The Preparation of Plantation Rubber

by Sidney Morgan

On a small scale a primitive smoke-house could be built easily and cheaply, and such a building might be fully as efficacious as the most elaborate and expensive installation. In the early days of estates it was not uncommon to see temporary smoke-houses constructed of wood, and roofed with “attaps” (palm leaves). Some of the best rubber in the market has come from wooden buildings, but naturally the risk of destruction by fire is considerable.

For imperative reasons it may be sometimes found necessary to smoke rubber when the only available building is a single-storey one. As a temporary measure, the building may be converted into a smoke-house by placing the fires in pits sunk deeply into the ground, and effectively screened above by iron baffle plates. But it is not advisable that smoking be continued in such a single-storey building, as the best effects are not obtained, and the risk of fire is far too great.

Usual Types.—At first sight it would appear that the best type of smoke-house would be one consisting of a tall building, covering a comparatively small superficial area, and having a number of superimposed chambers in which the rubber could be hung to dry. In practice there are several solid objections which limit the height and the number of floors. Chief among these is the question of temperature. If smoke-curing is to be effective, a certain temperature must be attained and maintained. To obtain such results in a house of excessive height would be difficult, if not impossible, under normal conditions. It would be found that the chamber immediately above the furnace-room would be overheated if the temperature in the upper rooms was within the desired range, etc.

Until recent years smoke-houses could be classed as belonging to one of two types:

(1) Those having external furnaces.

(2) Those having internal furnaces.

The number of the former existing at the present time must be very small, as it has been shown that the arrangement of the furnace outside the house is unsatisfactory in comparison with the other type of house. In discussing the question of smoke-houses, therefore, it will be understood that the standard type accepted is that having an internal furnace. In its original form it was known as a “Kent” drier, and consisted of a tall two-storey wooden building. The walls of the lower chamber had the form of an inverted and truncated pyramid. By this arrangement it was possible to obtain from a comparatively small fire sufficient smoke and heat to cure the product placed in the room above. This is the principle upon which many smoke-houses in Malaya are designed. On a very large scale it is not claimed that the sloping sides of the lower chamber lead to economy in the number of fires, but merely divert the smoke in an upward direction. It is acknowledged that vertical lower walls are quite effective, and it is an easier matter to fit in doors.

It may be noted that the usual type of smoke-house now in general use consists of a building of two storeys, in the lower of which are situated the furnaces, while rubber is hung on racks in the upper room. Sometimes there may be a third storey, also used as a drying (curing) chamber. As a rule the drying-room is one long unit, as also is the furnace chamber; but in some cases they are subdivided by vertical partitions into smaller chambers, for ease of working and better control. This applies with some force in the case of very long houses standing in an open space. It is sometimes found in such cases that at certain seasons the prevailing winds have the effect of making drying and curing uneven in parts of the building.

With these exceptions, the ordinary type of smoke-house functions very efficiently, and is capable of drying average sheet (from standardised latex) in a period ranging from seven to eleven days. Should the building not be capable of such performance, in spite of the strict observance of all rules laid down for the processes of preparation, then there is some defect in ventilation or in the distribution of heat.

General Ventilation.—The ordinary rules of ventilation in drying-houses apply equally to a smoke-house. There should be a slow current of air and smoke from the lowest point to the highest point in the building.