(b) That in which, after noting the volume, the calculation is based upon a reading of the dry rubber content of the latex, obtained by means of an instrument such as the “Metrolac,” or any other instrument working on the same principle.
Quite a number of estates which have not adopted the full system of payment by result yet employed some such method of checking the yields of individual coolies, as the observed results act as a great deterrent against various malpractices, such as neglecting to tap trees, adulteration of the latex, etc.
Tree-Scrap.—The thin film of latex which coagulates naturally upon the surface of the tapping cut after the latex has ceased to flow is known as “tree-scrap.” Normally it is collected on all estates, but the method of collection varies according to the class of labour employed. On most estates, where the labour is Tamil or Javanese, it is supposed to be removed as fully as possible before the tapping cut is reopened. The narrow strips are then placed in a bag or basket carried by the tapper. Chinese tappers usually decline to follow this practice of first peeling off the scrap, and remove it by the operation of tapping, with the result that the scrap when brought into the store has adhering to it various shavings of bark. Unless these can be thoroughly cleaned off the scrap cannot truly be classed as “tree-scrap.”
Oxidation of Tree-Scrap.—It is often noted that some scrap is dark in colour, and in this condition it is generally spoken of as “oxidised” scrap. The oxidation is probably due to an enzyme, and also to the presence of chemical 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.
Care of Tree-Scrap.—As these scraps eventually give a grade of rubber which compares well with other and better-looking grades care should be exercised in collection and treatment so that its quality is not impaired in any way.
To Prevent Oxidation.—As a rule the scraps are picked over, and heavily oxidised pieces are sorted out; otherwise the crepe rubber prepared exhibits black streaks. The scraps should not be allowed to remain in the sun (which induces “tackiness”), and if they have to be kept over night they may be placed in a weak solution (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.
Bark Shavings.—In the matter of collecting bark-shavings much depends upon the organisation and nature of the labour force. Probably, on the majority of estates bark-shavings are collected systematically, but on quite a number considerable laxity in this respect has been noted. This may arise from lack of adequate supervision or from the peculiar systems of working which seem to pertain to Chinese labour. Granted that the trees are well “scrapped,” and that the percentage of rubber obtained from shavings under such circumstances would be extremely small (say 2 per cent. by weight on the total output), it does not need much calculation to see that annually the loss of rubber to the estate must be considerable. It would also seem to follow that, if the adult labour declines to pick up bark-shavings carefully, it might pay to employ children for the purpose. Or, as is done in some places, the adult labour might find it advantageous to collect bark-shavings at low rates per pound.
It is a well-known fact that if bark-shavings be allowed to accumulate in a heap for any but a short period, a fermentative and heating action is set up. The heat developed in these piles of shavings is so considerable that it is impossible to keep the hand in a heap for more than a second or two. Should this be allowed to persist, as would happen in the case of a breakdown of engine or machines, it usually results in the final crepe rubber becoming tacky when approaching dryness.
To avoid this heating effect it is necessary to have spare jars or proper tanks in which the shavings may be soaked in water. In this condition bark-shavings may be kept for many days.
For the same reason (i.e., the heating effect and consequent tackiness) the custom followed on some estates of allowing coolies to keep bark-shavings in their “lines” until they have accumulated a fair quantity cannot be commended, quite apart from the possibility of actual loss by theft, which is thus rendered easy.