SUN-DRYING SHEET RUBBER.--Among the first curious sights which impress the visitor or newcomer to this country is the spectacle of sheet rubber hanging in the sun on native holdings. From what one has learned of the extraordinary care which must be exercised in all the processes of rubber preparation, one fails to understand how such rubber reaches the market without becoming tacky. That some of it does become slightly tacky is certain, but on the whole native rubber, though crudely prepared, is usually sound. The native idea of giving sheet rubber a preliminary drying in the sun is to hasten the total period of drying. That the period is curtailed would seem to be the case, but it is open to doubt, as the effect of sun-drying, if unduly prolonged, is to create a thin surface film of dry rubber which retards the drying of the rubber below the surface. Working with wet crepe rubber, the writer found that, to all external appearances, there was no effect upon the rubber when it was allowed to sun-dry for four or five hours. With periods of from six to ten hours the crepe becomes slightly sticky, chiefly on that portion across the support. When removed to the air-drying house this tackiness developed further, and the rubber, on the line of support, became so weak that it stretched and broke. Reasoning by analogy, it would appear that no apparent harm would result to sheet rubber from sun-drying for periods up to four or five hours. From experience (see Chapter IX.), not the slightest ill-effect is found to result from the short interval of preliminary drying or dripping practised on many estates preparatory to smoke-curing. ARTIFICIAL DRIERS FOR SHEET RUBBER.--It is understood that when vacuum driers were first applied to the drying of rubber it was thought possible to dry sheet rubber in this way. The practice was found to be impossible, as the length of time required and the temperature were responsible for the destruction of the form of the rubber; it became tacky and semi-liquid. THE "CHULA" DRIER.--Although several suggestions of devices for artificially drying sheet have been made, only one is known to be in use at the present time. In the original form this was used for drying other tropical products. It consists of a large iron chamber, in which are several compartments divided by means of baffle-plates. At one end there is a small furnace and, by means of a fan, smoke and hot air are drawn through the compartments. Owing to the temperature attained (140° to 160° F.) sheet rubber cannot be completely dried in the chambers, and is, as a rule, only treated in this manner for one or two days. Drying is then completed in an ordinary air-drying house. It is claimed that drying is expedited, and that the rubber can be packed in ten days.