The Preparation of Plantation Rubber

by Sidney Morgan

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.

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 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.

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.

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.

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 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.

All precautions taken in preparation and curing can be nullified, as already indicated, by unsuitable storage conditions.

Tool-Sheds and Store-Rooms.—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.

Situation of Factory Buildings.—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.

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, 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.

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.