1 to 20; 1 gallon necessary for 50 gallons pure latex.
1 to 100; 5 gallons necessary for 50 gallons pure latex.
It may be pointed out that the quantities worked out in the foregoing examples are not absolutely and mathematically correct, but they are quite close enough for all practical purposes.
It may be advanced by someone that if a dilute solution of acid, such as 1 in 100, is used the bulk of this stock solution (5 gallons to 50 gallons of latex) is very great, and might be injurious to the quality of the resulting rubber. A moment’s consideration will show that, after all, the volume of acid solution is only one-tenth that of the volume of latex. This can have no effect upon the quality of the rubber. Even dilution of the pure latex with half its bulk of water in the factory will have no effect upon the quality of the resulting rubber. It is to be remembered that, except in cases where the proportion of added water to latex is absurdly large, the main argument against putting water into the latex-cups is against the possible poor quality of the water rather than against the actual small quantity theoretically added. It is acknowledged that, where the water to be put into the cups can be guaranteed to be of good quality, no great objection would be raised against placing the smallest possible quantity of such water in the cups. But how many estates have such good water easily available to the coolies, and how many estates can be sure that only that smallest possible quantity would be used? It is a notorious fact that, even on estates where the quantity of water used was supposed to be a minimum, the proportion of water to latex in some cups often exceeded even three or four to one. In any case it may be stated as an elementary truism that the absence of water is more to be desired than water of doubtful quality.
Quantity of Acid.—As a result of repeated experimental work it has been found that, for pure average latex, the quantity of acid necessary for complete coagulation, reckoned in parts of pure acid to parts of latex, is:
1 part pure acid; 1,000 parts average latex.
Where the latex is rather richer than average (above 30 per cent. dry rubber) probably a little more acid would be required, and similarly if the dry rubber content is lower the quantity of acid must be less.
It used to be a common belief that the more dilute the latex the greater the quantity of acid necessary, but this would only apply to cases of extreme dilution of latex.
As a matter of fact, up to certain limits of added water, the reverse is actually the case—i.e., the more water in the latex the less acid must be added, assuming that for pure latex the proportion of pure acid to latex is taken as 1 part to 1,000 parts. This was found to be the case up to dilutions of three or four times the volume of latex. To take concrete examples which will perhaps make the truth more clear:
Assuming we commence by making up our stock solution of acid by adding 100 parts of water to 1 part of pure acid, this gives us a mixture of 1 to 100. For 1 gallon of pure latex it would be necessary to add one-tenth of its volume of the above mixture—i.e., 16 ozs.
Suppose we take a gallon of pure latex and add a gallon of water, we now have 2 gallons of so-called latex. But we still have only 1 gallon of real latex present in the diluted latex, and it is only necessary to add sufficient acid to coagulate this gallon—i.e., 16 ozs.