, will not be discussed at this stage. Neither will mention be made of any patent processes of coagulation

t, 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 efficac

tion. In many cases no harm resulted, for the simple reason that, owing to the large proportion of water in the latex, the acid w

to 20 of water, and use this with success because o

portions-i.e., the respective volumes of acid and water in the solution of acid made up every day. That the strength of the

ng the quantity of acid employed was sufficient for coagulation, the best and most uniform coagulation is obtained from the use of the most dilute acid, within limits. It will often be found that where pure acid has been employed coagulation is local-i.e., we have lumpy coagulation, and often a very milky r

e mixing is more thorough and uniform. Coagulation i

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 dilu

luting 1 pint of acid with 20 pints of water, and 1 gallon

5 gallons of this stock solution contain only the same quantity of pure acid as 1 gallon of the old s

necessary for 50 g

s necessary for 50

oregoing examples are not absolutely and mathematically corre

on 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

found that, for pure average latex, the quantity of acid necessary for c

id; 1,000 part

rubber) probably a little more acid would be required, and similarly

atex the greater the quantity of acid necessary, but thi

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

r to 1 part of pure acid, this gives us a mixture of 1 to 100. For 1 gallon of pure late

so-called latex. But we still have only 1 gallon of real latex present in the diluted lat

, 3, or even 4 gallons of water it is still onl

r, it is necessary to add a little mor

where the rubber undergoes protracted washing on the machines, the presence of a slight excess of acid in coagulation is not calculated to cause any deterioration in the quality of the rubber. Advantage

the beginner that any further experimental work as to the quantity of acetic acid

ccepted as the rough basis for working. In modern practice, however, undiluted latex is usually dilut

dardised latex; and this quantity need not be exceeded, except in cases where an appreciable amoun

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

ent. strength for all practical purposes, into a simple operation of mixing pur

ex can be calculated easily from the ratio 1:1,200. As the strength of solution is 1:100 it wi

s of standardised latex, 71?2 gallons

s of latex would need 10 gallons

e system of standardising latex in order to obtain uniformity. They are ill-advised if they do not follow this practice; but in case

ssary for complete coagulation unless anti-coagulants have been used, when the quantity must be increased as experience directs. It will be recognised, of course,

ecially 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

forated 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

Dilution and

ar end strainers. Each dilution tank is of equal

ept 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 pal

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

e substance capable o

that solutions could easily b

must b

t of any harmful effect upo

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

been made in conjunction with Messrs. Beadle and Stevens for fully eight months before the name of the chemical was mentioned in reports, and they had decided from the results of vulcanisation tests that the chemical was quite innocuous. Then, and only then, did we consider it advisable to recommend the use of sodium bisulphite in general estate practice. Owing to the initial prejudice against rubber prepared with sodium bisulphite, the results of our preliminary work were published by permission of the Rubber Growers' Association.[3] The original instructions to estates regarding the proper employment of this chemical were given in the private reports issued b

onal Rubber and Allied

reparation of Plantation Rubber," Beadle, Stevens

order to obtain the best possible price for their product, and not because we desire to continue a pract

e 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

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 var

en the latex is of a rich yellow colour. Sodium bisulphite will not "bleach" this colour, and it is well to

volume of undiluted latices from different areas of the estate, the effect upon the dry rubbers wi

rubber content as is done in sheet preparation. One is thus assured that the prescribed quanti

. dry rubber per gallon the followi

Use of Sodiu

phite in water at the rat

use 1 gallon to every

er 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 th

hen there may often be seen at the bottom undissolved particles, sand, and other impurity. It is necessary, therefore, in such ca

cess, leads mainly to delay in the period of drying and the production of an overpale rubber.[5] It is probable that

of Plantation Rubber,

hat 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 o

e 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. Formul? have been given for its use in the field w

te: For Use i

anhydrous sodium sulphi

ption jar or tank, is sufficient for the treatment of 40 gal

lutions is here reiterated. Stirring should be thorough, say for five minutes, and if there is

on 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 conten

with the latex, as the latter is strained into the solution and the conti

nowledged that when not abused there are points in favour of its employment in preference to sodi

up freshly it is an ef

s in water, there is no residual substa

ives a bright

t at all times is greater t

there is loss by evaporatio

tain. Even in normal quantity it is sai

e following formula is stated to give satisfactory results in the preparation of sheet rubbe

e of Formalin

lin is diluted with

lon is required for 50 gal

e effect of formalin upon the vulcanisation of rubber, when used in minimum proportions, there can be no question concerni