CHAPTER XI
DRYING OF RUBBER
Air-Drying of Crepe.—It is still the prevailing custom to air-dry crepe rubbers. A few estates, it is true, have artificial driers installed, and in some necessary cases others will be erected. But in the majority of cases where money has been expended in building air-drying sheds, as long as it is only possible to ship rubber regularly air-drying is likely to remain in favour.
The great drawback to air-drying is that one is so dependent upon the weather conditions. In favourable weather the rubber dries well, but in a long period of wet weather rubber may accumulate at an alarming rate, and the accommodation is sometimes severely taxed. Of course, the rate of drying under the best conditions is mainly dependent on the thickness of the crepe, and every endeavour should be made to maintain a thin style of preparation. If this precaution is not taken, the rubber is liable to recurrent attacks of “spot” disease, and one’s troubles are very much augmented. This is a disability to which rubber treated in artificial driers is not liable. Still, air-dried rubber can be made equal, if not superior, in appearance to pale rubbers prepared by other processes.
For the lowest grades of crepe air-drying is always likely to remain the only method, as it would be extremely unsafe to submit them to heat.
It is noted in ordinary practice that the rate of drying on different estates, for the same type of rubber, may vary widely. Naturally the construction of the house has a great effect, and this subject will receive attention in a [subsequent chapter].
Similarly the position of the drying-shed exerts an important influence, and the erection of the building in low-lying surroundings is always calculated to prolong the drying period appreciably. Incidentally this means that the building must be larger than a normal rate of drying would otherwise demand.
The combination of a poor type of drying-house, a low-lying situation, and a prolonged wet season, might render it advisable to abandon the air-drying of high grade crepes in favour of artificial drying.
Artificial Driers for Crepe.—It is more common to find artificial driers in use in Ceylon than in Malaya, possibly because these driers have been in use in Ceylon for other products. Some time ago the question of installing artificial driers received the serious attention of a number of estates in this country, chiefly on account of the incidence of fungoid and bacterial diseases in crepe rubber. The simple treatment for the prevention of these diseases is to get the rubber dry in the shortest possible space of time. In most cases it is found sufficient to roll crepe thin for air-drying in order to prevent the appearance of coloured spots. It is found, however, that some drying-houses are so badly planned and constructed, that quick drying under even the best of conditions is a practical impossibility. Cases have been known in which the disease may disappear almost entirely during a period of freedom from rain, only to recur as soon as wet weather sets in again. There can be no doubt that, on the whole, the number of cases of “spot” disease is on the decline; but equally it is certain that a very few estates will always be liable to outbreaks as long as drying is attempted in existing houses. For these reasons it is a poor policy to temporise, and the only sound policy in extreme cases would be to give up ordinary air-drying in favour of some method of artificial drying. As regards the majority of estates preparing pale crepe for various reasons, it is not expected that any will instal artificial driers. Money has been expended in elaborate buildings which certainly do the work for which they were designed. As long, therefore, as the accommodation is sufficient, and regular shipments are the rule, it is expected that ordinary air-drying will still remain the general practice.
Of the better-known artificial driers, there are only three which merit serious consideration in these pages. They are the vacuum driers, the Colombo Commercial Company’s hot-air drier, and the Michie-Golledge process.