664 RUBBER 



hot-air driers is that the temperature must be carefully 

 regulated, especially towards the end of the drying", to 

 avoid tackiness. With vacuum-dried crepe it is usual to 

 pass the rubber again through the washing rollers after 

 drying; only surface moisture is then taken up by the 

 rubber, which can be quickly dried in an ordinary drying 

 room. The chief advantages of artificial methods of 

 drying are rapidity in drying, economy in space, and 

 absence of " spot " diseases. 



No satisfactory vulcanizing experiments appear to have 

 been carried out so far to test the value or otherwise of 

 any of these processes, but experiments will be carried 

 out shortly at the Department of Agriculture, Federated 

 Malay States. 



Before passing from this subject another process offers 

 interesting possibilities, namely, drying in the presence 

 of carbon dioxide. This may be carried out in an 

 ordinary two-story building similar to the smoke-houses 

 in common use, charcoal fires, instead of the usual 

 fuel, being used in the fire-boxes. The atmosphere of 

 carbonic gas inhibits the slow natural oxidation which 

 continues during the drying of the rubber and prevents 

 the growth of the usual chromogenic organisms, which 

 are aerobic. 



It might be stated here that these statements refer to 

 the drying of crepe rubber, since no unsmoked sheet is 

 now made on the larger estates; there is, however, no 

 difference in method, the only difference being in the 

 distance between the racks which hold the rubber. 



Smoke Curing of Rubber. 



Smoke curing of plantation rubber probably had its 

 origin as an imitation of the Amazonian smoke-curing 

 process, and the recent vulcanizing tests carried out by 

 Messrs. Beadle and Stevens on behalf of the Rubber 

 Growers' Association appear to have proved definitely 

 that the smoking of plantation sheet or other forms of 

 rubber does undoubtedly in some way improve the 

 physical properties of the rubber to a marked extent. 

 Whether the results obtained depend on one or more of 



