.</p></div> + +<p><a name="Sec1_5" id="Sec1_5"></a><span class="smcap">Stumps.</span>—At a stage, varying according to the requirements +of the estate, when the plants are from twelve to +eighteen months old, they are lifted from the earth. The +roots and head are cut off, and the “stump” is ready for +immediate planting in the field. Naturally any appreciable +delay in planting, or unfavourable weather conditions, will +militate against the chances of successful “striking”; and it +is not uncommon to find that a certain number of “supplies” +will be necessary.</p> + +<p><span class='pagenum'><a name="Page_10" id="Page_10">[10]</a></span><a name="Sec1_6" id="Sec1_6"></a><span class="smcap">Seed +at Stake.</span>—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.</p> + +<p><a name="Sec1_7" id="Sec1_7"></a><span class="smcap">Basket Plants.</span>—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.</p> + +<p><a name="Sec1_8" id="Sec1_8"></a><a name="Sec1_9" id="Sec1_9"></a><span class="smcap">Preparation +for Planting.</span>—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,<span class='pagenum'><a name="Page_11" id="Page_11">[11]</a></span> +it is plain that as far as stumps are concerned, the chief source +of danger lies in the existence of the roots. If these were +carefully exposed and removed, the isolated stumps would then +not be such potential infection points. It follows from this +argument that the importance of removing buried timber +cannot be too strongly insisted upon. It is not uncommon to +find that some years after the opening of an estate, and after +surface timber has been removed, a large number of trees +are affected with <i>Fomes lignosus</i> (formerly known as <i>Fomes +semitostus</i>). Such cases are directly attributable to the existence +of buried timber, and no local treatment will be successful +unless the whole of the area is dug over carefully, and all +pieces of timber removed.</p> + +<div class="figcenter"><a name="Fig9" id="Fig9"></a><img src="images/illo028.jpg" alt="New Clearing; Slopes “Holed” +for Planting; Flat Area being Drained" /> +<p class="caption"><span class="smcap">New Clearing; Slopes “Holed” for Planting; Flat Area +being Drained.</span><br />(<i>By courtesy of manager, Membakut Estate, British North Borneo.</i>)</p></div> + +<p><a name="Sec1_10" id="Sec1_10"></a><a name="Sec1_11" id="Sec1_11"></a><a name="Sec1_12" id="Sec1_12"></a><span class="smcap">Silt +Catchment Trenches.</span>—Granted the ultimate necessity +of clean clearing, it becomes necessary to take some precautions +to prevent loss of soil by “wash” in young areas<span class='pagenum'><a name="Page_12" id="Page_12">[12]</a></span> +planted on sloping land. An argument often used in extenuation +of the practice of allowing large surface timber to remain +until it becomes rotten is that it is an aid in preventing loss of +soil by wash. Its removal necessitates the institution of some +method of preventing “wash.” The establishment of terraces +on steep slopes tends to the achievement of the desired result, +but this method is not extended to more moderate slopes where +loss by wash is still considerable. It is the opinion of the +writers and others that the general case calls for the institution +of silt catchment trenches, which, as the name denotes, fulfil +the duty of catching any surface soil and of retaining rainwater. +These trenches are usually laid out on contour, and +do not exceed a length of 20 feet. They are usually from +18 inches to 2 feet wide and deep, and are so arranged on the +slope that they occupy overlapping positions. The actual +number of trenches required will depend upon the angle of +slope; the steeper the slope the greater the number required—<i>i.e.</i>, +the shorter will be the length of slope between any two +trenches. Given a clean area, it is obvious that the momentum +acquired by running water (and hence the amount of soil +removed) on any one slope will depend upon the distance +travelled. It is advisable, therefore, to place a larger proportion +of the trenches on the upper part of the slope than on the +lower, so as to guard against the breaking down of the trench +system under an abnormal downpour of rain.</p> + +<p>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.</p> + + +<p class='pagenum'><a name="Page_13" id="Page_13">[13]</a></p> +<hr class="c25" /> +<h2><a name="Ch2" id="Ch2"></a>CHAPTER II</h2> + +<h3><i>FIELD MAINTENANCE</i></h3> + + +<p><a name="Sec2_1" id="Sec2_1"></a><span class="smcap">Clean Weeding.</span>—Intimately connected with the growth +and development of the rubber tree one has to consider the +conditions under which it is allowed to mature. The argument +has been used that, since the habitat of <i>Hevea Brasiliensis</i> +is in the jungle, we should be proceeding against nature +by introducing conditions unlike those under which the +“wild” rubber tree grows. It is difficult to treat such an +argument seriously, as by quoting parallel instances in arboriculture +it could be shown that growth, development, and +yields are improved by cultivation of “wild” plants.</p> + +<p>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.</p> + +<p>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.”</p> + +<p>Naturally, if these weeds are allowed to flourish and seed, +their eventual eradication may be a matter of extreme difficulty +and expense. It is the aim, therefore, of properly conducted +estates generally to institute such a system of work that +the weeding-gangs cover the whole estate at regular intervals; +and, as a general rule, it may be accepted that the shorter the +interval between successive visits by the gang to any particular +area, the easier it is to keep weeds in check, and the cheaper +the work will eventually be done. This procedure defines +roughly what is implied by the term “clean weeding,” and it +is the policy adopted by most estates.<span class='pagenum'><a name="Page_14" id="Page_14">[14]</a></span></p> + +<p>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.</p> + +<p><a name="Sec2_2" id="Sec2_2"></a><a name="Sec2_3" id="Sec2_3"></a>In latter years the wisdom of scrupulous clean weeding +under all conditions has been questioned; and there can be no +doubt that under certain special conditions a continuation of the +policy of clean weeding is calculated to produce, in course of +time, more harm than benefit. As an instance, the case might +be cited of steep slopes on poor land. Continual clean weeding +on such areas will lead eventually to a great loss of the surface +soil, unless some precautions are adopted for catching and +retaining the fine silt particles. It is to be noted that such a +type of soil and slope, when the shade is appreciable, often +produces no weeds heavier in growth than a very light grass. +It is urged that the necessity for strict clean weeding on such +soils does not exist, and, in fact, that it would be an injurious +policy. Such arguments appear to be well founded in experience, +and the writers are in thorough agreement that such +special cases deserve special consideration. Rigid adherence +to a policy of clean weeding, without regard to special conditions, +would be most inadvisable.</p> + +<p>Nevertheless, such exceptional cases do not detract from the +wisdom of clean weeding in general. Every planter of experience +realises how easily fields become infested with weeds if +the regular work is suspended or delayed. It is probably +quite true that the harm due to the presence of some weeds +on an occasion is negligible; but apart from this debatable +point, there is the solid fact that if once an area is allowed to +become weedy it may soon demand a much greater expenditure +to bring it back to normal condition than if it had been regularly +weeded. This is common experience, and for that reason +alone a general policy of clean weeding is thoroughly sound; +especially if combined with some system of silt-retention.</p> + +<p><a name="Sec2_4" id="Sec2_4"></a><span class="smcap">Grass Squares.</span>—On some estates the practice of clean +weeding is undertaken in combination with a system of silt-retention, +which depends upon the development and maintenance +of ridges. These are built up from the débris of<span class='pagenum'><a name="Page_15" id="Page_15">[15]</a></span> +weeding in the form of hollow squares. Grass is allowed to +sprout and grow in these ridges, and when it attains a certain +height it is trimmed down so as to keep it within bounds. The +soil within the hollow square is clean weeded; and it is maintained +that loss of soil by wash is avoided. Under certain +conditions there is a great deal to be said in favour of the +method, but in the opinion of the writers it should be regarded +only as a method of expediency. It is not to be preferred to +the more thorough practice of soil-retention by means of silt-trenches, +although the latter method may be slightly more +expensive in the end.</p> + +<div class="figcenter"><a name="Fig10" id="Fig10"></a><img src="images/illo032.jpg" alt="Typical Young Clearing, with Timber" /> +<p class="caption"><span class="smcap">Typical Young Clearing, with Timber.</span></p> +<p class="center">Planted “rubber-stump” in foreground.</p></div> + +<p><a name="Sec2_5" id="Sec2_5"></a><span class="smcap">“Lallang” Eradication.</span>—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<span class='pagenum'><a name="Page_16" id="Page_16">[16]</a></span> +any half-hearted measure otherwise taken will eventually prove +to be even more costly.</p> + +<p>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.</p> + +<p>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<a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" +class="fnanchor">[1]</a> on areas which one may have in view for +planting at some future date.</p> + +<div class="footnote"><p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span +class="label">[1]</span></a> “Eradication of Lallang,” W. P. Handover, <i>The Planter</i>, Vol. I., +No. 1, August, 1920.</p></div> + +<p><a name="Sec2_6" id="Sec2_6"></a>It consists in the employment of <i>Mimosa gigantea</i>, which +eventually smothers the growth of lallang.</p> + +<p>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.</p> + +<p><a name="Sec2_7" id="Sec2_7"></a><span class="smcap">Green Cover Plants.</span>—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<span class='pagenum'><a name="Page_17" id="Page_17">[17]</a></span> +removed, it was often found that an abundant crop of lallang +and weeds resulted.</p> + +<p><a name="Sec2_8" id="Sec2_8"></a>There can be no question that certain plants can be employed +with advantage, not only in the control of weeds, but also by +reason of benefit to the soil in which they are established. +These plants are leguminous, and their use is restricted almost +entirely to young areas, inasmuch as they will not continue to +grow when shade becomes marked. Of those best known in +modern practice might be mentioned <i>Tephrosia candida</i> +(Boga bean), <i>Centrosema Plumerii</i>, and <i>Dolichos Hoseii</i> +(Sarawak bean).</p> + +<div class="figcenter"><a name="Fig11" id="Fig11"></a><img src="images/illo034.jpg" alt="Typical Young Clearing, with Timber" /> +<p class="caption"><span class="smcap">Typical Young Clearing, with Timber.</span></p> +<p class="capt500">Young rubber plants in foreground. Two of these are easily +distinguishable, both with small crowns of leaves.</p></div> + +<p>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.</p> + +<p><span class='pagenum'><a name="Page_18" id="Page_18">[18]</a></span>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.</p> + +<p class='pagenum'><a name="Page_19" id="Page_19">[19]</a></p> +<hr class="c25" /> +<h2><a name="Ch3" id="Ch3"></a>CHAPTER III</h2> + +<h3><i>THINNING OF AREAS</i></h3> + + +<p><a name="Sec3_1" id="Sec3_1"></a><a name="Sec3_2" id="Sec3_2"></a>On this subject there is unanimity regarding the necessity for +the operation. Divergence of opinion exists only as to a +matter of degree.</p> + +<p><a name="Sec3_3" id="Sec3_3"></a>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.</p> + +<p>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.</p> + +<p>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).</p> + +<p><a name="Sec3_4" id="Sec3_4"></a>Before this stage has been reached, stunted or deformed trees +will have been noted and removed, so that in the first year of +tapping thinning proper can be commenced. In the past<span class='pagenum'><a name="Page_20" id="Page_20">[20]</a></span> +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.</p> + +<p><a name="Sec3_5" id="Sec3_5"></a>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.</p> + +<div class="figcenter"><a name="Fig12" id="Fig12"></a><img src="images/illo037.jpg" alt="Typical Young Planted Area" /> +<p class="caption"><span class="smcap">Typical Young Planted Area.</span></p> +<p class="center">Heavy original jungle timber.</p></div> + +<p>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.</p> + +<p><a name="Sec3_6" id="Sec3_6"></a>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<span class='pagenum'><a name="Page_21" id="Page_21">[21]</a></span> +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—</p> + +<div class="blockquot"><p>(<i>a</i>) A small uniform vessel in which the latex is measured +by means of a thin slip of bamboo upon which graduations +are marked.</p> + +<p>(<i>b</i>) A glass measure graduated regularly.</p></div> + +<div class="figcenter"><a name="Fig13" id="Fig13"></a><img src="images/illo038.jpg" alt="Another example of a Recently Planted Area" /> +<p class="caption"><span class="smcap">Another example of a Recently Planted Area.</span></p></div> + +<p>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.</p> + +<p>The first stage in the operations is to number all trees in<span class='pagenum'><a name="Page_22" id="Page_22">[22]</a></span> +the field to be tested, and to prepare a rough register, with three +or five vacant columns opposite each tree number.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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>i.e.</i>, +it should really be confined to one task only at a time. +In this way the worst trees in any task are indicated.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>Any trees which failed to yield sufficient latex to reach the +first mark were registered at zero. The following percentages +were obtained:</p> + +<p class='pagenum'><a name="Page_23" id="Page_23">[23]</a></p> + +<table summary="Table p23"> + +<tr> +<td colspan="3" class="left">Zero</td> +<td class="center padr padl"> </td> +<td class="right">3</td> +<td class="center">per cent.</td> +</tr> + +<tr> +<td class="left">Above</td> +<td class="center">mark</td> +<td class="right">1</td> +<td class="center padr padl"> </td> +<td class="right">6</td> +<td class="center">„</td> +</tr> + + +<tr> +<td class="center">„</td> +<td class="center">„</td> +<td class="right">2</td> +<td class="center padr padl"> </td> +<td class="right">16</td> +<td class="center">„</td> +</tr> + +<tr> +<td class="center">„</td> +<td class="center">„</td> +<td class="right">3</td> +<td class="center padr padl"> </td> +<td class="right">42</td> +<td class="center">„</td> +</tr> + +<tr> +<td class="center">„</td> +<td class="center">„</td> +<td class="right">4</td> +<td class="center padr padl"> </td> +<td class="right">12</td> +<td class="center">„</td> +</tr> + +<tr> +<td class="center">„</td> +<td class="center">„</td> +<td class="right">5</td> +<td class="center padr padl"> </td> +<td class="right">14</td> +<td class="center">„</td> +</tr> + +<tr> +<td class="center">„</td> +<td class="center">„</td> +<td class="right">6</td> +<td class="center padr padl"> </td> +<td class="right">6</td> +<td class="center">„</td> +</tr> + +<tr> +<td class="center">„</td> +<td class="center">„</td> +<td class="right">7</td> +<td class="center padr padl"> </td> +<td class="right">0</td> +<td class="center">„</td> +</tr> + +<tr> +<td class="center">„</td> +<td class="center">„</td> +<td class="right">8</td> +<td class="center padr padl"> </td> +<td class="right">1</td> +<td class="center">„</td> +</tr> + +<tr> +<td class="center">„</td> +<td class="center">„</td> +<td class="right">9</td> +<td class="center padr padl"> </td> +<td class="right bb">0</td> +<td class="center">„</td> +</tr> + +<tr> +<td class="center"> </td> +<td class="center"> </td> +<td class="right"> </td> +<td class="center padr padl"> </td> +<td class="right">100</td> +<td class="center">„</td> +</tr> + +</table> + +<p>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.</p> + +<p>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.</p> + +<p>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.</p> + +<p><a name="Sec3_7" id="Sec3_7"></a><span class="smcap">Yields per Tree.</span>—A great feature is made in estate reports +of the figure showing the average yield per tree per annum. +Assuming an area to be yielding at the average high rate of +540 lbs. per acre per annum, with an average stand of ninety +trees per acre, the yield per tree per annum averaged over +all trees is 6 lbs. Keeping in mind the test-figures on a previous +page, it will be obvious that some of these trees may have given +very much more than 6 lbs. during the year, and some less.<span class='pagenum'><a name="Page_24" id="Page_24">[24]</a></span> +In view of present information it would not be surprising to +find that a few might have been yielding upwards of 15 lbs. +per annum. Unfortunately this information is only to be +obtained by individual tests, and under normal estate conditions +the facts escape notice. Cases are known in which +out-standing individual trees have been known to yield at the +rate of 25 lbs. and more per annum.</p> + +<div class="figcenter"><a name="Fig14" id="Fig14"></a><img src="images/illo041.jpg" alt="Widely Planted +Young Area, just ready to be brought into Tapping" /> +<p class="caption"><span class="smcap">Widely Planted Young Area, just ready to be brought<br /> +into Tapping.</span></p></div> + +<p><span class='pagenum'><a name="Page_25" id="Page_25">[25]</a></span><span class="smcap">Future +Yields per Tree.</span>—It has been shown that by selective +methods based on yields, poor trees can be eliminated. +Whether by a process of seed-selection or by means of propagation +based on bud-grafting and marcotting, it needs no +great stretch of imagination to forecast future conditions under +which trees may be bred which will be capable eventually of<span class='pagenum'><a name="Page_26" id="Page_26">[26]</a></span> +giving an average yield of 25 lbs. per annum over any given +area. Yields of 1,000 lbs. per acre per annum should be +obtained easily.</p> + +<div class="figcenter"><a name="Fig15" id="Fig15"></a><img src="images/illo042.jpg" alt="Field of +Old Rubber Trees in which Thinning had been delayed too long" /> +<p class="caption"><span class="smcap">Field of Old Rubber Trees in which Thinning had been<br /> +delayed too long.</span></p> +<p class="center">Note height and comparative lack of girth.</p></div> + +<p><a name="Sec3_8" id="Sec3_8"></a><span class="smcap">Trees per Acre.</span>—This brings us to the question as to how +many trees one should leave to the acre after thinning operations. +Figures have been given by various authorities, but it +appears to the writer at the present time to be impossible to +lay down a general rule. So much depends upon conditions. +In certain cases where the soil is admittedly poor, the average +growth below normal, and thinning has been postponed too +long, the writer has been forced to the conclusion that it would +be most inadvisable, and commercially unsound, to reduce +the stand of trees below 120 per acre. In such instances the +average yield per tree equalled only 3 lbs. per annum, and +although the trees were upwards of nine or ten years old the +crowns were small and sparse. It is doubtful whether such +trees will ever exhibit any further development, and to thin +them further would probably lead only to a diminution in the +crop per acre.</p> + +<p>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>i.e.</i>, +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.</p> + +<p>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.</p> + +<p>Similarly, intelligence must be displayed in deciding which<span class='pagenum'><a name="Page_27" id="Page_27">[27]</a></span> +of several uniformly-yielding trees should be removed. In +the average sense of this consideration one must pay no attention +to symmetry of spacing, but when dealing with trees of +fairly uniform yields one needs to study the characteristic +development of the trees individually, in order to retain those +which would appear to be most favourably situated with regard +to surrounding trees.</p> + + +<p class='pagenum'><a name="Page_28" id="Page_28">[28]</a></p> +<hr class="c25" /> +<h2><a name="Ch4" id="Ch4"></a>CHAPTER IV</h2> + +<h3><i>TAPPING SYSTEMS</i></h3> + + +<p><a name="Sec4_1" id="Sec4_1"></a>Broadly there are only two methods employed in obtaining +the latex from <i>Hevea Brasiliensis</i>. 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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>In the employment of “paring and pricking,” a thin shaving +of bark was excised on one occasion. At the next tapping no +bark was excised, but a pricking instrument was used along +the previously cut surface. It was not proved that any +advantage was gained by this method, which was more commonly<span class='pagenum'><a name="Page_29" id="Page_29">[29]</a></span> +employed in Ceylon than elsewhere, and it would be +surprising to find it in use at the present day.</p> + +<p>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.</p> + +<p>Planters with original views, and of an enquiring nature, +often query the common practice; and it has been suggested +that “as the latex descends by the force of gravity,” one’s +paring should be done in an upward direction, thus obtaining +a greater pressure of latex—and hence a greater flow. It will +be obvious that it would be no simple matter to collect effectively +the latex thus obtained from the under edge of a sloping +cut, but apart from this the argument would appear to be +founded upon what is now accepted to be a fallacy—viz., that +the latex <i>per se</i> is manufactured in the leaves and gravitates +down the tree.</p> + +<p><a name="Sec4_2" id="Sec4_2"></a><span class="smcap">Former Systems of Tapping.</span>—To hark back ten years in +the plantation rubber industry is equivalent to delving into +history, since development has been so rapid. It was then +thought necessary to place upon the trees a number of simultaneous +cuts which the modern planter would judge to be +inconceivably excessive. Were it not for evidence in the +shape of photographs extant, it would be difficult to convince +a young planter that such systems were employed.</p> + +<p>It was not uncommon for trees to have from six to ten cuts, +sometimes all placed on one half of the tree in a herring-bone +fashion, and sometimes divided into two portions, each of which +tapped the opposite quarter panel of the tree’s circumference. +Such superimposed cuts were spaced from 1 foot to 18 inches +apart.</p> + +<p>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.</p> + +<p>Later systems varied from several cuts on a half-circumference, +or on a quarter of the tree, tapped either daily, or on +alternate days, to cases in which one-third or one-fifth of the +tree was employed. Also popular were the systems of the +<span class="ssfont">V</span> and half-spiral cuts on half the circumference.</p> + +<p><a name="Sec4_3" id="Sec4_3"></a><span class='pagenum'><a name="Page_30" id="Page_30">[30]</a></span>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.</p> + +<p><a name="Sec4_4" id="Sec4_4"></a>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.</p> + +<p>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.</p> + +<p><a name="Sec4_5" id="Sec4_5"></a>In the main the most popular systems of tapping are:</p> + +<div class="blockquot"><p>(<i>a</i>) One cut on a quarter of the tree, tapped daily.</p> + +<p>(<i>b</i>) One cut on a third of the tree, tapped daily.</p> + +<p>(<i>c</i>) One cut on half the circumference, tapped on alternate days.</p> + +<p>(<i>d</i>) A <span class="ssfont">V</span> cut on half the circumference, tapped on alternate +days.</p></div> + +<p>Variants and extremes are:</p> + +<div class="blockquot"><p>(1) One cut on a quarter, tapped on alternate days.</p> + +<p>(2) One cut on a half, tapped daily.</p></div> + +<p>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.</p> + +<div class="figcenter"><a name="Fig16" id="Fig16"></a><img src="images/illo048.jpg" alt="Two +Cuts on a Quarter Circumference, on an Old Tree" /> +<p class="caption"><span class="smcap">Two Cuts on a Quarter Circumference, on an Old Tree.</span></p></div> + +<p><a name="Sec4_6" id="Sec4_6"></a>A few estates in +this country still continue to tap trees by<span class='pagenum'><a name="Page_31" id="Page_31">[31]</a></span> +means of two superimposed cuts on a quarter of the tree. +This was a very popular system some four or five years ago, +but it has come to be recognised by practical experience that +any system employing superimposed cuts leads to a high +consumption of bark without proportionate increase in yield. +For instance, if one compares the system of two cuts on a +quarter tapped daily with a similar system employing only one +cut, one finds that the major quantity of latex is yielded by the<span class='pagenum'><a name="Page_32" id="Page_32">[32]</a></span> +lower cut, and that the single-cut system which excises approximately +half the amount of bark gives about 80 per cent. +of the yield obtained by the tapping of two superimposed cuts.</p> + +<p>Of experiments to test the relative values of different systems +of tapping there have been many. Most of them suffered +from the initial handicap that they dealt with systems which +were then popular. In order to obtain any valid result they +had to be undertaken over a long period. Meantime there +was a progressive movement in actual estate practice towards +a greater conservatism in bark removal, and hence the experiments +as originally planned lost value.</p> + +<p>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.</p> + +<p>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.</p> + +<p>It would have been a great advantage to have included in that +experiment other features which have since come into prominence, +but the original scope of the experiment had to be +confined to the point of comparing yields obtained in making +comparative tests based on one system of tapping with different +frequencies. Such data were required as a check upon a +Ceylon tapping experiment which had attracted much attention. +In that experiment trees were tapped at intervals ranging from +one day to seven days; and it was concluded that after a period +of three and a half years trees tapped with greater intervals<span class='pagenum'><a name="Page_33" id="Page_33">[33]</a></span> +gave yields equalling or exceeding those obtained from trees +tapped with shorter intervals.</p> + +<div class="figcenter"><a name="Fig17" id="Fig17"></a><img src="images/illo050.jpg" alt="The Single Cut on a +Quarter Circumference, on an Old Tree and on Renewed Bark" /> +<p class="caption"><span class="smcap">The Single Cut on a Quarter Circumference, on an Old Tree<br /> +and on Renewed Bark.</span></p></div> + +<p>In the Semenyih experiment the system chosen was that +which had the greatest contemporary vogue—viz., two superimposed +cuts on a quarter of the tree. The various blocks +were tapped respectively every day, every second day, and +every third day.</p> + +<p><span class='pagenum'><a name="Page_34" id="Page_34">[34]</a></span>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.</p> + +<p>The actual average yields from these systems over the whole +period were in the order of—</p> + +<table summary="Table p34"> + +<tr> +<td class="center"><i>Daily.</i></td> +<td> </td> +<td class="center"><i>Two Days.</i></td> +<td> </td> +<td class="center"><i>Three Days.</i></td> +</tr> + +<tr> +<td class="center">100 per cent.</td> +<td class="padr padl"> </td> +<td class="center">60 per cent.</td> +<td class="padr padl"> </td> +<td class="center">45 per cent.</td> +</tr> + +</table> + +<p>and throughout the course of the experiment neither of the +other sections showed any appreciable improvement in position +relative to the daily section.</p> + +<p>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.</p> + +<p><a name="Sec4_7" id="Sec4_7"></a>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.</p> + +<p><a name="Sec4_8" id="Sec4_8"></a><a name="Sec4_9" id="Sec4_9"></a>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.</p> + +<p>This result has been used by advocates of daily tapping +generally, but it does not constitute a fair argument, inasmuch +as the single cut was tapped twice as often, and its position was +always relatively low on the hole of the tree. It has been +shown in the comparison between the daily single cut and the +two cuts daily that the influence on yields of the superimposed +cut is relatively small. A fairer comparison would have been +obtained if the two cuts tapped alternate-daily had been either +amalgamated to form one long cut on half the tree or to form +a <span class="ssfont">V</span> on half the tree, thus placing the cuts in the opposing +sections on the same level. With the knowledge that the yield<span class='pagenum'><a name="Page_35" id="Page_35">[35]</a></span> +obtained from cuts is <i>always greater per tapping</i> by using the +alternate-daily system, it would appear to be plain that the +one long cut on half the tree would at least equal the yield of +the single short cut tapped daily on a quarter tree.</p> + +<div class="figcenter"><a name="Fig18" id="Fig18"></a><img src="images/illo052.jpg" alt="Single Cut on Half Circumference (Half Spiral)" /> +<p class="caption"><span class="smcap">Single Cut on Half Circumference (Half Spiral).</span></p> +<p class="capt350"><i>Note.</i>—In this particular instance the cut is changed to the +opposite half of the tree every half-year.</p></div> + +<p>Unfortunately no opportunity has been afforded up to the +present of definitely proving this point by prolonged experiment<span class='pagenum'><a name="Page_36" id="Page_36">[36]</a></span> +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.</p> + +<p>In a number of instances this view is probably correct, and +the writers are in agreement; but it is necessary to clear away +some misconceptions which confuse the issue. In the main +there are two schools, one of which plumps for alternate-daily +tapping, while the other adheres strongly to daily excision. +Great confusion exists, inasmuch as in many instances the +disciples of these schools are really discussing different matters. +In the case of managers who argue for alternate-daily tapping +their experience is gained, with very few exceptions, from +systems in which the excision covers half the circumference of +the tree; whereas in almost all cases daily tapping is confined to +a single cut on a quarter of the girth. Bearing on such a comparison +there are, as far as the writers are aware, no reliable +published experimental results. To compare the results +obtained from one system practised on one estate with the +results of the other system established on another estate is not +strictly permissible, as we know that conditions generally may +vary to an enormous degree.</p> + +<p>The controversy has raged, however, to such an extent that +many who are not directly engaged in estate practice have +obtained confused impressions. For instance, it appears to be +the belief in some quarters that alternate-daily tapping, when +applied to a single cut on a quarter of the tree, will yield more +than an exactly similar cut tapped daily. In support of such +a statement there does not appear to be any confirmation under +normal conditions; although such a result might be obtained +in the case of old trees which have been heavily over-tapped +in the past, and on which the rate of bark renewal has been +appreciably retarded. It might also be the case eventually +when trees with the opposing frequencies have been tapped +for a period extending into many years; but it is the opinion +of the writers that under normal conditions such a result would +be extremely doubtful.</p> + +<p><a name="Sec4_10" id="Sec4_10"></a>When we come, however, to a comparison +of daily tapping<span class='pagenum'><a name="Page_37" id="Page_37">[37]</a></span> +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 +<span class="ssfont">V</span>—we arrive at a contrast which gives a clear issue. As already +stated, facts and figures of reliable experiment are wanting; +but it is the opinion and experience of the writers that the +alternate-daily system at least suffers no disadvantage on the +point of yields, and in other respects, such as conservation of +labour and costs, is superior to the daily system.</p> + +<div class="figcenter"><a name="Fig19" id="Fig19"></a><img src="images/illo054.jpg" alt="A V-Cut on Half the Circumference" /> +<p class="caption"><span class="smcap">A <span class="ssfont">V</span>-Cut on Half the Circumference.</span></p></div> + + +<p class='pagenum'><a name="Page_38" id="Page_38">[38]</a></p> +<hr class="c25" /> +<h2><a name="Ch5" id="Ch5"></a>CHAPTER V</h2> + +<h3><i>TAPPING AND COLLECTING</i></h3> + + +<p><a name="Sec5_1" id="Sec5_1"></a><span class="smcap">Tapping Knives.</span>—The choice of a tapping knife is a subject +upon which there is much divergence of opinion. This must +be so because no known knife has such apparent outstanding +superior features or claims as would enable one to settle the +point. Moreover, the personal factor is so large that, as far +as the knives in common use are concerned, it appears to exert +the greatest influence. The possibility of obtaining the ideal +knife, which will go to sufficient depth into barks of varying +thickness to yield the maximum quantity of latex without +wounding, is quite as remote at the present time as it was some +years ago. Meanwhile the search for that ideal knife continues, +and occasionally one learns of the alleged merits of some +new instrument which, it is said, fulfils all requirements. It is +only to be regretted, both for the sake of the inventor and for +the expectant buyers, that the claims always fail in some one +or more particulars.</p> + +<p>In Malaya probably the number of different types of tapping +knives may amount to a half-dozen, but those most commonly +in use are:</p> + +<div class="blockquot"><p>(1) The gouge—straight or bent.</p> + +<p>(2) The ordinary farrier’s knife.</p> + +<p>(3) Modifications of the farrier’s knife, such as the “Jebong.”</p></div> + +<p>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<span class='pagenum'><a name="Page_39" id="Page_39">[39]</a></span> +shavings taken off by the bent gouge should be thinner than +those obtained by the use of the straight instrument.</p> + +<p>For similar reasons it is asserted that the “Jebong” and +other modifications are superior to the original form of the +farrier’s knife. These points are generally accepted without +great argument, but when comparisons are made between the +gouge and the farrier’s knife (with its modifications) the opinions +of planters are so varied and conflicting as to be almost irreconcilable. +Two opinions based on experience with both +types of knives are often wholly contradictory.</p> + +<p><a name="Sec5_2" id="Sec5_2"></a>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.</p> + +<p>Naturally there is a limit to such leniency, and this limit is +soon reached in the case of knives having adjustable parts controlled +by screws, or nuts and bolts, etc. Some knives of this +description really merit a much wider use than is afforded them +at present; but in view of the potential damage which might +be done as a result of adjustments made by the coolies these +knives do not become popular.</p> + +<p>It is not proposed here to enter into a description of even +recent instruments for which strong claims are being made by +their inventors or vendors. If they possess the merits attributed +to them they will soon find favour, as managers are always +keen on studying the points of any new knife which will lead +to a conservation of bark and a reduction in the number of<span class='pagenum'><a name="Page_40" id="Page_40">[40]</a></span> +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.</p> + +<p><a name="Sec5_3" id="Sec5_3"></a><span class="smcap">The Choice of Latex Cups.</span>—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.</p> + +<p>Terne-plate cups ousted the coco-nut shell, and they had +the merit of being cheap. The interior coating of tin did not +last long if the cups were properly cleaned. The iron being +exposed, with a minutely roughened surface, each microscopic +projection served as a point around which latex coagulated. +Scrapping the film of interior rubber became more and more +difficult, and often the cups were burnt in order to get rid of +the accumulation of rubber. The last state of such cups was +worse than the preceding one. On some estates fairly successful +attempts were made to keep these cups clean by making +the coolies bring them into the store each day. Terne-plate +cups are not now in common use.</p> + +<p>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.</p> + +<p>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—<i>e.g.</i>, 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<span class='pagenum'><a name="Page_41" id="Page_41">[41]</a></span> +cups, whereas in the case of glass the point is settled by visual +examination at a comparative distance.</p> + +<div class="figcenter"><a name="Fig20" id="Fig20"></a><img src="images/illo058.jpg" alt="Single Cut on Two-Fifths of Circumference" /> +<p class="caption"><span class="smcap">Single Cut on Two-Fifths of Circumference.</span></p> +<p class="capt350">The opening cut covers two-fifths. Subsequent cuts occupy +one-fifth of circumference.</p></div> + +<p>Glass cups are made in two patterns, one having a flat +bottom and the other a conical base. The latter is convenient +for use when wire supports are employed, the cup fitting into a +loop placed beneath the spout. Used on the ground its shape<span class='pagenum'><a name="Page_42" id="Page_42">[42]</a></span> +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.</p> + +<p>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.</p> + +<p>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.</p> + +<p><a name="Sec5_4" id="Sec5_4"></a><span class="smcap">Cleaning Cups.</span>—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.</p> + +<p>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<span class='pagenum'><a name="Page_43" id="Page_43">[43]</a></span> +wet cup when replaced becomes coated with a thin film of +rubber. If the latex is always collected in one direction it will +be clear that, while the cups at one end of the task are comparatively +clean, those at the other end have the chance of being +correspondingly dirty.</p> + +<p>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.</p> + +<p>There are certain economic factors entering into the difference +of opinion regarding the two broad methods employed. In +some cases—<i>e.g.</i>, on old areas—it would be practically impossible +to follow the older method of daily cup-washing, as the +tappers have to employ two buckets for the collection of the +latex. The employment of special coolies for cup-washing +would be necessitated, such as may be seen sometimes on +estates working Chinese “squatter” labour—where the man +taps, a child assists in collecting, and another child, or the +mother, washes the cups. It may be pointed out that in +such instances the helpers are not paid by the estate. Their +services merely mean a saving in time which is spent in the +squatter’s garden, and perhaps the permission to the tapper +to work a larger number of trees than would be allotted +ordinarily to a task.</p> + +<p>Again, on some estates, the tappers, while not being required +to carry a bucket of water for cup-washing, are given an increased +number of trees to tap. Furthermore, on hilly areas +under tapping, it is often manifestly unfair to expect the +tapper to be able to carry two buckets during collection, when +the slope is such, as to make the manipulation of even one +bucket a matter of difficulty.</p> + +<p><span class='pagenum'><a name="Page_44" id="Page_44">[44]</a></span>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.</p> + +<div class="figcenter"><a name="Fig21" id="Fig21"></a><img src="images/illo061.jpg" alt="Effects upon Renewed Bark of Previous Tapping" /> +<p class="caption"><span class="smcap">Effects upon Renewed Bark of Previous Tapping.</span></p> +<p class="center">Note uneven surface and callosities.</p></div> + +<p><a name="Sec5_5" id="Sec5_5"></a><span class="smcap">Water in Cups.</span>—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<span class='pagenum'><a name="Page_45" id="Page_45">[45]</a></span> +the permission to use water (with the idea of preventing +coagulation) led to much abuse, apart from the question as +to the utility of the method. Dirty water was often used, +although clean water may have been placed in the buckets when +coolies left the muster-ground. The small quantity of water +often exceeded the actual yield of pure latex by hundreds per<span class='pagenum'><a name="Page_46" id="Page_46">[46]</a></span> +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.</p> + +<div class="figcenter"><a name="Fig22" id="Fig22"></a><img src="images/illo062.jpg" alt="Another Example Showing the Effects of Previous +Tapping" /> +<p class="caption"><span class="smcap">Another Example Showing the Effects of Previous<br /> +Tapping.</span></p></div> + +<p><a name="Sec5_6" id="Sec5_6"></a><span class="smcap">Premature Coagulation.</span>—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—<i>e.g.</i>:</p> + +<div class="blockquot"><p>(<i>a</i>) Cleanliness of cups and spouts (the latter an important +item often overlooked, and involving the presence of certain +organisms which effect coagulation).</p> + +<p>(<i>b</i>) Climatic conditions.</p> + +<p>(<i>c</i>) Rate and volume of flow of latex.</p> + +<p>(<i>d</i>) Size of tappers’ tasks (involving the length of interval +between tapping, and the collection of latex).</p> + +<p>(<i>e</i>) Distance to be traversed between the site of the task and +the store.</p> + +<p>(<i>f</i>) Care in collecting, to exclude extraneous matter.</p> + +<p>(<i>g</i>) Nature of transport; agitation of the latex to be reduced +to a minimum.</p> + +<p>(<i>h</i>) Nature of the soil, and situation of the estate.</p></div> + +<p>The last mentioned factor is of great importance. As a +general rule it is noted that premature coagulation is less +marked on estates situated on comparatively hilly land. The +greatest effect is remarked on estates situated on the flat lands +of the coastal area where peaty soils are a feature. On many +such estates, in spite of the observance of all ordinary precautions, +it is not possible to receive the latex at the factory +without a large percentage of prematurely coagulated rubber +being found in the transport vessels.</p> + +<p><a name="Sec5_7" id="Sec5_7"></a><span class="smcap">Anti-Coagulants.</span>—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.</p> + +<p><a name="Sec5_8" id="Sec5_8"></a>Among the better known agents which have such an effect +upon latex, formalin and sodium sulphite (not bisulphite) are<span class='pagenum'><a name="Page_47" id="Page_47">[47]</a></span> +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.</p> + +<p>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.</p> + +<p>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.</p> + +<p class="center"><i>Formula for Use of Sodium Sulphite in the Field.</i></p> + +<div class="blockquot"><p>(<i>a</i>) Dissolve anhydrous sodium sulphite in water at the rate +of 1 pound to 3 gallons.</p> + +<p>(<i>b</i>) Of this solution each coolie is given about <span class="enum">3</span>⁄<span class="denom">4</span> 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.</p></div> + +<div class="figcenter"><a name="Fig23" id="Fig23"></a><img src="images/illo065.jpg" alt="Showing Effect of 'Wintering'" /> +<p class="caption">1. <span class="smcap">Showing Effect of “Wintering.”</span></p></div> + +<p><span class='pagenum'><a name="Page_48" id="Page_48">[48]</a></span>On some estates it is found either unnecessary or impracticable +to use the solution in this manner. Instead the anti-coagulant +is placed in the bottom of the bucket prior to the commencement +of collection. The solution is made as in (<i>a</i>) above, +and roughly half an ordinary latex-cupful is placed in +each bucket.</p> + +<div class="figcenter"><a name="Fig24" id="Fig24"></a><img src="images/illo066.jpg" alt="New Growth of Young Leaf on Same Tree" /> +<p class="caption">2. <span class="smcap">New Growth of Young Leaf on Same Tree.</span></p></div> + +<p><a name="Sec5_9" id="Sec5_9"></a><span class="smcap">Collecting Pails.</span>—All vessels intended for the transport +of latex should have a smooth and curved interior, so that<span class='pagenum'><a name="Page_49" id="Page_49">[49]</a></span> +cleansing may be easy. Preferably the interior and exterior +surfaces should be glazed, but it is often found that the enamel +chips easily, and that the handles are too frail in construction. +The shoulder-pieces, to which the handles are joined, are +often too lightly attached to the bucket. Something stouter +in the shape of enamelled ware is required, without an appreciable +increase in weight. Until such a utensil is available, +the heavily galvanised and brass-bound milk-pails used on some<span class='pagenum'><a name="Page_50" id="Page_50">[50]</a></span> +estates are as good as anything at present in vogue, providing +they are kept scrupulously clean.</p> + +<table summary="Mouldy Rot"> + +<tr> +<td class="figcenter"><a name="Fig25" id="Fig25"></a><img src="images/illo067.jpg" alt="Mouldy Rot 1" /></td> +<td class="padr padl"> </td> +<td class="figcenter"><a name="Fig26" id="Fig26"></a><img src="images/illo068.jpg" alt="Mouldy Rot 2" /></td> +</tr> + +<tr> +<td class="caption"><span class="smcap">Effects of Disease—“Mouldy Rot.”</span></td> +<td class="padr padl"> </td> +<td class="caption"><span class="smcap">Effects of Disease—“Mouldy Rot.”</span></td> +</tr> + +<tr> +<td style="text-align: justify; width: 350px;">(<i>a</i>) Note on right hand the panel next in order for tapping; a hopeless position.</td> +<td class="padr padl"> </td> +<td style="text-align: justify; width: 350px;">(<i>b</i>) The present cut badly infected; above there is no renewal of bark.</td> +</tr> + +<tr> +<td class="figcenter"><a name="Fig27" id="Fig27"></a><img src="images/illo069.jpg" alt="Mouldy Rot 3" /></td> +<td class="padr padl"> </td> +<td class="figcenter"><a name="Fig28" id="Fig28"></a><img src="images/illo070.jpg" alt="Mouldy Rot 4" /></td> +</tr> + +<tr> +<td class="caption"><span class="smcap">Effects of Disease—“Mouldy Rot.”</span></td> +<td class="padr padl"> </td> +<td class="caption"><span class="smcap">Effects of Disease—“Mouldy Rot.”</span></td> +</tr> + +<tr> +<td style="text-align: justify; width: 350px;">(<i>c</i>) As in (<i>b</i>); another tree.</td> +<td class="padr padl"> </td> +<td style="text-align: justify; width: 350px;">(<i>d</i>) At close quarters. Note wounds due, apparently, to bad +tapping, but really caused by the disease.</td> +</tr> + +</table> + +<p>The collecting pails should be kept under cover, when not in +use, either at the muster grounds or at the factory. On some +estates coolies are allowed to take them to their quarters, where +they are used for various purposes. Curious effects of this<span class='pagenum'><a name="Page_51" id="Page_51">[51]</a></span> +practice have sometimes been noticed. As an example might +be quoted an instance in which premature coagulation was +found to take place to a surprising degree. It was discovered +eventually that the coolies (Javanese in this case) were in the +habit of utilising the buckets for the preparation of their food. +A liquid extract of a popular fruit was often made. This extract<span class='pagenum'><a name="Page_52" id="Page_52">[52]</a></span> +was very markedly acid in character, and as the buckets were +not afterwards thoroughly cleansed, the latex of the following +day suffered.</p> + +<p>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.</p> + +<p><a name="Sec5_10" id="Sec5_10"></a><span class='pagenum'><a name="Page_53" id="Page_53">[53]</a></span><span class="smcap">Payment +by Result.</span>—The arguments for and against the +institution of this practice are many. In actual result there +can be no question that a higher yield is obtained by the +adoption of a scheme under which the coolie is either given a +bonus based on result or is paid at a definite rate per pound. +It is fully recognised, both by advocates and opponents of +payment by result, that the personal equation of the tapper +is a very important factor. A good skilled tapper will always<span class='pagenum'><a name="Page_54" id="Page_54">[54]</a></span> +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.</p> + +<p>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.</p> + +<p><a name="Sec5_11" id="Sec5_11"></a>It will be recognised by planters that apart from the personal +factor in tapping, the worker might be so unfortunate as to be +placed in an area from which the yield is naturally low, either +by reason of its youth or from other natural causes. Obviously +such individuals are entitled to special consideration in respect +of the rate per pound paid for the rubber obtained. Again, on +very hilly land it may be not humanly possible for a worker to +tap the usual number of trees. Hence to place him on a +parity with other tappers, as far as wage-earning capacity is +concerned, a higher rate than ordinary must be given. It will +be plain, therefore, that on any one estate it is generally impossible +to set a standard rate per pound for payment by result;<span class='pagenum'><a name="Page_55" id="Page_55">[55]</a></span> +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.</p> + +<p>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.).</p> + +<p>The methods of arriving at the yield of rubber brought in by +individual tappers vary, but broadly they fall into two classes:</p> + +<div class="blockquot"><p>(<i>a</i>) 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.</p> + +<p>(<i>b</i>) That in which, after noting the volume, the calculation is +based upon a reading of the dry rubber content of the latex, +obtained by means of an instrument such as the “Metrolac,” +or any other instrument working on the same principle.</p></div> + +<p>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.</p> + +<p><span class="smcap">Tree-Scrap.</span>—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.”</p> + +<p><span class='pagenum'><a name="Page_56" id="Page_56">[56]</a></span><a name="Sec5_12" id="Sec5_12"></a><span class="smcap">Oxidation +of Tree-Scrap.</span>—It is often noted that some +scrap is dark in colour, and in this condition it is generally +spoken of as “oxidised” scrap. The oxidation is probably +due to an enzyme, and also to the presence of chemical substances +of a phenolic nature. In the course of laboratory +experiments with normal latex, it was found possible to reproduce +this darkening due to oxidation by the addition of very +small quantities of various phenols used in general chemical +processes, and the rapidity with which the darkening was +effected depended upon the quantity of the phenol added. +If this rapidly oxidising latex be mixed with normal latex, it +would seem that the whole bulk of the latex is affected by this +tendency to rapid oxidation. It is observed that this condition +under which any tree may yield rapidly oxidising latex is not +a permanent one.</p> + +<p><span class="smcap">Care of Tree-Scrap.</span>—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.</p> + +<p><a name="Sec5_13" id="Sec5_13"></a><span class="smcap">To Prevent Oxidation.</span>—As a rule the scraps are picked +over, and heavily oxidised pieces are sorted out; otherwise the +crepe rubber prepared exhibits black streaks. The scraps +should not be allowed to remain in the sun (which induces +“tackiness”), and if they have to be kept over night they may +be placed in a weak solution (1 per cent.) of sodium bisulphite +to arrest oxidation. It should be recognised that such a +solution will not “bleach” already darkened scrap-rubber, and +the nature of its action is only anti-oxidant.</p> + +<p><a name="Sec5_15" id="Sec5_15"></a><span class="smcap">Bark +Shavings.</span>—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<span class='pagenum'><a name="Page_57" id="Page_57">[57]</a></span> +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.</p> + +<p><a name="Sec5_16" id="Sec5_16"></a>It is a well-known fact that if bark-shavings be allowed to +accumulate in a heap for any but a short period, a fermentative +and heating action is set up. The heat developed in these piles +of shavings is so considerable that it is impossible to keep the +hand in a heap for more than a second or two. Should this +be allowed to persist, as would happen in the case of a breakdown +of engine or machines, it usually results in the final +crepe rubber becoming tacky when approaching dryness.</p> + +<p>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.</p> + +<p>For the same reason (<i>i.e.</i>, 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.</p> + +<p>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.</p> + +<p><a name="Sec5_17" id="Sec5_17"></a>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.</p> + +<p><a name="Sec5_18" id="Sec5_18"></a><span class='pagenum'><a name="Page_58" id="Page_58">[58]</a></span><span class="smcap">Collection +of Earth-Scrap.</span>—This, the lowest grade of +rubber, is found at the base of the tree. Theoretically, if +proper precautions are observed, the amount should be comparatively +small, but in actual practice it may be very appreciable. +The usual contributory causes are:</p> + +<div class="blockquot"><p>(<i>a</i>) Failure to replace cups beneath the spouts of trees which +continue to drip latex after collection.</p> + +<p>(<i>b</i>) Collection of latex at too early a stage.</p> + +<p>(<i>c</i>) Failure on the part of the tapper to ensure the flow of +latex, by means of the spout, into the cup.</p> + +<p>(<i>d</i>) Flowing of latex over the edge of the cut before it reaches +the vertical channel.</p> + +<p>(<i>e</i>) “Wash-cuts” on wet days, when the volume of rainwater +down the tree is sufficient to wash the latex out of the +cup.</p></div> + +<p>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.</p> + + +<p class='pagenum'><a name="Page_59" id="Page_59">[59]</a></p> +<hr class="c25" /> +<h2><a name="Ch6" id="Ch6"></a>CHAPTER VI</h2> + +<h3><i>TRANSPORT OF LATEX AND COAGULUM</i></h3> + + +<p><a name="Sec6_1" id="Sec6_1"></a><span class="smcap">Percentage of First Latex and Other Grades.</span>—One of the +problems confronting any manager is the question of the +percentage of first-grade rubber calculated upon the whole +output. Inquiries are constantly being received for advice as +to what the various percentages of each grade of rubber should +be. This is a question to which no definite list of figures can +apply. There are so many little factors influencing the result. +Some estates are not particularly careful in collecting tree-scrap. +Hence quite a quantity of tree-scrap finds its way into +the crepe made from bark-shavings. On the other hand, +bark-shavings are not collected systematically on some estates, +and the total output is thereby diminished. In consequence +the first-grade rubber shows a higher percentage than it would +otherwise. Again, if the earth-rubber is not regularly collected +the percentages of the best grades are higher than they should +be. In comparing the percentages of each grade of rubber +from any two estates, therefore, one should have all the information +possible as to the various working details of the estates. +Without wishing to lay down any definite proportions which +can be applied to all estates it might be said that, taking +averages over a large number of estates, the percentages to +be aimed at are:</p> + +<table summary="Table p59"> + +<tr> +<td class="left" style="padding-right: .5em;">First-grade latex</td> +<td class="right">75</td> +<td class="left">per cent.</td> +<td class="left" style="padding-right: .5em;">to</td> +<td class="right">80</td> +<td class="left">per cent.</td> +</tr> + +<tr> +<td class="left">Other grades</td> +<td class="right">20</td> +<td class="center">„</td> +<td class="center">„</td> +<td class="right">25</td> +<td class="center">„</td> +</tr> + +</table> + +<p>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<span class='pagenum'><a name="Page_60" id="Page_60">[60]</a></span> +be given for an estate keeping all lower grades distinctly +separate:</p> + +<table summary="Table p60"> + +<tr> +<td class="left">First-grade latex</td> +<td class="left"> </td> +<td class="right">75</td> +<td class="left">per cent.</td> +</tr> + +<tr> +<td class="left">Cup-washings</td> +<td rowspan="2" class="left" style="font-size: 1.75em; vertical-align: middle;">}</td> +<td rowspan="2" class="right" style="vertical-align: middle;">10</td> +<td rowspan="2" class="center" style="vertical-align: middle;">„</td> +</tr> + +<tr> +<td class="left">Coagulated lump, etc.</td> +</tr> + +<tr> +<td class="left">Tree-scrap</td> +<td class="left"> </td> +<td class="right">9</td> +<td class="center">„</td> +</tr> + +<tr> +<td class="left">Bark-shavings</td> +<td class="left"> </td> +<td class="right">4</td> +<td class="center">„</td> +</tr> + +<tr> +<td class="left">Earth rubber</td> +<td class="left"> </td> +<td class="right bb">2</td> +<td class="center">„</td> +</tr> + +<tr> +<td colspan="2"> </td> +<td class="right">100</td> +<td class="center">„</td> +</tr> + +</table> + +<p>Emphasis is again laid on the statement that these figures +must not be accepted as a standard. Nevertheless, they may +prove of some service to managers in giving an idea of what the +general line of percentages may be. There are special circumstances, +such as distance of transport and the nature of the land, +which at present would render the attainment of more than +75 per cent. first-grade rubber impossible on some estates. +Still the fact remains that if the percentage is low through +distance of transport, etc., some method will have to be discovered +by means of which the difficulty maybe overcome. +On a few estates the percentage of first-grade rubber obtained +sometimes reaches 85, but these results are rather out of the +ordinary. An estate which collects all lower grades properly +is doing well if the percentage of first-grade rubber is 75 or +over.</p> + +<p><a name="Sec6_2" id="Sec6_2"></a><span class="smcap">Early Collection.</span>—As already noted in the <a href="#Ch5">preceding +chapter</a>, 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.</p> + +<p><a name="Sec6_3" id="Sec6_3"></a><a name="Sec6_4" id="Sec6_4"></a><a name="Sec6_5" id="Sec6_5"></a><a +name="Sec6_6" id="Sec6_6"></a><span class="smcap">Transport.</span>—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<span class='pagenum'><a name="Page_61" id="Page_61">[61]</a></span> +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 (<i>a</i>) by means of vessels +conveyed on light railways; (<i>b</i>) in large cans placed on motor-lorries; +(<i>c</i>) 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.</p> + +<p>Where possible, the best system is that employing a trolley-line, +as great agitation of the latex is avoided, and the time in +transit is much reduced.</p> + +<p>The usual method of transport by bullock power is slow, +and as estate roads (and even Government roads) are often +below the standard expected in this country, the jolting undergone +by the latex is, to say the least, not calculated to afford a +high yield of first-grade rubber. The late Mr. F. W. F. Day +advocated the use of a circular perforated wooden grid, to be +floated on the latex, in order to moderate the wave effect +produced by jolting.</p> + +<p><a name="Sec6_7" id="Sec6_7"></a>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.</p> + +<p>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.</p> + +<p><a name="Sec6_8" id="Sec6_8"></a><span class="smcap">Anti-Coagulant for Transport.</span>—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.</p> + + +<p class='pagenum'><a name="Page_62" id="Page_62">[62]</a></p> +<p class="center"><i>Formula for Use of Sodium Sulphite in Transport.</i></p> + +<div class="blockquot"><p>(<i>a</i>) Dissolve 1 pound of powder in 3 gallons of water.</p> + +<p>(<i>b</i>) Of this solution, place half a gallon in the vessel for +every 30 to 40 gallons of latex.</p></div> + +<p><a name="Sec6_9" id="Sec6_9"></a><span class="smcap">Transport by Coolie.</span>—As already pointed out, the extent +to which man-power can be used in transport of latex is generally +limited. On small estates it is an easy matter for coolies to +carry the latex to the factory, but on larger estates many +difficulties may arise, which may also militate against the +successful use of other means of transport. It is not uncommon +to find, therefore, that a policy of decentralisation +has been adopted.</p> + +<p><a name="Sec6_10" id="Sec6_10"></a><span class="smcap">Coagulation Centres.</span>—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.</p> + +<p>In the matter of costs of working the writer has had to +investigate several cases regarding which there was dissatisfaction. +In some instances it was found that the stations +had not been placed advantageously with respect to a water-supply; +and instead of one or two coolies pumping for an +hour or two, a larger number had to be employed for hours in +the carriage of water from the nearest available source. This<span class='pagenum'><a name="Page_63" id="Page_63">[63]</a></span> +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.</p> + +<p><a name="Sec6_11" id="Sec6_11"></a><span class="smcap">Transport of Coagulum.</span>—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.</p> + +<p>If proper precautions are taken, the transport of coagulum +intended for the preparation of crepe should present no difficulty, +and should have no injurious effect upon the quality of +the resultant rubber. It is only too common, nevertheless, +to note defects, in the finished crepes, which can only be attributed +to a failure to observe reasonable care in the transport +of the coagulum. For example, it has been observed that a +mass of coagulum from a coagulation station has been conveyed +on the floor of a bullock-cart, or motor-lorry, previously used +in the carriage of other materials. Unless the boards have +been most scrupulously cleansed, the coagulum is found to be +contaminated, often to a marked degree. Again, although the +cart may be clean, it may have to travel some distance on roads +carrying a fair amount of motor traffic. Even should the cart +have a canopy, road-dust is often whirled through the open sides +of the cart; and in the districts where red laterite roads are +common, the stain of such dust often persists in the finished +crepe. It scarcely need be remarked that coagulum should be +transported in closed wooden boxes or in galvanised iron drums +fitted with lids; and that preferably sufficient water should be<span class='pagenum'><a name="Page_64" id="Page_64">[64]</a></span> +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.</p> + +<p>The successful transport of coagulum for sheet-making is +fraught with much greater disabilities, and it is usual to note +on most estates that the resulting sheets from out-stations are +always inferior, in final result, to those coagulated and prepared +at the central factory. If the flat pieces of coagulum are +placed in piles of any height it is common to find, on arrival +at the factory, that much adhesion has been caused. There is +great difficulty in separating the pieces, and often the successful +operation is impossible. It is usual to hand-roll the coagulum +before transport, but it is often found that by the time +the rubber reaches the factory it has become too hard for +subsequent good results.</p> + +<p>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.</p> + +<p>If it is found necessary to transport sheet-coagulum, every +possible precaution should be taken against piling the pieces.</p> + +<p>After hand-rolling some estates bring the rubber from the +field-stations to the central factory in drums of water, others in +shallow boxes containing not more than half a dozen sheets +in a pile. A method proposed long ago, but not in practice, +was to have a number of shallow trays subdivided so that each +compartment held one sheet only. If these trays were properly +made and carefully fitted there appeared to be no reason why +they should not form sliding parts of a large box, in which +squeezing and adhesion of the pieces of coagulum would be +avoided. Naturally any such device would increase appreciably +the weight to be transported, and on this ground would +not find popular favour except where motor-power is used +for road transport.</p> + + +<p class='pagenum'><a name="Page_65" id="Page_65">[65]</a></p> +<hr class="c25" /> +<h2><a name="Part2" id="Part2"></a>PART II</h2> + +<h3>FACTORY OPERATIONS</h3> + + +<hr class="c25" /> +<h2><a name="Ch7" id="Ch7"></a>CHAPTER VII</h2> + +<h3><i>PRELIMINARY TREATMENT OF LATEX</i></h3> + + +<p><a name="Sec7_1" id="Sec7_1"></a><a name="Sec7_2" id="Sec7_2"></a><span class="smcap"><a name="Sec7_3" id="Sec7_3"></a><a +name="Sec7_4" id="Sec7_4"></a>Reception +of Latex at the Store.</span>—Bearing in mind the +remarks in <a href="#Sec6_3">Chapter VI.</a> on the conditions under which latex +is transported, it follows that nothing but the very best and +most suitable vessels should be used in the store. A point to +which adequate attention is not given in many factories might +be mentioned here. Considering the importance attached to +colour in the dry rubber by brokers and consumers, and knowing +how extremely trivial are the causes which may mar the colour, +it is rather surprising that better provision is not made for +the reception and handling of latex in factories. Too often the +receiving vessels are placed on the floor of the store close to the +entrance. Coolies bringing in latex cannot avoid bringing +with them quite a considerable amount of dirt. Presuming +that a hose-pipe has been installed, and that the floor is constantly +being sluiced down with water, no great harm will +result. But would it not be ever so much better if the dirt +were kept out? In how many factories is provision made for +this? Such an arrangement is not difficult to make, and is +already in practice on a few estates. A verandah is built outside +the wall of the factory and all latex is received there. In +another place open chutes are provided which terminate in the +straining sieves. The coolie thus stands on the verandah +where he removes coagulated lump and impurities from the +latex, which is then poured down the chute, passing through +the sieve into large coagulating jars or tanks.</p> + +<p><a name="Sec7_5" id="Sec7_5"></a>Too often it would appear, from the writers’ observation, +there is a lack of adequate supervision on the arrival of latex<span class='pagenum'><a name="Page_66" id="Page_66">[66]</a></span> +at the store. Much can be learned from an inspection of the +coolies’ buckets, and the cause of small defects in the finished +rubber can often be thus traced. Leaves, stems, bark-shavings, +and dirt appear in the buckets, and it is a source of constant +surprise to imagine how even unintelligent coolies can allow +such things to happen. These objects are removed before or +during straining, but still they ought not to be there in the +first place, and the fact that such a state of things exists is +evidence of neglect on the part of the coolies or lack of supervision. +Efforts are made in a large number of cases to cope +with these troubles, but on some estates things are allowed +to proceed in the same slipshod way, and too much responsibility +is thrown on the straining process.</p> + +<div class="figcenter"><a name="Fig29" id="Fig29"></a><img src="images/illo083.jpg" alt="Raised Verandah for Reception of Latex" /> +<p class="caption"><span class="smcap">Raised Verandah for Reception of Latex; likewise equipped<br /> +with Facilities for calculating Individual Daily<br /> +“Yield per Coolie” by Sampling of Latex.</span></p></div> + +<p>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.</p> + +<p><a name="Sec7_6" id="Sec7_6"></a><span class='pagenum'><a name="Page_67" id="Page_67">[67]</a></span>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.</p> + +<p>It might not be credited to Tamil coolies, but yet it is +probably true, that the moral effect of working under the +cleanest and best conditions has an influence upon the store +coolies, and that their work is better in consequence. Everything +which will tend to simplify the cleansing of the factory +should therefore be installed. Hose-pipes, glazed tiles, clean +floors, plenty of light and air are not fads or fancies, but considerable +factors in determining the final quality of the rubber. +There is considerable truth in the suggestion that the coagulating +room and machine room should be as “spick and span” +as a modern home dairy.</p> + +<p><a name="Sec7_7" id="Sec7_7"></a><span class="smcap">Straining of Latex.</span>—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.</p> + +<p>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.</p> + +<p><a name="Sec7_8" id="Sec7_8"></a>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<span class='pagenum'><a name="Page_68" id="Page_68">[68]</a></span> +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.</p> + +<p>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.</p> + +<p><a name="Sec7_9" id="Sec7_9"></a>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<span class='pagenum'><a name="Page_69" id="Page_69">[69]</a></span> +method of working. This can be explained by an outline of +the system adopted on a particular estate:</p> + +<div class="blockquot"><p>(<i>a</i>) On arrival of the rich latex at the store, all visible coagulated +lumps and other extraneous matter are removed by +the tapper.</p> + +<p>(<i>b</i>) Each tapper’s latex is diluted with a quantity of water.</p> + +<p>(<i>c</i>) 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.</p> + +<p>(<i>d</i>) The latex flows by means of a chute into the coagulating +tanks, passing through a large “60 mesh” sieve.</p></div> + +<p>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.</p> + +<p>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.</p> + +<p><a name="Sec7_10" id="Sec7_10"></a><span class="smcap">Bulking of Latex.</span>—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.</p> + +<p>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.</p> + +<p><a name="Sec7_11" id="Sec7_11"></a><span class="smcap">Standardisation of Latex.</span>—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<span class='pagenum'><a name="Page_70" id="Page_70">[70]</a></span> +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.</p> + +<div class="figcenter"><a name="Fig30" id="Fig30"></a><img src="images/illo087.png" alt="End-Section Sketch of Verandah, etc." /> +<p class="caption"><span class="smcap">End-Section Sketch of Verandah, etc., showing a Good<br /> +Method for receiving Latex and filling Tank.</span></p> +<p class="capt500">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.</p></div> + +<p><a name="Sec7_12" id="Sec7_12"></a><a name="Sec7_13" id="Sec7_13"></a>In the successful working of a tank it is necessary, in order +to obtain the best results, to standardise all latex. This cannot +be effected properly in the tank itself, and hence it is the +practice to dilute each lot of latex to standard before it is run +into the tank. In the ordinary way this would entail a great +deal of labour in handling the diluted latex. To obviate +this, the scheme outlined in the accompanying <a href="#Fig30">sketch</a> has been +suggested on several occasions and in various quarters. Such +a scheme or modification of it has been put into successful +practice on several estates. Although the drawing was made +some considerable time ago when estates were not then prepared +to go so far in this direction, subsequent modifications show +only minor differences which, while leaving the original principle +intact, testify to a fertility of resource in adapting the idea +to existing circumstances and buildings. The drawing is <i>in +toto</i> almost a replica of the original installation now in successful<span class='pagenum'><a name="Page_71" id="Page_71">[71]</a></span> +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.</p> + +<div class="figcenter"><a name="Fig31" id="Fig31"></a><img src="images/illo088.jpg" alt="Raised +Verandah for Reception and Handling of Latex" /> +<p class="caption"><span class="smcap">Raised Verandah for Reception and Handling of Latex.</span></p></div> + +<p><a name="Sec7_14" id="Sec7_14"></a><span class="smcap">Verandah.</span>—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.</p> + +<p><a name="Sec7_15" id="Sec7_15"></a><span class="smcap">Latex Reception Vessels.</span>—These cylinders may be similar +to the tanks commonly used for transport of latex from distant +fields to the factory. An 80-gallon cylinder is easily mounted<span class='pagenum'><a name="Page_72" id="Page_72">[72]</a></span> +by its trunnions on a suitable iron framework which is superimposed +on a skeleton truck.</p> + +<div class="figcenter"><a name="Fig32" id="Fig32"></a><img src="images/illo089.jpg" alt="Another +Set of Dilution Tanks on Raised Verandah" /> +<p class="caption"><span class="smcap">Another Set of Dilution Tanks on Raised Verandah.</span></p></div> + +<p>The latex is diluted down to standard in the cylinders, the +truck is moved opposite the compartment to be filled, and a +light movable gutter is placed beneath the vent of the outlet +pipe. This pipe is fixed in the bottom of the cylinder, and is +provided with a large stop-cock which is operated by a spanner +key. The stop-cock should be of the simplest type, capable +of being taken apart and assembled in a minute or so. The +orifices should be large enough for a coolie to insert at least two +or three fingers so as to facilitate cleaning, and the pipe should +have no right-angle bends.</p> + +<p><span class='pagenum'><a name="Page_73" id="Page_73">[73]</a></span>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.</p> + +<p><span class="smcap">A Screw Plug Unsatisfactory.</span>—It may be of benefit to +managers who contemplate such an installation to know that +the adoption of a stop-cock in the vent pipe of the cylinder +is the outcome of experience. In one instance the vent pipe +as designed was fitted with a screw plug at the end. Unfortunately +with this arrangement the flow could not be regulated, +and owing to the “head” of the latex it dashed violently +down the gutter, struck the bottom of the coagulating tank, +and thence was scattered over the factory.</p> + +<p><span class="smcap">Another Installation.</span>—In another type of installation, +in place of the vessels travelling upon a raised verandah platform, +the standardised latex is conveyed to the coagulating +tanks by means of drums supported by hooks to a chain-block +and pulley which travels on an overhead gantry. This method +is practicable, but may be regarded as less satisfactory in general +working than the verandah method of treatment.</p> + +<p><span class="smcap">A Modern Installation.</span>—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.</p> + +<p>The accompanying illustrations show the general arrangement +and some details of the system of reception tanks employed +on the well-known Pataling Estate.</p> + + +<p class='pagenum'><a name="Page_74" id="Page_74">[74]</a></p> +<hr class="c25" /> +<h2><a name="Ch8" id="Ch8"></a>CHAPTER VIII</h2> + +<h3><i>COAGULATION</i></h3> + + +<p>Whether it is necessary to employ any coagulant, or whether +latex should be allowed to coagulate naturally, will not be discussed +at this stage. Neither will mention be made of any +patent processes of coagulation which employ other than acid +mediums. These subjects will be treated in a <a href="#Ch20">subsequent +section</a> of the book.</p> + +<p><a name="Sec8_1" id="Sec8_1"></a><span class="smcap">Choice of Coagulants.</span>—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.</p> + +<p><a name="Sec8_2" id="Sec8_2"></a><span class="smcap">Strength of Acid Solution.</span>—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.</p> + +<p>Some estates make up a stock solution of 1 part acid to 20 +of water, and use this with success because of the fair amount +of added water present in the latex.</p> + +<p>It must be understood that what is being referred to now is +not the absolute quantity necessary for coagulation, but the +proportions—<i>i.e.</i>, the respective volumes of acid and water<span class='pagenum'><a name="Page_75" id="Page_75">[75]</a></span> +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:</p> + +<p>Take separate and equal lots of the same latex, and to each +add the same quantity of pure acid, but in each case diluted +with varying quantities of water. It will be found that coagulation +is quickest where pure acid is employed, and slowest +where the acid is most dilute. It will also be found that, providing +the quantity of acid employed was sufficient for coagulation, +the best and most uniform coagulation is obtained from +the use of the most dilute acid, within limits. It will often +be found that where pure acid has been employed coagulation +is local—<i>i.e.</i>, we have lumpy coagulation, and often a very +milky remaining liquor. This is due to the fact that, as coagulation +is immediate upon the spot which is first touched by +the pure acid, a deal of the acid is enclosed within the rubber at +that spot, and hence other portions of the latex are deprived of +acid. It is in such cases that most air-bubbles are enclosed.</p> + +<p>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.</p> + +<p><a name="Sec8_3" id="Sec8_3"></a><span class="smcap">Method of Making Stock Solution.</span>—Experiments have +been repeatedly made in the laboratory with acid solutions of +varying dilution, from pure acid down to 1 part of acid in 500 +parts of water. While it has been found that a 1 in 5 solution +can be used where the latex is very dilute (say, 1 part of latex +to 5 parts of water), and a 1 in 20 solution may be used in +fairly dilute latex (for crepe-making), it is undoubtedly a fact +that for latex as generally “standardised” on estates a much +more dilute solution of acid should be used—<i>e.g.</i>, 1 in 100, or +even 1 in 200, of water. It must be borne in mind that the +quantity of acid necessary for coagulation is not changed, but +merely the dilution. Let us take a concrete case to illustrate +the point:</p> + +<div class="blockquot"><p>On an estate at present the stock solution is made up by +diluting 1 pint of acid with 20 pints of water, and 1 gallon of +this is necessary to coagulate 50 gallons of pure latex.</p> + +<p><span class='pagenum'><a name="Page_76" id="Page_76">[76]</a></span>It is desired to use a stock solution of 1 pint of acid to 100 +pints of water. Evidently, therefore, 5 gallons of this stock +solution contain only the same quantity of pure acid as 1 gallon +of the old solution contained, and it will be necessary to add +5 gallons for every 50 gallons of pure latex. Thus:</p> + +<div class="blockquot"><p>1 to 20; 1 gallon necessary for 50 gallons pure latex.<br /> +1 to 100; 5 gallons necessary for 50 gallons pure latex.</p></div></div> + +<p>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.</p> + +<p>It may be advanced by someone that if a dilute solution of +acid, such as 1 in 100, is used the bulk of this stock solution +(5 gallons to 50 gallons of latex) is very great, and might be +injurious to the quality of the resulting rubber. A moment’s +consideration will show that, after all, the volume of acid +solution is only one-tenth that of the volume of latex. This +can have no effect upon the quality of the rubber. Even +dilution of the pure latex with half its bulk of water in the +factory will have no effect upon the quality of the resulting +rubber. It is to be remembered that, except in cases where +the proportion of added water to latex is absurdly large, the +main argument against putting water into the latex-cups is +against the possible poor quality of the water rather than +against the actual small quantity theoretically added. It is +acknowledged that, where the water to be put into the cups +can be guaranteed to be of good quality, no great objection +would be raised against placing the smallest possible quantity +of such water in the cups. But how many estates have such +good water easily available to the coolies, and how many +estates can be sure that only that smallest possible quantity +would be used? It is a notorious fact that, even on estates +where the quantity of water used was supposed to be a minimum, +the proportion of water to latex in some cups often exceeded +even three or four to one. In any case it may be stated as +an elementary truism that the absence of water is more to be +desired than water of doubtful quality.</p> + +<p><a name="Sec8_4" id="Sec8_4"></a><span class="smcap">Quantity of +Acid.</span>—As a result of repeated experimental<span class='pagenum'><a name="Page_77" id="Page_77">[77]</a></span> +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:</p> + +<div class="blockquot"><p>1 part pure acid; 1,000 parts average latex.</p></div> + +<p>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.</p> + +<p>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.</p> + +<p>As a matter of fact, up to certain limits of added water, the +reverse is actually the case—<i>i.e.</i>, the more water in the latex the +less acid must be added, assuming that for pure latex the proportion +of pure acid to latex is taken as 1 part to 1,000 parts. +This was found to be the case up to dilutions of three or four +times the volume of latex. To take concrete examples which +will perhaps make the truth more clear:</p> + +<div class="blockquot"><p>Assuming we commence by making up our stock solution of +acid by adding 100 parts of water to 1 part of pure acid, this +gives us a mixture of 1 to 100. For 1 gallon of pure latex it +would be necessary to add one-tenth of its volume of the above +mixture—<i>i.e.</i>, 16 ozs.</p> + +<p>Suppose we take a gallon of pure latex and add a gallon of +water, we now have 2 gallons of so-called latex. But we still +have only 1 gallon of real latex present in the diluted latex, +and it is only necessary to add sufficient acid to coagulate this +gallon—<i>i.e.</i>, 16 ozs.</p> + +<p>Further, if 1 gallon of latex be diluted with 2, 3, or even +4 gallons of water it is still only necessary to add 16 ozs. of the +acid mixture.</p> + +<p>At dilutions beyond this limit, however, it is necessary to +add a little more acid to obtain complete coagulation.</p></div> + +<p>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<span class='pagenum'><a name="Page_78" id="Page_78">[78]</a></span> +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.</p> + +<p><a name="Sec8_5" id="Sec8_5"></a><span class="smcap">Quantities Necessary for Modern Requirements.</span>—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.</p> + +<p>The general figure given in a preceding paragraph (1 part +pure acid to 1,000 parts of latex) may be accepted as the +rough basis for working. In modern practice, however, +undiluted latex is usually diluted to a standard which may +vary on different estates from 1<span class="enum">1</span>⁄<span +class="denom">4</span> lbs. to 1<span class="enum">1</span>⁄<span class="denom">2</span> lbs. dry rubber per +gallon.</p> + +<p>Latices of these strengths can be coagulated at a ratio of +1 part pure acid to 1,200 parts of standardised latex; and this +quantity need not be exceeded, except in cases where an appreciable +amount of some anti-coagulant is present in the latex. +The proportion may then be raised to 1 in 1,000.</p> + +<p>If considered advisable the acid may be used in a <span class="enum">1</span>⁄<span class="denom">2</span> per cent. +solution for sheet preparation; but in any case it is advised +for the sake of uniformity that a 1 per cent. solution should be +employed in the preparation of both sheet rubber and crepe +rubber. In most modern factories, measuring vessels of +various capacities are to be found, and it is always more satisfactory +to have the solution made up in approximately correct +strength at the rate of 1 oz. of pure acid to 5 pints of water. +Often, however, on some estates European supervision of this +work is not possible, and the preparation of the acid solution +has to be left in the hands of a (more or less) skilled coolie. +It is thus necessary to find some less fine, but still approximately +correct, method of procedure. In the East the kerosene tin is +in universal favour for the carriage of water, and there is no +reason why it should not be utilised as a standard measure for +preparing the dilute acid solution, <i>providing it is not allowed to +become rusty</i>. The capacity of the tin is 4 gallons (640 fluid ozs.), +so that a one-hundredth part would be approximately +6<span class="enum">1</span>⁄<span class="denom">2</span> ozs.<span class='pagenum'><a name="Page_79" id="Page_79">[79]</a></span> +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.</p> + +<p>This would reduce the making of a solution, sufficiently +approximate to 1 per cent. strength for all practical purposes, +into a simple operation of mixing pure acid and water in the +ratio of one cupful of acid to 1 kerosene tin of water.</p> + +<p>The actual quantity of solution required for the coagulation +of any volume of standardised latex can be calculated easily +from the ratio 1:1,200. As the strength of solution is 1:100 +it will be seen that the quantity to be taken is <i>always one-twelfth</i> +that of the volume of latex—<i>e.g.</i>:</p> + +<div class="blockquot"><p>(<i>a</i>) If the latex tank holds 90 gallons of standardised latex, +7<span class="enum">1</span>⁄<span class="denom">2</span> gallons of dilute acid solution are required.</p> + +<p>(<i>b</i>) A tank containing 120 gallons of latex would need 10 +gallons of the 1 per cent. acid solution.</p></div> + +<p>It is assumed that all estates, not only in the preparation of +sheet rubber, but also in the making of crepe rubber, always +employ the system of standardising latex in order to obtain +uniformity. They are ill-advised if they do not follow this +practice; but in case average undiluted latex is treated in +coagulation, the quantity of acetic acid to be used should be +calculated from the ratio 1:1,000.</p> + +<p>If the acid solution is to be employed in 1 per cent. strength, +<i>one-tenth</i> 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.</p> + +<p><a name="Sec8_6" id="Sec8_6"></a><span class="smcap">Care in Mixing.</span>—It is essential that the mixture of dilute +acid and latex should be thoroughly intimate. This can only be +attained by careful manipulation, especially in the case of sheet +preparation. Where crepe rubber is to be made it may be +permissible to employ a solution stronger than 1 per cent., +but it is not advised. The acid should be poured into the<span class='pagenum'><a name="Page_80" id="Page_80">[80]</a></span> +latex while stirring, and the agitation should continue for such +a period as to ensure thorough mixing in all parts.</p> + +<p><a name="Sec8_7" id="Sec8_7"></a>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.</p> + +<p class='pagenum'><a name="Page_81" id="Page_81">[81]</a></p> + +<div class="figcenter"><a name="Fig33" id="Fig33"></a><img src="images/illo098.jpg" alt="Two Views of Dilution and Mixing Tanks" /> +<p class="caption"><span class="smcap">Two Views of Dilution and Mixing Tanks.</span></p> +<p class="capt350">Below, on the right, coagulating tanks. At the far end strainers. +Each dilution tank is of equal capacity to the corresponding coagulating +tank.</p></div> + +<p><a name="Sec8_8" id="Sec8_8"></a><span class="smcap">Use of Sodium Bisulphite</span>.—Some few years ago a demand +for pale crepe rubbers sprang up, and this demand has been +maintained. The total quantity of pale rubber put on the +market previously could only have amounted to very little, +and that little was obtained by luck and various tricks in manipulation. +It must be premised that if coagulation is allowed to +take place, either naturally or with the aid of acetic acid, the +resulting rubber will almost inevitably oxidise on the +surface,<span class='pagenum'><a name="Page_82" id="Page_82">[82]</a></span> +except in the cases of very dilute or young latices. Even +supposing that this darkening of the surface does not take +place in the wet stage, it is often found that a rubber expected +to dry to a pale colour does not fulfil expectations, and a dull +neutral shade results. This darkening of crepe rubber may +be attributed to a slow process of oxidation, which continues +until the rubber is dry. From these remarks it will be seen +that the process of oxidation is a natural one, and that any +pale rubber formerly shipped was the outcome of circumstances +outside the control of the estate, except in such cases +where boiling of the coagulum, etc., was resorted to. The +fact that one rubber happened to be a shade darker than another +was absolutely no criterion as to the value of the rubber, but +apparently the market thought, and still thinks, otherwise, +although the actual necessities of manufacturers for a pale crepe +to be employed in special processes must be comparatively +small.</p> + +<p>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:</p> + +<div class="blockquot"><p>1. It must be a simple substance capable of being easily +handled.</p> + +<p>2. It must be very soluble, so that solutions could easily be +made up by inexpert workers.</p> + +<p>3. It must be cheap.</p> + +<p>4. It must be quite innocent of any harmful effect upon the +quality of the rubber.</p></div><p><span class='pagenum'><a name="Page_83" id="Page_83">[83]</a></span></p> + +<p>After months of investigation into the properties of other +chemicals the writers decided that the only one which satisfactorily +answered all requirements was sodium bisulphite. +The writers make no pretension to any claim of having discovered +the properties of this substance, which was a common +chemical, and widely known. Even its action on latex was +suspected before they engaged upon the work. These matters +are only mentioned because the credit, if any, should be given +to the laboratories of the Rubber Growers’ Association.</p> + +<p>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,<a name="FNanchor_2_2" +id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">[2]</a> +and it was definitely stated that rubber prepared with this +chemical was brittle. It must be remembered that brokers +had some legitimate excuse in raising objections to the introduction +of new and strange chemicals for preparing rubber, +as they were quite without means of judging whether the rubber +had suffered harm or not. Still, on the other hand, private +tests had been made in conjunction with Messrs. Beadle and +Stevens for fully eight months before the name of the chemical +was mentioned in reports, and they had decided from the +results of vulcanisation tests that the chemical was quite +innocuous. Then, and only then, did we consider it advisable +to recommend the use of sodium bisulphite in general estate +practice. Owing to the initial prejudice against rubber prepared +with sodium bisulphite, the results of our preliminary +work were published by permission of the Rubber Growers’ +Association.<a name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3" +class="fnanchor">[3]</a> The original instructions to estates regarding +the proper employment of this chemical were given in the +private reports issued by the Rubber Growers’ Association in +1911. At the present time it is probably accurate to state that +it is now used by all estates preparing fine crepes. Representatives<span class='pagenum'><a name="Page_84" id="Page_84">[84]</a></span> +of manufacturers have sometimes given us to understand +that the question of paleness of colour in such rubber is +of no such importance as is impressed upon us as producers. +While we are prepared to believe, we can only plead that from +our point of view the supply arises from the demand. Such +are the conditions governing the sale of rubber that, irrespective +of the requirements of the ultimate user, we have to market +rubber which is valued almost completely upon its appearance +at the time of sale.</p> + +<div class="footnote"><p><a name="Footnote_2_2" id="Footnote_2_2"></a><a href="#FNanchor_2_2"><span +class="label">[2]</span></a> Williams, International Rubber and Allied Congress, London, +1914.</p></div> + +<div class="footnote"><p><a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span +class="label">[3]</span></a> “The Employment of Sodium Bisulphite in the Preparation of +Plantation Rubber,” Beadle, Stevens, and Morgan, <i>India-rubber +Journal</i>, August 2, 1913.</p></div> + +<p>As long as such conditions prevail estates must continue to +adopt any device of proved harmlessness, in order to obtain +the best possible price for their product, and not because we +desire to continue a practice which some assure us to be unnecessary, +and which, moreover, adds somewhat to the cost +of production.</p> + +<p><a name="Sec8_9" id="Sec8_9"></a><span class="smcap">Quantities of Sodium Bisulphite.</span>—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 <a href="#Sec8_13">following</a>). 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.</p> + +<p>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>i.e.</i>, 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.<a name="FNanchor_4_4" id="FNanchor_4_4"></a><a href="#Footnote_4_4" class="fnanchor">[4]</a></p> + +<div class="footnote"><p><a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span +class="label">[4]</span></a> 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).</p></div> + +<p>Hence it follows that if in any factory uniform quantities of<span class='pagenum'><a name="Page_85" id="Page_85">[85]</a></span> +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.</p> + +<p>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.</p> + +<p><a name="Sec8_10" id="Sec8_10"></a>Working with a standard of 1<span class="enum">1</span>⁄<span +class="denom">2</span> lbs. dry rubber per gallon +the following formula should serve as a <i>maximum</i>:</p> + + +<p class="center"><i>Formula for Use of Sodium Bisulphite.</i></p> + +<div class="blockquot"><p>(<i>a</i>) Dissolve sodium bisulphite in water at the rate of 1 lb. +to 10 gallons.</p> + +<p>(<i>b</i>) Of this solution use 1 gallon to every 10 gallons of latex.</p></div> + +<p><span class="smcap">Making a Solution.</span>—The making of a solution of the +chemical would seem to be a simple matter, but to judge by +the ill-effects sometimes observed in the dry rubber the simplicity +of the operation appears to have been overrated. Great +care must be exercised in preparing the solution, and the work +should not be left to the few minutes preceding its actual +requirement; such has been found to be the case in several +factories, so that it is not surprising if the rubber is defective.</p> + +<p>The powder should be added gradually to water with +thorough stirring, which should be continued for five minutes +at least. Even then there may often be seen at the bottom +undissolved particles, sand, and other impurity. It is necessary, +therefore, in such cases to decant the solution through a +piece of cotton cloth before using. No solid particles should +be allowed to enter the latex.</p> + +<p><a name="Sec8_11" id="Sec8_11"></a><span class="smcap">Abuse of Sodium Bisulphite.</span>—It is now generally recognised +that the abuse of sodium bisulphite, in the form of an +excess, leads mainly to delay in the period of drying and the +production of an overpale rubber.<a name="FNanchor_5_5" id="FNanchor_5_5"></a><a href="#Footnote_5_5" +class="fnanchor">[5]</a> It is probable that few +estates, if any, now experience trouble due to this non-observance +of the rules and quantities laid down for use.</p> + +<div class="footnote"><p><a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span +class="label">[5]</span></a> “The Preparation of Plantation Rubber,” Morgan, 1913, p. 74.</p></div> + +<p><a name="Sec8_12" id="Sec8_12"></a><span class='pagenum'><a name="Page_86" id="Page_86">[86]</a></span><span +class="smcap">Residual Traces of Sodium Bisulphite.</span>—The prolongation +of the drying period was attributed to the fact that traces +of substances caused by the decomposition of sodium bisulphite +remained in the rubber if the rubber were not sufficiently +worked and washed on the rolls. These traces must have +been very minute, but they were sufficient to retard the progress +of drying. That much depended on the care exercised in +washing is evident from the fact that samples prepared with +varying quantities of the chemical show varying results on +extraction. These samples were tested for the presence of +sulphates. Of the series tested that sample prepared with +bisulphite in the proportion of 1 part to 600 parts latex showed +only a trace of sulphate present; while the one prepared +1:2,400 gave an equal quantity. Intermediate samples contained +no trace of sulphate. On the whole, therefore, the +presence of sulphate in crepe rubber is adventitious, and +properly washed crepe prepared with moderate quantities of +bisulphite may be taken as free from any residual quantities. +Meanwhile there cannot possibly be any doubt of the advantages +gained by the use of sodium bisulphite, and it would not +be very wide of the mark if the statement were made that, in +the event of this chemical being discarded, most contracts for +pale crepe could not be fulfilled.</p> + +<p><a name="Sec8_13" id="Sec8_13"></a><span class="smcap">Sodium Sulphite.</span>—It would not be amiss to insist upon +the point that while the nature of sodium <i>bisulphite</i>, 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. Formulæ 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:</p> + + +<p class="center"><span class='pagenum'><a name="Page_87" id="Page_87">[87]</a></span><i>Sodium Sulphite: For Use in the Factory.</i> +<a name="Sec8_14" id="Sec8_14"></a></p> + +<div class="blockquot"><p>(<i>a</i>) Dissolve 2 ozs. of anhydrous sodium sulphite in a +gallon of water.</p> + +<p>(<i>b</i>) The gallon of solution, placed in the bottom of the +reception jar or tank, is sufficient for the treatment of 40 gallons +of standardised latex (1<span class="enum">1</span>⁄<span class="denom">2</span> lbs. dry rubber per gallon).</p></div> + +<p>The warning previously given regarding the necessity for +thoroughness in the preparation of solutions is here reiterated. +Stirring should be thorough, say for five minutes, and if there +is any sediment or undissolved matter the solution should be +strained through cloth before using.</p> + +<p>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.</p> + +<p>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.</p> + +<p><a name="Sec8_15" id="Sec8_15"></a><span class="smcap">Use of Formalin.</span>—Few estates now use formalin (formaldehyde) +as an anti-coagulant. It must be acknowledged +that when not abused there are points in favour of its employment +in preference to sodium sulphite, but these are outbalanced +by certain disadvantages. The argument may be +stated thus:</p> + +<div class="blockquot"><p><i>Points for</i>: (1) If made up freshly it is an effective anti-coagulant.</p> + +<p>(2) Formalin being the solution of a gas in water, there is no +residual substance left in the rubber to delay drying.</p> + +<p>(3) Its use gives a bright clear rubber.</p></div> + +<div class="blockquot"><p><span class='pagenum'><a name="Page_88" id="Page_88">[88]</a></span><i>Points +against</i>: (1) Its cost at all times is greater than that +of sodium sulphite.</p> + +<p>(2) If the jar is not sealed there is loss by evaporation, thus +increasing the cost.</p> + +<p>(3) Its effect upon the rubber is uncertain. Even in normal +quantity it is said to cause “brittleness” or “shortness.”</p></div> + +<p>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:</p> + + +<p class="center"><a name="Sec8_16" id="Sec8_16"></a><i>Formula for Use of Formalin (Formaldehyde).</i></p> + +<div class="blockquot"><p>(<i>a</i>) 1 pint of formalin is diluted with 5 gallons of water.</p> + +<p>(<i>b</i>) Of this solution 1 gallon is required for 50 gallons of +standardised latex.</p></div> + +<p>In noting this formula the writer gives no recommendation +regarding its use. Whatever may be the actual facts regarding +the effect of formalin upon the vulcanisation of rubber, when +used in minimum proportions, there can be no question concerning +its injurious effect if used in excess. Beyond this the +factors of cost and loss militate against its wider employment.</p> + + +<p class='pagenum'><a name="Page_89" id="Page_89">[89]</a></p> +<hr class="c25" /> +<h2><a name="Ch9" id="Ch9"></a>CHAPTER IX</h2> + +<h3><i>PREPARATION OF SHEET RUBBER</i></h3> + + +<p><a name="Sec9_1" id="Sec9_1"></a><span class="smcap">Pale Sheet.</span>—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.</p> + +<p>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.</p> + +<p>To those accustomed only to the preparation of crepe rubber, +where coagulation can be effected in large batches, the preparation +of sheet rubber always seems to demand much more +labour. As a matter of fact, although the preliminary operations +certainly do demand more care and labour than in crepe-making, +there are compensating advantages in the machining +stage. For the preparation of sheet of the highest quality on +any but the largest scale, elaborate installations of machinery<span class='pagenum'><a name="Page_90" id="Page_90">[90]</a></span> +are quite superfluous, as equal results can be obtained with +pairs of rolls worked by hand.</p> + +<p><a name="Sec9_2" id="Sec9_2"></a><span class="smcap">Uniformity of Product.</span>—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 <a href="#Ch7">Chapter VII</a>. 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.</p> + +<p><a name="Sec9_3" id="Sec9_3"></a>On any but a small scale the labour entailed in the handling +and cleaning of pans is excessive, and shallow tanks are now +employed on most estates. The reception and standardisation +of latex by dilution has already been discussed in +<a href="#Ch7">Chapter VII</a>. 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.</p> + +<p><a name="Sec9_4" id="Sec9_4"></a><span class="smcap">The Ideal Tank.</span>—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.</p> + +<p>The first tanks made erred in being too large, and as the +result of experience the size of units has now been reduced +to a maximum of 12 feet by 4 feet by 1 foot deep.</p> + +<p class='pagenum'><a name="Page_91" id="Page_91">[91]</a></p> + +<table summary="Fig 34"> + +<tr> +<td class="figcenter"><a name="Fig34" id="Fig34"></a><img src="images/illo108a.jpg" alt="Top Figure" /></td> +<td class="padr"> </td> +<td class="figcenter"><img src="images/illo108b.jpg" alt="Bottom Figure" /></td> +</tr> + +<tr> +<td colspan="3" class="caption"><span class="smcap">Unit Modern Coagulating Tank (Two Views).</span><br /> +Construction of brick and cement with lining of glazed tiles. Note +slots incorporated in side tiles. Partition boards in piles in the +background.</td> +</tr> + +</table> + +<p>Tanks are at present constructed either of hard timber or of +brick and cement faced with glazed tiles; both types have<span +class='pagenum'><a name="Page_92" id="Page_92">[92]</a></span> +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.</p> + +<div class="figcenter"><a name="Fig35" id="Fig35"></a><img src="images/illo109.jpg" alt="Another Battery of Tanks" /> +<p class="caption"><span class="smcap">Another Battery of Tanks, with Dilution Tanks, Raised,<br /> +on the Right.</span></p> +<p class="center">Note drainage cocks, chute, and sieve in position.</p></div> + +<p>It should not be a matter of difficulty for manufacturers to +make sheets of thick glass sufficiently large to form the bed-plate +and side-pieces necessary in the lining of a tank. If such +adjuncts could be secured, the disabilities indicated above +would be perhaps wholly removed. Unless there is a demand +from estates, however, it is idle to expect a supply to be forthcoming.</p> + +<p>An even greater improvement would take the form of unit +tanks cast in glazed white-ware with the necessary slots<span class='pagenum'><a name="Page_93" id="Page_93">[93]</a></span> +incorporated in the sides. At present no known firm makes +such tanks of sufficient size. A unit could measure (internally) +6 feet by 4 feet by 1 foot deep, with slots 1<span class="enum">1</span>⁄<span class="denom">2</span> inches apart, and +<span class="enum">3</span>⁄<span class="denom">8</span> inch in width. The tanks might be reinforced with iron +bars, so that they could either be used alone or embedded in +the usual brick structure. The junctions of the bed-plate and +side-pieces could be finely rounded so as to facilitate cleaning, +and at one end a draining-hole could be made, say, 1 inch in +diameter.</p> + +<div class="figcenter"><a name="Fig36" id="Fig36"></a><img src="images/illo110.jpg" alt="Closer View of Foregoing" /> +<p class="caption"><span class="smcap">Closer View of Foregoing.</span></p> +<p class="center">Note partitions in position and coagulum being removed.</p></div> + +<p>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.</p> + +<p><a name="Sec9_5" id="Sec9_5"></a><span class="smcap">Modern Installation.</span>—As an example of a modern +installation of coagulating tanks, we can do no better than<span class='pagenum'><a name="Page_94" id="Page_94">[94]</a></span> +offer reproductions of the system now in use on Pataling +Estate.</p> + +<p>A warning must be given against employing all tanks of +stone-ware or cement unless well glazed. Almost without +exception, irrespective of the material used in the construction +of coagulating tanks, wooden partitions are employed. +In the few exceptional cases the partitions are either of +glass or of aluminium. The former would appear to be +the ideal substance, were it not for initial cost and loss by +breakage. These disabilities may possibly be overcome in +course of time.</p> + +<p><a name="Sec9_6" id="Sec9_6"></a><span class="smcap">Care of Tanks.</span>—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 <span class="enum">1</span>⁄<span class="denom">4</span> 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.</p> + +<p>Naturally the cleansing of glass or aluminium partitions +presents no difficulty, but in the case of wood failure to ensure +thorough cleanliness leads to possible defects in the finished +dry rubber. Provided the wood could be made waterproof, +no trouble would ensue, and hence various measures have been +tried with that object in view. When new the boards have been +surface-waxed or varnished, and the treatment has been repeated +on occasions. But in course of time the surface film of waterproof +material has disappeared, partially or wholly, and the +trouble recurs. When partitions become sodden with serum, the +surfaces are liable to be coated with a slime, consisting largely +of organic growths which have an effect upon the latex, causing<span class='pagenum'><a name="Page_95" id="Page_95">[95]</a></span> +“pitting” on the surface of the coagulum and enclosed bubbles +within.</p> + +<div class="figcenter"><a name="Fig37" id="Fig37"></a><img src="images/illo112.jpg" alt="Another Battery of Tanks, +without Dilution Tanks or Means of Gravitating Latex" /> +<p class="caption"><span class="smcap">Another Battery of Tanks, without Dilution Tanks or Means<br /> +of Gravitating Latex.</span></p></div> + +<p>It is recommended, therefore, that wooden tanks, after +ordinary cleansing daily, should be swabbed out with a +5 per cent. solution of sodium bisulphite. Wooden partitions +should receive the same treatment, and once a week at least +(or every day if possible) they should be placed in the sun for +an hour or two, care being taken that both sides of a partition +are exposed in turn. Before being placed in the latex, all +wooden partitions should be made wet on the surfaces.</p> + +<p>Some years ago the writers had made a partition of vulcanite,<span class='pagenum'><a name="Page_96" id="Page_96">[96]</a></span> +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.</p> + +<div class="figcenter"><a name="Fig38" id="Fig38"></a><img src="images/illo113.jpg" alt="Sheeting Tank containing Coagulum for Crepe +Preparation" /> +<p class="caption"><span class="smcap">A Sheeting Tank containing Coagulum for Crepe<br /> +Preparation.</span></p> +<p class="capt500">Behind wall in background are the tanks in which latex is standardized. +Note vent, to the left, through which latex flows and +wooden “stopper” on edge of tank.</p></div> + +<p><a name="Sec9_7" id="Sec9_7"></a><span class="smcap">Standard Latex.</span>—Enough has been written (see <a href="#Ch7">Chapter +VII.</a>) 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.</p> + +<p><span class='pagenum'><a name="Page_97" id="Page_97">[97]</a></span>The selection of a standard has been the outcome of general +experience. It has been found that if too high a standard is +taken difficulties arise, such as (1) unsatisfactory and uneven +coagulation, (2) too thick a coagulum for easy working in +general, (3) too extended a period of drying and smoke-curing, +and hence too dark a colour in the finished rubber.</p> + +<div class="figcenter"><a name="Fig39" id="Fig39"></a><img src="images/illo114.jpg" alt="A +'Battery' of Sheeting Tanks (Pataling Estate)" /> +<p class="caption"><span class="smcap">A “Battery” of Sheeting Tanks (Pataling Estate).<br /> +Dilution Tanks, Raised, on the Left.</span></p></div> + +<p>On the other hand, too low a standard also brings trouble +in its train. The coagulum is too porous, will not stand handling, +and the resultant sheet is too thin unless an abnormal +thickness of coagulum is prepared. Furthermore, over-dilution +means an increase in the number of tanks required for any +original volume of latex. This involves an increase in floor +area, and perhaps in the size of the building. The soft sheets, +when rolled, may spread to such a width as to cause the edges +to be squeezed under the cheek-blocks of the machines, etc.</p> + +<p><a name="Sec9_8" id="Sec9_8"></a>For all practical purposes, whether sheets are prepared in +pans or in tanks, it has been found that the optimum results +are obtained by the adoption of a standard approximating and +not exceeding 1<span class="enum">1</span>⁄<span class="denom">2</span> lbs. dry rubber per gallon. Primarily this +standard has a direct connection and interdependence with<span class='pagenum'><a name="Page_98" id="Page_98">[98]</a></span> +the distance between the partitions (or between the slots) in +coagulating tanks. The distance found most practicable is +1<span class="enum">1</span>⁄<span class="denom">2</span> inches. This thickness of coagulum, when prepared from +latex not exceeding a standard of 1<span class="enum">1</span>⁄<span class="denom">2</span> lbs. dry rubber per gallon, +is found to yield a very satisfactory sheet in all respects.</p> + +<p>It will be seen that we have two possible main factors of +variation:</p> + +<div class="blockquot"><p>(<i>a</i>) Distance between partitions, causing visible differences +in thickness of coagulum.</p> + +<p>(<i>b</i>) Dry rubber content of latex, causing differences in the +density (<i>e.g.</i>, hardness or softness) of the coagulum.</p></div> + +<p>The effect of variation in (<i>a</i>) will be clear. Even when latex +of a standard of 1<span class="enum">1</span>⁄<span class="denom">2</span> lbs. per gallon is employed the resulting +sheet may be either too thin or too thick.</p> + +<p>Similarly, as already argued, the use of too low or too high +a standard of dilution (when the factor of distance between +partitions is not allowed to vary) is capable of causing much +difficulty. While this is correct, broadly, it is found in the +experience of some estates that their requirements are satisfied +by a slightly lower standard than 1<span class="enum">1</span>⁄<span class="denom">2</span> lbs. per gallon. Thus it +is not uncommon to note the adoption of a standard equivalent +to 1 lb. 4 ozs. or 1 lb. 6 ozs. dry rubber per gallon. Experience +dictates, however, that for the recognised standard measurements +of modern tanks the practical limits of satisfactory +density of latex lie between 1<span class="enum">1</span>⁄<span +class="denom">4</span> lbs. and 1<span class="enum">1</span>⁄<span class="denom">2</span> lbs. per gallon.</p> + +<p><a name="Sec9_9" id="Sec9_9"></a><span class="smcap">Standardising Instruments.</span>—For standardising latex by +dilution all that is required is an instrument which will preserve +a perpendicular position while floating in latex, will be sufficiently +sensitive to indicate fairly small differences in density +of latex, and has one mark on its aerial portion accurately +indicating a density corresponding to the required standard. +On scientific grounds it can be demonstrated that such an +instrument as employed in common practice would not be +strictly accurate.<a name="FNanchor_6_6" id="FNanchor_6_6"></a><a +href="#Footnote_6_6" class="fnanchor">[6]</a> It is not proposed, in this section of the +book, to discuss such considerations.</p> + +<div class="footnote"><p><a name="Footnote_6_6" id="Footnote_6_6"></a><a href="#FNanchor_6_6"><span +class="label">[6]</span></a> De Vries, “Archief voor de Rubbercultuur.”</p></div> + +<p>Instruments of this nature are represented by the “Metrolac”<span +class='pagenum'><a name="Page_99" id="Page_99">[99]</a></span> +(originating from the Rubber Growers’ Association) and +other similar recorders. They generally consist of a submersible +bulb with a projecting stem which is graduated. The +“Metrolac” differs from others in that the bulb is of torpedo +form (thus reducing “skin friction”), and the graduations on +the stem indicate actual weight of dry rubber per gallon instead +of the ordinary specific gravity figures.</p> + +<p>Theoretical considerations to the contrary, it is found in +actual practice in Malaya and Ceylon that, although such +instruments are naturally delicate and require careful manipulation, +they are of considerable practical value and satisfy +a definite requirement. Until an instrument of greater +accuracy and equal simplicity can be discovered all estates +should regard the possession of a few “Metrolacs” as essential.</p> + +<p>The nature of their construction and the average conditions +under which they are used (and abused) make it impossible +to rely upon their accuracy indefinitely or for any long period. +It is always recommended, therefore, that there should be at +least two instruments available, one of which may be in daily +use, while the other is kept in safe custody and only employed, +say, once a week for purposes of checking the accuracy or degree +of inaccuracy of the other. This can be done with reasonable +approximity by placing both instruments in a tall vessel containing +well-mixed and diluted latex. Instruments showing a +marked degree of inaccuracy should not be preserved; but in +cases of necessity “Metrolacs” from estates belonging to +company members of the Rubber Growers’ Association may +be sent to the laboratories for repair and adjustment.<a name="FNanchor_7_7" +id="FNanchor_7_7"></a><a href="#Footnote_7_7" class="fnanchor">[7]</a></p> + +<div class="footnote"><p><a name="Footnote_7_7" id="Footnote_7_7"></a><a +href="#FNanchor_7_7"><span class="label">[7]</span></a> 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.</p></div> + +<p>Where field coagulating stations have been instituted on +estates, it is strictly necessary that instruments should be provided +in all cases; and it should be a rule that these are tested +and corrected weekly by a standard instrument employed for +that purpose only. This need was well recognised by many +estates when, during the War and the consequent shortage of<span class='pagenum'><a name="Page_100" id="Page_100">[100]</a></span> +supply of “Metrolacs,” a demand arose which was met in +some degree by crude instruments of local manufacture, such +as that commonly known as the “Castlefield bobber,” contrived +and made by the enterprising manager of the estate of +that name. The demand for the more accurate instruments +can now be met.</p> + +<p><a name="Sec9_10" id="Sec9_10"></a><span class="smcap">Methods of Using the Instruments.</span>—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.</p> + +<p><a name="Sec9_11" id="Sec9_11"></a><span class="smcap">Skimming.</span>—During the gravitation of the latex from the +reception vessels (in which the standardising of the latex is +effected) to the coagulating tanks, much surface froth is usually +caused. This is best removed by means of a thin board of a +width slightly less than the breadth of the tank. The skimmings +are sometimes placed in pans and subsequently made +into a second grade of sheet rubber, or they receive treatment +with a small proportion of sodium bisulphite and eventually +appear as fine pale crepe. The practice varies usually according +to the form in which the general No. 1 grade is prepared.</p> + +<p><span class='pagenum'><a name="Page_101" id="Page_101">[101]</a></span>On some estates a great deal of the frothing is avoided by +placing in position at the receiving end of the tank a perforated +partition. This partition may be made of wood, or of stout +zinc (or aluminium) carrying ten circular holes to the inch. +Through this the latex percolates, while the froth is retained on +a small area. The froth is removed prior to the addition of the +acid. After stirring in the acid solution most estates again +skim the surface of the latex; but if the stirring has been performed +properly there should be little froth. This, when it +collapses, in any case will appear only on the upper edge of the +strip of coagulum, and after rolling should not be visible. It +would appear, therefore, that the second skimming is not +necessary.</p> + +<p><a name="Sec9_12" id="Sec9_12"></a><span class="smcap">Style of Sheet.</span>—Within the last few years the custom of +making plain sheet—<i>i.e.</i>, sheet having a plain surface—has +gradually given place to the preparation of ribbed sheet—<i>i.e.</i>, +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.</p> + +<p>On these grounds the “marking” of sheet rubber is to be +commended. These reasons apart, it is really astonishing the<span class='pagenum'><a name="Page_102" id="Page_102">[102]</a></span> +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.”</p> + +<p><a name="Sec9_13" id="Sec9_13"></a><span class="smcap">Standard Sheet.</span>—Leaving for the present the question of +pattern of mark, one cannot do better by way of introduction +than to reproduce the instructions<a name="FNanchor_8_8" id="FNanchor_8_8"></a><a +href="#Footnote_8_8" class="fnanchor">[8]</a> given generally to estates.</p> + +<div class="footnote"><p><a name="Footnote_8_8" id="Footnote_8_8"></a><a +href="#FNanchor_8_8"><span class="label">[8]</span></a> “Handbook on Preparation of Rubber,” Rubber Growers’ +Association, May, 1917, p. 28.</p></div> + +<p><a name="Sec9_14" id="Sec9_14"></a><span class="smcap">Rolling and Marking of Sheet Rubber.</span>—Working with +standard latex it is found that strips of coagulum 1<span class="enum">1</span>⁄<span class="denom">2</span> inches in +thickness require little rolling to produce sheets of desirable +thickness.</p> + +<div class="blockquot"><p>(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.</p> + +<p>(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.</p> + +<p>(3) The sheets or strips are then passed once through a +pair of marking rollers. Various types of patterns are used, +but the one which appears to give the most satisfactory results +is that known as the “close-cut spiral.” This produces the +semblance of a small diamond pattern on the rubber. The +surface of the sheet is raised in well-defined ridges, which appear +to present the maximum drying surface exposed to the atmosphere +of the smoke-house. Thus, not only is the appearance +of the sheet rendered attractive, but also the period of drying +is reduced. Starting with standard latex and following the +procedure here described for rolling and marking, sheets +should be ready for packing in ten or eleven days. If the +period is longer, it is possible that the design or structure of +the smoke-house is at fault.</p></div> + +<p><a name="Sec9_15" id="Sec9_15"></a><span class='pagenum'><a +name="Page_103" id="Page_103">[103]</a></span></p><p><span class="smcap">When +to Work the Coagulum.</span>—Before proceeding to +discuss other points the question remains to be settled as to +how long it may be necessary or advisable to allow the coagulum +to remain in the serum before rolling it. For reasons +of practical economy in factory working, it is usual to allow +sheet rubber to remain over night, and the coagulum receives +attention early next morning. During the interval (averaging +about eighteen hours), the coagulum consolidates, leaving an +almost clear serum if the correct quantity of acid has been added +to the latex. Any but the very slightest trace of milkiness in the +serum indicates an insufficiency of coagulant. If the serum is +always definitely clear, there may be grounds for believing +that an excess is being used. If the quantity of coagulant +has been calculated to an average nicety, the serum should be +just dubiously free from milkiness.</p> + +<p>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.</p> + +<p>Some estates prefer to handle the coagulum while rather +softer, as it is claimed:</p> + +<div class="blockquot"><p>(<i>a</i>) That the coagulum is easier to work, and sheets of +improved appearance can be made.</p> + +<p>(<i>b</i>) That there is greater freedom from “bubbles.”</p> + +<p>(<i>c</i>) That the incidence of “rust” is lessened.</p> + +<p>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.</p></div> + +<p>In such cases all latex must reach the store comparatively +early in the day—<i>e.g.</i>, before noon. Three hours is allowed +for coagulation, and the working of the rubber is then commenced. +As a general rule this means that the operations of +rolling and marking must be completed, a short interval given +for dripping, weighing must be done, and the rubber placed in +the smoke-house before night falls (as a rule about 6.30 p.m.).</p> + +<p>Unless factories dealing with a large crop are well equipped<span class='pagenum'><a name="Page_104" id="Page_104">[104]</a></span> +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.</p> + +<p><a name="Sec9_16" id="Sec9_16"></a><span class="smcap">Hand-Rolling.</span>—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.</p> + +<p>On most estates hand-rolling is found necessary, owing to the +tendency of the long strips to stretch unduly, giving badly +shaped sheets. This hand-rolling should be done carefully, +and is best effected on a specially constructed table. This +consists essentially of an inch-thick hard-wood plank about +2 inches wider, and 4 or 5 feet longer, than the strip of coagulum. +Along the edges of the plank, and at right angles to its +upper flat surface, may be fastened strips of wood about <span class="enum">1</span>⁄<span class="denom">2</span> inch square +in section, thus forming a shallow tray open at either end. +These strips serve two purposes:</p> + +<div class="blockquot"><p>(<i>a</i>) As the wooden roller is wider than the plank, they prevent +the coagulum being rolled too thin and too firm.</p> + +<p>(<i>b</i>) They prevent the coagulum being squashed too wide, +and tend to keep the edges straight.</p></div> + +<p>To avoid “thick ends” it is sometimes considered advisable +to insert, at either end of the rolling table, shallow wedges +about 6 inches long, of the same width as the table (between +the edge-strips), and with the sharp end of the wedge pointing +in the direction of the length of the table. The ends of the +coagulum are drawn up and finished on these inclined planes.</p> + +<p>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.</p> + +<p><a name="Sec9_17" id="Sec9_17"></a><span class="smcap">Smooth-Rolling.</span>—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<span class='pagenum'><a name="Page_105" id="Page_105">[105]</a></span> +effected, of course, on one machine; but obviously the distance +between the rolls would have to be readjusted at each operation +and for each piece of coagulum. Apart from the time +thus wasted, there is the certainty, in view of the rough adjustment +of the machines, that the chances of obtaining uniformly +thick sheets would be slight.</p> + +<p>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.</p> + +<p><a name="Sec9_18" id="Sec9_18"></a><span class="smcap">Marking.</span>—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.</p> + +<p>Rolls are cut in various designs: some with “diamond” +grooves on both rolls; some with grooves of varying width and +depth encircling the circumference of the rolls, thus creating +a “stripe” effect on the rubber; and some with diagonally-cut +spiral grooves placed closely together. The last has the +greatest vogue at present, while the first has almost gone out +of favour. An objection lodged against the second design +is that the edges of the grooves sometimes cut through the +rubber, so that the dried sheet divides in strips. It would +appear in such instances that either the coagulum was too +thin and soft, or that the grooves had been cut too deeply +and sharply. In any case the choice of a design is an arbitrary +matter, and should depend upon the effect produced on +the rate of drying and the general appearance.</p> + +<p>The popular “close-cut spiral” roll is machined with +varying measurements, but the usual design has grooves +<span class="enum">1</span>⁄<span class="denom">8</span> +inch wide by <span class="enum">1</span>⁄<span class="denom">8</span> +inch deep and <span class="enum">3</span>⁄<span class="denom">16</span> inch apart.</p> + +<p>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<span +class='pagenum'><a name="Page_106" id="Page_106">[106]</a></span> +portion, and a certain amount of “cockling” of the sheets +will result.</p> + +<p>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.</p> + +<p>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>i.e.</i>, the grooves cannot be +filled, and the ridges are low.</p> + +<p>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.</p> + +<p>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 <span class="enum">1</span>⁄<span class="denom">8</span> inch.</p> + +<p><a name="Sec9_19" id="Sec9_19"></a><span class="smcap">Preparation for Smoke-Curing.</span>—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<span class='pagenum'><a name="Page_107" id="Page_107">[107]</a></span> +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.</p> + +<p>Other defects may arise which can be traced to faulty treatment +of the marked coagulum prior to hanging in the smoke-house +and subsequent to rolling. These will be enlarged upon +in a <a href="#Ch11">subsequent section</a> of the book, and at present it will +suffice to indicate the procedure which experience directs as +likely to give the best results.</p> + +<p><a name="Sec9_20" id="Sec9_20"></a>When the lengths of coagulum leave the marking machine +they are usually laid in piles containing two dozen or more +strips. The piles are then cut into the required lengths, the +exact length generally being determined by the available perpendicular +distance between the supports in the smoke-house. +It is necessary to remark that the piles of sheets should not be +allowed to accumulate, but should be dealt with in subsequent +treatment progressively. If for some reason this is not possible, +then all piles of sheets should be turned on edge so as to assist +the draining away of the serum or “mother-liquor,” which +continues to ooze from the rubber for some time after the +squeezing in the machines.</p> + +<p><a name="Sec9_21" id="Sec9_21"></a>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.</p> + +<p><a name="Sec9_22" id="Sec9_22"></a>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.</p> + +<p><span class='pagenum'><a name="Page_108" id="Page_108">[108]</a></span>While the sheets are fresh and loaded with internal moisture, +the effect of sun-heat upon the surface, when exposed for, say, +two hours, is nil; and the safety of the process can be guaranteed, +provided the stated limit is not exceeded to an appreciable +extent.</p> + +<div class="figcenter"><a name="Fig40" id="Fig40"></a><img src="images/illo125.jpg" alt="The Old Method +of 'Dripping' Freshly Rolled Sheets within the Factory" /> +<p class="caption"><span class="smcap">The Old Method of “Dripping” Freshly Rolled Sheets<br /> +within the Factory.</span></p></div> + +<p>After dripping for an hour or so, the sheets should be placed +in the smoke-house. If it is a bright sunny day, no extra +precautions need be taken; but on cool, dull days it would be +advisable to light the fires earlier than usual, consistent with +the work required to be done in the house—<i>e.g.</i>, 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.</p> + +<p>On a few estates where the smoke-houses are worked continuously, +except for a few hours in the morning, a portion +of the building is separated by a partition for the reception +of the wet rubber. The sheets are taken directly from the +marking rolls and placed in the chamber, beneath which a<span class='pagenum'><a name="Page_109" id="Page_109">[109]</a></span> +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.</p> + +<p>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.</p> + +<div class="figcenter"><a name="Fig41" id="Fig41"></a><img src="images/illo126.jpg" alt="The Newer Method of Hanging in the Open Air" /> +<p class="caption"><span class="smcap">The Newer Method of Hanging in the Open Air.</span></p></div> + +<p><a name="Sec9_23" id="Sec9_23"></a><span class="smcap">Smoking of Rubber.</span>—The assumption may have been noted +above that the sheet is to be smoked. As far as our knowledge +extends, none but small native estates now prepare sheet rubber +of any other type, with the exception of certain patent processes. +Air-dried sheets are generally made on small-holdings, and are +bought in the market chiefly for the purpose of macerating +and making into blanket crepe. We have no intention, therefore, +of discussing the possibilities or qualities of air-dried +sheets, as the output of sheet-rubber from our estates is always +in smoked form. The drying (or, properly, smoking) stage +will be discussed in <a href="#Ch11">Chapter XI</a>.</p> + + +<p class='pagenum'><a name="Page_110" id="Page_110">[110]</a></p> +<hr class="c25" /> +<h2><a name="Ch10" id="Ch10"></a>CHAPTER X</h2> + +<h3><i>PREPARATION OF CREPE RUBBER</i></h3> + + +<p><a name="Sec10_1" id="Sec10_1"></a><span class="smcap">No. 1, or Fine Pale Crepe.</span>—Considering first the preparation +of the highest grade, fine pale crepe, it must be stated +that the difficulties attached to the process are generally not +sufficiently appreciated. In this pale rubber minor blemishes +are so plainly apparent that their importance is highly exaggerated, +and what would worthily escape notice in smoked +rubber assumes disproportionate prominence in pale crepes. +The very fact that such a delicate material as colourless coagulum +has to be manipulated in coarse iron rollers, with the +attendant oil and grease worries, should be sufficient to deter +one from criticising too harshly the occasional lapses of an +estate struggling to give of its best to the market. At the +same time there can be no doubt that if precautions are taken +to attend to all likely sources of contamination, defects in pale +crepe may be avoided to a wonderful extent; and on some +estates the observance of elementary rules enables the preparation +of the finest pale crepe to be made almost mechanically.</p> + +<p><a name="Sec10_2" id="Sec10_2"></a><span class="smcap">Standardisation of Latex.</span>—The question of the standardisation +of latex has been dealt with in a general way in <a href="#Ch7">Chapter +VII.</a>, 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.</p> + +<p>It may be pointed out that it is not <i>essential</i> to adopt the +same standard of dilution as for sheet preparation. Given +that latices from all fields or divisions are fairly uniform, and +of high rubber content, the standard may be taken at a figure +equivalent, for example, to 2 lbs., or 2<span class="enum">1</span>⁄<span +class="denom">2</span> lbs., or even 3 lbs.<span class='pagenum'><a name="Page_111" id="Page_111">[111]</a></span> +per gallon. It is wise, nevertheless, to take a lower standard +for several reasons. For instance:</p> + +<div class="blockquot"><p>(<i>a</i>) 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.</p> + +<p>(<i>b</i>) Recording instruments often fail to give even approximately +correct readings in rich latex. Errors may thus be +made easily.</p> + +<p>(<i>c</i>) A fairly soft coagulum means easier working on the +machines, less labour, and proportionately cheaper costs.</p></div> + +<div class="figcenter"><a name="Fig42" id="Fig42"></a><img src="images/illo128.jpg" alt="Three Grades of Crepe Rubber" /> +<p class="caption"><span class="smcap">Three Grades of Crepe Rubber.</span></p> +<p class="center">Left to right: fine pale crepe; second quality pale crepe; compound +crepe.</p></div> + +<p>It is advised, therefore, that for general purposes the same +standard as that found suitable for sheet rubber should be +taken—viz., 1<span class="enum">1</span>⁄<span class="denom">2</span> lbs. dry rubber per gallon. At all events the +standard should not exceed 2 lbs. per gallon.</p> + +<p><a name="Sec10_3" id="Sec10_3"></a><span class="smcap">Coagulation and Coagulant.</span>—Coagulation may be +undertaken without any special arrangement of tanks, and is +usually effected in the ordinary “Shanghai” glazed +earthenware<span class='pagenum'><a name="Page_112" id="Page_112">[112]</a></span> +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.</p> + +<div class="figcenter"><a name="Fig43" id="Fig43"></a><img src="images/illo129.jpg" alt="A Washing Shed" /> +<p class="caption"><span class="smcap">A Washing Shed.</span></p> +<p class="capt350">Sheets are soaked in hot water in tanks in the background, and +then scrubbed under a spray of cold water.</p></div> + +<p>On a larger scale it is advised that proper reception tanks, +in which standardisation can be effected, should be installed. +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.</p> + +<p>If ordinary jars are used, and the coagulum is left until the<span class='pagenum'><a name="Page_113" id="Page_113">[113]</a></span> +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.</p> + +<p>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.</p> + +<p><a name="Sec10_4" id="Sec10_4"></a><span class="smcap">Quantity of Coagulant.</span>—For a general discussion on +the coagulant and quantities employed, the reader is referred +to <a href="#Ch8">Chapter VIII</a>. It is there recommended that for latex +standardised to a level of 1<span class="enum">1</span>⁄<span class="denom">2</span> lbs. per gallon, the proportion of +pure acetic acid should be in the ratio of 1:1,200. Directions +are there given for the making of the solution, and the calculation +of the quantity required for any given volume of latex.</p> + +<p>It is pointed out that for average <i>undiluted</i> latex the basis of +calculation, for quantities of acetic acid required, should be +taken on the ratio 1:1,000. Where latex exceeds a dry rubber +content of 3 lbs. per gallon, it may be necessary to increase +the quantity of acid to 1:800.</p> + +<p>If a standard of 2 lbs. per gallon is adopted, the formula given +for the 1<span class="enum">1</span>⁄<span class="denom">2</span> lbs. 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 1 per cent. strength, the following +difference would be noted:</p> + +<div class="blockquot"> + +<table summary="Table p113"> + +<tr> +<td class="left">(<i>a</i>)</td> +<td colspan="2" class="left">One part pure acetic acid to 100 parts water (theoretically 99 parts).</td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">(<i>b</i>)</td> +<td class="center br"><i>1<span class="enum">1</span>⁄<span class="denom">2</span> lbs. per gallon.</i></td> +<td class="center"><i>2 lbs. per gallon.</i></td> +</tr> + +<tr> +<td class="left"> </td> +<td class="left br">Of the above solution use 1 gallon to every 12 gallons of standardised latex.</td> +<td class="left">Of the above solution use 1 gallon to every 10 or 11 gallons of standardised latex.</td> +</tr> + +</table> +</div> + +<p>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.<span class='pagenum'><a name="Page_114" id="Page_114">[114]</a></span></p> + +<p>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 1 per cent.</p> + +<p>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 +formulæ 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.</p> + +<p><a name="Sec10_5" id="Sec10_5"></a><span class="smcap">Colour of Fine Crepe.</span>—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.</p> + +<p>Probably without exception all estates employ sodium +bisulphite as the agent for the prevention of that darkening +(oxidation) which is natural in drying rubber.</p> + +<p><a name="Sec10_6" id="Sec10_6"></a><span class="smcap">Sodium Bisulphite.</span>—A formula for use of this chemical +is given in <a href="#Ch8">Chapter VIII.</a>, and is applicable to latex standardised +to 1<span class="enum">1</span>⁄<span class="denom">2</span> +lbs. dry rubber per gallon. If a higher standard is<span class='pagenum'><a name="Page_115" id="Page_115">[115]</a></span> +chosen the quantity calculated as in (<i>b</i>) of that formula may +be increased slightly, and the exact requirements found by +experience. The caution must again be given that the employment +of an excess of sodium bisulphite will lead to the production +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.</p> + +<p>It must be emphasised that the formula in <a href="#Ch8">Chapter VIII.</a> +indicates the <i>maximum</i> 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.</p> + +<p><a name="Sec10_7" id="Sec10_7"></a><span class="smcap">Evaluation and Deterioration of Sodium Bisulphite +and Sodium Sulphite.</span>—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.</p> + +<p>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 between +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 <a href="#Page_116">page 116</a>. Samples of doubtful +specimens may be sent to the laboratories for analysis, but +the bulk of the chemical should not be used.</p> + +<p>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 manufacturers<span +class='pagenum'><a name="Page_116" id="Page_116">[116]</a></span> +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.</p> + +<table id="Sec10_8" style="width: 80%;" summary="Table p116"> + +<tr> +<td class="left"> </td> +<td class="center br" style="width: 48%;"><i>Sodium Bisulphite.</i></td> +<td class="left"> </td> +<td class="center" style="width: 48%;"><i>Sodium Sulphite.</i></td> +</tr> + +<tr> +<td class="right">1.</td> +<td class="left br">If in good condition it has a powerful odour of sulphur dioxide.<a name="FNanchor_9_9" +id="FNanchor_9_9"></a><a href="#Footnote_9_9" class="fnanchor">[9]</a></td> +<td class="right">1.</td> +<td class="left">It has no perceptible odour.</td> +</tr> + +<tr> +<td class="right">2.</td> +<td class="left br">In solution it should turn a blue litmus-paper red.</td> +<td class="right">2.</td> +<td class="left">In solution it should turn a red litmus-paper blue.</td> +</tr> + +<tr> +<td class="right">3.</td> +<td class="left br">It exhibits a marked tendency to “cake” if the drum is allowed to remain open.</td> +<td class="right">3.</td> +<td class="left">The tendency to “cake” is less marked than in the case of the bisulphite.</td> +</tr> + +</table> + +<div class="footnote"><p><a name="Footnote_9_9" id="Footnote_9_9"></a><a href="#FNanchor_9_9"><span class="label">[9]</span></a> 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.</p></div> + +<p>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 exposure. +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.</p> + +<p><a name="Sec10_9" id="Sec10_9"></a><span class="smcap">Care of Sodium Bisulphite.</span>—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.</p> + +<p>Drums are of two sizes, generally containing <span class="enum">1</span>⁄<span +class="denom">4</span> or <span class="enum">1</span>⁄<span class="denom">2</span> cwt. +respectively. It will be obvious that, although the prime cost +may be cheaper with the larger quantity, it would always be<span class='pagenum'><a name="Page_117" id="Page_117">[117]</a></span> +preferable to secure the smaller drums, as the loss on exposure +will be less.</p> + +<p>Most commonly the 56 lb. 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 1 lb. per +100 gallons of latex. A 56 lb. drum, assuming no loss or +waste, should be sufficient to treat <i>at least</i> 5,600 gallons of latex +(say, 8,500 lbs. of rubber)—if the bisulphite is of first-class +quality, and the use is applied only to the preparation of fine +pale crepe.</p> + +<p>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 sealed 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.</p> + +<p><a name="Sec10_10" id="Sec10_10"></a><span class="smcap">Mixing Solution with Latex.</span>—Emphasis has been laid, in +<a href="#Ch8">Chapter VIII.</a>, 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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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<span class='pagenum'><a name="Page_118" id="Page_118">[118]</a></span> +be responsible for prolonged drying, surface deposits, and +possibly “spot disease.”</p> + +<p><a name="Sec10_11" id="Sec10_11"></a><span class="smcap">Former Methods of Making Pale Rubber.</span>—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:</p> + +<div class="blockquot"><p>(<i>a</i>) Use of excessive quantities of strong acetic acid.</p> + +<p>(<i>b</i>) Extreme dilution of latex in conjunction with excessive +quantities of acid.</p> + +<p>(<i>c</i>) Extreme dilution in conjunction with steaming and +excess of acid.</p> + +<p>(<i>d</i>) Extreme dilution of latex in conjunction with excess +of acid and subsequent heating of the coagulum in hot water.</p> + +<p>(<i>e</i>) The use of excess of a mineral acid such as sulphuric acid.</p> + +<p>(<i>f</i>) The skimmings and very dilute latex, coagulated with +excess of acid.</p></div> + +<p><a name="Sec10_12" id="Sec10_12"></a><span class="smcap">Working the Coagulum.</span>—Description of the details of +necessary machinery for crepe-making is relegated to <a href="#Part3">Section +III.</a> of this book. Here we shall treat only of the matter +in general.</p> + +<p>In the preparation of crepe rubber heavy machinery is +necessary, and ample engine-power must be available. The +machines should comprise three types:</p> + +<div class="blockquot"><p>(<i>a</i>) 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.”</p> + +<p>(<i>b</i>) 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 (<i>c</i>). They are sometimes called “crepers,” +but as this term may be applied equally to the macerating +rolls, they will be termed the “intermediate” rolls.</p> + +<p>(<i>c</i>) Smooth rolls usually run at approximately even speeds +and, as their name denotes, devoid of any grooving. They +are called “smooth” rolls or “finishers.”</p></div> + +<p>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. 1 quality generally +connotes fineness and paleness with a thin crepe which has a +good, smooth, and fairly well-knit texture.</p> + +<p><span class='pagenum'><a name="Page_119" id="Page_119">[119]</a></span>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 <i>sine qua non</i>.</p> + +<p>For reasons which will be explained more fully in the <a href="#Ch17">chapter</a> +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.</p> + +<p>The bulk of the output of No. 1 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.</p> + +<p>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.</p> + +<p>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 (<i>a</i>) the size of the rolls, (<i>b</i>) the number of machines of each +type, (<i>c</i>) the gearing of the pinions, (<i>d</i>) 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.</p> + +<p>It has been shown by the writers in previous publications +that over-working of the coagulum has an effect on the vulcan<span class='pagenum'><a name="Page_120" +id="Page_120">[120]</a></span>isation +of the rubber; and this has been confirmed by others.<a name="FNanchor_10_10" +id="FNanchor_10_10"></a><a href="#Footnote_10_10" class="fnanchor">[10]</a> +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.</p> + +<div class="footnote"><p><a name="Footnote_10_10" id="Footnote_10_10"></a><a +href="#FNanchor_10_10"><span class="label">[10]</span></a> Bulletin No. 27, Department of Agriculture F.M.S., April, 1918, +“Preparation and Vulcanisation of Plantation Para Rubber,” +Eaton, Grantham and Day.</p></div> + +<p>Owing to the existing differences in equipment and speed of +drive, etc., the regular practice of any one estate may be unsuitable +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.</p> + +<p><a name="Sec10_13" id="Sec10_13"></a><span class="smcap">Lower Grades of Crepe Rubber.</span>—Even a few years ago it +was plain that the lower grades of crepe (<i>i.e.</i>, 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 preparation +of the lower grades.</p> + +<p><a name="Sec10_14" id="Sec10_14"></a><span class="smcap">Naturally Coagulated Lump Rubber.</span>—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<span class='pagenum'><a name="Page_121" id="Page_121">[121]</a></span> +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.</p> + +<p>Providing that the coagulated lump is free from bark, leaves, +and leaf-stems, and certain other precautions taken, the difference +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.</p> + +<p>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 corresponding +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 1 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 submerged +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.</p> + +<p><span class='pagenum'><a name="Page_122" id="Page_122">[122]</a></span>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. 1 grade.</p> + +<p><a name="Sec10_15" id="Sec10_15"></a><span class="smcap">Skimmings and Washings.</span>—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.</p> + +<p>The cup-washings, as they arrive at the store, represent a +very dilute latex, the rubber from which is generally of a +greyish colour.</p> + +<p>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. 1 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.</p> + +<p><a name="Sec10_16" id="Sec10_16"></a><span class="smcap">Tree-Scrap.</span>—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.</p> + +<p>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<span class='pagenum'><a name="Page_123" id="Page_123">[123]</a></span> +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.</p> + +<p>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.</p> + +<p><a name="Sec10_17" id="Sec10_17"></a><span class="smcap">Bark-Shavings.</span>—It +has been intimated in a <a href="#Sec5_16">previous section</a> +that the method of obtaining and collecting bark-shavings +varies with the type of labour employed.</p> + +<p>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.</p> + +<p>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>i.e.</i>, 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.</p> + +<p>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.</p> + +<p>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.</p> + +<p><a name="Sec10_18" id="Sec10_18"></a><span class='pagenum'><a name="Page_124" id="Page_124">[124]</a></span><span +class="smcap">Earth-Scrap.</span>—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.</p> + +<p><a name="Sec10_19" id="Sec10_19"></a><span class="smcap">Fibrous Matter in Low-Grade Rubbers.</span>—It is sometimes +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.</p> + +<p><a name="Sec10_20" id="Sec10_20"></a><span class="smcap">Scrap-Washers.</span>—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.</p> + +<p>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.</p> + +<p>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<span class='pagenum'><a name="Page_125" id="Page_125">[125]</a></span> +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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>Again a deal of extra work, and much wear and tear, is caused +by the <i>abuse</i> of the scrap-washer—<i>e.g.</i>, 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.</p> + +<p>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<span class='pagenum'><a name="Page_126" id="Page_126">[126]</a></span> +easy to transport and to manipulate in the ordinary crepeing +battery.</p> + +<p><a name="Sec10_21" id="Sec10_21"></a><span class="smcap">Compound Crepes.</span>—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:</p> + +<div class="blockquot"><p>(1) A pale rubber (often streaked) obtained from coagulation +of cup washings and bucket rinsings.</p> + +<p>(2) A pale rubber (often streaked) obtained by coagulation of +the skimmings from the surface of the No. 1 latex.</p> + +<p>(3) A streaked and dull rubber prepared from naturally-coagulated +clots found in cups, buckets, and latex carts.</p> + +<p>(4) A streaked rubber prepared from scrap which had coagulated +upon the face of the cut bark.</p> + +<p>(5) A brownish and streaked rubber made by maceration of +bark-shavings to which pieces of tree-scrap adhered.</p> + +<p>(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.</p></div> + +<p>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 introduced, +one may realise the difficulty attaching to the evaluation +of these rubbers as they appeared upon the market.</p> + +<p>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.</p> + +<p>In the case of many, it has been realised that the manufacturer +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<span class='pagenum'><a name="Page_127" id="Page_127">[127]</a></span> +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.</p> + +<p>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 compound +crepe—</p> + +<div class="blockquot"><p>(<i>a</i>) Naturally coagulated lump rubber.</p> + +<p>(<i>b</i>) Tree-scrap.</p> + +<p>(<i>c</i>) Bark-shavings scrap.</p></div> + +<p>The product would be darker in colour than (<i>a</i>) and slightly +better than (<i>b</i>). Let it be granted that there might be a +monetary loss on (<i>a</i>), it is probable that there would be a slight +gain in comparison with the usual prices obtained for (<i>b</i>) +and (<i>c</i>). Now, as a general rule, the actual percentage of crop +made into (<i>b</i>) is appreciably less than that made into (<i>c</i>) and +still less than (<i>b</i>) and (<i>c</i>) 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.</p> + +<p>Unfortunately this process is not open to estates which do +not possess a scrap-washer. <i>It is essential that the rubber should +be free from grit, sand, and bark particles.</i> In the absence of a<span class='pagenum'><a name="Page_128" id="Page_128">[128]</a></span> +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.</p> + +<p>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.:</p> + +<div class="blockquot"><p>(<i>a</i>) No. 1. From latex coagulated in the store.</p> + +<p>(<i>b</i>) No. 2. Compound.</p> + +<p>(<i>c</i>) No. 3. Earth-rubber.</p></div> + +<p>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.</p> + +<p>Besides the estates having only three grades, there are others +which make four—viz.:</p> + +<div class="blockquot"><p>(<i>a</i>) No. 1. From latex coagulated in the store.</p> + +<p>(<i>b</i>) No. 2. Compound, from cup washings, etc., skimmings, +and naturally coagulated lump.</p> + +<p>(<i>c</i>) No. 3. Compound, from tree-scrap and bark-shavings +rubber.</p> + +<p>(<i>d</i>) No. 4. Earth-scrap.</p> + +<p>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.</p></div> + +<p><a name="Sec10_22" id="Sec10_22"></a><span class='pagenum'><a name="Page_129" id="Page_129">[129]</a></span><span +class="smcap">Need for Increased Care with Lower Grade Rubber.</span>—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 preparation +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. 1 product. +Often, as in the case of naturally coagulated rubbers, they are +superior in some respects to ordinary fine pale crepe. Doubtless +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.</p> + +<p>As to the particular form of the lower grade crepe rubber, +one may apply the remarks made under the <a href="#Sec10_1">section</a> 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.</p> + +<p><a name="Sec10_23" id="Sec10_23"></a><span class="smcap">Block Rubber.</span>—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<span class='pagenum'><a name="Page_130" id="Page_130">[130]</a></span> +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.</p> + +<p>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.</p> + +<p>The advantages which block rubber possesses are the compactness +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.</p> + +<p><a name="Sec10_24" id="Sec10_24"></a><span class="smcap">Smoked Crepe and Sheet Clippings.</span>—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 (1) clippings +obtained from the ends of sheets, (2) sheets which have +been malformed in machining, or (3) sheets showing the +presence of many “bubbles.”</p> + +<p>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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>It cannot possibly be argued that rubber of this description +would be in any way inferior to the best smoked sheet for<span class='pagenum'><a name="Page_131" id="Page_131">[131]</a></span> +manufacturing purposes, but owing to the prevailing system +of evaluation for market purposes, it is necessary to resort to +the expedients indicated above.</p> + +<p>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.</p> + + +<p class='pagenum'><a name="Page_132" id="Page_132">[132]</a></p> +<hr class="c25" /> +<h2><a name="Ch11" id="Ch11"></a>CHAPTER XI</h2> + +<h3><i>DRYING OF RUBBER</i></h3> + +<p><a name="Sec11_1" id="Sec11_1"></a><span class="smcap">Air-Drying of Crepe.</span>—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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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 <a href="#Ch15">subsequent chapter</a>.</p> + +<p>Similarly the position of the drying-shed exerts an important +influence, and the erection of the building in low-lying sur<span class='pagenum'><a +name="Page_133" id="Page_133">[133]</a></span>roundings +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.</p> + +<p>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.</p> + +<p><a name="Sec11_2" id="Sec11_2"></a><span class="smcap">Artificial Driers for Crepe.</span>—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, therefore, +as the accommodation is sufficient, and regular shipments +are the rule, it is expected that ordinary air-drying will still +remain the general practice.</p> + +<p>Of the better-known artificial driers, there are only three<span class='pagenum'><a name="Page_134" id="Page_134">[134]</a></span> +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.</p> + +<p><a name="Sec11_3" id="Sec11_3"></a><span class="smcap">Vacuum Driers.</span>—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 continuous +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:</p> + +<div class="blockquot"><p>(1) That the rubber must be fairly thin.</p> + +<p>(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.<a name="FNanchor_11_11" id="FNanchor_11_11"></a><a href="#Footnote_11_11" class="fnanchor">[11]</a></p></div> + +<div class="footnote"><p><a name="Footnote_11_11" id="Footnote_11_11"></a><a +href="#FNanchor_11_11"><span class="label">[11]</span></a> These figures refer to temperatures recorded by thermometers +placed in the folds of the rubber.</p></div> + +<p>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<span class='pagenum'><a name="Page_135" id="Page_135">[135]</a></span> +starting the pump; and with the pump stopped, there should +not be a greater fall in pressure than 1 inch within ten minutes +after stopping the pump.</p> + +<p>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 lbs., 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.</p> + +<p>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 satisfactorily. +A case was noted in which thin crepe was excellently +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.</p> + +<p>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<span class='pagenum'><a name="Page_136" id="Page_136">[136]</a></span> +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>i.e.</i>, +nearly 14 lbs. 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.</p> + +<p>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 determine +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 temperature +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.</p> + +<p><a name="Sec11_4" id="Sec11_4"></a><span class="smcap">Colombo Commercial Company’s Drier.</span>—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 1 lb.<span class='pagenum'><a name="Page_137" id="Page_137">[137]</a></span> +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.</p> + +<p>Figures obtained from the actual working of a drier in +Ceylon are given below:</p> + +<table summary="Table p137"> + +<tr> +<td colspan="7" class="center bt br bb"><span class="smcap">Chamber 1.—Temperature 160°-180°F.</span></td> +<td rowspan="2" class="center bt bb"><span class="smcap">Chamber 2.—<br />Temperature<br />150°-165°F.</span></td> +</tr> + +<tr> +<td class="center bb br"><i>No. of<br />Tray.</i></td> +<td colspan="2" class="center br bb"><i>Drying<br />Period.</i></td> +<td colspan="2" class="center br bb"><i>Weight of<br />Wet Rubber.</i></td> +<td colspan="2" class="center br bb"><i>Weight of<br />Dry Rubber.</i></td> +</tr> + +<tr> +<td class="left br"> </td> +<td class="center fsize80">Hrs.</td> +<td class="center fsize80 br">Mins.</td> +<td colspan="2" class="center fsize80 br">Lbs.</td> +<td colspan="2" class="center fsize80 br">Lbs.</td> +<td class="left"> </td> +</tr> + +<tr> +<td class="right br" style="padding-right: 1.25em;">1</td> +<td class="right" style="padding-right: .5em;">1</td> +<td class="right br" style="padding-right: .5em;">22</td> +<td class="right" style="padding-right: 0; padding-left: .75em;">7</td> +<td class="left br" style="padding-left: 0; padding-right: .5em;"><span class="enum">1</span>⁄<span class="denom">2</span></td> +<td class="right" style="padding-right: 0; padding-left: .75em;">6</td> +<td class="left br" style="padding-left: 0; padding-right: .5em;"> </td> +<td class="left">Worked similarly</td> +</tr> + +<tr> +<td class="right br" style="padding-right: 1.25em;">2</td> +<td class="right" style="padding-right: .5em;">1</td> +<td class="right br" style="padding-right: .5em;">42</td> +<td class="right" style="padding-right: 0; padding-left: 1em;">7</td> +<td class="left br" style="padding-left: 0;"><span class="enum">1</span>⁄<span class="denom">2</span></td> +<td class="right" style="padding-right: 0; padding-left: .75em;">6</td> +<td class="left br" style="padding-left: 0; padding-right: .5em;"> </td> +<td class="left">to No. 1. Yielded</td> +</tr> + +<tr> +<td class="right br" style="padding-right: 1.25em;">3</td> +<td class="right" style="padding-right: .5em;">1</td> +<td class="right br" style="padding-right: .5em;">57</td> +<td class="right" style="padding-right: 0; padding-left: 1em;">7</td> +<td class="left br" style="padding-left: 0;"><span class="enum">1</span>⁄<span class="denom">2</span></td> +<td class="right" style="padding-right: 0; padding-left: .75em;">6</td> +<td class="left br" style="padding-left: 0; padding-right: .5em;"> </td> +<td class="left">in 2 hrs. 23 mins.</td> +</tr> + +<tr> +<td class="right br" style="padding-right: 1.25em;">4</td> +<td class="right" style="padding-right: .5em;">1</td> +<td class="right br" style="padding-right: .5em;">57</td> +<td class="right" style="padding-right: 0; padding-left: 1em;">7</td> +<td class="left br" style="padding-left: 0;"><span class="enum">1</span>⁄<span class="denom">2</span></td> +<td class="right" style="padding-right: 0; padding-left: .75em;">6</td> +<td class="left br" style="padding-left: 0; padding-right: .5em;"> </td> +<td class="left">70<span class="enum">3</span>⁄<span class="denom">4</span> lbs. dry rubber,</td> +</tr> + +<tr> +<td class="right br" style="padding-right: 1.25em;">5</td> +<td class="right" style="padding-right: .5em;">1</td> +<td class="right br" style="padding-right: .5em;">57</td> +<td class="right" style="padding-right: 0; padding-left: 1em;">7</td> +<td class="left br" style="padding-left: 0;"> </td> +<td class="right" style="padding-right: 0; padding-left: .75em;">5</td> +<td class="left br" style="padding-left: 0; padding-right: .5em;"><span class="enum">3</span>⁄<span class="denom">4</span></td> +<td class="left">from 87<span class="enum">1</span>⁄<span class="denom">2</span> lbs. wet</td> +</tr> + +<tr> +<td class="right br" style="padding-right: 1.25em;">6</td> +<td class="right" style="padding-right: .5em;">1</td> +<td class="right br" style="padding-right: .5em;">57</td> +<td class="right" style="padding-right: 0; padding-left: 1em;">7</td> +<td class="left br" style="padding-left: 0;"><span class="enum">1</span>⁄<span class="denom">2</span></td> +<td class="right" style="padding-right: 0; padding-left: .75em;">6</td> +<td class="left br" style="padding-left: 0; padding-right: .5em;"> </td> +<td class="left">rubber.</td> +</tr> + +<tr> +<td class="right br" style="padding-right: 1.25em;">7</td> +<td class="right" style="padding-right: .5em;">2</td> +<td class="right br" style="padding-right: .5em;">0</td> +<td class="right" style="padding-right: 0; padding-left: 1em;">7</td> +<td class="left br" style="padding-left: 0;"><span class="enum">1</span>⁄<span class="denom">2</span></td> +<td class="right" style="padding-right: 0; padding-left: .75em;">6</td> +<td class="left br" style="padding-left: 0; padding-right: .5em;"> </td> +<td class="left"> </td> +</tr> + +<tr> +<td class="right br" style="padding-right: 1.25em;">8</td> +<td class="right" style="padding-right: .5em;">2</td> +<td class="right br" style="padding-right: .5em;">0</td> +<td class="right" style="padding-right: 0; padding-left: 1em;">7</td> +<td class="left br" style="padding-left: 0;"><span class="enum">1</span>⁄<span class="denom">2</span></td> +<td class="right" style="padding-right: 0; padding-left: .75em;">6</td> +<td class="left br" style="padding-left: 0; padding-right: .5em;"> </td> +<td class="left"> </td> +</tr> + +<tr> +<td class="right br" style="padding-right: 1.25em;">9</td> +<td class="right" style="padding-right: .5em;">2</td> +<td class="right br" style="padding-right: .5em;">11</td> +<td class="right" style="padding-right: 0; padding-left: 1em;">6</td> +<td class="left br" style="padding-left: 0;"><span class="enum">1</span>⁄<span class="denom">2</span></td> +<td class="right" style="padding-right: 0; padding-left: .75em;">5</td> +<td class="left br" style="padding-left: 0; padding-right: .5em;"> </td> +<td class="left"> </td> +</tr> + +<tr> +<td class="right br" style="padding-right: 1.25em;">10</td> +<td class="right" style="padding-right: .5em;">2</td> +<td class="right br" style="padding-right: .5em;">11</td> +<td class="right" style="padding-right: 0; padding-left: 1em;">7</td> +<td class="left br" style="padding-left: 0;"><span class="enum">1</span>⁄<span class="denom">2</span></td> +<td class="right" style="padding-right: 0; padding-left: .75em;">6</td> +<td class="left br" style="padding-left: 0; padding-right: .5em;"> </td> +<td class="left"> </td> +</tr> + +<tr> +<td class="right br" style="padding-right: 1.25em;">11</td> +<td class="right" style="padding-right: .5em;">2</td> +<td class="right br" style="padding-right: .5em;">11</td> +<td class="right" style="padding-right: 0; padding-left: 1em;">7</td> +<td class="left br" style="padding-left: 0;"><span class="enum">1</span>⁄<span class="denom">2</span></td> +<td class="right" style="padding-right: 0; padding-left: .75em;">6</td> +<td class="left br" style="padding-left: 0; padding-right: .5em;"> </td> +<td class="left"> </td> +</tr> + +<tr> +<td class="right br bb" style="padding-right: 1.25em;">12</td> +<td class="right bb" style="padding-right: .5em;">2</td> +<td class="right br bb" style="padding-right: .5em;">18</td> +<td class="right bb" style="padding-right: 0; padding-left: 1em;">7</td> +<td class="left br bb" style="padding-left: 0;"><span class="enum">1</span>⁄<span class="denom">2</span></td> +<td class="right bb" style="padding-right: 0; padding-left: .75em;">6</td> +<td class="left br bb" style="padding-left: 0; padding-right: .5em;"> </td> +<td class="left bb"> </td> +</tr> + +<tr> +<td class="bb br"> </td> +<td colspan="2" class="bb br"> </td> +<td class="right bb" style="padding-right: 0; padding-left: 1em;">88</td> +<td class="left br bb" style="padding-left: 0;"><span class="enum">1</span>⁄<span class="denom">2</span></td> +<td class="right bb" style="padding-right: 0; padding-left: .75em;">80</td> +<td class="left br bb" style="padding-left: 0; padding-right: .5em;"><span class="enum">3</span>⁄<span class="denom">4</span></td> +<td class="left bb"> </td> +</tr> + +</table> + +<p>It will be seen, therefore, that the drier had an output in +2 hrs. 23 mins. of 141<span class="enum">1</span>⁄<span class="denom">2</span> lbs., which is at the rate of 1 lb. per +minute approximately.</p> + +<p>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,<span class='pagenum'><a name="Page_138" id="Page_138">[138]</a></span> +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.</p> + +<p><a name="Sec11_5" id="Sec11_5"></a><span class="smcap">Michie-Golledge System.</span>—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 revolving +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 <span class="enum">3</span>⁄<span class="denom">16</span> 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.</p> + +<p><a name="Sec11_6" id="Sec11_6"></a><span class="smcap">Rate of Air-Drying of Crepe Rubber.</span>—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.</p> + +<p>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.<span class='pagenum'><a name="Page_139" id="Page_139">[139]</a></span> +It has been advanced elsewhere<a name="FNanchor_12_12" id="FNanchor_12_12"></a><a +href="#Footnote_12_12" class="fnanchor">[12]</a> 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 inexplicable. +It has always been the opinion of the writers that the +actual rolling of the rubber plays an important part in determining +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.</p> + +<div class="footnote"><p><a name="Footnote_12_12" id="Footnote_12_12"></a><a +href="#FNanchor_12_12"><span class="label">[12]</span></a> “Preparation of Plantation Rubber,” Morgan, 1913, chapters +xii. and xiii.</p></div> + +<p>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 coagulum +is passed through three sets of rollers, and the stages +may be described as:</p> + +<div class="blockquot"><p>(1) Rough rolling.</p> + +<p>(2) Medium rolling.</p> + +<p>(3) Smooth rolling.</p></div> + +<p>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 “<span +class='pagenum'><a name="Page_140" id="Page_140">[140]</a></span>lumpiness” +and free from holes, which should dry in from ten to +twelve days.</p> + +<p>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.</p> + +<p>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 +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.</p> + +<div class="figcenter"><a name="Fig44" id="Fig44"></a><img src="images/illo157.png" alt="Drying Graph. Pale Crepe (Thin)" /> +<p class="caption"><span class="smcap">Drying Graph. Pale Crepe (Thin).</span></p></div> + +<p><a name="Sec11_7" id="Sec11_7"></a><span class="smcap">When does +Air-Drying take place?</span>—Experiments<a name="FNanchor_13_13" +id="FNanchor_13_13"></a><a href="#Footnote_13_13" class="fnanchor">[13]</a> +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<span class='pagenum'><a name="Page_141" id="Page_141">[141]</a></span> +it is a very clear night the air is generally saturated with moisture. +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—<i>i.e.</i>, the rubber weighed slightly more when taken +out in the morning than it had weighed the previous afternoon.</p> + +<div class="footnote"><p><a name="Footnote_13_13" id="Footnote_13_13"></a><a +href="#FNanchor_13_13"><span class="label">[13]</span></a> Rubber Growers’ Association, Malaya Local Report, No. 2, 1914.</p></div> + +<p><a name="Sec11_8" id="Sec11_8"></a><span class="smcap">Crepe may Increase in Weight.</span>—As an instance of the +kind of result obtained a graph is here given of the rate of drying +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.</p> + +<p>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 moisture +instead of abstraction. It will be noted that when drying +takes place the slopes more nearly approximating the vertical<span class='pagenum'><a name="Page_142" id="Page_142">[142]</a></span> +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>i.e.</i>, 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 attributed +to the presence of surface moisture after hanging overnight, +when the rains had become frequent. Some light is +thus shed upon a subject which has puzzled both shippers and +receivers of crepe rubber.</p> + +<p><a name="Sec11_9" id="Sec11_9"></a><span class="smcap">Differences in Weight.</span>—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 1 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.</p> + +<p>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 counterbalanced, +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<span class='pagenum'><a name="Page_143" id="Page_143">[143]</a></span> +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.</p> + +<p><a name="Sec11_10" id="Sec11_10"></a><span class="smcap">Aids to Normal Air-Drying.</span>—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.</p> + +<p><a name="Sec11_11" id="Sec11_11"></a><span class="smcap">Smoke-Curing of Sheet Rubber.</span>—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.</p> + +<p>The manipulation of the rubber, after it leaves the marking +rolls and preparatory to smoke-curing, has been discussed in +<a href="#Ch9">Chapter IX</a>. 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.</p> + +<p><span class='pagenum'><a name="Page_144" id="Page_144">[144]</a></span>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.</p> + +<p><a name="Sec11_12" id="Sec11_12"></a><span class="smcap">Recording Instruments.</span>—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 temperatures +attained in the smoke-house. Ordinary thermometers +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.</p> + +<p>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 superintendent’s +office or house, on the attainment of a certain temperature. +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 attention, +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.</p> + +<p><a name="Sec11_13" id="Sec11_13"></a><span class="smcap">Temperature of Smoke-Curing.</span>—In the question of temperature +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<span class='pagenum'><a name="Page_145" id="Page_145">[145]</a></span> +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<a name="FNanchor_14_14" id="FNanchor_14_14"></a><a href="#Footnote_14_14" +class="fnanchor">[14]</a> that the temperature giving the maximum benefit +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.</p> + +<div class="footnote"><p><a name="Footnote_14_14" id="Footnote_14_14"></a><a href="#FNanchor_14_14"><span +class="label">[14]</span></a> “Preparation of Plantation Rubber,” Morgan, 1913, chapter x.</p></div> + +<p>The figure given in previous publications as a maximum +working temperature for smoke-houses was 110° F., but certainly +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.</p> + +<p><a name="Sec11_14" id="Sec11_14"></a><span class="smcap">Period of Drying.</span>—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:</p> + +<div class="blockquot"><p>(1) Relative thickness of rubber.</p> + +<p>(2) Extent and quality of rolling.</p> + +<p>(3) Temperature of drying.</p></div> + +<p>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<span class='pagenum'><a name="Page_146" id="Page_146">[146]</a></span> +rolled, the shorter the period of drying; the higher the temperature, +the more rapid the drying.</p> + +<p>It has been shown in <a href="#Ch9">Chapter IX.</a> 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>i.e.</i>, 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.</p> + +<p>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:</p> + +<div class="blockquot"><p>(1) If smoked sheet develops surface moulds within a short +period after smoking, the duration of curing has been insufficient, +or the quality of the smoking is at fault.</p> + +<p>(2) The actual time taken to smoke-dry rubber may be +insufficient to smoke-cure it.</p> + +<p>(3) The rate of drying of smoked sheet depends upon—</p> + +<div class="blockquot"><p>(<i>a</i>) The relative thickness of the rubber.</p> + +<p>(<i>b</i>) The preliminary treatment of rolling.</p> + +<p>(<i>c</i>) The temperature of the smoke-house, and</p> + +<p>(<i>d</i>) The type of smoke-house used. This point will +be treated in a <a href="#Sec15_8">subsequent chapter</a>.</p></div></div> + +<p><a name="Sec11_15" id="Sec11_15"></a><span class="smcap">Fuels for Smoking.</span>—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 substances. +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 <span class='pagenum'><a name="Page_147" id="Page_147">[147]</a></span>existence +of the typical odour, but it is becoming increasingly +known that the employment of substances rich in creosote is +not required or desirable.</p> + +<p>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.</p> + +<p>It is not true that <i>any kind of timber</i> 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.</p> + +<p>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.</p> + +<p>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.</p> + +<p><a name="Sec11_16" id="Sec11_16"></a><span class="smcap">Sun-Drying Sheet Rubber.</span>—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<span class='pagenum'><a name="Page_148" id="Page_148">[148]</a></span> +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.</p> + +<p>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 <a href="#Ch9">Chapter IX.</a>), +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.</p> + +<p><a name="Sec11_17" id="Sec11_17"></a><span class="smcap">Artificial Driers for Sheet Rubber.</span>—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.</p> + +<p><span class="smcap">The “Chula” Drier.</span>—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<span class='pagenum'><a name="Page_149" id="Page_149">[149]</a></span> +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.</p> + +<p>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.</p> + +<p>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.</p> + + +<p class='pagenum'><a name="Page_150" id="Page_150">[150]</a></p> +<hr class="c25" /> +<h2><a name="Ch12" id="Ch12"></a>CHAPTER XII</h2> + +<h3><i>SORTING, GRADING, AND PACKING</i></h3> + + +<p>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.</p> + +<p><a name="Sec12_1" id="Sec12_1"></a>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—<i>e.g.</i>, 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:</p> + +<p><span class="smcap">Crepes</span>—1. <i>First Quality Latex.</i>—<i>I.e.</i>, 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.”</p> + +<p>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. 1 crepe in the past.</p> + +<p>Comparatively few estates in Malaya now prepare thick +(or blanket) crepes in the No. 1 grade, but in such cases the +same rules must be applied as govern the sorting of thin fine +pale crepes.</p> + +<p><span class='pagenum'><a name="Page_151" id="Page_151">[151]</a></span>2. +<i>Compound Crepe, No. 1.</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 <a href="#Ch10">Chapter X.</a> 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.</p> + +<p>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 (1 per cent. solution) and acid +are added. The resulting conglomerate mass is cut up for +working.</p> + +<p>3. <i>Compound Crepe, No. 2.</i>—This grade would include the +remaining lower grades—viz., bark-shavings, scrap, and earth-rubber +scrap.</p> + +<p><a name="Sec12_2" id="Sec12_2"></a><span class="smcap">Reduction Carried too Far.</span>—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. 1 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.</p> + +<p><span class="smcap">Sheets.</span>—Broadly there are no fine distinctions to be made at +present in the grading of smoked-sheet rubber; it is either<span class='pagenum'><a name="Page_152" id="Page_152">[152]</a></span> +No. 1, or if any so-called defect is visible the sheets must be +rejected and plainly marked as “off-quality.”</p> + +<p>Clippings (trimmings) may either be made into crepe or +shipped under their own description.</p> + +<p><a name="Sec12_3" id="Sec12_3"></a><span class="smcap">Rubber Growers’ Association’s Recommendations.</span>—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.</p> + +<p>In its handbook,<a name="FNanchor_15_15" id="FNanchor_15_15"></a><a href="#Footnote_15_15" +class="fnanchor">[15]</a> the Rubber Growers’ Association remarks:</p> + +<div class="blockquot"><p>“The fewer grades the better, and regularity of each grade +is most important.</p> + +<p>“The grading should be as follows:</p> + +<div class="blockquot"><p>“(No. 1) Fine crepe (or No. 1 sheet), made from the free +or liquid latex.</p> + +<p>“(No. 2) Clean light brown crepe, made from lumps and +skimmings.</p> + +<p>“(No. 3) Scrap crepe, made from tree-scrap.</p> + +<p>“(No. 4) Dark crepe, made from bark-shavings, earth +rubber, and the lower quality of scrap.</p> + +<p>“Tacky rubber should be packed separately.</p></div> + +<p>“<i>Compound Scrap Crepe.</i>—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.”</p></div> + +<div class="footnote"><p><a name="Footnote_15_15" id="Footnote_15_15"></a><a +href="#FNanchor_15_15"><span class="label">[15]</span></a> “Preparation of Plantation Rubber,” 1917.</p></div> + +<p>Concerning these recommendations the remarks in preceding +paragraphs should be studied.</p> + +<p><a name="Sec12_4" id="Sec12_4"></a><span class="smcap">Care in Sorting.</span>—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 superintendent. +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<span class='pagenum'><a name="Page_153" id="Page_153">[153]</a></span> +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.</p> + +<p><a name="Sec12_5" id="Sec12_5"></a><span class="smcap">Choice of Cases.</span>—Consumers complain justly of the presence +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.</p> + +<p>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.</p> + +<p>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 complete +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 lbs. +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 demonstration +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,<span class='pagenum'><a name="Page_154" id="Page_154">[154]</a></span> +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.</p> + +<p>More recently there is announced a new packing case which +is stated to be made from low-grade rubbers, but information +is rather vague.</p> + +<p><a name="Sec12_7" id="Sec12_7"></a><span class="smcap">Bags.</span>—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 employment +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.”</p> + +<p><a name="Sec12_8" id="Sec12_8"></a><span class="smcap">Bales.</span>—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 unsuitable +portions.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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<span class='pagenum'><a name="Page_155" id="Page_155">[155]</a></span> +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.</p> + +<p><a name="Sec12_9" id="Sec12_9"></a><span class="smcap">Folding for Packing.</span>—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.</p> + +<div class="figcenter"><a name="Fig45" id="Fig45"></a><img src="images/illo172.jpg" alt="A +Shipment of Rubber, Packed and Ready for Transport" /> +<p class="caption"><span class="smcap">A Shipment of Rubber, Packed and Ready for Transport.</span></p></div> + +<p>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.</p> + +<p><a name="Sec12_10" id="Sec12_10"></a>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<span class='pagenum'><a name="Page_156" id="Page_156">[156]</a></span> +any packing case. It is called the “Senang” folder, and is +made by the General Engineering Company (Radcliffe) Ltd., +Radcliffe, near Manchester.</p> + +<p><a name="Sec12_6" id="Sec12_6"></a><span class="smcap">Care in Assembling.</span>—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.</p> + +<p>All wood should be planed, and in cases other than three-ply +should be of stout wood, not less than <span class="enum">5</span>⁄<span class="denom">8</span> inch in thickness. +All timber used should be of uniform type and thickness.</p> + +<p><a name="Sec12_11" id="Sec12_11"></a><span class="smcap">Methods of Packing.</span>—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.</p> + +<p>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.</p> + +<p>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.</p> + +<p><a name="Sec12_12" id="Sec12_12"></a><span class="smcap">Weight of Contents.</span>—The dimensions of average cases +are 19 inches by 19 inches by 24 inches, giving a capacity of +5 cubic feet.</p> + +<p>In these it is possible to pack 150 lbs. of crepe rubber and +200 lbs. of sheet rubber (about 5 per cent. more in cases of<span class='pagenum'><a name="Page_157" id="Page_157">[157]</a></span> +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 expedient +to ship rubber in actual ton lots, and for this purpose pack +only 140 lbs. 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.</p> + +<div class="figcenter"><a name="Fig46" id="Fig46"></a><img src="images/illo174.jpg" +alt="On its Road to the Railway: Bullock-Cart Transport" /> +<p class="caption"><span class="smcap">On its Road to the Railway: Bullock-Cart Transport.</span></p></div> + +<p>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.</p> + +<p><a name="Sec12_13" id="Sec12_13"></a><span class="smcap">“Short” Weights.</span>—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.<span class='pagenum'><a name="Page_158" id="Page_158">[158]</a></span> +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.</p> + +<div class="blockquot"><p>(<i>a</i>) 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.</p> + +<p>(<i>b</i>) 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.</p></div> + + +<p class='pagenum'><a name="Page_159" id="Page_159">[159]</a></p> +<hr class="c25" /> +<h2><a name="Part3" id="Part3"></a>PART III</h2> + +<h3>MACHINERY AND BUILDINGS</h3> + + +<h2><a name="Ch13" id="Ch13"></a>CHAPTER XIII</h2> + +<h3><i>MACHINES</i></h3> + + +<p><a name="Sec13_1" id="Sec13_1"></a>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 +was 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.</p> + +<p>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.</p> + +<p>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<span class='pagenum'><a name="Page_160" id="Page_160">[160]</a></span> +clear that if the rolls are allowed to run idle for more than the +briefest possible interval grinding must take place.</p> + +<p><a name="Sec13_2" id="Sec13_2"></a><a name="Sec13_3" id="Sec13_3"></a>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 <a href="#Ch17">later +chapter</a>. 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.”</p> + +<p><a name="Sec13_4" id="Sec13_4"></a><i>En passant</i> 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.</p> + +<p>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.</p> + +<p><a name="Sec13_5" id="Sec13_5"></a><span class="smcap">Adequacy of Machines.</span>—In general, the factories which +prepare sheet rubber are usually equipped with adequate +machinery. This arises from the fact that machines are necessary +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<span class='pagenum'><a name="Page_161" id="Page_161">[161]</a></span> +with at once, and that the whole work of the factory is +expedited.</p> + +<p>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 finishing +machine (smooth rolls). With five macerators and intermediate +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 substitute +a pair of smooth rolls, with suitable gear ratio, for a +pair of macerators or “intermediates.”</p> + +<p>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.</p> + +<p>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 inadequately +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>i.e.</i>, the +gearing between the machines and the engines. Thus, while<span class='pagenum'><a name="Page_162" id="Page_162">[162]</a></span> +one machine will out-turn 40 lbs. of crepe per hour, another +may only have an output of 30 lbs., 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.</p> + +<p>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.</p> + +<p>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.</p> + +<p><a name="Sec13_6" id="Sec13_6"></a><span class="smcap">Ideal Arrangement.</span>—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 practicable +limits of speed, beyond which the second alternative +measure must be adopted.</p> + +<p><a name="Sec13_7" id="Sec13_7"></a><span class="smcap">Speed.</span>—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<span class='pagenum'><a name="Page_163" id="Page_163">[163]</a></span> +is equivalent, with a 15-inch diameter roll, to a peripheral +speed of about 60 to 65 feet per minute.</p> + +<p>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 practicable +limits.</p> + +<p>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>i.e.</i>, differentially +geared), as opposed to the smooth rolls on which the +cog-wheels are usually of the same size (<i>i.e.</i>, 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.</p> + +<p>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:</p> + +<p><a name="Sec13_8" id="Sec13_8"></a><span class="smcap">Gear Ratios.</span>—</p> + +<table summary="Table p163"> + +<tr> +<td> </td> +<td colspan="5" class="center">Machine.</td> +<td class="center">Differential Ratio.</td> +</tr> + +<tr> +<td class="right">1.</td> +<td colspan="5" class="left">Macerator</td> +<td class="center">32-17</td> +</tr> + +<tr> +<td class="right">2.</td> +<td colspan="2" class="left">Intermediate</td> +<td colspan="3">(coarse grooved)</td> +<td class="center">32-17</td> +</tr> + +<tr> +<td class="right">3.</td> +<td colspan="2" class="center">„</td> +<td colspan="3">(fine grooved)</td> +<td class="center">30-19</td> +</tr> + +<tr> +<td class="right">4.</td> +<td class="left">Smooth</td> +<td colspan="4">(uneven speed)</td> +<td class="center">30-19</td> +</tr> + +<tr> +<td class="right">5.</td> +<td class="center">„</td> +<td colspan="3">(finishing)</td> +<td> </td> +<td class="center">25-24</td> +</tr> + +<tr> +<td class="right">6.</td> +<td class="center">„</td> +<td colspan="3" class="center">( „ )</td> +<td> </td> +<td class="center">25-24</td> +</tr> + +</table> + +<p>It will be seen that the so-called “even-speed” smooth rolls +run at approximately the same rate.</p> + +<p>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.</p> + +<p><a name="Sec13_9" id="Sec13_9"></a><span class='pagenum'><a name="Page_164" id="Page_164">[164]</a></span><span +class="smcap">Grooving of Rolls.</span>—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.</p> + +<p>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:</p> + +<table summary="Table p164"> + +<tr> +<td colspan="3" class="center bt br bb"><i>Machine.</i></td> +<td class="center bt br bb"><i>Grooving.</i></td> +<td colspan="2" class="center bt bb"><i>No. of Times<br />Rubber passes<br />through.</i></td> +</tr> + +<tr> +<td class="right top">1.</td> +<td colspan="2" class="left top br">Macerator</td> +<td class="left br">Deep horizontal grooves;<br />square-cut, <span class="enum">5</span>⁄<span +class="denom">16</span> inch × <span class="enum">5</span>⁄<span class="denom">16</span> inch<br /> +× <span class="enum">5</span>⁄<span class="denom">8</span> inch spaces</td> +<td class="right bottom" style="padding-left: 3em; vertical-align: bottom;">3</td> +<td> </td> +</tr> + +<tr> +<td class="right top">2.</td> +<td colspan="2" class="left top br">Intermediate</td> +<td class="left br">Horizontal grooves; <span class="enum">3</span>⁄<span class="denom">16</span> inch<br /> + × <span class="enum">3</span>⁄<span class="denom">16</span> inch × <span class="enum">3</span>⁄<span +class="denom">8</span> inch spaces</td> +<td class="right" style="padding-left: 3em; vertical-align: bottom;">2</td> +<td> </td> +</tr> + +<tr> +<td class="right top">3.</td> +<td colspan="2" class="center top br">„</td> +<td class="left br">Fine spiral grooves; <span class="enum">1</span>⁄<span class="denom">8</span> inch<br /> +× <span class="enum">1</span>⁄<span class="denom">8</span> inch × +<span class="enum">1</span>⁄<span class="denom">4</span> inch spaces</td> +<td class="right bottom" style="padding-left: 3em; vertical-align: bottom;">2</td> +<td> </td> +</tr> + +<tr> +<td class="right">4.</td> +<td colspan="2" class="left br" style="padding-right: .5em;">Geared smooth</td> +<td class="left br">Nil</td> +<td class="right" style="padding-left: 3em; vertical-align: bottom;">1</td> +<td> </td> +</tr> + +<tr> +<td class="right">5.</td> +<td colspan="2" class="left br">“Even” smooth</td> +<td class="left br"> „</td> +<td class="right" style="padding-left: 3em; vertical-align: bottom;">1</td> +<td> </td> +</tr> + +<tr> +<td class="right bb">6.</td> +<td class="center bb">„</td> +<td class="center bb br">„</td> +<td class="left br bb"> „</td> +<td class="right bb" style="padding-left: 3em; vertical-align: bottom;">1</td> +<td class="bb"> </td> +</tr> + +<tr> +<td colspan="3" class="bb br"> </td> +<td class="center bb br">Total</td> +<td class="center bb" style="padding-left: 3em; vertical-align: bottom;">10</td> +<td class="left bb">times</td> +</tr> + +</table> + +<p>The actual rate of output of this installation is the capacity +of the last smooth machine. This is about 180 lbs. 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—(1), (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.</p> + +<p>As already stated, it is not intended to lay down definitely +that, <i>e.g.</i>, horizontal grooving alone should be cut on macerating +rolls. Some estates employ with satisfaction a deep square-<span class='pagenum'><a name="Page_165" id="Page_165">[165]</a></span>cut +spiral <span class="enum">1</span>⁄<span class="denom">4</span> inch by <span class="enum">1</span>⁄<span class="denom">4</span> inch by <span class="enum">1</span>⁄<span class="denom">4</span> inch or <span class="enum">1</span>⁄<span class="denom">2</span> inch spacing; others +use a large diamond pattern. Similarly various types of grooving +are cut in the intermediate rolls.</p> + +<div class="figcenter"><a name="Fig47" id="Fig47"></a><img src="images/illo182.jpg" alt="A Battery of Machines" /> +<p class="caption"><span class="smcap">A Battery of Machines.</span></p> +<p class="capt500">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.</p></div> + +<p>It has been remarked in the <a href="#Ch10">chapter</a> dealing with crepe preparation +that much depends upon the condition of the coagulum. +There is no necessity, or desirability, for having a standard +higher than 2 lbs. dry rubber per gallon, and it has been +argued that it would be better to select a standard of 1<span class="enum">1</span>⁄<span class="denom">2</span> lbs. +The tougher the coagulum, the more the power required, +and the slower the rate of output of the leading machines.</p> + +<p>In ordering machines for crepe-making, only large rolls +should be considered—<i>e.g.</i>, rolls having a diameter of 12 inches +to 18 inches and from 15 inches to 18 inches face.</p> + +<p><a name="Sec13_10" id="Sec13_10"></a><span class="smcap">Rolls Running Hot or “Free.”</span>—If the rolls are found +to become hot, work on that machine should be stopped, and an<span class='pagenum'><a name="Page_166" id="Page_166">[166]</a></span> +examination made, otherwise there is the possibility of the +crepe becoming sticky and “tacky” when dry.</p> + +<p>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.</p> + +<p>Allusion has been made to the necessity for avoiding the +running “free” of rolls—<i>i.e.</i>, 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.</p> + +<p><a name="Sec13_11" id="Sec13_11"></a><span class="smcap">Sheeting Machines.</span>—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 <a href="#Ch9">Chapter IX</a>.</p> + +<p>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.</p> + +<p>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 lbs 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.</p> + +<p><a name="Sec13_12" id="Sec13_12"></a><span class="smcap">Lubrication of Machines.</span>—It must always appear to those +inexperienced in engineering matters that existing methods +for lubricating rubber machinery are distinctly crude, when<span class='pagenum'><a name="Page_167" id="Page_167">[167]</a></span> +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 transferred +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.</p> + +<p>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.</p> + +<p><a name="Sec13_13" id="Sec13_13"></a><span class="smcap">Trays.</span>—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 preparation +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.</p> + +<p>It must be recorded that the foregoing paragraph appeared +in our 1913 publication. After a lapse of over seven years,<span class='pagenum'><a name="Page_168" id="Page_168">[168]</a></span> +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.</p> + +<p><a name="Sec13_14" id="Sec13_14"></a><span class="smcap">Arrangement of Machines.</span>—In considering the future +arrangement of machines, the first care should be to see that +machines and windows are to be found together.<a name="FNanchor_16_16" id="FNanchor_16_16"></a><a +href="#Footnote_16_16" class="fnanchor">[16]</a> Of all the +factory operations, rolling of rubber should be given the maximum +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 convenient +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.</p> + +<div class="footnote"><p><a name="Footnote_16_16" id="Footnote_16_16"></a><a +href="#FNanchor_16_16"><span class="label">[16]</span></a> Windows imply the existence of walls. Such is the conventional +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 requirements +and gives the maximum of light and air. Many new factories +have been erected to such a design.</p></div> + +<p>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 workmanship, +and on many machines bearings run hot for no apparent +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.</p> + +<p>There is no reason why everything in a factory should not +be made as easy to clean as possible. For this desirable condition +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<span class='pagenum'><a name="Page_169" id="Page_169">[169]</a></span> +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.</p> + +<p><a name="Sec13_15" id="Sec13_15"></a><a name="Sec13_16" id="Sec13_16"></a><span +class="smcap">Access to Back of Machine.</span>—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 accumulations +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.</p> + +<p>In conclusion it might be said that the manager needing +advice as to the best machines cannot go far wrong in purchasing +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—</p> + +<div class="blockquot"><p>1. Cost.</p> + +<p>2. The experience of those already using the machines.</p> + +<p>3. Simplicity of parts.</p> + +<p>4. Lubrication system.</p> + +<p>5. Mode of adjusting rolls.</p> + +<p>6. Fitting of trays.</p></div> + +<p><a name="Sec13_17" id="Sec13_17"></a><span class='pagenum'><a name="Page_170" id="Page_170">[170]</a></span><span +class="smcap">Engines.</span>—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.</p> + +<p>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.</p> + +<p>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.</p> + +<p><a name="Sec13_18" id="Sec13_18"></a><span class="smcap">Power.</span>—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,” inasmuch +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<span class='pagenum'><a name="Page_171" id="Page_171">[171]</a></span> +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.</p> + + +<p class='pagenum'><a name="Page_172" id="Page_172">[172]</a></p> +<hr class="c25" /> +<h2><a name="Ch14" id="Ch14"></a>CHAPTER XIV</h2> + +<h3><i>FACTORIES</i></h3> + + +<p><a name="Sec14_1" id="Sec14_1"></a><span class="smcap">General Construction.</span>—On the question of general construction +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.</p> + +<p>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.</p> + +<p><a name="Sec14_2" id="Sec14_2"></a><span class="smcap">Plenty of Light.</span>—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.</p> + +<p>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<span class='pagenum'><a name="Page_173" id="Page_173">[173]</a></span> +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.</p> + +<p><a name="Sec14_3" id="Sec14_3"></a><a name="Sec14_4" id="Sec14_4"></a><span +class="smcap">The Floor.</span>—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.</p> + +<p><span class="smcap">Position of Machines.</span>—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 compartment, +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.</p> + +<p><span class='pagenum'><a name="Page_174" id="Page_174">[174]</a></span><span +class="smcap">Position of Engines.</span>—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.</p> + +<p><a name="Sec14_5" id="Sec14_5"></a><span class="smcap">How many Storeys.</span>—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<span class='pagenum'><a name="Page_175" id="Page_175">[175]</a></span> +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.</p> + +<p><a name="Sec14_6" id="Sec14_6"></a><span class="smcap">Verandahs.</span>—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 considerable +floor-space and time are wasted.</p> + +<p>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 outside +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 unnecessary +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.</p> + +<p>An indication of types of verandahs is given in <a href="#Ch7">Chapters VII.</a> +and <a href="#Ch9">IX</a>. These are not intended to be representative of a +universal design, but may be suggestive in the planning of +others according to local conditions.</p> + +<p><a name="Sec14_7" id="Sec14_7"></a><span class="smcap">Situation of Tanks.</span>—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<span class='pagenum'><a name="Page_176" id="Page_176">[176]</a></span> +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.</p> + +<p>In some modern designs it is proposed to place the coagulating +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.</p> + +<p><a name="Sec14_8" id="Sec14_8"></a><span class="smcap">Designs and “Lay-Out.“</span>—In a +previous publication<a name="FNanchor_17_17" id="FNanchor_17_17"></a><a href="#Footnote_17_17" class="fnanchor">[17]</a> +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.</p> + +<div class="footnote"><p><a name="Footnote_17_17" id="Footnote_17_17"></a><a +href="#FNanchor_17_17"><span class="label">[17]</span></a> “Preparation of Plantation Rubber,” Morgan, 1913.</p></div> + +<p>In considering the first installation of a factory and equipment +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 forethought +should govern the lay-out of the machinery.</p> + +<p><a name="Sec14_9" id="Sec14_9"></a><span class="smcap">Drains.</span>—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 acquainted +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;<span class='pagenum'><a name="Page_177" id="Page_177">[177]</a></span> +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.</p> + +<p><a name="Sec14_10" id="Sec14_10"></a><span class="smcap">Water Supply.</span>—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.</p> + +<p>Summing up, it might be said that a good factory, therefore, +should have the following features:</p> + +<div class="blockquot"><p>1. Plenty of windows, or walls of expanded metal.</p> + +<p>2. A jack-roof in the ridge, and hence a good system of ventilation.</p> + +<p>3. Engines in compartments outside the walls of the factory.</p> + +<p>4. Machines close to and parallel with the wall outside of +which the engines are placed.</p> + +<p>5. Latex tanks and other fixtures along the wall opposite the +machines.</p> + +<p>6. A long middle free space, at either end of which a large +double door should be placed in the end walls.</p> + +<p>7. A good concrete and cement floor sloping slightly from +the middle towards each long wall.</p> + +<p>8. An abundant water supply, and several lengths of hose.</p> + +<p>9. The building should be of only one floor, and have ample +head room.</p> + +<p>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.</p> + +<p>11. The system of drainage should be thorough, and the +drains should be adequately screened, so that all particles of +rubber may be collected.</p></div> + + +<p class='pagenum'><a name="Page_178" id="Page_178">[178]</a></p> +<hr class="c25" /> +<h2><a name="Ch15" id="Ch15"></a>CHAPTER XV</h2> + +<h3><i>OTHER BUILDINGS</i></h3> + + +<p><a name="Sec15_1" id="Sec15_1"></a><span class="smcap">Drying-Houses for Crepe.</span>—It has already been shown in the +previous <a href="#Ch15">chapter</a> 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.</p> + +<p>In houses of two floors this objection would not have to be +met, and drying-houses of this type are successful and common.</p> + +<p><a name="Sec15_2" id="Sec15_2"></a><span class="smcap">How Many Storeys?</span>—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 negligence +in not allowing wet crepe a preliminary dripping period, +water might fall upon the packed rubber below.</p> + +<p><span class='pagenum'><a name="Page_179" id="Page_179">[179]</a></span>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 1<span class="enum">1</span>⁄<span class="denom">2</span> inches, +otherwise there is a certain amount of danger to the limbs of +individuals who have to work 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 objection +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.</p> + +<p>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.</p> + +<p>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 buildings +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<span class='pagenum'><a name="Page_180" id="Page_180">[180]</a></span> +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.</p> + +<p><a name="Sec15_3" id="Sec15_3"></a><span class="smcap">Ventilation.</span>—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 ventilation +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.</p> + +<p>In some drying-houses, besides the ridge openings, the space +along the eaves is left open. This would seem to be undesirable, +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.</p> + +<p>In the tropics, on days of sunshine, there must always +be an upward current of air in well-designed houses. Temperatures +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<span class='pagenum'><a name="Page_181" id="Page_181">[181]</a></span> +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.</p> + +<p>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 temperatures +much above 100° F., for the rubber stretches and breaks +across the support.</p> + +<p><a name="Sec15_4" id="Sec15_4"></a><a name="Sec15_5" id="Sec15_5"></a><a name="Sec15_6" id="Sec15_6"></a><span +class="smcap">Windows.</span>—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<span class='pagenum'><a name="Page_182" id="Page_182">[182]</a></span> +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.</p> + +<p><a name="Sec15_7" id="Sec15_7"></a><span class="smcap">Hot-Air Drying-Houses.</span>—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 impracticably +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<span class='pagenum'><a name="Page_183" id="Page_183">[183]</a></span> +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.</p> + +<p><a name="Sec15_8" id="Sec15_8"></a><span class="smcap">Smoke-Houses.</span>—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., (1) drying, (2) preservation—except +that while herrings are only dried partially, rubber should be +dried perfectly.</p> + +<p>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 temporary +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.</p> + +<p>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.</p> + +<p><a name="Sec15_9" id="Sec15_9"></a><span class="smcap">Usual Types.</span>—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<span class='pagenum'><a name="Page_184" id="Page_184">[184]</a></span> +above the furnace-room would be overheated if the temperature +in the upper rooms was within the desired range, etc.</p> + +<p>Until recent years smoke-houses could be classed as belonging +to one of two types:</p> + +<div class="blockquot"><p>(1) Those having external furnaces.</p> + +<p>(2) Those having internal furnaces.</p></div> + +<p>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 comparatively +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.</p> + +<p><a name="Sec15_10" id="Sec15_10"></a>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.</p> + +<p><span class='pagenum'><a name="Page_185" id="Page_185">[185]</a></span>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.</p> + +<p><a name="Sec15_11" id="Sec15_11"></a><span class="smcap">General Ventilation.</span>—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.</p> + +<p>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 slowness of drying have +been investigated, it has been necessary to point out the need +for providing a rational system of ventilation.</p> + +<p>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.</p> + +<p><a name="Sec15_12" id="Sec15_12"></a><span class="smcap">Windows.</span>—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<span class='pagenum'><a name="Page_186" id="Page_186">[186]</a></span> +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.</p> + +<p><a name="Sec15_13" id="Sec15_13"></a><span class="smcap">Racks of Supports.</span>—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 1<span class="enum">1</span>⁄<span class="denom">2</span> inches +square in section.</p> + +<p>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 <i>between</i> 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.</p> + +<p>Care should be taken to see that the vacant racks are thoroughly +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.</p> + +<p>A more effective way of dealing with the trouble, provided +other precautions have been taken, is to have plenty of spare<span class='pagenum'><a name="Page_187" id="Page_187">[187]</a></span> +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.</p> + +<p><a name="Sec15_14" id="Sec15_14"></a><span class="smcap">Floor of Drying-Chamber.</span>—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.</p> + +<p>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.</p> + +<p><a name="Sec15_15" id="Sec15_15"></a><span class="smcap">Furnaces Generally.</span>—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.</p> + +<p>From this primitive type of furnace, others have been evolved. +These usually take the form of more or less shallow trucks,<span class='pagenum'><a name="Page_188" id="Page_188">[188]</a></span> +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.</p> + +<p><a name="Sec15_16" id="Sec15_16"></a><span class="smcap">Pits.</span>—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 <i>in situ</i>, 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.</p> + +<p><a name="Sec15_17" id="Sec15_17"></a><span class="smcap">“Pot” +Furnaces.</span>—The next development was the employment +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.</p> + +<p>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 consumption +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.</p> + +<p><a name="Sec15_18" id="Sec15_18"></a><span class='pagenum'><a name="Page_189" id="Page_189">[189]</a></span><span +class="smcap">Iron Stoves.</span>—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.</p> + +<p><a name="Sec15_19" id="Sec15_19"></a><span class="smcap">Horizontal Drum-Furnaces.</span>—To overcome difficulties +inherent to drums or “pot-furnaces,” the next development +was 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.</p> + +<p>In the second set of drawings (No. 1) 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.</p> + +<p class='pagenum'><a name="Page_190" id="Page_190">[190]</a></p> + +<div class="figcenter"><a name="Fig48" id="Fig48"></a><img src="images/illo207a.png" alt="'Third Mile' Type; Horizontal Drum" /> +<p class="caption"><span class="smcap">“Third Mile” Type; Horizontal Drum.</span></p> +<p class="capt500">This type of furnace is suitable for adapting to existing buildings +with perpendicular lower walls.</p></div> + +<div class="figcenter"><a name="Fig49" id="Fig49"></a><img src="images/illo207b.png" alt="Third Mile' Type of Furnace, used in Conjunction +with 'Third Mile' Smoke-House" /> +<p class="caption"><span class="smcap">“Third Mile” Type of Furnace, used in Conjunction<br /> +with “Third Mile” Smoke-House.</span></p></div> + +<p>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<span class='pagenum'><a name="Page_191" id="Page_191">[191]</a></span> +in too great a draught, it is well to insist upon good workmanship. +Other adjustable air-inlets are provided, and the drum +is enclosed in a brick chamber.</p> + +<p><a name="Sec15_20" id="Sec15_20"></a><span class="smcap">Rate of Combustion.</span>—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 original forms of +drums or pot-furnaces of various kinds, a very slow rate of +combustion was attained. Naturally a relatively larger proportion +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.</p> + +<p>It will be clear that, under ordinary circumstances, the condition +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.</p> + +<p>Simple drum furnaces, with slow combustion, have the +further advantages that a “charge” of fuel will need no attention +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<span class='pagenum'><a name="Page_192" id="Page_192">[192]</a></span> +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.</p> + +<p>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.</p> + +<p>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.</p> + +<p><a name="Sec15_21" id="Sec15_21"></a><span class="smcap">Brick Stoves.</span>—Developing from “drum” furnaces, another +type comes into existence. In principle it consists of an enclosed +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 department +of Messrs. Harrisons and Crosfield, and is understood +to give satisfaction.</p> + +<p><a name="Sec15_22" id="Sec15_22"></a><span class="smcap">Pataling Type.</span>—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.</p> + +<p class='pagenum'><a name="Page_193" id="Page_193">[193]</a></p> + +<div class="figcenter"><a name="Fig50" id="Fig50"></a><img src="images/illo210a.png" alt="Side Sectional +Elevation (Pataling Type of Furnace)" /> +<p class="caption"><span class="smcap">Side Sectional Elevation (Pataling Type of Furnace).</span></p></div> + +<div class="figcenter"><a name="Fig51" id="Fig51"></a><img src="images/illo210b.png" alt="Pataling Type of Furnace" /> +<p class="caption"><span class="smcap">Pataling Type of Furnace.</span></p></div> + +<p>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 satisfactory, +and have a low rate of fuel consumption. They are<span class='pagenum'><a name="Page_194" id="Page_194">[194]</a></span> +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.</p> + +<p>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. +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.</p> + +<div class="figcenter"><a name="Fig52" id="Fig52"></a><img src="images/illo211.jpg" alt="Large Smoke-House of +Ordinary Construction, with Shielded Ventilators Permanently Open" /> +<p class="caption"><span class="smcap">Large Smoke-House of Ordinary Construction, with Shielded<br /> +Ventilators Permanently Open.</span></p> +<p class="capt500">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).</p></div> + +<p>From the <a href="#Fig50">drawings</a> 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<span class='pagenum'><a name="Page_195" id="Page_195">[195]</a></span> +which the coolie may stand upright. The outer face of the +brick furnace forms the inner end of the tunnel, and accommodates +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, +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.</p> + +<div class="figcenter"><a name="Fig53" id="Fig53"></a><img src="images/illo212.jpg" alt="Brick and Cement +Superstructure of Furnace Inside the Building, but fed from Outside" /> +<p class="caption"><span class="smcap">Brick and Cement Superstructure of Furnace Inside the<br /> +Building, but fed from Outside.</span></p> +<p class="capt500">On the top of the superstructure 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.</p></div> + +<p>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<span class='pagenum'><a name="Page_196" id="Page_196">[196]</a></span> +to provide the necessary air-inlet, but in any case it should +not be more than slight.</p> + +<p><a name="Sec15_23" id="Sec15_23"></a><span class="smcap">Consumption of Fuel.</span>—Regarding this furnace, it may be +said in conclusion that it is more satisfactory in general working +than any other furnaces yet encountered. Obtaining information +from over sixty estates, on the question of fuel consumption +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.</p> + +<div class="figcenter"><a name="Fig54" id="Fig54"></a><img src="images/illo213.jpg" alt="General View of Shelters covering Approaches to +Furnaces" /> +<p class="caption"><span class="smcap">General View of Shelters covering Approaches to +Furnaces.</span></p></div> + +<p>This was at the rate of slightly less than 1 lb of fuel per 1 lb of +thoroughly cured sheet rubber. The figure on some estates +mounted as high as 4<span class="enum">1</span>⁄<span class="denom">2</span> lbs. of fuel per lb. 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.</p> + +<p><a name="Sec15_24" id="Sec15_24"></a><span class="smcap">Floor of Furnace-Room.</span>—As a rule no attempt is made to +improve the natural earthen floor. Whether open-hearth fires,<span class='pagenum'><a name="Page_197" id="Page_197">[197]</a></span> +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. Cleanliness +should be as zealously attempted in the smoke-house as +in other departments.</p> + +<div class="figcenter"><a name="Fig55" id="Fig55"></a><img src="images/illo214.jpg" alt="Near View of Shelter" /> +<p class="caption"><span class="smcap">Near View of Shelter.</span></p> +<p class="center">Steps lead downwards where the wall of the smoke-house has +been removed.</p></div> + +<p><a name="Sec15_25" id="Sec15_25"></a><span class="smcap">Roof.</span>—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.</p> + +<p>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.</p> + +<p><span class='pagenum'><a name="Page_198" id="Page_198">[198]</a></span>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 withstand +growths of mildew which would otherwise form.</p> + +<p>If proper smoke-vents are not provided, the moisture evaporating +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.</p> + +<p><span class="smcap">Other Types of Smoke-House.</span>—So far we have confined +the arguments to smoke-houses of the usual type. There +are 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.</p> + +<p><a name="Sec15_25a" id="Sec15_25a"></a><span class="smcap">Brick Houses.</span>—Some houses are constructed of brick, and +may have one or two storeys above the furnace chamber. The +floors are sometimes made of ferro-concrete, and the furnaces<span class='pagenum'><a name="Page_199" id="Page_199">[199]</a></span> +may also be of this material. These brick houses give satisfaction, +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.</p> + +<p><a name="Sec15_26" id="Sec15_26"></a><span class="smcap">“Third Mile” Type.</span>—Reference has been made to the +“Third Mile” type of furnace. This is an integral part of a +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.</p> + +<div class="figcenter"><a name="Fig56" id="Fig56"></a><img src="images/illo216.png" alt="'Third Mile' Type of Smoke-House" /> +<p class="caption"><span class="smcap">“Third Mile” Type of Smoke-House.</span></p></div> + +<p>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.</p> + +<p>It will be seen that the principles of ventilation employed are +those indicated for an ordinary house—viz., air-inlet near the<span class='pagenum'><a name="Page_200" id="Page_200">[200]</a></span> +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.</p> + +<p>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.</p> + +<p><a name="Sec15_27" id="Sec15_27"></a><span class="smcap">Jackson House.</span>—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 <a href="#Sec17_20">subsequent chapter</a>.)</p> + +<p><a name="Sec15_28" id="Sec15_28"></a><span class="smcap">“Devon” +Type.</span>—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 installations +worked under a scheme of decentralisation.</p> + +<p>The original units consisted of a building erected with an +iron framework covered with sheets of asbestos-slate, and a +roof of galvanised iron.</p> + +<p>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.</p> + +<p>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<span class='pagenum'><a name="Page_201" id="Page_201">[201]</a></span> +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.</p> + +<div class="figcenter"><a name="Fig57" id="Fig57"></a><img src="images/illo218.jpg" alt="General +View of Double 'Devon' Type of Smoke-House." /> +<p class="caption"><span class="smcap">General View of Double “Devon” Type of +Smoke-House.</span></p> +<p class="capt350">The platforms are common to both units. Building of brick with +iron roof (Batu Caves Estate).</p></div> + +<p>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<span class='pagenum'><a name="Page_202" id="Page_202">[202]</a></span> +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.</p> + +<div class="figcenter"><a name="Fig58" id="Fig58"></a><img src="images/illo219.jpg" alt="General View of Double +'Devon' Smoke-House and Factory Buildings" /> +<p class="caption"><span class="smcap">General View of Double “Devon” Smoke-House and Factory Buildings.</span></p> +<p class="capt500">Timber in foreground cut to length for stoking. Note water-tower and engine cooling-tanks +adjacent to factory.</p></div> + +<p>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<span class='pagenum'><a name="Page_203" id="Page_203">[203]</a></span> +of internal condensation of moisture and creosotic matter. +The exact degree to which it should be open must be found +by experience.</p> + +<div class="figcenter"><a name="Fig59" id="Fig59"></a><img src="images/illo220.jpg" alt="View of +Platform of 'Devon' Smoke-House; Doors of Compartments Open, and +One Rack Partially Withdrawn" /> +<p class="caption"><span class="smcap">View of Platform of “Devon” Smoke-House; Doors of Compartments Open, and<br /> +One Rack Partially Withdrawn.</span></p> +<p class="center">Note below each rack opening through which smoke rises, covered with wire netting.</p></div> + +<p>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<span class='pagenum'><a name="Page_204" id="Page_204">[204]</a></span> +the form of the eight swinging doors which allow for the +withdrawal of, or insertion of, any one unit of racks +at any time without interference with the bulk of the +rubber.</p> + +<p class='pagenum'><a name="Page_205" id="Page_205">[205]</a></p> + +<div class="figcenter"><a name="Fig60" id="Fig60"></a><img src="images/illo221.jpg" alt="Double 'Devon' Smoke-House of Brick, with Roof of +Chinese Tiles, showing Loading Platforms with Racks Withdrawn from Smoking Chambers" /> +<p class="caption"><span class="smcap">Double “Devon” Smoke-House of Brick, with Roof of<br /> +Chinese Tiles, showing Loading Platforms with Racks<br /> +Withdrawn from Smoking Chambers.</span></p> +<p class="center">Federated Engineering Co., Ltd., Kuala Lumpur.</p></div> + +<p><a name="Sec15_29" id="Sec15_29"></a><span class="smcap">Detailed Description.</span>—As enquiries are often received it +is permissible to reproduce the following detailed description +of the original house. This appeared in the Fourth Local +Report (Malaya) 1916, issued to subscribers by the Rubber +Growers’ Association.<span class='pagenum'><a name="Page_206" id="Page_206">[206]</a></span></p> + +<div class="blockquot"><p>“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 measurements +can be varied. The whole of the width (16 feet) is +occupied by compartments of which one series is placed above +the other.</p></div> + +<div class="figcenter"><a name="Fig61" id="Fig61"></a><img src="images/illo222.jpg" alt="Side View of Preceding +Photograph, showing External Arrangement for Stoking Furnaces" /> +<p class="caption"><span class="smcap">Side View of Preceding Photograph, showing External<br /> +Arrangement for Stoking Furnaces.</span></p> +<p class="center">Federated Engineering Co., Ltd., Kuala Lumpur.</p></div> + +<div class="blockquot"><p>“<i>Platforms.</i>—The loading verandahs or platforms are of +ordinary ’seriah’ timber.</p></div> + +<div class="blockquot"><p>“<i>Compartments and Furnace Chamber.</i>—These are enclosed +with Bell’s ’Poilite’ sheets, each of which measures 8 feet by +4 feet by <span class="enum">3</span>⁄<span class="denom">16</span> inch. The sheets are affixed to the steel stanchions, +doors, etc., by galvanised bolts (1 inch by <span class="enum">1</span>⁄<span class="denom">4</span> inch) which pass +through iron flats measuring 8 feet by 2 inches by <span class="enum">3</span>⁄<span class="denom">8</span> 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.</p> + +<div class="figcenter"><a name="Fig62" id="Fig62"></a><img src="images/illo223.jpg" alt="Front +View of Double 'Devon' Type of Smoke-House" /> +<p class="caption"><span class="smcap">Front View of Double “Devon” Type of Smoke-House.</span></p> +<p class="center">Glenmarie Estate: Batu Tiga Co.</p></div> + +<p>“<i>Racks.</i>—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 lbs., of dry sheet rubber. The racks are +mounted on 6-inch iron wheels, running on rails of stock size, +’T’ iron (1<span class="enum">3</span>⁄<span class="denom">4</span> +inches by 1<span class="enum">3</span>⁄<span class="denom">4</span> inches by +<span class="enum">1</span>⁄<span class="denom">4</span> inch).</p> + +<p><span class='pagenum'><a name="Page_207" id="Page_207">[207]</a></span>“The sheets are hung on split bamboos. To prevent these +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 +<span class="enum">1</span>⁄<span class="denom">2</span> inch high, is nailed along the sides of the rack.</p> + +<div class="figcenter"><a name="Fig63" id="Fig63"></a><img src="images/illo224.jpg" alt="Side +View of Double 'Devon' Type of Smoke-House" /> +<p class="caption"><span class="smcap">Side View of Double “Devon” Type of Smoke-House.</span></p> +<p class="capt350">Building constructed of galvanised iron. Shows door to furnace +chamber, and ventilator.</p></div> + +<p>“<i>Furnace.</i>—This is of the type that aims at slow combustion. +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.</p> + +<p>“The furnace chamber is a pit lined with concrete, just<span class='pagenum'><a name="Page_208" id="Page_208">[208]</a></span> +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 <a href="#Footnote_18_18">note</a> below). +There are no holes in the sides or bottom of the cylinder.</p> + +<p>“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.</p> + +<p>“<i>Method of Stoking.</i>—The timber used is a mixture of +jungle wood and rubber-tree wood, cut to lengths of about 1<span class="enum">1</span>⁄<span class="denom">2</span> +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.</p> + +<p>“<i>Temperature.</i>—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 110 hours of smoke-curing, which is at least +equal to ten days’ intermittent smoking in an ordinary house.</p> + +<p>“<i>Capacity.</i>—There are eight racks, each accommodating +450 lbs. of standardised sheet rubber. The loading capacity +of the house, therefore, is 3,600 lbs. As each charge is cured in +five days, the monthly output may be 21,000 lbs.</p> + +<p>“The cubic capacity is 2,048 cubic feet. As there are no gangways, +etc., this is fully utilised. This gives a rate of monthly +output capacity to over 10<span class="enum">1</span>⁄<span class="denom">4</span> lbs. 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.”<a name="FNanchor_18_18" +id="FNanchor_18_18"></a><a href="#Footnote_18_18" class="fnanchor">[18]</a></p></div> + +<div class="footnote"><p><a name="Footnote_18_18" id="Footnote_18_18"></a><a +href="#FNanchor_18_18"><span class="label">[18]</span></a> 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.</p></div> + +<p>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 asbestos-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<span class='pagenum'><a name="Page_209" id="Page_209">[209]</a></span> +latest buildings consist of two of the original houses face to +face, under a common roof, and served by common platforms.</p> + +<p>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 lbs. of sheet rubber per +month. The possibility of an extension of this idea has been +shown to be great.</p> + +<p>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.</p> + +<p>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.</p> + +<hr class="c05" /> + +<p>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 designated +the “Barker” smoke-house.</p> + +<p><a name="Sec15_30" id="Sec15_30"></a><span class="smcap">Barker Patent.</span>—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 framework. +This frame slides, by its own weight, upon timber +side supports. A sufficient number of these units occupies<span class='pagenum'><a name="Page_210" id="Page_210">[210]</a></span> +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.</p> + +<div class="figcenter"><a name="Fig64" id="Fig64"></a><img src="images/illo227.jpg" alt="The New 'Barker' +Type of Smoke-House: a Small Unit" /> +<p class="caption"><span class="smcap">The New “Barker” Type of Smoke-House: a Small Unit.</span></p> +<p class="capt500">The racks slide automatically from top to bottom on withdrawal +of the lower frames through door at front. The furnace is contained +in the brick compartment at the lower (front) end.</p></div> + +<p>Thus far only small units have been seen. It is claimed +that, properly prepared, sheet rubber can be smoke-cured in +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 lbs. 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.</p> + + +<p class='pagenum'><a name="Page_211" id="Page_211">[211]</a></p> +<hr class="c25" /> +<h2><a name="Ch16" id="Ch16"></a>CHAPTER XVI</h2> + +<h3><i>OTHER BUILDINGS (continued) AND SITUATION OF +BUILDINGS</i></h3> + + +<p><a name="Sec16_1" id="Sec16_1"></a><a name="Sec16_2" id="Sec16_2"></a><span +class="smcap">Sorting-Room and Packing-Room.</span>—It is in these departments +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.</p> + +<p>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.</p> + +<p>Where, for economic reasons, the sorting and packing operations +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.</p> + +<p><span class='pagenum'><a name="Page_212" id="Page_212">[212]</a></span>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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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 minimum.</p> + +<p>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.</p> + +<p><a name="Sec16_3" id="Sec16_3"></a><a name="Sec16_4" id="Sec16_4"></a><span class="smcap">Store-Rooms +for Rubber and Storage.</span>—The question +of storage of rubber in factory buildings has always possessed +importance, but has demanded increased consideration recently.</p> + +<p><a name="Sec16_5" id="Sec16_5"></a>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.</p> + +<p><a name="Sec16_6" id="Sec16_6"></a>Experience indicates that the best type of floor is that already +advised for sorting and packing rooms—<i>i.e.</i>, 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<span class='pagenum'><a name="Page_213" id="Page_213">[213]</a></span> +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.</p> + +<p>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.</p> + +<p>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 prominence, +and we were able to tender advice on the lines given +in this chapter. The necessity passed, but has again arisen.</p> + +<p><a name="Sec16_7" id="Sec16_7"></a>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 determined. +The assumption of “proper preparation” leaves great +room for reservations.</p> + +<p>In the case of crepe rubbers, there is no great difficulty, provided +that the recognised methods and formulæ 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.</p> + +<p>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<span class='pagenum'><a name="Page_214" id="Page_214">[214]</a></span> +initially present only in small degree, but the final damage may +be immensely greater by close contact of the folded rubber +during prolonged storage.</p> + +<p><a name="Sec16_8" id="Sec16_8"></a>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” conditions, +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.</p> + +<p>In discussing this question, as far as it refers to the preservation +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, superficially, +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.</p> + +<p>It cannot be argued that the present good condition of these +old specimens may be due to correct preparation. In those +days methods and formulæ were rather haphazard, especially +in view of the fact that the daily variability of dry rubber +content of latices was not then recognised.</p> + +<p>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<span class='pagenum'><a name="Page_215" id="Page_215">[215]</a></span> +was thoroughly impregnated with the products of wood combustion. +There would seem to be little doubt that this +procedure was responsible for the prolonged freedom from +mould growths.</p> + +<p>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.</p> + +<p><a name="Sec16_9" id="Sec16_9"></a><a name="Sec16_10" id="Sec16_10"></a>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 +“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.</p> + +<p>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<span class='pagenum'><a name="Page_216" id="Page_216">[216]</a></span> +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.</p> + +<p>All precautions taken in preparation and curing can be +nullified, as already indicated, by unsuitable storage conditions.</p> + +<p><a name="Sec16_11" id="Sec16_11"></a><span class="smcap">Tool-Sheds and Store-Rooms.</span>—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.</p> + +<p><a name="Sec16_12" id="Sec16_12"></a><span class="smcap">Situation of Factory Buildings.</span>—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.</p> + +<p>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,<span class='pagenum'><a name="Page_217" id="Page_217">[217]</a></span> +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.</p> + +<p>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 surrounding +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. Presuming +that the thin crepes made in two factories are equal in thickness, +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.</p> + +<p><a name="Sec16_13" id="Sec16_13"></a>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<span class='pagenum'><a name="Page_218" id="Page_218">[218]</a></span> +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.</p> + +<p>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 +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 <i>vice versa</i>. +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 correspondingly +unequal. The total wall area heated by the sun at<span class='pagenum'><a name="Page_219" id="Page_219">[219]</a></span> +any time of the day would be less in this position than if the +house ran north and south.</p> + +<p>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.</p> + + +<div class="figcenter"><a name="Fig65" id="Fig65"></a><img src="images/illo235.png" alt="Suggested Arrangement of Building" /> +<p class="caption"><span class="smcap">Suggested Arrangement of Building.</span></p></div> + +<p><i>References to <a href="#Fig65">Sketch Plan</a>.</i></p> + +<p>Drying-house No. 2 should be of two storeys, and unless a +separate sorting and packing room is to be built, No. 1 should +also have two floors (see <a href="#Sec16_2">previous notes</a> on packing-rooms).</p> + +<p>In the factory—</p> + +<div class="blockquot"><p><i>V</i> shows the position of the verandah, which may be quite +open and only divided from the inner room by</p> + +<p><i>S</i>, a wall composed of very strong expanded metal, which +allows light and air to enter the factory.</p> + +<p><i>T,T</i> are the glazed tile tanks for the reception of latex, +scrap rubbers, and bark-shavings.</p> + +<p><i>M</i> shows the position of the machines on the south side +of the factory, with the direction of extensions, and</p> + +<p><i>E,E</i> the compartments in which the engines are bedded. +In these positions it is possible to obtain direct drive to the +machines.</p> + +<p><i>D,D</i> 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.</p></div> + +<p>If possible the scrap-washing machine should be placed +outside the wall of the factory, and tanks for the reception +of scrap rubbers may then be situated in convenient +proximity.</p> + +<p>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<span class='pagenum'><a name="Page_220" id="Page_220">[220]</a></span> +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.</p> + +<p><a name="Sec16_14" id="Sec16_14"></a><span class="smcap">Choosing a Factory Site.</span>—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 buildings +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.</p> + +<p>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.</p> + +<p>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:</p> + +<div class="blockquot"><p>(<i>a</i>) Area.</p> + +<p>(<i>b</i>) Shape of the estate.</p> + +<p>(<i>c</i>) Topography of the estate.</p> + +<p>(<i>d</i>) Available supplies of water.</p></div> + +<p>Naturally the ideal site for factory buildings would lie in a +central position, given other favourable conditions.</p> + +<p><a name="Sec16_15" id="Sec16_15"></a><span class='pagenum'><a name="Page_221" id="Page_221">[221]</a></span><span +class="smcap">Centralisation or Decentralisation.</span>—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 thousands +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 product, +involving the question of transport of latex or coagulum, +and the possible provision of batteries of heavy machinery.</p> + +<p>The differentiation between the transport of latex and coagulum, +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.</p> + +<p>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 working on a large +scale.</p> + +<p><span class='pagenum'><a name="Page_222" id="Page_222">[222]</a></span>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.</p> + +<p><a name="Sec16_16" id="Sec16_16"></a>The successful preparation of sheet rubber is, on the contrary, +governed chiefly by the factor of transport. With this consideration +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 <i>a priori</i> 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 variable +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.</p> + +<p>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. 1 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. 1 crepe rubber, in order to be able to comply +with prevailing market demands under which preferential +rates fluctuate between pale crepe and smoked sheet.</p> + + +<p class='pagenum'><a name="Page_223" id="Page_223">[223]</a></p> +<hr class="c25" /> +<h2><a name="Part4" id="Part4"></a>PART IV</h2> + +<h3>THE FINISHED RUBBER</h3> + + +<h2><a name="Ch17" id="Ch17"></a>CHAPTER XVII</h2> + +<h3><i>DEFECTS IN CREPE RUBBERS</i></h3> + + +<p><a name="Sec17_1" id="Sec17_1"></a><span class="smcap">General Style of Finish.</span>—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.</p> + +<p>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 Singapore +market, but it should generally be regarded as re-made +rubber—<i>i.e.</i>, 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.</p> + +<p>The general preference of the market at present is for a thin, +smooth-finished crepe, with a close-knitted surface—<i>i.e.</i>, 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.</p> + +<p>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<span class='pagenum'><a name="Page_224" id="Page_224">[224]</a></span> +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.</p> + +<p>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 impression +that the market price is influenced by the evenness of the +edges of crepe rubbers.</p> + +<p>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.</p> + +<p>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.</p> + +<p>Methods of preparation and formulæ for the employment of +chemicals are so well laid down that, up to the stage of machining, +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>i.e.</i>, +macerators, intermediate crepers, and smooth finishing-rolls. +This subject has received full discussion in <a href="#Ch13">Chapter XIII.</a>, +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.</p> + +<p>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.</p> + +<p><a name="Sec17_2" id="Sec17_2"></a><span class='pagenum'><a name="Page_225" id="Page_225">[225]</a></span><span +class="smcap">Dirty Edges.</span>—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.</p> + +<p>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.</p> + +<p><a name="Sec17_3" id="Sec17_3"></a><span class="smcap">Iron-Stains.</span>—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<span class='pagenum'><a name="Page_226" id="Page_226">[226]</a></span> +the quality of the roll material. Some rolls seem to be excessively +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.</p> + +<p><a name="Sec17_4" id="Sec17_4"></a><span class="smcap">Rust-Stains.</span>—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.</p> + +<p>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.</p> + +<p>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.</p> + +<p><a name="Sec17_5" id="Sec17_5"></a><span class="smcap">Oil-Marks.</span>—The origin of oil-marks in crepe has already +been described in <a href="#Ch13">Chapter XIII</a>. 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.</p> + +<p>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.</p> + +<p><a name="Sec17_6" id="Sec17_6"></a>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 case it is almost certain<span class='pagenum'><a name="Page_227" id="Page_227">[227]</a></span> +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.</p> + +<p>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 bearings +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.</p> + +<p>This point in connection with the damage possible by the +existence of wide trays is commended to the notice of manufacturers +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 intervals. +The trouble due to this cause is intensified when the +same machines are employed for the preparation of scrap-rubber +crepes and No. 1 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. 1 (pale) grade, contamination may +be continuous.</p> + +<p><a name="Sec17_7" id="Sec17_7"></a><span class="smcap">Dirt.</span>—Streaks due to the presence of dirt (as apart from oil +or grease contamination, or that due to pieces of oxidised scrap)<span class='pagenum'><a name="Page_228" id="Page_228">[228]</a></span> +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 imagine +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.</p> + +<p><a name="Sec17_8" id="Sec17_8"></a><span class="smcap">Holes.</span>—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.</p> + +<p>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.</p> + +<p><a name="Sec17_9" id="Sec17_9"></a><span class="smcap">Greenish and Tacky Streaks.</span>—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 superficially, +inasmuch as they contain traces of brass from the<span class='pagenum'><a name="Page_229" id="Page_229">[229]</a></span> +“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.</p> + +<p>This contamination of crepe rubber may take place in two +ways:</p> + +<div class="blockquot"><p>(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.</p> + +<p>(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.</p></div> + +<p>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.</p> + +<p>When the defect is discovered, the affected portions should be +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.</p> + +<p>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.</p> + +<p><a name="Sec17_10" id="Sec17_10"></a><a name="Sec17_11" id="Sec17_11"></a><span class='pagenum'><a name="Page_230" +id="Page_230">[230]</a></span>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.”</p> + +<p>Notes were made at intervals extending over a period of two +years. The conclusions arrived at were:</p> + +<div class="blockquot"><p>(1) Although there was surface discoloration, no tackiness +had been caused by fresh (unadulterated) lubricant; neither +were the “blanks” affected.</p> + +<p>(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.”</p> + +<p>(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 exhibited +a similar appearance in lesser degree, or were merely +affected by a characteristic brownish stain.</p></div> + +<p>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 substances. +Satisfaction is obtained without the use of brass.</p> + +<p><a name="Sec17_12" id="Sec17_12"></a><span class="smcap">Cotton and other Fibre.</span>—One of the most +frequent<span class='pagenum'><a name="Page_231" id="Page_231">[231]</a></span> +complaints made against low grade crepes is the presence of +fibre—generally classed in a wholesale fashion as “cotton-waste.”</p> + +<p>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 extenuation. +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.</p> + +<p>As far as the complaint concerns itself with cotton-waste +only, the remedy is plain, and lies in the power of the management +by reason of the ability to restrict the use of “waste” +only to the engine-drivers and mechanics.</p> + +<p>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.</p> + +<p>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.</p> + +<p>It will be clear that contamination by fibrous matter should +be limited practically to the lowest grades of rubber.</p> + +<p><span class='pagenum'><a name="Page_232" id="Page_232">[232]</a></span>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 evident +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 coagulum, +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.</p> + +<p><a name="Sec17_13" id="Sec17_13"></a><span class="smcap">Bark and Grit.</span>—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<span class='pagenum'><a name="Page_233" id="Page_233">[233]</a></span> +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.</p> + +<p><a name="Sec17_14" id="Sec17_14"></a>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 spreading +a piece of crepe over the upturned and hollowed palm of +one hand, while striking the rubber with the other hand.</p> + +<p>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 embedded +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.</p> + +<p>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 impurities, +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 sometimes +contains evident pieces of bark, leaves, and stems of leaves. +For lack of supervision the average coolie would not think of<span class='pagenum'><a name="Page_234" id="Page_234">[234]</a></span> +picking out these obvious impurities, and would pass the whole +mass into the machines.</p> + +<p><a name="Sec17_15" id="Sec17_15"></a><span class="smcap">Oxidation Streaks.</span>—Since the introduction of sodium +bisulphite defects due to streaks, caused by portions of the coagulum +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. 1 crepes, +now being made, would imply either that no anti-oxidant substance +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>i.e.</i>, 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.</p> + +<p><a name="Sec17_16" id="Sec17_16"></a><span class="smcap">“Yellow +Latex” Streaks.</span>—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 coagulate +it separately, if at all possible. In such case the resultant +crepe may be of a distinct canary yellow in tint.</p> + +<p><span class='pagenum'><a name="Page_235" id="Page_235">[235]</a></span>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.</p> + +<p><a name="Sec17_17" id="Sec17_17"></a><span class="smcap">Bisulphite Streaks.</span>—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. Especially +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 coagulation +takes place quickly, it is easy to see that the possibilities +of obtaining a uniform and intimate mixture are small. Probably +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 solutions. +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.</p> + +<p><a name="Sec17_18" id="Sec17_18"></a><span class="smcap">“Spot” Disease.</span>—Few managers of estates preparing pale +crepe rubbers are unacquainted with this defect. It is manifested +by the appearance of small coloured spots varying in<span class='pagenum'><a name="Page_236" id="Page_236">[236]</a></span> +density (<i>i.e.</i>, 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 practically +the whole surface of the rubber as a “flush.”</p> + +<p><a name="Sec17_19" id="Sec17_19"></a>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.</p> + +<p><a name="Sec17_25" id="Sec17_25"></a>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.</p> + +<p>The subject of “‘Spot’ Diseases” has been treated fully in +previous publications,<a name="FNanchor_19_19" id="FNanchor_19_19"></a><a href="#Footnote_19_19" +class="fnanchor">[19]</a> and it is not proposed here to enter +into any lengthy discussion.</p> + +<div class="footnote"><p><a name="Footnote_19_19" id="Footnote_19_19"></a><a href="#FNanchor_19_19"><span +class="label">[19]</span></a> “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.</p></div> + +<p><a name="Sec17_20" id="Sec17_20"></a>If any reader is desirous of producing the defect experimentally, +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.</p> + +<p>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.</p> + +<p>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 +on edge, to allow free drainage of surface moisture, if the rubber +cannot be taken at once to the drying-sheds.</p> + +<div class="figcenter"><a name="Fig66" id="Fig66"></a><img src="images/illo254.jpg" alt="Three +Specimens of Fine Pale Crepe suffering from 'Spot' Disease" /> +<p class="caption"><span class="smcap">Three Specimens of Fine Pale Crepe suffering from<br /> +“Spot” Disease.</span></p></div> + +<p><span class='pagenum'><a name="Page_238" id="Page_238">[238]</a></span></p><p><span +class='pagenum'><a name="Page_237" id="Page_237">[237]</a></span></p><p>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>i.e.</i>, upon the raised pattern.</p> + +<p><a name="Sec17_21" id="Sec17_21"></a>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 (1) between machining and +hanging, (2) in drying.</p> + +<p><a name="Sec17_22" id="Sec17_22"></a><a name="Sec17_23" id="Sec17_23"></a>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. 1 product or to consider the installation of artificial +aids to drying.</p> + +<p>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).</p> + +<p>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,<a name="FNanchor_20_20" id="FNanchor_20_20"></a><a +href="#Footnote_20_20" class="fnanchor">[20]</a> of the Malang<span class='pagenum'><a name="Page_239" id="Page_239">[239]</a></span> +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 conditions +in factory practice, such aids should not be necessary, +and where keen supervision is not available may lead to other +difficulties.</p> + +<div class="footnote"><p><a name="Footnote_20_20" id="Footnote_20_20"></a><a +href="#FNanchor_20_20"><span class="label">[20]</span></a> “Guide to the Preparation of Rubber,” Arens, 1918; Communications +from the Experimental Station (Malang, Java).</p></div> + +<p>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.</p> + +<p>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.</p> + +<p>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.</p> + +<p><a name="Sec17_24" id="Sec17_24"></a>In a general sense, the answer to both queries is in the negative. +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.</p> + +<p>A dry crepe, even when in close contact with an infected +dry specimen, has not been found to be affected.</p> + +<p>Unless, therefore, pieces of rubber are pressed together, +under favourable conditions as to moisture, there has been +observed no transfer of disease.</p> + +<p>Similarly it has not been found that the presence of spotted +rubber in one part of the drying-house has been responsible for<span class='pagenum'><a name="Page_240" id="Page_240">[240]</a></span> +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 intermediate +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 communicated +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.</p> + +<p>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 possibility +of the appearance of “spot” disease.</p> + +<p><a name="Sec17_26" id="Sec17_26"></a>In conclusion, the chief points in any discussion of this subject +may be summarised thus:</p> + +<div class="blockquot"><p>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.</p> + +<p>2. Thin crepe only should be made. The quicker the rate +of drying the less possibility is there of the coloured spots +appearing.</p> + +<p>3. Crepe should never be allowed to remain folded overnight, +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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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.</p> + +<p><span class='pagenum'><a name="Page_241" id="Page_241">[241]</a></span>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.</p> + +<p>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.</p> + +<p>9. The natural habitat of the fungi would appear to be decaying +vegetable matter in the field.</p> + +<p>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.</p></div> + +<p><a name="Sec17_27" id="Sec17_27"></a><span class="smcap">Surface Moulds or Mildews on Crepe Rubber.</span>—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.</p> + +<p>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:</p> + +<div class="blockquot"><p>(<i>a</i>) Making the crepe too thick.</p> + +<p>(<i>b</i>) Hanging the crepe in a badly ventilated or badly situated +building.</p> + +<p>(<i>c</i>) Occasionally by abnormally wet weather.</p> + +<p>(<i>d</i>) Allowing piles of crepe to remain too long before hanging.</p> + +<p>(<i>e</i>) Using excessive quantities of deteriorated sodium bisulphite. +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 <i>bisulphate</i>, +an oxidation product of the bisulphite. This is hygroscopic +to some degree—<i>i.e.</i>, it takes up moisture from the atmosphere.<span +class='pagenum'><a name="Page_242" id="Page_242">[242]</a></span> +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.”</p></div> + +<p>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.</p> + +<p><a name="Sec17_28" id="Sec17_28"></a><a name="Sec17_29" id="Sec17_29"></a><span +class="smcap">Tackiness in Rubber.</span>—“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.</p> + +<p>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 unfortunately +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<span class='pagenum'><a name="Page_243" id="Page_243">[243]</a></span> +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.</p> + +<p><span class="smcap">Tackiness the Result of a Slow Process of Change.</span>—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 tackiness +to appear in rubber arriving in London, which showed +no indications of tackiness when packed for shipment.</p> + +<p><span class="smcap">Tackiness caused by Traces of Copper Salts.</span>—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.</p> + +<p><a name="Sec17_30" id="Sec17_30"></a>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.</p> + +<p>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,<span class='pagenum'><a name="Page_244" id="Page_244">[244]</a></span> +the remainder being in solution in the serum. Furthermore, +as the rubber was well washed and worked down to thin crepe, +<i>the total quantity of copper salt remaining in the dry crepe must +have been exceedingly small</i>. 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.</p> + +<table summary="Table p244"> + +<tr> +<td rowspan="2" class="center bt br bb"><i>Sample.</i></td> +<td rowspan="2" colspan="2" class="center bt br bb"><i>Amount of Copper Salt.</i></td> +<td colspan="6" class="center bt bb"><i>Weight of Rubber.</i></td> +</tr> + +<tr> +<td class="center br bb">When Dry.</td> +<td class="center br bb">After<br />Interval<br />of Four<br />Weeks.</td> +<td class="center br bb">Further<br />Interval<br />of Seven<br />Weeks.</td> +<td class="center br bb">Further<br />Interval<br />of Three<br />Weeks.</td> +<td colspan="2" class="center bb">Percentage<br />in Increase<br />in Weight.</td> +</tr> + +<tr> +<td class="br"> </td> +<td colspan="2" class="br"> </td> +<td class="center fsize80 br">Grms.</td> +<td class="center fsize80 br">Grms.</td> +<td class="center fsize80 br">Grms.</td> +<td class="center fsize80 br">Grms.</td> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="center br top">1</td> +<td colspan="2" class="left br">0·02 grms. copper sulphate,<br />per 100 c.c. latex</td> +<td class="rightbot br" style="padding-right: 1.5em;">430</td> +<td class="rightbot br" style="padding-right: 1em;">441</td> +<td class="rightbot br" style="padding-right: 1em;">482</td> +<td class="rightbot br" style="padding-right: 1em;">488</td> +<td class="rightbot" style="padding-right: 0;">13·</td> +<td class="leftbot" style="padding-left: 0;">5</td> +</tr> + +<tr> +<td class="center br top">2</td> +<td colspan="2" class="left br">Ditto</td> +<td class="rightbot br" style="padding-right: 1.5em;">428</td> +<td class="rightbot br" style="padding-right: 1em;">439</td> +<td class="rightbot br" style="padding-right: 1em;">481</td> +<td class="rightbot br" style="padding-right: 1em;">486</td> +<td class="rightbot" style="padding-right: 0;">13·</td> +<td class="leftbot" style="padding-left: 0;">55</td> +</tr> + +<tr> +<td class="center br top">3</td> +<td class="left">0·01 grms. copper sulphate,<br />per 100 c.c. latex</td> +<td rowspan="2" class="right br" style="font-size: 2.5em; vertical-align: middle;">}</td> +<td rowspan="2" class="right br" style="padding-right: 1.5em; vertical-align: middle;">962</td> +<td rowspan="2" class="right br" style="padding-right: 1em; vertical-align: middle;">987</td> +<td rowspan="2" class="right br" style="padding-right: 1em; vertical-align: middle;">1035</td> +<td rowspan="2" class="right br" style="padding-right: 1em; vertical-align: middle;">1036</td> +<td rowspan="2" class="right" style="padding-right: 0; vertical-align: middle;">7·</td> +<td rowspan="2" class="left" style="padding-left: 0; vertical-align: middle;">7</td> +</tr> + +<tr> +<td class="center br top"> </td> +<td class="left">0·01 grms. copper acetate,<br />per 100 c.c. latex</td> +</tr> + +<tr> +<td class="center br bb top">4</td> +<td colspan="2" class="left br bb">0·025 grms. copper sulphate,<br />per 100 c.c. latex</td> +<td class="rightbot br bb" style="padding-right: 1.5em;">502</td> +<td class="rightbot br bb" style="padding-right: 1em;">513</td> +<td class="rightbot br bb" style="padding-right: 1em;">558</td> +<td class="rightbot br bb" style="padding-right: 1em;">560</td> +<td class="rightbot bb" style="padding-right: 0;">11·</td> +<td class="leftbot bb" style="padding-left: 0;">5</td> +</tr> + +</table> + +<p>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!</p> + +<p>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.</p> + +<p>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<span class='pagenum'><a name="Page_245" id="Page_245">[245]</a></span> +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.</p> + +<p>Regarding the question as to whether tackiness may be communicated +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<a name="FNanchor_21_21" +id="FNanchor_21_21"></a><a href="#Footnote_21_21" class="fnanchor">[21]</a> 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.</p> + +<div class="footnote"><p><a name="Footnote_21_21" id="Footnote_21_21"></a><a +href="#FNanchor_21_21"><span class="label">[21]</span></a> Report I., 1916 (Sidney Morgan), Rubber Growers’ Association +(Malaya).</p></div> + +<p>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.</p> + +<p><span class="smcap">No Cure for Tackiness.</span>—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:</p> + +<div class="blockquot"><p>(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—<i>e.g.</i>, ruby glass or +ruby glazed cloth.</p> + +<p>(2) Rubber should under no circumstances be placed near +any source of heat.</p> + +<p>(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.</p> + +<p>(4) Instruments or vessels of copper or brass should not +be used where acids are employed.</p></div> + +<p><a name="Sec17_31" id="Sec17_31"></a><span class='pagenum'><a name="Page_246" id="Page_246">[246]</a></span></p><p><span +class="smcap">Lack of Uniformity in Colour.</span>—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. Previously +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.</p> + +<p>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.</p> + +<p>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—<i>e.g.</i>, +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 differences +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.</p> + +<p><a name="Sec17_32" id="Sec17_32"></a><span class="smcap">Block Rubber.</span>—This mode of preparation is employed only +in comparatively few instances. The block is prepared from<span class='pagenum'><a name="Page_247" id="Page_247">[247]</a></span> +crepe rubber, which has been dried either in a hot-air drier +or in a vacuum chamber.</p> + +<p>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>i.e.</i>, 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.</p> + +<p>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 homogeneous +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.</p> + +<p>Prepared in slabs which are three or four inches in thickness, +the product is easily handled, and should be sufficiently translucent +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.</p> + +<p>The only complaints which it should be possible to lodge +against block rubbers are:</p> + +<div class="blockquot"><p>(<i>a</i>) The inclusion of dirt and other matter.</p> + +<p>(<i>b</i>) The use of layers of crepe which have some defect.</p> + +<p>(<i>c</i>) The inclusion of air-bubbles.</p></div> + +<p>The remedy for (<i>a</i>) and (<i>b</i>) 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.</p> + +<p>When layers of crepe are placed one upon the other, and submitted +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.</p> + +<p>It must be obvious to all acquainted with the processes +involved in the preparation of block rubber, that no possibility<span class='pagenum'><a name="Page_248" id="Page_248">[248]</a></span> +exists for the presence of air-bells actually enclosed <i>in</i> 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.</p> + +<p>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 expected +to contain less air-bells than a block composed of layers +of a rough crepe.</p> + +<p>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 commercial preparations.</p> + + +<p class='pagenum'><a name="Page_249" id="Page_249">[249]</a></p> +<hr class="c25" /> +<h2><a name="Ch18" id="Ch18"></a>CHAPTER XVIII</h2> + +<h3><i>DEFECTS IN SHEET RUBBER</i></h3> + + +<p>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.</p> + +<p><a name="Sec18_1" id="Sec18_1"></a><span class="smcap">Milky Residue or Serum.</span>—If the serum is not clear after +the ordinary period allowed for coagulation, it indicates one of +the following possible causes:</p> + +<div class="blockquot"><p>(<i>a</i>) Failure to obtain complete mixture by thorough stirring.</p> + +<p>(<i>b</i>) 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.</p> + +<p>(<i>c</i>) 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—<i>e.g.</i>, hydrochloric acid.</p></div> + +<p><a name="Sec18_2" id="Sec18_2"></a><span class="smcap">Coloured Surface Blotches and Unpleasant Odour.</span>—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.</p> + +<p><a name="Sec18_3" id="Sec18_3"></a><span class="smcap">Dark Discoloration of the Rubber.</span>—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 <a href="#Ch8">Chapters VIII.</a> and <a href="#Ch9">IX.</a>) +by the use of small quantities of sodium sulphite (for preference) +or bisulphite.</p> + +<p><a name="Sec18_4" id="Sec18_4"></a><a name="Sec18_5" id="Sec18_5"></a><a name="Sec18_6" id="Sec18_6"></a><span +class="smcap">Soft Coagulum, Spongy under-surface, Tearing of +Coagulum.</span>—If the whole mass of coagulum is too soft, while<span +class='pagenum'><a name="Page_250" id="Page_250">[250]</a></span> +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 coagulating +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 coagulum +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.</p> + +<p><a name="Sec18_7" id="Sec18_7" ></a><span class="smcap">“Pitting” +of Surfaces.</span>—In pan coagulation this “pitted” +appearance is usually limited to the under-surface, while coagulum +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 unable +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:</p> + +<div class="blockquot"><p>(<i>a</i>) The latex had begun to “sour” before arrival at the +factory or while waiting to be treated. This premature coagulation +is usually checked or diminished by the employment of +anti-coagulants (see <a href="#Ch8">Chapters VIII.</a> and <a href="#Ch9">IX.</a>). It +is generally<span class='pagenum'><a name="Page_251" id="Page_251">[251]</a></span> +accompanied by the appearance of enclosed gas-bubbles in +the dry rubber.</p> + +<p>(<i>b</i>) There may have been a slight insufficiency of coagulant, +or the admixture was not thorough, thus allowing a slow putrefactive +change to take place in the incompletely coagulated areas.</p> + +<p>(<i>c</i>) 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.</p></div> + +<p><a name="Sec18_8" id="Sec18_8"></a><span class="smcap">Thickened Ends or Edges, after Rolling.</span>—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.</p> + +<p><a name="Sec18_9" id="Sec18_9"></a><span class="smcap">Mis-shapen Sheets.</span>—It is sometimes noted that sheets may +be wider and thicker at the ends than in the middle. Manipulation +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.</p> + +<p><a name="Sec18_10" id="Sec18_10"></a><span class="smcap"><a name="Sec18_11" id="Sec18_11"></a><a name="Sec18_12" +id="Sec18_12"></a><a name="Sec18_13" id="Sec18_13"></a>Thickened Patches, Torn Sheets, “Dog-Ears,” Creases.</span>—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.</p> + +<p>Thickened patches are often caused in conjunction with torn<span class='pagenum'><a name="Page_252" id="Page_252">[252]</a></span> +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.</p> + +<p>“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.</p> + +<p><a name="Sec18_14" id="Sec18_14"></a><span class="smcap">Greasiness before Smoking.</span>—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—<i>e.g.</i>, 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.</p> + +<p>In the preparation of smoked sheet, the greasy appearance +and the cause outlined contribute to a defect which is eventually +described as “stretching rusty.”</p> + +<p><a name="Sec18_15" id="Sec18_15"></a><span class="smcap">Surface Blemishes.</span>—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.</p> + +<p>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.</p> + +<p><span class='pagenum'><a name="Page_253" id="Page_253">[253]</a></span>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.</p> + +<p>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.</p> + +<hr class="c05" /> + +<p>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.</p> + +<p>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.</p> + +<p><a name="Sec18_16" id="Sec18_16"></a><span class="smcap">Unevenness of Appearance.</span>—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.</p> + +<p>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.</p> + +<p>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.<span class='pagenum'><a name="Page_254" id="Page_254">[254]</a></span></p> + +<p>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>i.e.</i>, when the rubber is held between the eye and the +source of light.</p> + +<p>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.</p> + +<p><a name="Sec18_17" id="Sec18_17"></a><span class="smcap">Variation due to Oxidation.</span>—The subject of oxidation +has been mentioned in the <a href="#Ch18">opening paragraphs</a> 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-oxidants +such as the sulphite or bisulphite of soda. In earlier +days it was sometimes prevented by steeping the thin rubber +in very hot water.</p> + +<p>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<span class='pagenum'><a name="Page_255" id="Page_255">[255]</a></span> +darkening of the surface would be masked by the colour induced +by the smoke-drying process.</p> + +<p>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 formulæ prescribed by +experience.</p> + +<p><a name="Sec18_18" id="Sec18_18"></a><span class="smcap">Colour of Smoked Sheets.</span>—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—<i>e.g.</i>, 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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>Similarly it is now plain that when anti-oxidants are employed +in excess the paleness of the rubber is in no degree truly indicative +of the period during which the rubber has been smoke-cured.</p> + +<p>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 within 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<span class='pagenum'><a name="Page_256" id="Page_256">[256]</a></span> +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 thickness, +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>i.e.</i>, that piece of coagulum +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.</p> + +<p>To attain uniformity in colour, therefore, the following +points must be studied and controlled as far as is possible:</p> + +<div class="blockquot"><p>(<i>a</i>) Uniform dilution of all latices.</p> + +<p>(<i>b</i>) Uniform dimensions of coagulating receptacles.</p> + +<p>(<i>c</i>) Uniform volumes of standardised latex.</p> + +<p>(<i>d</i>) Uniform quality and quantities of chemicals.</p> + +<p>(<i>e</i>) Uniform methods of manipulating the coagulum.</p> + +<p>(<i>f</i>) Uniform conditions of fuel and accommodation during +smoke-curing.</p></div> + +<p><a name="Sec18_19" id="Sec18_19"></a><span class="smcap">Surface Gloss.</span>—In the choice of fuel there is room for control +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 appearance +of the surface of sheets.</p> + +<p>Three main factors are involved:</p> + +<div class="blockquot"><p>(1) The nature of the fuel.</p> + +<p>(2) The ratio between furnace capacity and the capacity of +the smoke-house.</p> + +<p>(3) The rate of combustion.</p> + +<p>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.</p></div> + +<p>It is impossible to lay down any general rules for the guidance +of estates, as the timber available varies so widely in +nature. Experience must be the only guide, and it should not<span class='pagenum'><a name="Page_257" id="Page_257">[257]</a></span> +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.</p> + +<p>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 maintained +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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>In order to guard against the appearance of a heavy glaze, +then, the following points must be observed:</p> + +<div class="blockquot"><p>1. The fuel must be carefully selected by experience.</p> + +<p>2. The sheets must not be thick. No sheets should be +thicker than <span class="enum">1</span>⁄<span class="denom">8</span> inch measured in average section across the ribs.</p> + +<p>3. The temperature must not be too high. An average +working temperature of 120° to 125° F. should be ample.</p> + +<p><span class='pagenum'><a name="Page_258" id="Page_258">[258]</a></span>4. If the sheets are fairly thick, a low average temperature +should be avoided. No lower average than 110° F. should be +allowed.</p></div> + +<p><a name="Sec18_20" id="Sec18_20"></a><span class="smcap">Dull, Black Surface.</span>—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.</p> + +<p>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 comparatively +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.</p> + +<p><a name="Sec18_21" id="Sec18_21"></a><span class="smcap">Moist Glaze, Greasiness of Surface.</span>—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.</p> + +<p>As far as experience shows at present it may be due to two +causes:</p> + +<div class="blockquot"><p>(<i>a</i>) 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 +pale in colour, and the abuse of it may delay the drying unduly. +In 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 atmosphere +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.</p> + +<p><span class='pagenum'><a name="Page_259" id="Page_259">[259]</a></span>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 excess +is present the drying period will be protracted, and the +sheets will have a very moist surface film.</p> + +<p>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.</p> + +<p>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.</p> + +<p>(<i>b</i>) 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.</p> + +<p>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 systematically. +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.</p></div> + +<p><a name="Sec18_22" id="Sec18_22"></a><span class="smcap">Virgin Spots and Patches.</span>—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. 1 product nowadays<span class='pagenum'><a name="Page_260" id="Page_260">[260]</a></span> +can have this complaint levelled at it. In the extreme case +it points to gross negligence on the part of the packer.</p> + +<p>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 examining +the cut edges.</p> + +<p><a name="Sec18_23" id="Sec18_23"></a><span class="smcap">Surface Moulds or Mildew.</span>—During the last two years, +complaints regarding the incidence of “mouldy rubber” (<i>i.e.</i>, +relating chiefly to the presence of mildews on the surface) +have become increasingly common.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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<span class='pagenum'><a name="Page_261" id="Page_261">[261]</a></span> +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 comparatively +brief period mildew was to be seen.</p> + +<p>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 temperature +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.</p> + +<p>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 paragraphs.</p> + +<p>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:</p> + +<div class="blockquot"><p>(<i>a</i>) Storing sheets in a damp place before packing.</p> + +<p>(<i>b</i>) Packing sheets in wooden cases which are not thoroughly +dry.</p> + +<p><span class='pagenum'><a name="Page_262" id="Page_262">[262]</a></span>(<i>c</i>) +Piling up cases of rubber in a badly ventilated store-room.</p> + +<p>(<i>d</i>) Placing the cases on a cement floor.</p> + +<p>(<i>e</i>) Wetting of cases by sea-water or by rain during transport, +etc.</p></div> + +<p><a name="Sec18_24" id="Sec18_24"></a><span class="smcap">Black Streaks, Spots or Patches.</span>—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. Sackcloth +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.</p> + +<p>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.</p> + +<p><a name="Sec18_25" id="Sec18_25"></a><span class="smcap">Whitish or Grey Streaks.</span>—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.</p> + +<p><a name="Sec18_26" id="Sec18_26"></a><span class="smcap">Rust.</span>—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.</p> + +<p><a name="Sec18_27" id="Sec18_27"></a>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<span class='pagenum'><a name="Page_263" id="Page_263">[263]</a></span> +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 characteristic +of the earlier years of the plantation industry, the remaining +liquid in the pan after coagulation would contain an appreciable +quantity of soluble substances which would otherwise +have been retained in the coagulum.</p> + +<p>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.</p> + +<p>It will be seen, therefore, that sheets which have been +prepared from rich latex or from too deep a layer of comparatively +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<span class='pagenum'><a name="Page_264" id="Page_264">[264]</a></span> +it is not difficult to understand that some brokers regarded +the presence of the so-called “rust” as an indication of over-smoking.</p> + +<p>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 <i>the presence of this protein film may be seen on +unsmoked sheets</i> 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.</p> + +<p>When the sheets were bent or twisted, the apparent surface +of the rubber (<i>i.e.</i>, 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.</p> + +<p>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.</p> + +<p>It will be noted that since the introduction of standard +methods of preparation, involving uniform dilution of latex, +say, to a content of 1<span class="enum">1</span>⁄<span class="denom">4</span> +or 1<span class="enum">1</span>⁄<span class="denom">2</span> lbs. dry rubber per gallon, complaints +as to “rust” have decreased considerably.</p> + +<p>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.</p> + +<p><a name="Sec18_28" id="Sec18_28"></a><span class='pagenum'><a name="Page_265" id="Page_265">[265]</a></span>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—<i>e.g.</i>, allowing sheets to remain too long in a moist +atmosphere before placing in the smoke-house.</p> + +<p><a name="Sec18_29" id="Sec18_29"></a>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:</p> + +<div class="blockquot"><p>A. <span class="smcap">The Hot-Water Treatment.</span>—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.</p> + +<p>(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 overnight, +the presence of the exuded matter may be detected +also by its odour.</p> + +<p>(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.</p> + +<p>(3) After remaining in the hot water for the period mentioned, +the sheets are removed singly, each one being surface +washed or swilled as it is taken out.</p> + +<p><span class='pagenum'><a name="Page_266" id="Page_266">[266]</a></span>(4) +<i>It is important to see that the sheets are now well washed or +scrubbed under running cold water, or in frequent changes of +water.</i> 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.</p> + +<p>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.</p> + +<p>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 treatment.</p> + +<p>The explanation of the action which takes place is rather +obscure, but two theories may be advanced.</p> + +<p>(<i>a</i>) 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.</p> + +<p>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<span class='pagenum'><a name="Page_267" id="Page_267">[267]</a></span> +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.</p> + +<p>(<i>b</i>) The other theory also demands the first assumption propounded +in the preceding theory, but subsequently perhaps is +less feasible as it assumes a chemical action of which we have +no definite knowledge.</p> + +<p>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 +<i>in situ</i> 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 coagulant +employed, of sugars, of protein matter, and of inorganic +salts. Of these the substances which would evaporate would +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.</p></div> + +<p>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 successfully +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 successful.</p> + +<p><a name="Sec18_30" id="Sec18_30"></a><span class="smcap">Other Views on “Rust” Causation.</span>—Later experimental +work on “rust” formation by Hellendoorn<a name="FNanchor_22_22" id="FNanchor_22_22"></a><a +href="#Footnote_22_22" class="fnanchor">[22]</a> leads to the +observation that “rustiness” is caused, not actually by the +deposition of original serum-substances, but by the decomposition +thereof, under the action of aerobic micro-organisms.</p> + +<div class="footnote"><p><a name="Footnote_22_22" id="Footnote_22_22"></a><a href="#FNanchor_22_22"><span +class="label">[22]</span></a> “The Cause of Rustiness in Sheet-Rubber,” H. J. Hellendoorn, +Archief voor de Rubbercultuur, October, 1919 (Communication from +the Central Rubber Station, Buitenzorg, Java).</p></div> + +<p><span class='pagenum'><a name="Page_268" id="Page_268">[268]</a></span>Without +going into a full discussion of the subject, the following +points noted in the experimental work may be quoted:</p> + +<div class="blockquot"><p>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.</p> + +<p>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.</p> + +<p>3. “Rust” can be prevented by soaking freshly prepared +sheets in dilute solutions of disinfectants—<i>e.g.</i>, formalin, sodium +bisulphite, or chinosol.</p> + +<p>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.</p> + +<p>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.</p> + +<p>4. It was shown that the micro-organisms which cause +decomposition of the serum-products flourish only in the +presence of air—<i>i.e.</i>, 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.</p> + +<p>5. The optimal temperature for development of the particular +organisms appeared to be about 100° F., in a moist +atmosphere.</p> + +<p>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.”</p> + +<p>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.</p> + +<p>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.<a name="FNanchor_23_23" id="FNanchor_23_23"></a><a href="#Footnote_23_23" class="fnanchor">[23]</a></p></div> + +<div class="footnote"><p><a name="Footnote_23_23" id="Footnote_23_23"></a><a +href="#FNanchor_23_23"><span class="label">[23]</span></a> We advise and practise hanging sheets in the open, without +shade or cover.</p></div> + +<p>It will be gathered that, although there may be a slight difference +between our previous views and those advanced by<span class='pagenum'><a name="Page_269" id="Page_269">[269]</a></span> +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.</p> + +<p><a name="Sec18_31" id="Sec18_31"></a><span class="smcap">Bubbles.</span>—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.</p> + +<p>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.</p> + +<p><a name="Sec18_32" id="Sec18_32"></a>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.</p> + +<p>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 decomposition +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<span class='pagenum'><a name="Page_270" id="Page_270">[270]</a></span> +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.</p> + +<p>With this preamble we may proceed to classify possible +causes of the formation of bubbles into two groups:</p> + +<div class="blockquot"><p>(<i>a</i>) Those originating in field operations.</p> + +<p>(<i>b</i>) Others which may arise after the arrival of the latex +at the factory.</p></div> + +<p><a name="Sec18_33" id="Sec18_33"></a><span class="smcap">In the Field.</span>—Decomposition may be caused by:</p> + +<div class="blockquot"><p>(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.</p> + +<p>(2) Delay in commencing work. This means similar delay +in collecting the latex which is exposed to greater heat than +under ordinary circumstances.</p> + +<p>(3) Exposure to the sun’s rays. The heating of the latex +may provide improved conditions favourable to the development +and action of micro-organisms.</p> + +<p>(4) Allowing latex to stand too long before collection. +This usually is the result of giving tappers too great a task.</p> + +<p>(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.</p> + +<p>(6) Tapping trees at too great a height. The latex generally +has an abnormal distance to travel before reaching the cup.</p> + +<p>(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 (<i>e.g.</i>, sugars), which are +capable of effecting flocculation or coagulation.</p> + +<p>(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<span class='pagenum'><a name="Page_271" id="Page_271">[271]</a></span> +action augments the effect likely to be produced by long +standing.</p></div> + +<p>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.</p> + +<p>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 <a href="#Ch5">Chapter V</a>.</p> + +<p><a name="Sec18_34" id="Sec18_34"></a><span class="smcap">In the Factory.</span>—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.</p> + +<p>Contributory factors in the store are:</p> + +<div class="blockquot"><p>(1) Lack of cleanliness of utensils, particularly of coagulating +dishes or tanks.</p> + +<p>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.</p> + +<p>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.</p> + +<p>(2) Allowing latex to stand too long before treatment. This +point needs no further expansion.</p> + +<p>(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.</p> + +<p>(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<span class='pagenum'><a name="Page_272" id="Page_272">[272]</a></span> +(and subsequent formation of gas), but also to the formation +of true “air-bubbles” by inclusion of air during stirring.</p> + +<p>(5) The use of insufficient coagulant. Coagulation is slow +and incomplete.</p> + +<p>(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.</p> + +<p>(7) The proximity of the coagulating latex to some source of +heat, or exposure to sunlight.</p> + +<p>(8) Any delay of drying in the preliminary stages, either +before or after the rubber enters the smoke-house.</p></div> + +<p><a name="Sec18_35" id="Sec18_35"></a><span class="smcap">Blisters.</span>—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.</p> + +<p>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.</p> + +<p>The view held is that decomposition had supervened or was +taking place—probably from one or more of the causes enumerated +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.”</p> + +<p>Beyond this point we are not in a position to put forward +any definite supposition as to the apparently haphazard occurrence +of the phenomenon.</p> + +<p>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<span class='pagenum'><a name="Page_273" id="Page_273">[273]</a></span> +to arrive at any satisfactory idea of the exact conditions governing +the incidence of “blisters.” Our investigations only lead +us to two observations:</p> + +<div class="blockquot"><p>(<i>a</i>) That blisters have appeared on the rubber of some +estates after wintering, and during the period of new leaf-development.</p> + +<p>(<i>b</i>) 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.</p></div> + +<p>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.</p> + +<p><a name="Sec18_36" id="Sec18_36"></a><span class="smcap">“Spot” +Disease in Sheet Rubber.</span>—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.</p> + +<p><a name="Sec18_37" id="Sec18_37"></a><span class="smcap">Support Marks.</span>—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,<span class='pagenum'><a name="Page_274" id="Page_274">[274]</a></span> +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 supervision. +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 required. +This will ensure that fresh rubber always rests upon +a clean support.</p> + +<p>On some estates, in order to guard against a pronounced +“bar-mark,” sheets are moved and turned daily.</p> + +<p>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.</p> + +<p><a name="Sec18_38" id="Sec18_38"></a><span class="smcap">Stickiness.</span>—This +is not to be confounded with “tackiness,” +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 “ribbing,” +and which may have been coated with light tarry deposits +(see <a href="#Sec18_21">Glaze</a>). 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.</p> + +<p><a name="Sec18_39" id="Sec18_39"></a><span class="smcap">Ribbing, Surface Pattern.</span>—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.</p> + +<p>The practice ensures an increase of superficial area which is +an aid in drying, improves the appearance of the rubber for<span class='pagenum'><a name="Page_275" id="Page_275">[275]</a></span> +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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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.</p> + +<p><a name="Sec18_40" id="Sec18_40"></a><span class="smcap">Thick Ends, “Sheet Clippings.“</span>—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 manipulation +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. 1 Standard +Crepe.</p> + +<p>The other alternative is to trim the ends when the bulk of +the rubber is thoroughly smoke-dried. The moisture containing<span class='pagenum'><a name="Page_276" id="Page_276">[276]</a></span> +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.</p> + +<p><a name="Sec18_41" id="Sec18_41"></a><span class="smcap">Other Infrequent Defects.</span>—This chapter will be closed +with a reference to other small defects which, although infrequent, +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.</p> + +<p><a name="Sec18_42" id="Sec18_42"></a><span class="smcap">Dirt.</span>—Trouble from this source should be absent, but carelessness +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.</p> + +<p><a name="Sec18_43" id="Sec18_43"></a><span class="smcap">Ash.</span>—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.</p> + +<p><a name="Sec18_44" id="Sec18_44"></a><span class="smcap">Bark.</span>—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.</p> + +<p><a name="Sec18_45" id="Sec18_45"></a><span class="smcap">Splinters.</span>—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<span class='pagenum'><a name="Page_277" id="Page_277">[277]</a></span> +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.</p> + + +<p class='pagenum'><a name="Page_278" id="Page_278">[278]</a></p> +<hr class="c25" /> +<h2><a name="Part5" id="Part5"></a>PART V</h2> + +<h3>GENERAL</h3> + +<h2><a name="Ch19" id="Ch19"></a>CHAPTER XIX</h2> + +<h3><i>CHOICE OF COAGULANT</i></h3> + + +<p><a name="Sec19_1" id="Sec19_1"></a>Almost without exception, the agent employed in the coagulation +of plantation (<i>Hevea</i>) 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 expediency. +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.</p> + +<p><a name="Sec19_2" id="Sec19_2"></a>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 coagulation. +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 <a href="#Ch20">later</a>.</p> + +<p>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.</p> + +<p><a name="Sec19_3" id="Sec19_3"></a><span class='pagenum'><a name="Page_279" id="Page_279">[279]</a></span><span +class="smcap">Acetic Acid.</span>—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.</p> + +<p><a name="Sec19_4" id="Sec19_4"></a><span class="smcap">Formic Acid.</span>—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.</p> + +<p><a name="Sec19_5" id="Sec19_5"></a><a name="Sec19_6" id="Sec19_6"></a><span class="smcap">Citric +Acid, Tartaric Acid.</span>—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.</p> + +<p><a name="Sec19_7" id="Sec19_7"></a><span class="smcap">Oxalic Acid.</span>—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.</p> + +<p>It would not be a safe agent in the hands of coolies, as it is +classed as a poison.</p> + +<p><a name="Sec19_8" id="Sec19_8"></a><span class="smcap">Sulphuric Acid.</span>—During the War, in a period of shortage +of acetic acid and of high prices, this agent was used with +success on some estates.</p> + +<p>It scarcely need be remarked that it is a dangerous substance +to handle, and that its employment must be accompanied by +close European supervision.</p> + +<p>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 with sulphuric acid.</p> + +<p>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 <i>only in the absence +of the commoner, and much safer, coagulants</i>.</p> + +<p>In view of the possible incidence of such an emergency,<span class='pagenum'><a name="Page_280" id="Page_280">[280]</a></span> +the following notes are given. It is impressed that strict adherence +to the rules must be given.</p> + +<p><span class="smcap">Handling Sulphuric Acid.</span>—(<i>a</i>) Always use glass or glazed +earthenware vessels.</p> + +<p>(<i>b</i>) 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.</p> + +<p>(<i>c</i>) When diluting this agent always remember to pour the +acid into the water (<i>i.e.</i>, the lesser into the greater), and never +<i>vice versa</i>. Pour the acid carefully and slowly down the side +of the vessel, and stir well.</p> + +<p><a name="Sec19_8d" id="Sec19_8d"></a>(<i>d</i>) 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.</p> + +<p><span class="smcap">Storing Sulphuric Acid.</span>—(<i>a</i>) 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.</p> + +<p>(<i>b</i>) 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.</p> + +<p>(<i>c</i>) See (<i><a href="#Sec19_8d">d</a></i>) above.</p> + +<p><span class="smcap">Buying Sulphuric Acid.</span>—(<i>a</i>) Commercial acid of specific +gravity 1·84 is the best of its kind. It contains impurities +which are non-injurious to rubber preparation.</p> + +<p>(<i>b</i>) It is always advisable, if possible, to buy the acid in +small jars containing not more than 100 lbs. each. Smaller +jars, with a content not exceeding 50 lbs., would be preferable.</p> + +<p>(<i>c</i>) 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.</p> + +<p><span class="smcap">Formula for Use of Sulphuric Acid.</span>—It will be understood +that as this formula has been calculated for working with latex, +having a consistency of 1<span class="enum">1</span>⁄<span class="denom">2</span> lbs. 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.</p> + +<p>(Sulphuric acid of specific gravity 1·84.)</p> + +<div class="blockquot"><p><span class='pagenum'><a name="Page_281" id="Page_281"><span class="fsize110">[281]</span></a></span><span +class="smcap">Note.</span>—The directions must be followed carefully, and +glass measuring vessels should be used if procurable.</p> + +<p>(<i>a</i>) Measure out 1 pint of strong acid, and pour it carefully +and slowly <i>down the inner surface</i> of a jar containing 20 gallons +of water. Do not pour it directly into the water.</p> + +<p>The heavy acid will sink to the bottom of the jar, and a good +mixture must be obtained by stirring well.</p> + +<p>(<i>b</i>) Of this solution (which is approximately 1 per cent. by +weight), use 1 gallon to 20 gallons of latex.</p></div> + +<p>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.</p> + +<p>The formula given above works out at approximately 1 part +strong acid to 2,000 parts of latex (of dry rubber content 1<span class="enum">1</span>⁄<span class="denom">2</span> lbs. +per gallon). The formula for using acetic acid with the same +latex works out at about 1: 1,200. 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—</p> + +<div class="blockquot"><p>1 lb. sulphuric acid will produce 300 lbs. dry rubber. +1 lb. acetic acid will produce 180 lbs. dry rubber.</p></div> + +<p>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.</p> + +<p>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<span class='pagenum'><a name="Page_282" id="Page_282">[282]</a></span> +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.</p> + +<p>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 exercised +in the observance of the strict formula for use.</p> + +<p><a name="Sec19_9" id="Sec19_9"></a><span class="smcap">Hydrochloric Acid, Nitric Acid.</span>—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.</p> + +<p><a name="Sec19_10" id="Sec19_10"></a><span class="smcap">Hydrofluoric Acid.</span>—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.</p> + +<p>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.</p> + +<p><a name="Sec19_11" id="Sec19_11"></a><span class="smcap">Alum.</span>—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 appreciably +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.</p> + +<p><a name="Sec19_12" id="Sec19_12"></a><span class="smcap">Pyroligneous Acid.</span>—This is otherwise +known under the<span class='pagenum'><a name="Page_283" id="Page_283">[283]</a></span> +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“—<i>i.e.</i>, the wood is not burned but heated in a retort. +The enquiries could be placed in two classes:</p> + +<div class="blockquot"><p>1. Those which aimed at making the pure, strong acid of +commerce.</p> + +<p>2. Those which sought information concerning a crude +coagulant (pyroligneous acid) on estates.</p></div> + +<p>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:</p> + +<div class="blockquot"><p>“Probably the most common enquiry encountered since +the rise in the price of acetic acid is concerned with the possibility +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:</p> + +<div class="blockquot"><p>“1. 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.</p> + +<p>“2. There would appear to be less valuable timber which +would be suitable for heating the retorts. Or, local coal might +be used.</p> + +<p>“3. Supplies of lime at reasonable rates are available, as the +limestone formation in the peninsula is quite considerable in +extent.</p> + +<p>“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 conditions, +supplies from England and parts of Europe would +be much cheaper than at current rates.</p> + +<p>“For the benefit of many readers perhaps a brief and nontechnical +description of the preparation of acetic acid would<span class='pagenum fsize100'><a name="Page_284" id="Page_284">[284]</a></span> +not be amiss, and would explain the necessity for the essentials +indicated above. In brief, the process is as follows:</p> + +<p>“(<i>a</i>) A suitable timber is heated in a closed retort. This +is termed ’dry distillation,’ and results eventually in the +carbonisation of the wood—<i>i.e.</i>, charcoal is obtained in the +retort.</p> + +<p>“(<i>b</i>) 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 (1) wood tar, (2) a watery liquor called +pyroligneous acid or crude wood vinegar.</p> + +<p>“(<i>c</i>) The pyroligneous acid is separated from the tar, and +again distilled to obtain the acetic acid present.</p> + +<p>“(<i>d</i>) This crude acid is steam-heated with milk of lime, which +fixes the acid, forming calcium acetate (or acetate of lime).</p> + +<p>“(<i>e</i>) 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.</p> + +<p>“(<i>f</i>) 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 earthenware +for the distillation.</p></div> + +<p>“Such is the process in outline, and it will be seen that no proposal +to manufacture <i>glacial acetic acid</i> on an estate could be +considered feasible, although it would not present any great +difficulty on a large scale and under skilled direction. Furthermore, +the cost of the plant would be far too great for any estate.”</p></div> + +<p>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.</p> + +<p>The pyroligneous acid obtained, is generally clear, after +nitration, and of a dark brown colour. It has a peculiar odour<span class='pagenum'><a name="Page_285" id="Page_285">[285]</a></span> +reminiscent of smoked sheet-rubber, or of creosotic substances +in general.</p> + +<p>Its acid content depends chiefly upon:</p> + +<div class="blockquot"><p>(<i>a</i>) The kind of timber heated in the retort.</p> + +<p>(<i>b</i>) The efficiency of the apparatus.</p> + +<p>(<i>c</i>) Condition of the timber as to moisture.</p> + +<p>(<i>d</i>) The temperature employed, and rate of working.</p> + +<p>(<i>e</i>) The point at which distillation ceases (<i>i.e.</i>, the duration of +interval between commencement of heating and cessation of +collection).</p></div> + +<p>Samples received from estates for testing purposes were found +to contain equivalents varying from 2 per cent. to 10 per cent. +of acetic acid.</p> + +<p>They were all suitable coagulants when used in quantity +calculated from the discovered acidity, but produced rubber +darker than ordinary when 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.</p> + +<p>This darkening in colour is to be ascribed to the presence of +traces of phenols,<a name="FNanchor_24_24" id="FNanchor_24_24"></a><a href="#Footnote_24_24" class="fnanchor">[24]</a> +which are stated to exert an effect upon the +rubber during and after vulcanisation.<a name="FNanchor_25_25" id="FNanchor_25_25"></a><a +href="#Footnote_25_25" class="fnanchor">[25]</a> This subject will be +discussed in <a href="#Ch17">another section</a>.</p> + +<div class="footnote"><p><a name="Footnote_24_24" id="Footnote_24_24"></a><a +href="#FNanchor_24_24"><span class="label">[24]</span></a> Whitby, <i>Journal Soc. Chem. Industry</i>, vol. xxxv., No. 9, 1916.</p></div> + +<div class="footnote"><p><a name="Footnote_25_25" id="Footnote_25_25"></a><a +href="#FNanchor_25_25"><span class="label">[25]</span></a> See also “Preparation and Vulcanisation of Plantation Rubber” +(Eaton, Grantham, and Day), Bulletin No. 27, F.M.S. Department of +Agriculture, April, 1918.</p></div> + +<p>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 demijohn +of 44 lbs.</p> + +<p><a name="Sec19_13" id="Sec19_13"></a><span class='pagenum'><a name="Page_286" id="Page_286">[286]</a></span></p><p><span +class="smcap">Smoked Water.</span>—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.</p> + +<p><a name="Sec19_14" id="Sec19_14"></a><span class="smcap">Chinese Vinegar.</span>—This agent was found to be a satisfactory +coagulant, and, <i>a priori</i>, there is no reason why it should not be +suitable, as it is essentially a dilute solution of acetic acid.</p> + +<p>The qualities sold were generally colourless, and were +probably the result of acetic fermentation of rice.</p> + +<p>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.</p> + +<p>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.</p> + +<p><a name="Sec19_15" id="Sec19_15"></a><span class="smcap">Sulphurous Acid.</span>—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, forming +an acid solution called sulphurous acid.</p> + +<p>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.</p> + +<p>In the event of sulphurous acid being used, it would be<span class='pagenum'><a name="Page_287" id="Page_287">[287]</a></span> +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 1 per cent. solution. The maximum quantity +possible for use is about 15 c.c. of a 1 per cent, solution, so that +great care would have to be exercised in avoiding an excess of +coagulant, otherwise coagulation would be effectually prevented.</p> + +<p>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.</p> + +<p><a name="Sec19_16" id="Sec19_16"></a><span class="smcap">Sugars.</span>—Coagulation may be effected by the addition of +small quantities of sugars.<a name="FNanchor_26_26" id="FNanchor_26_26"></a><a +href="#Footnote_26_26" class="fnanchor">[26]</a> 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:</p> + +<div class="blockquot"><p>(<i>a</i>) As a direct coagulant.</p> + +<p>(<i>b</i>) 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<span class='pagenum fsize100'><a name="Page_288" id="Page_288">[288]</a></span> +far as we know no practical application has been made of the +employment of sugars as coagulating agents.</p></div> + +<div class="footnote"><p><a name="Footnote_26_26" id="Footnote_26_26"></a><a +href="#FNanchor_26_26"><span class="label">[26]</span></a> “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.</p></div> + +<p><a name="Sec19_17" id="Sec19_17"></a><span class="smcap">Various Salts.</span>—Of experimental interest only it may be +recorded that coagulation has been effected by means of various +chemical “salts“—<i>e.g.</i>, 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 coagulation, +which will receive mention in the <a href="#Ch20">following chapter</a>.</p> + +<p>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.</p> + +<p><a name="Sec19_18" id="Sec19_18"></a><span class="smcap">Various Proprietary Compounds.</span>—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.</p> + +<p>As as instance of a substance which fell under both classifications +might be mentioned the case of “Coagulatex.” Pretentious +claims were made, and it was emphasised that the +liquid contained no <i>vegetable acids</i>. 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.”</p> + +<p>On analysis the liquid was found to consist mainly of sulphuric +acid, against the indiscriminate use of which warnings +have been given. Thus it was a dangerous substance for +common use.</p> + +<p>Furthermore, comparing the value with its sulphuric acid +content, it was found that the price required for “Coagulatex<span +class='pagenum'><a name="Page_289" id="Page_289">[289]</a></span>” +was roughly four times the contemporary cost of commercial +sulphuric acid in the Federated Malay States.</p> + +<p>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.</p> + +<p><a name="Sec19_19" id="Sec19_19"></a><span class="smcap">Carbonic Acid Gas, Carbon Dioxide.</span>—Now of only scientific +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 passing +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.</p> + +<p><a name="Sec19_20" id="Sec19_20"></a><span class="smcap">Alcohol.</span>—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.</p> + +<p>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 <a href="#Ch20">succeeding chapter</a>.</p> + +<p><a name="Sec19_21" id="Sec19_21"></a><span class="smcap">Vegetable Extracts.</span>—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 product +of tropical industry—the so-called “milk” (or water) +of ripe coconuts.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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 <a href="#Ch20">ensuing chapter</a>.</p> + + +<p class='pagenum'><a name="Page_290" id="Page_290">[290]</a></p> +<hr class="c25" /> +<h2><a name="Ch20" id="Ch20"></a>CHAPTER XX</h2> + +<h3><i>SPECIAL METHODS OF PREPARATION</i></h3> + + +<p>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>i.e.</i>, 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.</p> + +<p>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.</p> + +<p>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.</p> + +<p><a name="Sec20_1" id="Sec20_1"></a><span class="smcap">Da Costa Process.</span>—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. 1 product.</p> + +<p><a name="Sec20_2" id="Sec20_2"></a><span class="smcap">“Byrne Curing” Process.</span>—This is a process for treating +coagulum obtained by ordinary methods.</p> + +<p><span class='pagenum'><a name="Page_291" id="Page_291">[291]</a></span>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 produced +was in all respects equal to Fine Hard Para, and could +be shipped while still moist without detriment to the physical +qualities.</p> + +<p>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 prevent +leakage of the vapours, and a very dense smoke was +obtained.</p> + +<p>The furnaces were specially designed, and consisted essentially +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 (<i>a</i>) wood tar products, (<i>b</i>) 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 distributed +through perforations in the pipe.</p> + +<p>The coagulum usually remained under treatment in the shed +for three to four hours, and then was removed for ordinary +air-drying. 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.</p> + +<p><span class='pagenum'><a name="Page_292" id="Page_292">[292]</a></span>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.</p> + +<p>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.</p> + +<p>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 advantage +over ordinary methods.</p> + +<p><a name="Sec20_3" id="Sec20_3"></a><span class="smcap">Freezing Process.</span>—A patent was secured a few years ago +to cover a process whereby coagulation was effected by +refrigeration.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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.</p> + +<p><span class='pagenum'><a name="Page_293" id="Page_293">[293]</a></span>Finally, +it has not been found<a name="FNanchor_27_27" id="FNanchor_27_27"></a><a +href="#Footnote_27_27" class="fnanchor">[27]</a> that any advantage in the final +physical qualities of the rubber is obtained by the employment +of this process.</p> + +<div class="footnote"><p><a name="Footnote_27_27" id="Footnote_27_27"></a><a +href="#FNanchor_27_27"><span class="label">[27]</span></a> “Preparation and Vulcanisation of Plantation Rubber” (Eaton, +Grantham, and Day), Bulletin No. 27, F.M.S. Department of Agriculture.</p></div> + +<p><a name="Sec20_4" id="Sec20_4"></a><span class="smcap">Wickham Process.</span>—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.</p> + +<p>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 +<i>in situ</i>, formed a mass corresponding to “Fine Hard.”</p> + +<p>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.</p> + +<p><a name="Sec20_5" id="Sec20_5"></a><span class="smcap">Derry Process.</span>—The invention of Mr. R. Derry, 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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>The trays of latex were situated at the lower end of the +machine which 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.</p> + +<p>Smoke was generated by combustion of wood in an external +structure, was brought into the chamber by a wide duct, and<span class='pagenum'><a name="Page_294" id="Page_294">[294]</a></span> +was then distributed below the belt by means of perforated +pipes.</p> + +<p>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 (1) 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.</p> + +<p>It will be clear that success could only be obtained by a +careful adjustment of all these factors. The latex must, necessarily, +be of a fairly rich consistency (at least 2<span class="enum">1</span>⁄<span class="denom">2</span> lbs. 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.</p> + +<p>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.</p> + +<p>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 (1) 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.</p> + +<p><a name="Sec20_6" id="Sec20_6"></a><span class="smcap">Spontaneous Coagulation.</span>—All readers will be aware +of the phenomenon of the curdling or souring of milk. The +behaviour of <i>Hevea</i> 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.</p> + +<p><a name="Sec20_7" id="Sec20_7"></a>It is sometimes found, before the latex reaches the store, that +it may exhibit one of various stages of premature (spontaneous) +coagulation:</p> + +<div class="blockquot"><p><span class='pagenum fsize100'><a name="Page_295" id="Page_295">[295]</a></span>(<i>a</i>) +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).</p> + +<p>(<i>b</i>) In a later stage these particles coalesce to form larger +“flocks” (macroscopic coagulation).</p> + +<p>(<i>c</i>) The whole, or practically the whole, of the latex may have +coagulated, forming one mass of rubber with a milky residual +serum.</p></div> + +<p>Passing from this aspect of the question, it may be noted as +peculiar facts that:</p> + +<div class="blockquot"><p>(1) A shallow layer of latex is less likely to coagulate spontaneously +(<i>i.e.</i>, without the addition of a coagulant) than a +deeper volume.</p> + +<p>(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.</p> + +<p>(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.</p> + +<p>(4) On testing the surface film of both the shallow layer and +the deeper volume, it will be found to be <i>alkaline</i> in character; +whilst the lower liquid surrounding the main portion of the +coagulum in the deeper volume of latex is of an <i>acid</i> nature.</p></div> + +<p><a name="Sec20_8" id="Sec20_8"></a>These observed facts are sufficient to indicate that there are +apparently <i>two distinct types of spontaneous coagulation</i>, 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:</p> + +<div class="blockquot"><p><a name="Sec20_9" id="Sec20_9"></a>(<i>a</i>) <i>In contact with air (aerobic)</i>: incomplete spontaneous +coagulation, accompanied by yellowish slime, offensive in +odour and alkaline in character.</p> + +<p><a name="Sec20_10" id="Sec20_10"></a>(<i>b</i>) <i>Out of contact with air (Anaerobic)</i>: Practically or wholly +complete. There is no offensive odour under normal conditions +and the serum is acid in character.</p></div> + +<p><a name="Sec20_11" id="Sec20_11"></a><span class='pagenum'><a name="Page_296" id="Page_296">[296]</a></span>It +is concluded<a name="FNanchor_28_28" id="FNanchor_28_28"></a><a href="#Footnote_28_28" +class="fnanchor">[28]</a> 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 <i>prevent</i> 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.</p> + +<div class="footnote"><p><a name="Footnote_28_28" id="Footnote_28_28"></a><a +href="#FNanchor_28_28"><span class="label">[28]</span></a> “Preparation and Vulcanisation of Plantation Rubber” (Eaton, +Grantham, and Day), Bulletin No. 27, F.M.S. Department of Agriculture, +1918; “De la Coagulation naturelle du Latex d’Hevea +Brasiliensis” (Denier and Vernet), <i>Comptes Rendus l’Académie des +Sciences</i>, No. 3, July, 1917.</p></div> + +<p><a name="Sec20_12" id="Sec20_12"></a>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.</p> + +<p><a name="Sec20_13" id="Sec20_13"></a>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.</p> + +<p>Under the patent held the coagulum may be prepared either +for crepe-making, or for sheets by a modification of the tank.</p> + +<p>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.</p> + +<p>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.</p> + +<p>To prevent the oxidation of the rubber in actual practice, +the freshly prepared crepe is soaked in a solution of sodium<span class='pagenum'><a name="Page_297" id="Page_297">[297]</a></span> +bisulphite before hanging to dry. The resulting colour of +the rubber is quite good.</p> + +<p>It was shown by Eaton and Grantham that anaerobic coagulation +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.</p> + +<p><a name="Sec20_14" id="Sec20_14"></a>They found further that, by the addition of small quantities +of sugars, coagulation under both aerobic and anaerobic conditions +was improved. The conclusion formed was that the +addition of sugars created a medium favourable to the development +of anaerobic organisms and unfavourable to those which +cause decomposition of the natural nitrogenous constituents +of latex.</p> + +<p>This work was confirmed by Gorter and Swart,<a name="FNanchor_29_29" +id="FNanchor_29_29"></a><a href="#Footnote_29_29" class="fnanchor">[29]</a> who attributed +the action to the conversion of sugar to lactic, acetic, +and succinic acids by fermentation.</p> + +<div class="footnote"><p><a name="Footnote_29_29" id="Footnote_29_29"></a><a +href="#FNanchor_29_29"><span class="label">[29]</span></a> Gorter and Swart, Bulletin No. 6, West Java Station.</p></div> + +<p>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—<i>e.g.</i>, 1 gramme per litre of latex (1:1,000).</p> + +<p><a name="Sec20_15" id="Sec20_15"></a>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<a name="FNanchor_30_30" +id="FNanchor_30_30"></a><a href="#Footnote_30_30" class="fnanchor">[30]</a> +showed that the addition of 0·5 to 1 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.</p> + +<div class="footnote"><p><a name="Footnote_30_30" id="Footnote_30_30"></a><a +href="#FNanchor_30_30"><span class="label">[30]</span></a> “Archief voor de Rubbercultuur,” Nederlands Indies, 1920, +4, 273.</p></div> + +<p>On page 308 of the same publication, experiments on the +effect of sugars are described, in connection with <i>aerobic</i> +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<span class='pagenum'><a name="Page_298" id="Page_298">[298]</a></span> +heavy tapping causes a diminution in the latex of those substances +which act in some way as accelerating agents in +coagulation—<i>e.g.</i>, sugars. The smaller the proportion of these +substances, the slower and less complete is natural (spontaneous) +coagulation.</p> + +<p><a name="Sec20_16" id="Sec20_16"></a><span class="smcap">Ilcken-Down Process.</span>—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.</p> + +<p>It is a coagulating process, and, in the original specification, +employed as agents a mixture of alcohol (in the form of methylated +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.</p> + +<p>Later modifications covered the addition of a small quantity of +glycerine; or, failing supplies of that substance, coconut oil.</p> + +<p>Many advantages are claimed for the process, but most of +them cannot be substantiated. The two chief claims are:</p> + +<div class="blockquot"><p>1. The production of a uniform standard of rubber.</p> + +<p>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.</p></div> + +<p>Regarding the first of these claims, it has been shown<a name="FNanchor_31_31" +id="FNanchor_31_31"></a><a href="#Footnote_31_31" class="fnanchor">[31]</a> 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.</p> + +<div class="footnote"><p><a name="Footnote_31_31" id="Footnote_31_31"></a><a +href="#FNanchor_31_31"><span class="label">[31]</span></a> “Preparation and Vulcanisation of Plantation Rubber” +(Eaton, Grantham, and Day), Bulletin No. 27, F.M.S. Department +of Agriculture, 1918.</p></div> + +<p>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.</p> + +<p><span class='pagenum'><a name="Page_299" id="Page_299">[299]</a></span>Private +laboratory investigations led to a similar verdict, and +Eaton<a name="FNanchor_32_32" id="FNanchor_32_32"></a><a href="#Footnote_32_32" +class="fnanchor">[32]</a> records a confirmatory finding. More recently the +claims made for the process were investigated in Java<a name="FNanchor_33_33" +id="FNanchor_33_33"></a><a href="#Footnote_33_33" class="fnanchor">[33]</a> under +varying conditions. Three series of experiments were made:</p> + +<div class="footnote"><p><a name="Footnote_32_32" id="Footnote_32_32"></a><a +href="#FNanchor_32_32"><span class="label">[32]</span></a> <i>Ibid.</i></p></div> + +<div class="footnote"><p><a name="Footnote_33_33" id="Footnote_33_33"></a><a +href="#FNanchor_33_33"><span class="label">[33]</span></a> “Archief voor de Rubbercultuur” (De Vries and Spoon), Central +Rubber Station, Java, May, 1921.</p></div> + +<div class="blockquot"><p>(1) During the rainy monsoon and at a height of 1,800 feet.</p> + +<p>(2) During the dry monsoon on a low-country estate.</p> + +<p>(3) In the experimental gardens at Buitenzorg during bright +sunny weather and the most favourable conditions.</p></div> + +<p>The agents used were (<i>a</i>) a mixture of alcohol and fusel oil, +(<i>b</i>) alcohol and petrol (benzene).</p> + +<p>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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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 <a href="#Sec20_6">previous section</a> on “Spontaneous +Coagulation,” the reader will perceive that results equal to +those obtained by the Ilcken-Down process can be obtained +<i>without</i> the necessity of using such agents as alcohol, petrol, or +fusel oil.</p> + +<p><a name="Sec20_17" id="Sec20_17"></a><span class="smcap">Slab Rubber.</span>—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.</p> + +<p>The coagulum, when removed from the serum, is subjected +to comparatively slight pressure, and the “slab” thus made is<span +class='pagenum'><a name="Page_300" id="Page_300">[300]</a></span> +either placed to air-dry at once, or may be subject to treatment +in other liquids before drying.</p> + +<p>The rubber is not allowed to remain until wholly dry, but is +shipped while still containing an appreciable percentage of +enclosed moisture.</p> + +<p>It is claimed<a name="FNanchor_34_34" id="FNanchor_34_34"></a><a href="#Footnote_34_34" +class="fnanchor">[34]</a> that the production of “slab” rubber by +standardised methods eliminates to a great degree the variability +which at present characterises plantation rubber, and +that a fast-curing medium is obtained. These claims will be +discussed in <a href="#Part6">later chapters</a> dealing with the vulcanisation of +rubber, and demand no notice in this section.</p> + +<div class="footnote"><p><a name="Footnote_34_34" id="Footnote_34_34"></a><a +href="#FNanchor_34_34"><span class="label">[34]</span></a> “Preparation and Vulcanisation of Plantation Rubber” +(Eaton, Grantham, and Day), Bulletin No. 27, F.M.S. Department +of Agriculture, 1918.</p></div> + +<p>From the producers’ point of view, it may be noted that the +preparation of slab rubber is a simple process, but not altogether +as pleasant probably as might be desired, when undertaken +in crude form.</p> + +<p>The appearance of the partially dry slabs is unattractive, +but that does not signify if the quality of the vulcanised +product satisfies requirements.</p> + +<p>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.</p> + +<p>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.</p> + +<p class='pagenum'><a name="Page_301" id="Page_301">[301]</a></p> + +<hr class="c25" /> +<h2><a name="Part6" id="Part6"></a>PART VI</h2> + +<h3>VULCANISATION</h3> + +<h4>(<span class="smcap">By Dr. H. P. Stevens</span>)</h4> + +<h2><a name="Ch21" id="Ch21"></a>CHAPTER XXI</h2> + +<h3><i>INTRODUCTORY DEALING WITH TREATMENT +AND VULCANISATION</i></h3> + + +<p>In the foregoing chapters the methods of treating latex, +coagulating, rolling and curing, or drying, have been described +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.</p> + +<p><a name="Sec21_1" id="Sec21_1"></a>Raw rubber, as produced on the plantations, is almost invariably +subjected to the process of vulcanisation in the production +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<span class='pagenum'><a name="Page_302" id="Page_302">[302]</a></span> +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.”</p> + +<p>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.</p> + +<p>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.</p> + +<p>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—<i>e.g.</i>, coagulation with acetic acid—does not +yield the hardest and toughest rubber.</p> + +<p><a name="Sec21_2" id="Sec21_2"></a>Hardness and toughness are actual drawbacks in the utilisation +of rubber which is required for vulcanising. When the +output of plantation rubber began to increase and to displace +the inferior wild sorts, manufacturers complained of the increased +power consumption of their machines. The power<span class='pagenum'><a name="Page_303" id="Page_303">[303]</a></span> +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.<a name="FNanchor_35_35" id="FNanchor_35_35"></a><a href="#Footnote_35_35" +class="fnanchor">[35]</a> 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 by 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<span class='pagenum'><a name="Page_304" id="Page_304">[304]</a></span> +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.</p> + +<div class="footnote"><p><a name="Footnote_35_35" id="Footnote_35_35"></a><a +href="#FNanchor_35_35"><span class="label">[35]</span></a> For instance, “India-Rubber and its Manufacture,” by H. L. +Terry.</p></div> + +<p><a name="Sec21_3" id="Sec21_3"></a>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 mastication +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 crepeing +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 expenditure +of power, <i>caeteris paribus</i>, the greater the working effect +on the rubber. Although the manufacturers possessed a relatively +soft rubber in the form of washed Fine Para, it was customary +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 difficult +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 something +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.</p> + +<p><a name="Sec21_4" id="Sec21_4"></a>Having incorporated sulphur and other ingredients, the +plastic mass is sheeted and run between layers of calico to prevent +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<span class='pagenum'><a name="Page_305" id="Page_305">[305]</a></span> +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 manufacture +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 plasticity +and power to absorb finely divided mineral matter will +be discussed in a <a href="#Ch22">later chapter</a>. 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.</p> + +<p>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, <i>e.g.</i>, 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.</p> + +<p>For other purposes the rubber is swollen in a solvent, such as<span class='pagenum'><a name="Page_306" id="Page_306">[306]</a></span> +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.</p> + +<p>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.<a name="FNanchor_36_36" +id="FNanchor_36_36"></a><a href="#Footnote_36_36" class="fnanchor">[36]</a> +But even the best grades give a vulcanised product which<span class='pagenum'><a name="Page_307" id="Page_307">[307]</a></span> +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.”<a +name="FNanchor_37_37" id="FNanchor_37_37"></a><a href="#Footnote_37_37" class="fnanchor">[37]</a> +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.</p> + +<div class="footnote"><p><a name="Footnote_36_36" id="Footnote_36_36"></a><a +href="#FNanchor_36_36"><span class="label">[36]</span></a> 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.</p></div> + +<div class="footnote"><p><a name="Footnote_37_37" id="Footnote_37_37"></a><a +href="#FNanchor_37_37"><span class="label">[37]</span></a> The terms “curing” +and “vulcanising” are generally employed +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.</p></div> + +<p>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 “overvulcanising,” +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 withstand +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.</p> + +<p>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<span class='pagenum'><a name="Page_308" id="Page_308">[308]</a></span> +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 manufacturer. +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 whenever +possible, so that the manufacturer may identify the rubber +he purchases. If found satisfactory, he can then secure further +supplies from the same estate.</p> + +<p class='pagenum'><a name="Page_309" id="Page_309">[309]</a></p> + +<hr class="c25" /> +<h2><a name="Ch22" id="Ch22"></a>CHAPTER XXII</h2> + +<h3><i>TESTING OF PLANTATION RUBBER</i></h3> + + +<p>This subject may be subdivided into (<i>a</i>) Tests on the raw +rubber; (<i>b</i>) tests on the vulcanised rubber.</p> + +<p><a name="Sec22_1" id="Sec22_1"></a><a name="Sec22_2" id="Sec22_2"></a>The tests on the raw rubber may be carried out (1) on the +sample of sheet and crepe as received. For this purpose the +rubber is 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. <a name="Sec22_3" id="Sec22_3"></a>(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.<a name="FNanchor_38_38" id="FNanchor_38_38"></a><a +href="#Footnote_38_38" class="fnanchor">[38]</a> 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.</p> + +<div class="footnote"><p><a name="Footnote_38_38" id="Footnote_38_38"></a><a +href="#FNanchor_38_38"><span class="label">[38]</span></a> Bulletin Rubber Growers’ Association, January, 1921, p. 43; +August, 1921, p. 340.</p></div> + +<p>The testing of vulcanised rubber has been treated in such<span class='pagenum'><a name="Page_310" id="Page_310">[310]</a></span> +detail in the recent works of Whitby<a name="FNanchor_39_39" +id="FNanchor_39_39"></a><a href="#Footnote_39_39" class="fnanchor">[39]</a> +and De Vries<a name="FNanchor_40_40" id="FNanchor_40_40"></a><a href="#Footnote_40_40" class="fnanchor">[40]</a> that a +few special points only will be dealt with here. The preparation +of samples for testing involves first the sheeting of the +mixture of rubber, sulphur, and other ingredients, if any. The +sheets may be 1 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 aluminium +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.<span class='pagenum'><a name="Page_311" id="Page_311">[311]</a></span> +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.</p> + +<div class="footnote"><p><a name="Footnote_39_39" id="Footnote_39_39"></a><a +href="#FNanchor_39_39"><span class="label">[39]</span></a> “Plantation Rubber and the Testing of Rubber.”</p></div> + +<div class="footnote"><p><a name="Footnote_40_40" id="Footnote_40_40"></a><a +href="#FNanchor_40_40"><span class="label">[40]</span></a> “Estate Rubber.”</p></div> + +<p>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 micrometer. +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.</p> + +<p><a name="Sec22_5" id="Sec22_5"></a><a name="Sec22_6" id="Sec22_6"></a>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—<i>e.g.</i>, 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.</p> + +<p><a name="Sec22_4" id="Sec22_4"></a><a name="Sec22_7" id="Sec22_7"></a>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<span +class='pagenum'><a name="Page_312" id="Page_312">[312]</a></span> +the original length reckoned either as unity or as 100 units). +Simultaneously a load-stretch curve is recorded on an autographic +attachment. The type of curve varies with (1) state +of cure, or degree to which the rubber is vulcanised; (2) proportion +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.</p> + +<p>The peculiar type of the curves has long been a subject of +comment and speculation. Special properties have been attributed +to the “slope” or inclination of the upper and approximately +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.<a name="FNanchor_41_41" id="FNanchor_41_41"></a><a +href="#Footnote_41_41" class="fnanchor">[41]</a> 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.<a name="FNanchor_42_42" +id="FNanchor_42_42"></a><a href="#Footnote_42_42" class="fnanchor">[42]</a> +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 hyperbolæ.</p> + +<div class="footnote"><p><a name="Footnote_41_41" id="Footnote_41_41"></a><a +href="#FNanchor_41_41"><span class="label">[41]</span></a> Bulletin R.G.A., October, 1921, p. 397.</p></div> + +<div class="footnote"><p><a name="Footnote_42_42" id="Footnote_42_42"></a><a +href="#FNanchor_42_42"><span class="label">[42]</span></a> <i>Hatschek Journal Soc. Chem. Ind.</i> 1921; <i>Trans.</i>, p. 251.</p></div> + + +<p class='pagenum'><a name="Page_313" id="Page_313">[313]</a></p> +<hr class="c25" /> +<h2><a name="Ch23" id="Ch23"></a>CHAPTER XXIII</h2> + +<h3><i>THE PROPERTIES OF RUBBER</i></h3> + + +<p>This section, like the last, is divisible into two subsections. +The first deals with <a href="#Sec23_1">raw rubber</a>, the second with <a href="#Sec23_3">vulcanised +rubber</a>.</p> + +<p><a name="Sec23_1" id="Sec23_1"></a><a name="Sec23_2" id="Sec23_2"></a>We have already explained that, until recently, rubber was not +used in the unvulcanised 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. elongation. +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.<a name="FNanchor_43_43" +id="FNanchor_43_43"></a><a href="#Footnote_43_43" class="fnanchor">[43]</a> 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, unfortunately, +these properties do not lend themselves to simple<span class='pagenum'><a name="Page_314" id="Page_314">[314]</a></span> +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.</p> + +<div class="footnote"><p><a name="Footnote_43_43" id="Footnote_43_43"></a><a +href="#FNanchor_43_43"><span class="label">[43]</span></a> <i>Journal Soc. Chem. Ind.</i>, 1916, p. 872.</p></div> + +<p>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 consideration +the diminution in sectional area of the test piece +during stretching, it will be seen that crepe and sheet rubber +have compensating properties.</p> + +<p>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 uncompounded +rubber. Hence the reduction of sectional area on +stretching bears a simple relationship to the amount of stretching. +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>i.e.</i>, length at break, taking the original length = 1), +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 +<i>moment of rupture</i> of the test piece. Adopting this formula, +we obtain for crepe—</p> + +<table style="width: 50%;" summary="Formula p314-1"> + +<tr> +<td class="center" style="width: 25%;"><i>Tensile<br />Strength.</i></td> +<td class="padr"> </td> +<td class="center" style="width: 25%;"><i>Final Length—i.e.,<br />Elongation + 1.</i></td> +<td class="padr"> </td> +<td class="center" style="width: 25%;"><i>Tensile<br />Product.</i></td> +</tr> + +<tr> +<td class="center">30</td> +<td class="center">×</td> +<td class="center">4</td> +<td class="center">=</td> +<td class="center">120</td> +</tr> + +</table> + +<p>and for smoked sheet</p> + +<table style="width: 50%;" summary="Formula p314-2"> + +<tr> +<td class="center" style="width: 25%;">15</td> +<td class="center">×</td> +<td class="center" style="width: 25%;">8</td> +<td class="center">=</td> +<td class="center" style="width: 25%;">120</td> +</tr> + +</table> + +<p>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<span class='pagenum'><a name="Page_315" id="Page_315">[315]</a></span> +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.<a name="FNanchor_44_44" +id="FNanchor_44_44"></a><a href="#Footnote_44_44" class="fnanchor">[44]</a></p> + +<div class="footnote"><p><a name="Footnote_44_44" id="Footnote_44_44"></a><a +href="#FNanchor_44_44"><span class="label">[44]</span></a> Bulletin R.G.A., February, 1922, p. 64.</p></div> + +<p>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.</p> + +<p>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.</p> + +<p><a name="Sec23_3" id="Sec23_3"></a><a name="Sec23_4" id="Sec23_4"></a><span +class="smcap">Vulcanised Rubber.</span>—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>i.e.</i>, 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<span class='pagenum'><a name="Page_316" id="Page_316">[316]</a></span> +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.</p> + +<p><a name="Sec23_5" id="Sec23_5"></a><span class="smcap">Crepe Rubber.</span>—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.</p> + +<p>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.</p> + +<p><span class="smcap">Sheet Rubber.</span>—The commonest defect is mould.<a +name="FNanchor_45_45" id="FNanchor_45_45"></a><a href="#Footnote_45_45" class="fnanchor">[45]</a> This is +usually of a light surface type, easily brushed off, and numbers of +vulcanising tests failed to trace any reduction in rate of vulcanising +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<span +class='pagenum'><a name="Page_317" id="Page_317">[317]</a></span> +of mould. The sheet feels damp and “heavy” or flabby, +and contains an excess of moisture; sometimes a moist exudation +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.</p> + +<div class="footnote"><p><a name="Footnote_45_45" id="Footnote_45_45"></a><a +href="#FNanchor_45_45"><span class="label">[45]</span></a> Bulletin R.G.A., February, 1921, p. 97; April, 1921, p. 190; June, +1921, p. 243; November, 1921, p. 472.</p></div> + +<p>“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.</p> + +<p>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.</p> + +<p>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<a name="FNanchor_46_46" +id="FNanchor_46_46"></a><a href="#Footnote_46_46" class="fnanchor">[46]</a> +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.</p> + +<div class="footnote"><p><a name="Footnote_46_46" id="Footnote_46_46"></a><a +href="#FNanchor_46_46"><span class="label">[46]</span></a> Bulletin R.G.A., December, 1921, p. 521.</p></div> + +<p><a name="Sec23_6" id="Sec23_6"></a><span class="smcap">Variation in Physical Properties.</span>—A very large number +of tests on vulcanised specimens of plantation rubber have been<span class='pagenum'><a name="Page_318" id="Page_318">[318]</a></span> +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 exceptionally +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 excessively +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.<a name="FNanchor_47_47" id="FNanchor_47_47"></a><a +href="#Footnote_47_47" class="fnanchor">[47]</a> 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.</p> + +<div class="footnote"><p><a name="Footnote_47_47" id="Footnote_47_47"></a><a +href="#FNanchor_47_47"><span class="label">[47]</span></a> “Estate Rubber,” p. 466.</p></div> + +<p><a name="Sec23_7" id="Sec23_7"></a><span class="smcap">The Rate of Cure or Rate of Vulcanisation</span> 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,<span class='pagenum'><a name="Page_319" id="Page_319">[319]</a></span> +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.</p> + +<p>As a measure of rate of cure we may take the actual measurements +made on the record.<a name="FNanchor_48_48" id="FNanchor_48_48"></a><a +href="#Footnote_48_48" class="fnanchor">[48]</a> 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 elongation +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.”</p> + +<div class="footnote"><p><a name="Footnote_48_48" id="Footnote_48_48"></a><a +href="#FNanchor_48_48"><span class="label">[48]</span></a> Bulletin R.G.A., June, 1921, p. 246.</p></div> + +<p>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.</p> + +<p>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 vulcanisation +has been in progress (under standard conditions of<span class='pagenum'><a name="Page_320" id="Page_320">[320]</a></span> +temperature, etc.), and, therefore, the coefficient is a measure +of the rate of cure.</p> + +<p>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.<a name="FNanchor_49_49" id="FNanchor_49_49"></a><a href="#Footnote_49_49" +class="fnanchor">[49]</a> 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 corresponds +to the elongation of 850 per cent. at a load of 130 kilos.</p> + +<div class="footnote"><p><a name="Footnote_49_49" id="Footnote_49_49"></a><a +href="#FNanchor_49_49"><span class="label">[49]</span></a> Bulletin R.G.A., June, 1921, p. 246, October, 1921, p. 398.</p></div> + +<p>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 elongation +of 850 per cent., whereas the standard takes three hours, +the rate of cure of the sample will be <span class="enum">3</span>⁄<span +class="denom">2</span> of standard or 150.<a name="FNanchor_50_50" +id="FNanchor_50_50"></a><a href="#Footnote_50_50" class="fnanchor">[50]</a></p> + +<div class="footnote"><p><a name="Footnote_50_50" id="Footnote_50_50"></a><a +href="#FNanchor_50_50"><span class="label">[50]</span></a> <i>Journal Soc. Chem. Ind.</i>, 1918, p. 280.</p></div> + +<p>As stated, the coefficient is approximately directly proportional +to the time of cure; it is also independent of the proportion +of sulphur, if in fair excess, and in the presence of inert +ingredients. It is also independent of the amount of mastication<span class='pagenum'><a name="Page_321" id="Page_321">[321]</a></span> +given 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 9:1 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 containing +litharge, whereas it shows no such defect when compounded +with sulphur only.<a name="FNanchor_51_51" id="FNanchor_51_51"></a><a +href="#Footnote_51_51" class="fnanchor">[51]</a> 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 conditions, +without corresponding alteration in the state of cure.<a name="FNanchor_52_52" +id="FNanchor_52_52"></a><a href="#Footnote_52_52" class="fnanchor">[52]</a></p> + +<div class="footnote"><p><a name="Footnote_51_51" id="Footnote_51_51"></a><a +href="#FNanchor_51_51"><span class="label">[51]</span></a> <i>Journal Soc. Chem. Ind.</i>, 1916, p. 874.</p></div> + +<div class="footnote"><p><a name="Footnote_52_52" id="Footnote_52_52"></a><a +href="#FNanchor_52_52"><span class="label">[52]</span></a> <i>Ibid.</i>, 1915, p. 524.</p></div> + +<p><a name="Sec23_8" id="Sec23_8"></a><span class='pagenum'><a name="Page_322" id="Page_322">[322]</a></span><span +class="smcap">Influence of Various Factors in Raw Rubber Preparation +on the “Rate of Cure,” or “Rate of Vulcanisation.”</span>—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 substances +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. Moreover, +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.<a name="FNanchor_53_53" id="FNanchor_53_53"></a><a +href="#Footnote_53_53" class="fnanchor">[53]</a> Also, the crude bases isolated +from fast vulcanising rubber have the power of increasing +the rate of vulcanisation when added to ordinary slow vulcanising +rubber.<a name="FNanchor_54_54" id="FNanchor_54_54"></a><a href="#Footnote_54_54" class="fnanchor">[54]</a></p> + +<div class="footnote"><p><a name="Footnote_53_53" id="Footnote_53_53"></a><a +href="#FNanchor_53_53"><span class="label">[53]</span></a> Eaton and Co-workers: See Bulletin No. 27, F.M.S. Department +of Agriculture.</p></div> + +<div class="footnote"><p><a name="Footnote_54_54" id="Footnote_54_54"></a><a +href="#FNanchor_54_54"><span class="label">[54]</span></a> <i>Journal Soc. Chem. Ind.</i>, 1917, p. 365.</p></div> + +<p>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<span class='pagenum'><a name="Page_323" id="Page_323">[323]</a></span> +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.</p> + +<p>As regards practical results, it follows that the rate of vulcanisation +(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 conditions. +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.</p> + +<p>Among other factors controlling the rate of cure, special +mention should be made of the nature and amount of coagulants. +Weak “organic” acids, such as acetic, lactic, tartaric, +etc., used in the minimal proportions (1 to 1,200 of standardised +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 (1 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).<a +name="FNanchor_55_55" id="FNanchor_55_55"></a><a href="#Footnote_55_55" class="fnanchor">[55]</a></p> + +<div class="footnote"><p><a name="Footnote_55_55" id="Footnote_55_55"></a><a +href="#FNanchor_55_55"><span class="label">[55]</span></a> Bulletin R.G.A., July, 1919, p. 39; September, 1920, p. 343; +November, 1920, p. 433; October, 1921, p. 393; March, 1922, p. 134.</p></div> + +<p><a name="Sec23_9" id="Sec23_9"></a><span class="smcap">Other Types of Plantation Rubber.</span>—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<span class='pagenum'><a name="Page_324" id="Page_324">[324]</a></span> +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 preparation +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 produced +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 experiments +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.</p> + +<p>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 penetrate +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<span class='pagenum'><a name="Page_325" id="Page_325">[325]</a></span> +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.<a name="FNanchor_56_56" id="FNanchor_56_56"></a><a +href="#Footnote_56_56" class="fnanchor">[56]</a> The rate of cure depends on the functions +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.<a name="FNanchor_57_57" id="FNanchor_57_57"></a><a +href="#Footnote_57_57" class="fnanchor">[57]</a> 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.</p> + +<div class="footnote"><p><a name="Footnote_56_56" id="Footnote_56_56"></a><a +href="#FNanchor_56_56"><span class="label">[56]</span></a> Bulletin R.G.A., January, 1920, p. 6; January, 1921, p. 47.</p></div> + +<div class="footnote"><p><a name="Footnote_57_57" id="Footnote_57_57"></a><a +href="#FNanchor_57_57"><span class="label">[57]</span></a> <i>Ibid.</i>, January, 1920, p. 68.</p></div> + +<p>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.</p> + +<p><a name="Sec23_10" id="Sec23_10"></a>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 manufacturers +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, however, +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<span class='pagenum'><a name="Page_326" id="Page_326">[326]</a></span> +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 unexpected.<a +name="FNanchor_58_58" id="FNanchor_58_58"></a><a href="#Footnote_58_58" class="fnanchor">[58]</a> +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 will 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 Brazilian +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.</p> + +<div class="footnote"><p><a name="Footnote_58_58" id="Footnote_58_58"></a><a +href="#FNanchor_58_58"><span class="label">[58]</span></a> Bulletin R.G.A., September, 1920, p. 347.</p></div> + + +<p class='pagenum'><a name="Page_327" id="Page_327">[327]</a></p> +<hr class="c25" /> +<h2><a name="INDEX" id="INDEX"></a>INDEX</h2> + +<table summary="Index"> + +<tr> +<td class="left">Acetic acid,</td> +<td class="right"><a href="#Page_74">74</a>, <a href="#Page_279">279</a></td> +</tr> + +<tr> +<td class="left">Acid, acetic,</td> +<td class="right"><a href="#Page_74">74</a>, <a href="#Page_279">279</a></td> +</tr> + +<tr> +<td class="left">—, carbonic, gas,</td> +<td class="right"><a href="#Page_289">289</a></td> +</tr> + +<tr> +<td class="left">—, formic,</td> +<td class="right"><a href="#Page_279">279</a></td> +</tr> + +<tr> +<td class="left">—, hydrochloric,</td> +<td class="right"><a href="#Page_282">282</a></td> +</tr> + +<tr> +<td class="left">—, hydrofluoric,</td> +<td class="right"><a href="#Page_282">282</a></td> +</tr> + +<tr> +<td class="left">—, mixing, with latex,</td> +<td class="right"><a href="#Page_79">79</a></td> +</tr> + +<tr> +<td class="left">—, nitric,</td> +<td class="right"><a href="#Page_282">282</a></td> +</tr> + +<tr> +<td class="left">—, oxalic,</td> +<td class="right"><a href="#Page_279">279</a></td> +</tr> + +<tr> +<td class="left">—, pyroligneous,</td> +<td class="right"><a href="#Page_282">282</a></td> +</tr> + +<tr> +<td class="left">—, quantity of,</td> +<td class="right"><a href="#Page_76">76</a></td> +</tr> + +<tr> +<td class="left">—, sulphuric,</td> +<td class="right"><a href="#Page_279">279</a>, <a href="#Page_286">286</a></td> +</tr> + +<tr> +<td class="left">Acids for coagulation, effect of, on rate of cure,</td> +<td class="right"><a href="#Page_323">323</a></td> +</tr> + +<tr> +<td class="left">—, quantities necessary for modern requirements,</td> +<td class="right"><a href="#Page_78">78</a></td> +</tr> + +<tr> +<td class="left">Air-drying, aids to normal,</td> +<td class="right"><a href="#Page_143">143</a></td> +</tr> + +<tr> +<td class="left">—, of crepe, rate of,</td> +<td class="right"><a href="#Page_138">138</a></td> +</tr> + +<tr> +<td class="left">—, progress of,</td> +<td class="right"><a href="#Page_140">140</a></td> +</tr> + +<tr> +<td class="left">Alcohol, coagulation with,</td> +<td class="right"><a href="#Page_289">289</a></td> +</tr> + +<tr> +<td class="left">Alum, coagulation with,</td> +<td class="right"><a href="#Page_282">282</a></td> +</tr> + +<tr> +<td class="left">Anti-coagulant for transport,</td> +<td class="right"><a href="#Page_61">61</a></td> +</tr> + +<tr> +<td class="left">Anti-coagulants,</td> +<td class="right"><a href="#Page_46">46</a></td> +</tr> + +<tr> +<td class="left">Artificial driers,</td> +<td class="right"><a href="#Page_133">133</a>, <a href="#Page_148">148</a></td> +</tr> + +<tr> +<td class="left">Ash on sheet,</td> +<td class="right"><a href="#Page_276">276</a></td> +</tr> + +<tr> +<td class="left">Assembling cases for shipment,</td> +<td class="right"><a href="#Page_156">156</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">Bags for packing,</td> +<td class="right"><a href="#Page_154">154</a></td> +</tr> + +<tr> +<td class="left">Bakau,</td> +<td class="right"><a href="#Page_147">147</a></td> +</tr> + +<tr> +<td class="left">Bales for packing,</td> +<td class="right"><a href="#Page_154">154</a></td> +</tr> + +<tr> +<td class="left">Bark in crepe,</td> +<td class="right"><a href="#Page_232">232</a></td> +</tr> + +<tr> +<td class="left">— — shavings,</td> +<td class="right"><a href="#Page_56">56</a>, <a href="#Page_123">123</a></td> +</tr> + +<tr> +<td class="left">— — sheet,</td> +<td class="right"><a href="#Page_276">276</a></td> +</tr> + +<tr> +<td class="left">Bases in vulcanised rubber,</td> +<td class="right"><a href="#Page_322">322</a></td> +</tr> + +<tr> +<td class="left">Basket plants,</td> +<td class="right"><a href="#Page_10">10</a></td> +</tr> + +<tr> +<td class="left">Blanket crepe, properties of,</td> +<td class="right"><a href="#Page_324">324</a></td> +</tr> + +<tr> +<td class="left">Blemishes of surface,</td> +<td class="right"><a href="#Page_252">252</a></td> +</tr> + +<tr> +<td class="left">Blister in sheet,</td> +<td class="right"><a href="#Page_272">272</a></td> +</tr> + +<tr> +<td class="left">Block rubber,</td> +<td class="right"><a href="#Page_129">129</a>, <a href="#Page_246">246</a></td> +</tr> + +<tr> +<td class="left">Breaking down of rubber,</td> +<td class="right"><a href="#Page_304">304</a></td> +</tr> + +<tr> +<td class="left">— load of test piece,</td> +<td class="right"><a href="#Page_311">311</a></td> +</tr> + +<tr> +<td class="left">Bubbles in sheet,</td> +<td class="right"><a href="#Page_269">269</a></td> +</tr> + +<tr> +<td class="left">Buildings,</td> +<td class="right"><a href="#Page_159">159</a></td> +</tr> + +<tr> +<td class="left">Bulking latex,</td> +<td class="right"><a href="#Page_69">69</a></td> +</tr> + +<tr> +<td class="left">Byrne curing process,</td> +<td class="right"><a href="#Page_270">270</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">Calendered sheet,</td> +<td class="right"><a href="#Page_304">304</a></td> +</tr> + +<tr> +<td class="left">Carbon dioxide,</td> +<td class="right"><a href="#Page_289">289</a></td> +</tr> + +<tr> +<td class="left">Carbonic acid gas,</td> +<td class="right"><a href="#Page_289">289</a></td> +</tr> + +<tr> +<td class="left">Cases, choice of, for packing,</td> +<td class="right"><a href="#Page_153">153</a></td> +</tr> + +<tr> +<td class="left">Catalysts, natural, in rubber,</td> +<td class="right"><a href="#Page_312">312</a></td> +</tr> + +<tr> +<td class="left">—, vulcanising,</td> +<td class="right"><a href="#Page_312">312</a></td> +</tr> + +<tr> +<td class="left">Centralisation of factories,</td> +<td class="right"><a href="#Page_221">221</a></td> +</tr> + +<tr> +<td class="left">Chinese vinegar,</td> +<td class="right"><a href="#Page_286">286</a></td> +</tr> + +<tr> +<td class="left">Chinosol,</td> +<td class="right"><a href="#Page_238">238</a></td> +</tr> + +<tr> +<td class="left">“Chula” drier,</td> +<td class="right"><a href="#Page_148">148</a></td> +</tr> + +<tr> +<td class="left">Clippings, sheet,</td> +<td class="right"><a href="#Page_275">275</a></td> +</tr> + +<tr> +<td class="left">Coagulant,</td> +<td class="right"><a href="#Page_111">111</a></td> +</tr> + +<tr> +<td class="left">—, choice of,</td> +<td class="right"><a href="#Page_74">74</a>, <a href="#Page_278">278</a></td> +</tr> + +<tr> +<td class="left">—, quantity of,</td> +<td class="right"><a href="#Page_113">113</a></td> +</tr> + +<tr> +<td class="left">Coagulation,</td> +<td class="right"><a href="#Page_74">74</a>, <a href="#Page_111">111</a></td> +</tr> + +<tr> +<td class="left">— centres,</td> +<td class="right"><a href="#Page_62">62</a></td> +</tr> + +<tr> +<td class="left">—, premature,</td> +<td class="right"><a href="#Page_46">46</a></td> +</tr> + +<tr> +<td class="left">—, spontaneous,</td> +<td class="right"><a href="#Page_294">294</a></td> +</tr> + +<tr> +<td class="left">— with alcohol,</td> +<td class="right"><a href="#Page_289">289</a></td> +</tr> + +<tr> +<td class="left">— — sugars,</td> +<td class="right"><a href="#Page_287">287</a></td> +</tr> + +<tr> +<td class="left">— — various salts,</td> +<td class="right"><a href="#Page_288">288</a></td> +</tr> + +<tr> +<td class="left">Coagulum, soft,</td> +<td class="right"><a href="#Page_249">249</a></td> +</tr> + +<tr> +<td class="left">—, spongy undersurface of,</td> +<td class="right"><a href="#Page_249">249</a></td> +</tr> + +<tr> +<td class="left">—, tearing of,</td> +<td class="right"><a href="#Page_249">249</a></td> +</tr> + +<tr> +<td class="left">—, transport of,</td> +<td class="right"><a href="#Page_59">59</a>, <a href="#Page_63">63</a></td> +</tr> + +<tr> +<td class="left">—, working of,</td> +<td class="right"><a href="#Page_103">103</a></td> +</tr> + +<tr> +<td class="left">Coefficient of vulcanisation,</td> +<td class="right"><a href="#Page_319">319</a></td> +</tr> + +<tr> +<td class="left">Collecting latex,</td> +<td class="right"><a href="#Page_38">38</a></td> +</tr> + +<tr> +<td class="left">— pails,</td> +<td class="right"><a href="#Page_48">48</a></td> +</tr> + +<tr> +<td class="left">Collection, advantages of early,</td> +<td class="right"><a href="#Page_60">60</a></td> +</tr> + +<tr> +<td class="left">Combustion, rate of, in smoke house,</td> +<td class="right"><a href="#Page_191">191</a></td> +</tr> + +<tr> +<td class="left">Compound crepes,</td> +<td class="right"><a href="#Page_126">126</a></td> +</tr> + +<tr> +<td class="left">— — No. 1,</td> +<td class="right"><a href="#Page_151">151</a></td> +</tr> + +<tr> +<td class="left">— — No. 2,</td> +<td class="right"><a href="#Page_151">151</a></td> +</tr> + +<tr> +<td class="left">Contents of cases, weight of,</td> +<td class="right"><a href="#Page_156">156</a></td> +</tr> + +<tr> +<td class="left">Copper salts, cause of tackiness,</td> +<td class="right"><a href="#Page_243">243</a></td> +</tr> + +<tr> +<td class="left">Cotton fibre in crepe,</td> +<td class="right"><a href="#Page_230">230</a></td> +</tr> + +<tr> +<td class="left">Creosotic substances,</td> +<td class="right"><a href="#Page_146">146</a></td> +</tr> + +<tr> +<td class="left">Crepe, air-drying of,</td> +<td class="right"><a href="#Page_132">132</a></td> +</tr> + +<tr> +<td class="left">—, bark in,</td> +<td class="right"><a href="#Page_232">232</a></td> +</tr> + +<tr> +<td class="left">—, bearing of defects in, on manufacture,</td> +<td class="right"><a href="#Page_316">316</a></td> +</tr> + +<tr> +<td class="left">—, bisulphite streaks in,</td> +<td class="right"><a href="#Page_235">235</a></td> +</tr> + +<tr> +<td class="left">—, colour of fine,</td> +<td class="right"><a href="#Page_114">114</a></td> +</tr> + +<tr> +<td class="left">—, dirt in,</td> +<td class="right"><a href="#Page_227">227</a></td> +</tr> + +<tr> +<td class="left">—, dirty edges of,</td> +<td class="right"><a href="#Page_225">225</a></td> +</tr> + +<tr> +<td class="left">—, drying houses for,</td> +<td class="right"><a href="#Page_178">178</a></td> +</tr> + +<tr> +<td class="left">—, fibre in,</td> +<td class="right"><a href="#Page_230">230</a></td> +</tr> + +<tr> +<td class="left">—, general style of finish,</td> +<td class="right"><a href="#Page_223">223</a></td> +</tr> + +<tr> +<td class="left">—, grades of,</td> +<td class="right"><a href="#Page_150">150</a></td> +</tr> + +<tr> +<td class="left">—, greenish, tacky streaks in,</td> +<td class="right"><a href="#Page_228">228</a></td> +</tr> + +<tr> +<td class="left">—, iron stains on,</td> +<td class="right"><a href="#Page_225">225</a></td> +</tr> + +<tr> +<td class="left"><span class='pagenum'><a name="Page_328" id="Page_328">[328]</a></span>Crepe, No. 1 fine pale,</td> +<td class="right"><a href="#Page_110">110</a></td> +</tr> + +<tr> +<td class="left">—, oil marks on,</td> +<td class="right"><a href="#Page_226">226</a></td> +</tr> + +<tr> +<td class="left">—, oxidation streaks in,</td> +<td class="right"><a href="#Page_234">234</a></td> +</tr> + +<tr> +<td class="left">—, rate of air-drying of,</td> +<td class="right"><a href="#Page_138">138</a></td> +</tr> + +<tr> +<td class="left">—, rust stains on,</td> +<td class="right"><a href="#Page_226">226</a></td> +</tr> + +<tr> +<td class="left">—, smoked,</td> +<td class="right"><a href="#Page_130">130</a></td> +</tr> + +<tr> +<td class="left">—, surface moulds on,</td> +<td class="right"><a href="#Page_241">241</a></td> +</tr> + +<tr> +<td class="left">—, weight increased in drying house,</td> +<td class="right"><a href="#Page_141">141</a></td> +</tr> + +<tr> +<td class="left">—, yellow latex streaks in,</td> +<td class="right"><a href="#Page_234">234</a></td> +</tr> + +<tr> +<td class="left">— rubber, defects in,</td> +<td class="right"><a href="#Page_223">223</a></td> +</tr> + +<tr> +<td class="left">— —, lower grades of,</td> +<td class="right"><a href="#Page_120">120</a></td> +</tr> + +<tr> +<td class="left">— —, preparation of,</td> +<td class="right"><a href="#Page_110">110</a></td> +</tr> + +<tr> +<td class="left">— —, tensile strength of,</td> +<td class="right"><a href="#Page_313">313</a></td> +</tr> + +<tr> +<td class="left">Cups, cleaning,</td> +<td class="right"><a href="#Page_40">40</a></td> +</tr> + +<tr> +<td class="left">—, water in,</td> +<td class="right"><a href="#Page_44">44</a></td> +</tr> + +<tr> +<td class="left">Cure, rate of,</td> +<td class="right"><a href="#Page_318">318</a></td> +</tr> + +<tr> +<td class="left">Curing,</td> +<td class="right"><a href="#Page_307">307</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">Da Costa process,</td> +<td class="right"><a href="#Page_290">290</a></td> +</tr> + +<tr> +<td class="left">Decentralisation of factories,</td> +<td class="right"><a href="#Page_221">221</a></td> +</tr> + +<tr> +<td class="left">Defects of sheet, infrequent,</td> +<td class="right"><a href="#Page_276">276</a></td> +</tr> + +<tr> +<td class="left">Derry process,</td> +<td class="right"><a href="#Page_293">293</a></td> +</tr> + +<tr> +<td class="left">Designs and “layout” of tanks,</td> +<td class="right"><a href="#Page_176">176</a></td> +</tr> + +<tr> +<td class="left">Dirt in sheet,</td> +<td class="right"><a href="#Page_276">276</a></td> +</tr> + +<tr> +<td class="left">Discoloration of rubber, dark,</td> +<td class="right"><a href="#Page_249">249</a></td> +</tr> + +<tr> +<td class="left">Drains for tanks,</td> +<td class="right"><a href="#Page_176">176</a></td> +</tr> + +<tr> +<td class="left">Drier, Colombo Commercial Company’s,</td> +<td class="right"><a href="#Page_136">136</a></td> +</tr> + +<tr> +<td class="left">Driers, artificial—for crepe rubber,</td> +<td class="right"><a href="#Page_133">133</a></td> +</tr> + +<tr> +<td class="left">— —, for sheet rubber,</td> +<td class="right"><a href="#Page_148">148</a></td> +</tr> + +<tr> +<td class="left">—, “Chula,”</td> +<td class="right"><a href="#Page_148">148</a></td> +</tr> + +<tr> +<td class="left">—, vacuum,</td> +<td class="right"><a href="#Page_134">134</a></td> +</tr> + +<tr> +<td class="left">Drum furnaces, horizontal,</td> +<td class="right"><a href="#Page_189">189</a></td> +</tr> + +<tr> +<td class="left">Drying chamber, floor of,</td> +<td class="right"><a href="#Page_187">187</a></td> +</tr> + +<tr> +<td class="left">— —, arrangements of,</td> +<td class="right"><a href="#Page_186">186</a></td> +</tr> + +<tr> +<td class="left">— houses for crepe,</td> +<td class="right"><a href="#Page_178">178</a></td> +</tr> + +<tr> +<td class="left">— —, hot air,</td> +<td class="right"><a href="#Page_182">182</a></td> +</tr> + +<tr> +<td class="left">— —, ventilation of,</td> +<td class="right"><a href="#Page_185">185</a></td> +</tr> + +<tr> +<td class="left">— —, windows of,</td> +<td class="right"><a href="#Page_185">185</a></td> +</tr> + +<tr> +<td class="left">— of rubber,</td> +<td class="right"><a href="#Page_132">132</a></td> +</tr> + +<tr> +<td class="left">—, period of,</td> +<td class="right"><a href="#Page_145">145</a></td> +</tr> + +<tr> +<td class="left">—, rate of, effect on rate of cure,</td> +<td class="right"><a href="#Page_323">323</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">Earth scrap,</td> +<td class="right"><a href="#Page_124">124</a></td> +</tr> + +<tr> +<td class="left">— —, collection of,</td> +<td class="right"><a href="#Page_58">58</a></td> +</tr> + +<tr> +<td class="left">Edges, thickened, after rolling,</td> +<td class="right"><a href="#Page_251">251</a></td> +</tr> + +<tr> +<td class="left">Elongation of test piece,</td> +<td class="right"><a href="#Page_311">311</a></td> +</tr> + +<tr> +<td class="left">Ends, thickened, after rolling,</td> +<td class="right"><a href="#Page_251">251</a></td> +</tr> + +<tr> +<td class="left">Engines,</td> +<td class="right"><a href="#Page_170">170</a></td> +</tr> + +<tr> +<td class="left">—, position of,</td> +<td class="right"><a href="#Page_174">174</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">Factories,</td> +<td class="right"><a href="#Page_172">172</a></td> +</tr> + +<tr> +<td class="left">—, centralisation of,</td> +<td class="right"><a href="#Page_221">221</a></td> +</tr> + +<tr> +<td class="left">—, decentralisation of,</td> +<td class="right"><a href="#Page_221">221</a></td> +</tr> + +<tr> +<td class="left">—, number of floors,</td> +<td class="right"><a href="#Page_174">174</a>, <a href="#Page_178">178</a></td> +</tr> + +<tr> +<td class="left">—, ventilation of,</td> +<td class="right"><a href="#Page_180">180</a></td> +</tr> + +<tr> +<td class="left">—, windows of,</td> +<td class="right"><a href="#Page_181">181</a></td> +</tr> + +<tr> +<td class="left">Factory buildings, situation of,</td> +<td class="right"><a href="#Page_216">216</a></td> +</tr> + +<tr> +<td class="left">—, choosing site for,</td> +<td class="right"><a href="#Page_220">220</a></td> +</tr> + +<tr> +<td class="left">—, ideal arrangement of,</td> +<td class="right"><a href="#Page_162">162</a></td> +</tr> + +<tr> +<td class="left">— operation,</td> +<td class="right"><a href="#Page_65">65</a></td> +</tr> + +<tr> +<td class="left">Fibre cotton, in crepe,</td> +<td class="right"><a href="#Page_230">230</a></td> +</tr> + +<tr> +<td class="left">Field maintenance,</td> +<td class="right"><a href="#Page_13">13</a></td> +</tr> + +<tr> +<td class="left">Fine hard Para properties of,</td> +<td class="right"><a href="#Page_325">325</a></td> +</tr> + +<tr> +<td class="left">First latex and other grades, percentage of,</td> +<td class="right"><a href="#Page_59">59</a></td> +</tr> + +<tr> +<td class="left">Floor of drying chamber,</td> +<td class="right"><a href="#Page_187">187</a></td> +</tr> + +<tr> +<td class="left">— factories,</td> +<td class="right"><a href="#Page_173">173</a></td> +</tr> + +<tr> +<td class="left">— furnace room,</td> +<td class="right"><a href="#Page_196">196</a></td> +</tr> + +<tr> +<td class="left">Formalin,</td> +<td class="right"><a href="#Page_87">87</a></td> +</tr> + +<tr> +<td class="left">Formic acid,</td> +<td class="right"><a href="#Page_74">74</a>, <a href="#Page_279">279</a></td> +</tr> + +<tr> +<td class="left">Formula for test mix,</td> +<td class="right"><a href="#Page_311">311</a></td> +</tr> + +<tr> +<td class="left">Freezing (coagulation) process,</td> +<td class="right"><a href="#Page_293">293</a></td> +</tr> + +<tr> +<td class="left">Fuel, consumption of,</td> +<td class="right"><a href="#Page_196">196</a></td> +</tr> + +<tr> +<td class="left">Fuels for smoking,</td> +<td class="right"><a href="#Page_146">146</a></td> +</tr> + +<tr> +<td class="left">Furnace room, floor of,</td> +<td class="right"><a href="#Page_196">196</a></td> +</tr> + +<tr> +<td class="left">— —, Petaling type of,</td> +<td class="right"><a href="#Page_192">192</a></td> +</tr> + +<tr> +<td class="left">Furnaces, horizontal drum,</td> +<td class="right"><a href="#Page_189">189</a></td> +</tr> + +<tr> +<td class="left">—, “pot,”</td> +<td class="right"><a href="#Page_188">188</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">Germination,</td> +<td class="right"><a href="#Page_6">6</a></td> +</tr> + +<tr> +<td class="left">Grades, number of,</td> +<td class="right"><a href="#Page_151">151</a></td> +</tr> + +<tr> +<td class="left">Grading,</td> +<td class="right"><a href="#Page_150">150</a></td> +</tr> + +<tr> +<td class="left">Grafting,</td> +<td class="right"><a href="#Page_8">8</a></td> +</tr> + +<tr> +<td class="left">Grass squares,</td> +<td class="right"><a href="#Page_14">14</a></td> +</tr> + +<tr> +<td class="left">Greasiness before smoking,</td> +<td class="right"><a href="#Page_252">252</a></td> +</tr> + +<tr> +<td class="left">— of surface,</td> +<td class="right"><a href="#Page_258">258</a></td> +</tr> + +<tr> +<td class="left">Grit in crepe,</td> +<td class="right"><a href="#Page_232">232</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">Hand rolling sheets,</td> +<td class="right"><a href="#Page_104">104</a></td> +</tr> + +<tr> +<td class="left">Hevea Brasiliensis,</td> +<td class="right"><a href="#Page_1">1</a></td> +</tr> + +<tr> +<td class="left">Hot air drying houses,</td> +<td class="right"><a href="#Page_182">182</a></td> +</tr> + +<tr> +<td class="left">Hydrochloric acid,</td> +<td class="right"><a href="#Page_282">282</a></td> +</tr> + +<tr> +<td class="left">Hydrofluoric acid,</td> +<td class="right"><a href="#Page_282">282</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">Ilcken-Down process,</td> +<td class="right"><a href="#Page_298">298</a></td> +</tr> + +<tr> +<td class="left">Instruments, method of using,</td> +<td class="right"><a href="#Page_100">100</a></td> +</tr> + +<tr> +<td class="left">—, recording,</td> +<td class="right"><a href="#Page_144">144</a></td> +</tr> + +<tr> +<td class="left">—, standardising,</td> +<td class="right"><a href="#Page_98">98</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">Lallang, eradication of,</td> +<td class="right"><a href="#Page_15">15</a></td> +</tr> + +<tr> +<td class="left">Latex, bulking,</td> +<td class="right"><a href="#Page_69">69</a></td> +</tr> + +<tr> +<td class="left">— cups, choice of,</td> +<td class="right"><a href="#Page_40">40</a></td> +</tr> + +<tr> +<td class="left">—, decomposition of, in the field,</td> +<td class="right"><a href="#Page_270">270</a></td> +</tr> + +<tr> +<td class="left">—, first and other grades, percentage of,</td> +<td class="right"><a href="#Page_59">59</a></td> +</tr> + +<tr> +<td class="left">—, first quality,</td> +<td class="right"><a href="#Page_150">150</a></td> +</tr> + +<tr> +<td class="left">—, mixing acid with,</td> +<td class="right"><a href="#Page_79">79</a></td> +</tr> + +<tr> +<td class="left">—, mixing sodium bisulphite solution with,</td> +<td class="right"><a href="#Page_117">117</a></td> +</tr> + +<tr> +<td class="left">—, preliminary treatment of,</td> +<td class="right"><a href="#Page_65">65</a></td> +</tr> + +<tr> +<td class="left">—, reception of, at the store,</td> +<td class="right"><a href="#Page_65">65</a></td> +</tr> + +<tr> +<td class="left">—, standard,</td> +<td class="right"><a href="#Page_96">96</a></td> +</tr> + +<tr> +<td class="left">—, standardisation of,</td> +<td class="right"><a href="#Page_69">69</a>, <a href="#Page_110">110</a></td> +</tr> + +<tr> +<td class="left">—, straining,</td> +<td class="right"><a href="#Page_67">67</a></td> +</tr> + +<tr> +<td class="left">—, transport of,</td> +<td class="right"><a href="#Page_59">59</a></td> +</tr> + +<tr> +<td class="left"><span class='pagenum'><a name="Page_329" id="Page_329">[329]</a></span>Light, importance of, in factories,</td> +<td class="right"><a href="#Page_172">172</a></td> +</tr> + +<tr> +<td class="left">Litharge,</td> +<td class="right"><a href="#Page_312">312</a></td> +</tr> + +<tr> +<td class="left">Load stretch curve,</td> +<td class="right"><a href="#Page_312">312</a>, <a href="#Page_319">319</a>, <a href="#Page_320">320</a>, <a href="#Page_321">321</a></td> +</tr> + +<tr> +<td class="left">Low grade rubbers, fibrous matter in,</td> +<td class="right"><a href="#Page_124">124</a></td> +</tr> + +<tr> +<td class="left">Lower grade rubber, care in manufacture,</td> +<td class="right"><a href="#Page_129">129</a></td> +</tr> + +<tr> +<td class="left">Lubrication of machines,</td> +<td class="right"><a href="#Page_166">166</a></td> +</tr> + +<tr> +<td class="left">Lump rubber, naturally coagulated,</td> +<td class="right"><a href="#Page_120">120</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">Machinery,</td> +<td class="right"><a href="#Page_159">159</a></td> +</tr> + +<tr> +<td class="left">Machines, access to,</td> +<td class="right"><a href="#Page_169">169</a></td> +</tr> + +<tr> +<td class="left">—, adequacy of,</td> +<td class="right"><a href="#Page_160">160</a></td> +</tr> + +<tr> +<td class="left">—, arrangement of,</td> +<td class="right"><a href="#Page_168">168</a></td> +</tr> + +<tr> +<td class="left">—, lubrication of,</td> +<td class="right"><a href="#Page_166">166</a></td> +</tr> + +<tr> +<td class="left">—, position of,</td> +<td class="right"><a href="#Page_173">173</a></td> +</tr> + +<tr> +<td class="left">—, sheeting,</td> +<td class="right"><a href="#Page_166">166</a></td> +</tr> + +<tr> +<td class="left">—, speed of,</td> +<td class="right"><a href="#Page_162">162</a></td> +</tr> + +<tr> +<td class="left">Mangrove,</td> +<td class="right"><a href="#Page_147">147</a></td> +</tr> + +<tr> +<td class="left">Marking sheets,</td> +<td class="right"><a href="#Page_105">105</a></td> +</tr> + +<tr> +<td class="left">Metrolac,</td> +<td class="right"><a href="#Page_98">98</a>, <a href="#Page_100">100</a></td> +</tr> + +<tr> +<td class="left">Michie-Golledge system,</td> +<td class="right"><a href="#Page_138">138</a></td> +</tr> + +<tr> +<td class="left">Mildew on surface,</td> +<td class="right"><a href="#Page_260">260</a></td> +</tr> + +<tr> +<td class="left">Milky residue on serum,</td> +<td class="right"><a href="#Page_249">249</a></td> +</tr> + +<tr> +<td class="left">Mixing acid with latex,</td> +<td class="right"><a href="#Page_79">79</a></td> +</tr> + +<tr> +<td class="left">Moist glaze of surface,</td> +<td class="right"><a href="#Page_258">258</a></td> +</tr> + +<tr> +<td class="left">Mould on surface,</td> +<td class="right"><a href="#Page_260">260</a></td> +</tr> + +<tr> +<td class="left">Moulds, surface, on crepe,</td> +<td class="right"><a href="#Page_241">241</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">Natural catalysts,</td> +<td class="right"><a href="#Page_312">312</a></td> +</tr> + +<tr> +<td class="left">Nitric acid,</td> +<td class="right"><a href="#Page_282">282</a></td> +</tr> + +<tr> +<td class="left">Nurseries,</td> +<td class="right"><a href="#Page_9">9</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">Overcured,</td> +<td class="right"><a href="#Page_307">307</a></td> +</tr> + +<tr> +<td class="left">Overvulcanised,</td> +<td class="right"><a href="#Page_306">306</a></td> +</tr> + +<tr> +<td class="left">Oxalic acid,</td> +<td class="right"><a href="#Page_279">279</a></td> +</tr> + +<tr> +<td class="left">Oxidation, prevention of,</td> +<td class="right"><a href="#Page_56">56</a></td> +</tr> + +<tr> +<td class="left">—, variation due to,</td> +<td class="right"><a href="#Page_254">254</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">Packing,</td> +<td class="right"><a href="#Page_150">150</a></td> +</tr> + +<tr> +<td class="left">—, bags for,</td> +<td class="right"><a href="#Page_154">154</a></td> +</tr> + +<tr> +<td class="left">—, bales for,</td> +<td class="right"><a href="#Page_154">154</a></td> +</tr> + +<tr> +<td class="left">—, cases, choice of,</td> +<td class="right"><a href="#Page_153">153</a></td> +</tr> + +<tr> +<td class="left">—, folding for,</td> +<td class="right"><a href="#Page_155">155</a></td> +</tr> + +<tr> +<td class="left">—, methods of,</td> +<td class="right"><a href="#Page_156">156</a></td> +</tr> + +<tr> +<td class="left">—, rooms,</td> +<td class="right"><a href="#Page_211">211</a></td> +</tr> + +<tr> +<td class="left">Pale crepe, No. 1 fine,</td> +<td class="right"><a href="#Page_110">110</a></td> +</tr> + +<tr> +<td class="left">—, rubber, former methods of making,</td> +<td class="right"><a href="#Page_118">118</a></td> +</tr> + +<tr> +<td class="left">—, sheet,</td> +<td class="right"><a href="#Page_89">89</a></td> +</tr> + +<tr> +<td class="left">Patches,</td> +<td class="right"><a href="#Page_259">259</a>, <a href="#Page_260">260</a></td> +</tr> + +<tr> +<td class="left">—, virgin,</td> +<td class="right"><a href="#Page_259">259</a></td> +</tr> + +<tr> +<td class="left">Payment by result,</td> +<td class="right"><a href="#Page_53">53</a></td> +</tr> + +<tr> +<td class="left">Perished rubber,</td> +<td class="right"><a href="#Page_306">306</a></td> +</tr> + +<tr> +<td class="left">Physical properties of rubber, variation of,</td> +<td class="right"><a href="#Page_317">317</a></td> +</tr> + +<tr> +<td class="left">Pits for smoke houses,</td> +<td class="right"><a href="#Page_188">188</a></td> +</tr> + +<tr> +<td class="left">Pitting of surface,</td> +<td class="right"><a href="#Page_250">250</a></td> +</tr> + +<tr> +<td class="left">Plantation rubber, testing of,</td> +<td class="right"><a href="#Page_309">309</a></td> +</tr> + +<tr> +<td class="left">Planting,</td> +<td class="right"><a href="#Page_1">1</a></td> +</tr> + +<tr> +<td class="left">Plasticising of rubber,</td> +<td class="right"><a href="#Page_304">304</a></td> +</tr> + +<tr> +<td class="left">Plasticity of plantation rubber,</td> +<td class="right"><a href="#Page_309">309</a></td> +</tr> + +<tr> +<td class="left">“Pot” furnaces,</td> +<td class="right"><a href="#Page_188">188</a></td> +</tr> + +<tr> +<td class="left">Power units,</td> +<td class="right"><a href="#Page_170">170</a></td> +</tr> + +<tr> +<td class="left">Premature coagulation,</td> +<td class="right"><a href="#Page_46">46</a></td> +</tr> + +<tr> +<td class="left">Preparation, special methods of,</td> +<td class="right"><a href="#Page_290">290</a></td> +</tr> + +<tr> +<td class="left">Pyroligneous acid,</td> +<td class="right"><a href="#Page_282">282</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">Racks,</td> +<td class="right"><a href="#Page_186">186</a></td> +</tr> + +<tr> +<td class="left">Rate of cure,</td> +<td class="right"><a href="#Page_307">307</a></td> +</tr> + +<tr> +<td class="left">Raw rubber, physical properties of,</td> +<td class="right"><a href="#Page_313">313</a></td> +</tr> + +<tr> +<td class="left">— —, tests on,</td> +<td class="right"><a href="#Page_309">309</a></td> +</tr> + +<tr> +<td class="left">— —, uses of,</td> +<td class="right"><a href="#Page_315">315</a></td> +</tr> + +<tr> +<td class="left">Recommendations, Rubber Growers’ Association,</td> +<td class="right"><a href="#Page_152">152</a></td> +</tr> + +<tr> +<td class="left">Recording instruments,</td> +<td class="right"><a href="#Page_144">144</a></td> +</tr> + +<tr> +<td class="left">Ribbing of sheet,</td> +<td class="right"><a href="#Page_274">274</a></td> +</tr> + +<tr> +<td class="left">Rolling,</td> +<td class="right"><a href="#Page_251">251</a></td> +</tr> + +<tr> +<td class="left">Rolls, grooving of,</td> +<td class="right"><a href="#Page_164">164</a></td> +</tr> + +<tr> +<td class="left">— running hot,</td> +<td class="right"><a href="#Page_165">165</a></td> +</tr> + +<tr> +<td class="left">— — “free,”</td> +<td class="right"><a href="#Page_165">165</a></td> +</tr> + +<tr> +<td class="left">Roof of smoke house,</td> +<td class="right"><a href="#Page_197">197</a></td> +</tr> + +<tr> +<td class="left">Rubber, drying of,</td> +<td class="right"><a href="#Page_132">132</a></td> +</tr> + +<tr> +<td class="left">Rubber Growers’ Association, Recommendations,</td> +<td class="right"><a href="#Page_152">152</a></td> +</tr> + +<tr> +<td class="left">Rubber, properties of,</td> +<td class="right"><a href="#Page_313">313</a></td> +</tr> + +<tr> +<td class="left">—, smoking,</td> +<td class="right"><a href="#Page_109">109</a></td> +</tr> + +<tr> +<td class="left">Rust, cause of,</td> +<td class="right"><a href="#Page_267">267</a></td> +</tr> + +<tr> +<td class="left">— on sheet,</td> +<td class="right"><a href="#Page_262">262</a></td> +</tr> + +<tr> +<td class="left">—, treatment to prevent,</td> +<td class="right"><a href="#Page_265">265</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">Scrap washers,</td> +<td class="right"><a href="#Page_57">57</a>, <a href="#Page_124">124</a></td> +</tr> + +<tr> +<td class="left">Screw plug, unsatisfactory,</td> +<td class="right"><a href="#Page_73">73</a></td> +</tr> + +<tr> +<td class="left">Seed at stake,</td> +<td class="right"><a href="#Page_10">10</a></td> +</tr> + +<tr> +<td class="left">Seeds,</td> +<td class="right"><a href="#Page_2">2</a></td> +</tr> + +<tr> +<td class="left">Selection,</td> +<td class="right"><a href="#Page_5">5</a></td> +</tr> + +<tr> +<td class="left">Senang folder,</td> +<td class="right"><a href="#Page_156">156</a></td> +</tr> + +<tr> +<td class="left">Serum, milky residue on,</td> +<td class="right"><a href="#Page_249">249</a></td> +</tr> + +<tr> +<td class="left">Sheet, ash on,</td> +<td class="right"><a href="#Page_276">276</a></td> +</tr> + +<tr> +<td class="left">—, bark in,</td> +<td class="right"><a href="#Page_276">276</a></td> +</tr> + +<tr> +<td class="left">—, bearing of defects on, in manufacture,</td> +<td class="right"><a href="#Page_316">316</a></td> +</tr> + +<tr> +<td class="left">—, blisters in,</td> +<td class="right"><a href="#Page_272">272</a></td> +</tr> + +<tr> +<td class="left">—, bubbles in,</td> +<td class="right"><a href="#Page_269">269</a></td> +</tr> + +<tr> +<td class="left">—, clippings,</td> +<td class="right"><a href="#Page_130">130</a>, <a href="#Page_275">275</a></td> +</tr> + +<tr> +<td class="left">—, creases in,</td> +<td class="right"><a href="#Page_251">251</a></td> +</tr> + +<tr> +<td class="left">—, dirt in,</td> +<td class="right"><a href="#Page_276">276</a></td> +</tr> + +<tr> +<td class="left">—, “dog ears,”</td> +<td class="right"><a href="#Page_251">251</a></td> +</tr> + +<tr> +<td class="left">—, grades of,</td> +<td class="right"><a href="#Page_151">151</a></td> +</tr> + +<tr> +<td class="left">—, infrequent defects of,</td> +<td class="right"><a href="#Page_276">276</a></td> +</tr> + +<tr> +<td class="left">—, pale,</td> +<td class="right"><a href="#Page_89">89</a></td> +</tr> + +<tr> +<td class="left">—, ribbing of,</td> +<td class="right"><a href="#Page_274">274</a></td> +</tr> + +<tr> +<td class="left">— rubber, artificial driers for,</td> +<td class="right"><a href="#Page_148">148</a></td> +</tr> + +<tr> +<td class="left">— —, defects in,</td> +<td class="right"><a href="#Page_249">249</a></td> +</tr> + +<tr> +<td class="left">— —, preparation of,</td> +<td class="right"><a href="#Page_89">89</a></td> +</tr> + +<tr> +<td class="left"><span class='pagenum'><a name="Page_330" id="Page_330">[330]</a></span>Sheet rubber, rolling and marking of,</td> +<td class="right"><a href="#Page_102">102</a></td> +</tr> + +<tr> +<td class="left">— —, tensile strength of,</td> +<td class="right"><a href="#Page_313">313</a></td> +</tr> + +<tr> +<td class="left">—, rust on,</td> +<td class="right"><a href="#Page_262">262</a></td> +</tr> + +<tr> +<td class="left">—, splinters in,</td> +<td class="right"><a href="#Page_276">276</a></td> +</tr> + +<tr> +<td class="left">—, stickiness in,</td> +<td class="right"><a href="#Page_274">274</a></td> +</tr> + +<tr> +<td class="left">—, style of,</td> +<td class="right"><a href="#Page_101">101</a></td> +</tr> + +<tr> +<td class="left">—, support marks on,</td> +<td class="right"><a href="#Page_273">273</a></td> +</tr> + +<tr> +<td class="left">—, surface pattern of,</td> +<td class="right"><a href="#Page_274">274</a></td> +</tr> + +<tr> +<td class="left">—, thick ends of,</td> +<td class="right"><a href="#Page_275">275</a></td> +</tr> + +<tr> +<td class="left">Sheeting machines,</td> +<td class="right"><a href="#Page_166">166</a></td> +</tr> + +<tr> +<td class="left">Sheets, mis-shapen,</td> +<td class="right"><a href="#Page_251">251</a></td> +</tr> + +<tr> +<td class="left">—, thickened patches in,</td> +<td class="right"><a href="#Page_251">251</a></td> +</tr> + +<tr> +<td class="left">—, torn,</td> +<td class="right"><a href="#Page_251">251</a></td> +</tr> + +<tr> +<td class="left">—, unevenness of appearance,</td> +<td class="right"><a href="#Page_253">253</a></td> +</tr> + +<tr> +<td class="left">Short weights,</td> +<td class="right"><a href="#Page_157">157</a></td> +</tr> + +<tr> +<td class="left">Skimming,</td> +<td class="right"><a href="#Page_100">100</a></td> +</tr> + +<tr> +<td class="left">Skimmings,</td> +<td class="right"><a href="#Page_122">122</a></td> +</tr> + +<tr> +<td class="left">Slab rubber,</td> +<td class="right"><a href="#Page_299">299</a></td> +</tr> + +<tr> +<td class="left">— —, properties of,</td> +<td class="right"><a href="#Page_324">324</a></td> +</tr> + +<tr> +<td class="left">Slope,</td> +<td class="right"><a href="#Page_312">312</a></td> +</tr> + +<tr> +<td class="left">Smoke curing of sheet rubber,</td> +<td class="right"><a href="#Page_143">143</a></td> +</tr> + +<tr> +<td class="left">— —, temperature of,</td> +<td class="right"><a href="#Page_144">144</a></td> +</tr> + +<tr> +<td class="left">—, houses,</td> +<td class="right"><a href="#Page_183">183</a></td> +</tr> + +<tr> +<td class="left">— —, Barker patent,</td> +<td class="right"><a href="#Page_209">209</a></td> +</tr> + +<tr> +<td class="left">— —, Devon type,</td> +<td class="right"><a href="#Page_200">200</a></td> +</tr> + +<tr> +<td class="left">— —, iron stoves for,</td> +<td class="right"><a href="#Page_189">189</a></td> +</tr> + +<tr> +<td class="left">— —, Jackson type,</td> +<td class="right"><a href="#Page_200">200</a></td> +</tr> + +<tr> +<td class="left">— — of brick,</td> +<td class="right"><a href="#Page_198">198</a></td> +</tr> + +<tr> +<td class="left">— — rate of combustion in,</td> +<td class="right"><a href="#Page_192">192</a></td> +</tr> + +<tr> +<td class="left">— —, roof of,</td> +<td class="right"><a href="#Page_197">197</a></td> +</tr> + +<tr> +<td class="left">— —, “Third Mile” type,</td> +<td class="right"><a href="#Page_199">199</a></td> +</tr> + +<tr> +<td class="left">— —, types of,</td> +<td class="right"><a href="#Page_198">198</a></td> +</tr> + +<tr> +<td class="left">Smoked crepe,</td> +<td class="right"><a href="#Page_130">130</a></td> +</tr> + +<tr> +<td class="left">— sheets, colour of,</td> +<td class="right"><a href="#Page_255">255</a></td> +</tr> + +<tr> +<td class="left">— water for coagulation,</td> +<td class="right"><a href="#Page_286">286</a></td> +</tr> + +<tr> +<td class="left">Smoking, effect on rate of cure,</td> +<td class="right"><a href="#Page_323">323</a></td> +</tr> + +<tr> +<td class="left">—, greasiness before,</td> +<td class="right"><a href="#Page_252">252</a></td> +</tr> + +<tr> +<td class="left">— rubber,</td> +<td class="right"><a href="#Page_109">109</a></td> +</tr> + +<tr> +<td class="left">Smooth rolling of sheets,</td> +<td class="right"><a href="#Page_104">104</a></td> +</tr> + +<tr> +<td class="left">Sodium bisulphite,</td> +<td class="right"><a href="#Page_80">80</a>, <a href="#Page_114">114</a></td> +</tr> + +<tr> +<td class="left">— —, abuse of,</td> +<td class="right"><a href="#Page_85">85</a></td> +</tr> + +<tr> +<td class="left">— —, care of,</td> +<td class="right"><a href="#Page_116">116</a></td> +</tr> + +<tr> +<td class="left">— —, deterioration of,</td> +<td class="right"><a href="#Page_115">115</a></td> +</tr> + +<tr> +<td class="left">— —, evaluation of,</td> +<td class="right"><a href="#Page_115">115</a></td> +</tr> + +<tr> +<td class="left">— —, making a solution of,</td> +<td class="right"><a href="#Page_85">85</a></td> +</tr> + +<tr> +<td class="left">— —, quantity of,</td> +<td class="right"><a href="#Page_84">84</a></td> +</tr> + +<tr> +<td class="left">— —, residual traces of,</td> +<td class="right"><a href="#Page_86">86</a></td> +</tr> + +<tr> +<td class="left">— — solution, mixing, with latex,</td> +<td class="right"><a href="#Page_117">117</a></td> +</tr> + +<tr> +<td class="left">— sulphite,</td> +<td class="right"><a href="#Page_86">86</a></td> +</tr> + +<tr> +<td class="left">— —, deterioration of,</td> +<td class="right"><a href="#Page_115">115</a></td> +</tr> + +<tr> +<td class="left">— —, evaluation of,</td> +<td class="right"><a href="#Page_115">115</a></td> +</tr> + +<tr> +<td class="left">Sorting,</td> +<td class="right"><a href="#Page_150">150</a>, <a href="#Page_152">152</a></td> +</tr> + +<tr> +<td class="left">— rooms,</td> +<td class="right"><a href="#Page_211">211</a></td> +</tr> + +<tr> +<td class="left">Spewing,</td> +<td class="right"><a href="#Page_305">305</a></td> +</tr> + +<tr> +<td class="left">Splinters in sheet,</td> +<td class="right"><a href="#Page_276">276</a></td> +</tr> + +<tr> +<td class="left">Spontaneous coagulation,</td> +<td class="right"><a href="#Page_294">294</a></td> +</tr> + +<tr> +<td class="left">Spot disease,</td> +<td class="right"><a href="#Page_235">235</a></td> +</tr> + +<tr> +<td class="left">— — in sheet rubber,</td> +<td class="right"><a href="#Page_273">273</a></td> +</tr> + +<tr> +<td class="left">Spots,</td> +<td class="right"><a href="#Page_259">259</a>, <a href="#Page_262">262</a></td> +</tr> + +<tr> +<td class="left">—, virgin,</td> +<td class="right"><a href="#Page_259">259</a></td> +</tr> + +<tr> +<td class="left">Standard latex,</td> +<td class="right"><a href="#Page_96">96</a></td> +</tr> + +<tr> +<td class="left">— sheet,</td> +<td class="right"><a href="#Page_102">102</a></td> +</tr> + +<tr> +<td class="left">Standardising instruments,</td> +<td class="right"><a href="#Page_98">98</a></td> +</tr> + +<tr> +<td class="left">Stickiness in sheet,</td> +<td class="right"><a href="#Page_274">274</a></td> +</tr> + +<tr> +<td class="left">Stock solution, method of making,</td> +<td class="right"><a href="#Page_75">75</a></td> +</tr> + +<tr> +<td class="left">Storage of rubber,</td> +<td class="right"><a href="#Page_212">212</a>, <a href="#Page_216">216</a></td> +</tr> + +<tr> +<td class="left">Stoves, iron, for smoke houses,</td> +<td class="right"><a href="#Page_189">189</a></td> +</tr> + +<tr> +<td class="left">Straining latex,</td> +<td class="right"><a href="#Page_67">67</a></td> +</tr> + +<tr> +<td class="left">Streaks,</td> +<td class="right"><a href="#Page_262">262</a></td> +</tr> + +<tr> +<td class="left">Stumps,</td> +<td class="right"><a href="#Page_9">9</a></td> +</tr> + +<tr> +<td class="left">Sugars, coagulation with,</td> +<td class="right"><a href="#Page_287">287</a></td> +</tr> + +<tr> +<td class="left">Sulphuric acid,</td> +<td class="right"><a href="#Page_280">280</a>, <a href="#Page_286">286</a></td> +</tr> + +<tr> +<td class="left">— —, buying,</td> +<td class="right"><a href="#Page_280">280</a></td> +</tr> + +<tr> +<td class="left">— —, formula for use of,</td> +<td class="right"><a href="#Page_280">280</a></td> +</tr> + +<tr> +<td class="left">— —, storing,</td> +<td class="right"><a href="#Page_280">280</a></td> +</tr> + +<tr> +<td class="left">Sun-drying sheet rubber,</td> +<td class="right"><a href="#Page_147">147</a></td> +</tr> + +<tr> +<td class="left">Support marks on sheet,</td> +<td class="right"><a href="#Page_273">273</a></td> +</tr> + +<tr> +<td class="left">Surface blotches, coloured,</td> +<td class="right"><a href="#Page_249">249</a></td> +</tr> + +<tr> +<td class="left">—, dull or black,</td> +<td class="right"><a href="#Page_258">258</a></td> +</tr> + +<tr> +<td class="left">— pattern of sheet,</td> +<td class="right"><a href="#Page_274">274</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">Tackiness, cause of,</td> +<td class="right"><a href="#Page_243">243</a></td> +</tr> + +<tr> +<td class="left">—, copper salts cause of,</td> +<td class="right"><a href="#Page_243">243</a></td> +</tr> + +<tr> +<td class="left">— in rubber,</td> +<td class="right"><a href="#Page_242">242</a></td> +</tr> + +<tr> +<td class="left">Tanks,</td> +<td class="right"><a href="#Page_90">90</a></td> +</tr> + +<tr> +<td class="left">—, care of,</td> +<td class="right"><a href="#Page_94">94</a></td> +</tr> + +<tr> +<td class="left">—, designs and “layout,”</td> +<td class="right"><a href="#Page_176">176</a></td> +</tr> + +<tr> +<td class="left">—, drains for,</td> +<td class="right"><a href="#Page_176">176</a></td> +</tr> + +<tr> +<td class="left">—, installation of,</td> +<td class="right"><a href="#Page_93">93</a></td> +</tr> + +<tr> +<td class="left">—, situation of,</td> +<td class="right"><a href="#Page_175">175</a></td> +</tr> + +<tr> +<td class="left">—, water-supply for,</td> +<td class="right"><a href="#Page_177">177</a></td> +</tr> + +<tr> +<td class="left">Tapping,</td> +<td class="right"><a href="#Page_38">38</a></td> +</tr> + +<tr> +<td class="left">—, former systems of,</td> +<td class="right"><a href="#Page_29">29</a></td> +</tr> + +<tr> +<td class="left">— knives,</td> +<td class="right"><a href="#Page_38">38</a></td> +</tr> + +<tr> +<td class="left">— systems,</td> +<td class="right"><a href="#Page_38">38</a></td> +</tr> + +<tr> +<td class="left">Tartaric acid,</td> +<td class="right"><a href="#Page_279">279</a></td> +</tr> + +<tr> +<td class="left">Tensile product,</td> +<td class="right"><a href="#Page_314">314</a></td> +</tr> + +<tr> +<td class="left">Test mix, formula for,</td> +<td class="right"><a href="#Page_311">311</a></td> +</tr> + +<tr> +<td class="left">— pieces, making of,</td> +<td class="right"><a href="#Page_310">310</a></td> +</tr> + +<tr> +<td class="left">Testing of plantation rubber,</td> +<td class="right"><a href="#Page_307">307</a></td> +</tr> + +<tr> +<td class="left">Thick ends of sheet,</td> +<td class="right"><a href="#Page_275">275</a></td> +</tr> + +<tr> +<td class="left">Thinning,</td> +<td class="right"><a href="#Page_19">19</a></td> +</tr> + +<tr> +<td class="left">Timber for smoking,</td> +<td class="right"><a href="#Page_147">147</a></td> +</tr> + +<tr> +<td class="left">Tool sheds,</td> +<td class="right"><a href="#Page_216">216</a></td> +</tr> + +<tr> +<td class="left">Transport,</td> +<td class="right"><a href="#Page_60">60</a></td> +</tr> + +<tr> +<td class="left">— by coolie,</td> +<td class="right"><a href="#Page_62">62</a></td> +</tr> + +<tr> +<td class="left">— of coagulum,</td> +<td class="right"><a href="#Page_59">59</a>, <a href="#Page_63">63</a></td> +</tr> + +<tr> +<td class="left">— of latex,</td> +<td class="right"><a href="#Page_59">59</a></td> +</tr> + +<tr> +<td class="left">Trays,</td> +<td class="right"><a href="#Page_167">167</a></td> +</tr> + +<tr> +<td class="left">Treatment of rubber in the factory,</td> +<td class="right"><a href="#Page_301">301</a></td> +</tr> + +<tr> +<td class="left">— to prevent rust,</td> +<td class="right"><a href="#Page_265">265</a></td> +</tr> + +<tr> +<td class="left">Tree scrap,</td> +<td class="right"><a href="#Page_55">55</a>, <a href="#Page_122">122</a></td> +</tr> + +<tr> +<td class="left">— —, care of,</td> +<td class="right"><a href="#Page_56">56</a></td> +</tr> + +<tr> +<td class="left">— —, oxidation of,</td> +<td class="right"><a href="#Page_56">56</a></td> +</tr> + +<tr> +<td class="left">Trees per acre,</td> +<td class="right"><a href="#Page_26">26</a></td> +</tr> + +<tr> +<td class="left">Trenches, silt catchment,</td> +<td class="right"><a href="#Page_11">11</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left"><span class='pagenum'><a name="Page_331" id="Page_331">[331]</a></span>Uniformity,</td> +<td class="right"><a href="#Page_90">90</a></td> +</tr> + +<tr> +<td class="left">— in colour, lack of,</td> +<td class="right"><a href="#Page_246">246</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">Vacuum driers,</td> +<td class="right"><a href="#Page_134">134</a></td> +</tr> + +<tr> +<td class="left">Variation due to oxidation,</td> +<td class="right"><a href="#Page_254">254</a></td> +</tr> + +<tr> +<td class="left">Vegetable extracts,</td> +<td class="right"><a href="#Page_289">289</a></td> +</tr> + +<tr> +<td class="left">Ventilation of drying houses,</td> +<td class="right"><a href="#Page_185">185</a></td> +</tr> + +<tr> +<td class="left">— factories,</td> +<td class="right"><a href="#Page_180">180</a></td> +</tr> + +<tr> +<td class="left">Verandas,</td> +<td class="right"><a href="#Page_175">175</a></td> +</tr> + +<tr> +<td class="left">Virgin spots,</td> +<td class="right"><a href="#Page_258">258</a></td> +</tr> + +<tr> +<td class="left">Viscosity of rubber solution,</td> +<td class="right"><a href="#Page_309">309</a></td> +</tr> + +<tr> +<td class="left">Vulcanisation,</td> +<td class="right"><a href="#Page_301">301</a></td> +</tr> + +<tr> +<td class="left">—, rate of,</td> +<td class="right"><a href="#Page_318">318</a></td> +</tr> + +<tr> +<td class="left">Vulcanised rubber,</td> +<td class="right"><a href="#Page_318">318</a></td> +</tr> + +<tr> +<td class="left">— —, tests on,</td> +<td class="right"><a href="#Page_309">309</a></td> +</tr> + +<tr> +<td class="left">Vulcanising,</td> +<td class="right"><a href="#Page_307">307</a></td> +</tr> + +<tr> +<td class="left">— catalysts,</td> +<td class="right"><a href="#Page_312">312</a></td> +</tr> + +<tr> +<td class="left">—, “heat,”</td> +<td class="right"><a href="#Page_306">306</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">Washers, scrap,</td> +<td class="right"><a href="#Page_57">57</a>, <a href="#Page_124">124</a></td> +</tr> + +<tr> +<td class="left">Washings,</td> +<td class="right"><a href="#Page_122">122</a></td> +</tr> + +<tr> +<td class="left">Water-supply for tanks,</td> +<td class="right"><a href="#Page_177">177</a></td> +</tr> + +<tr> +<td class="left">Weeding, clean,</td> +<td class="right"><a href="#Page_13">13</a></td> +</tr> + +<tr> +<td class="left">Weights, “short,”</td> +<td class="right"><a href="#Page_157">157</a></td> +</tr> + +<tr> +<td class="left">Wickham process,</td> +<td class="right"><a href="#Page_293">293</a></td> +</tr> + +<tr> +<td class="left">Windows of drying houses,</td> +<td class="right"><a href="#Page_185">185</a></td> +</tr> + +<tr> +<td class="left">— factories,</td> +<td class="right"><a href="#Page_181">181</a></td> +</tr> + +<tr> +<td class="left">Working of rubber,</td> +<td class="right"><a href="#Page_304">304</a></td> +</tr> + +<tr> +<td colspan="2"> </td> +</tr> + +<tr> +<td class="left">Yields,</td> +<td class="right"><a href="#Page_23">23</a>, <a href="#Page_25">25</a></td> +</tr> + +</table> + +<div class="bbox"> +<p class="center">Transcriber's notes:</p> +<ul> + <li>Some minor typographical and lay-out errors have been corrected.</li> + <li>Inconsistencies in spelling have not been corrected.</li> + <li>Changes made to original text: + <ul> + <li>Table of Contents: + <ul> + <li><i>Early collection of latex transport</i> changed to <i>Early collection of latex</i>—<i>Transport</i>.</li> + <li><i>Roof brick built houses</i> changed to <i>Roof</i>—<i>Brick built houses</i>.</li> + <li>Named sections in Table of Contents do not always match one-to-one with named sections in text. Links point to the + sections most closely resembling the description in the Table of Contents. Occasionally multiple links point to + the same section in the text; some named sections in the text are not mentioned in the Table of Contents.</li> + <li>The order of the sections under Chapters XII and XXII has been changed slightly to reflect the order of the sections + in the text.</li> + </ul> + </li> + <li><i>Tephrosia candiad</i> changed to <i>Tephrosia candida</i>.</li> + <li><i>Archiev</i> changed to <i>Archief</i>.</li> + <li><i>about <span class="enum">1</span>⁄<span class="denom">2</span> square</i> changed to <i>about <span + class="enum">1</span>⁄<span class="denom">2</span> inch square</i>.</li> + <li><i>asbesto-slate</i> changed to <i>asbestos-slate</i> as elsewhere.</li> + <li><i>Formaline</i> changed to <i>Formalin</i> as elsewhere.</li> + <li>Footnotes moved to under the paragraph they belong to.</li> + </ul></li> + <li>Page 141: <i>The lengths of crepe were weighed carefully at 8 a.m. and 4 <b>a</b>.m.</i> should probably read <i>The lengths of + crepe were weighed carefully at 8 a.m. and 4 <b>p</b>.m.</i></li> +</ul> +</div> + + + + + + + + +<pre> + + + + + +End of the Project Gutenberg EBook of The Preparation of Plantation Rubber, by +Sidney Morgan + +*** END OF THIS PROJECT GUTENBERG EBOOK RUBBER *** + +***** This file should be named 35510-h.htm or 35510-h.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/3/5/5/1/35510/ + +Produced by Chris Curnow, Harry Lamé, Robin Curnow and +the Online Distributed Proofreading Team at +http://www.pgdp.net + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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