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[30] 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.
[30] “Archief voor de Rubbercultuur,” Nederlands Indies, 1920, 4, 273.
On page 308 of the same publication, experiments on the effect of sugars are described, in connection with aerobic coagulation. Observations from a further set of experiments tended to indicate a direct connection between the effects of tapping and spontaneous coagulation. It is suggested that heavy tapping causes a diminution in the latex of those substances which act in some way as accelerating agents in coagulation—e.g., sugars. The smaller the proportion of these substances, the slower and less complete is natural (spontaneous) coagulation.
Ilcken-Down Process.—This process is the subject of patents granted in 1915 to Messrs. Ilcken and Down. It has been in fair prominence, and has been tried experimentally on several estates and in public demonstration.
It is a coagulating process, and, in the original specification, employed as agents a mixture of alcohol (in the form of 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.
Later modifications covered the addition of a small quantity of glycerine; or, failing supplies of that substance, coconut oil.
Many advantages are claimed for the process, but most of them cannot be substantiated. The two chief claims are:
1. The production of a uniform standard of rubber.
2. The obtainment from a unit volume of latex of a greater weight of rubber than can be obtained from an equal volume of the same latex by ordinary coagulation with acetic acid. It is to be inferred that the agents employed have the power of adding to the coagulum some of the substances which usually remain in solution in the clear serum.
Regarding the first of these claims, it has been shown[31] 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.