DRYING AND PACKING RUBBER FOR EXPORT. 137 



The flue is composed of heavy black iron from 12 to 15 inches 

 in diameter, and runs round the building at about 3 feet from the 

 walls. It issues from the same wall by which it enters the 

 building, but at the opposite corner, where it is connected with a 

 smoke stack and thus runs round three sides of the building. In 

 a building measuring 20 ft. by 20 ft. by 20 ft. a temperature 

 up to 1 10 Fahr. could be maintained if desired with a single 

 flue such as that described. Larger buildings would require 

 more flues in proportion to the increase in size. Shelves of wire 

 netting on which to place the rubber could also be arranged all 

 round this building. 



Drying of rubber by calcium chloride has also been suggested. 

 Ridley states that the expense is not great, as calcium chloride 

 is quite cheap and practically lasts for ever. 



VACUUM DRYING. 



Vacuum drying is the most expeditious method, and is being 

 employed on many rubber estates. 



By the adoption of this method moisture can be rapidly 

 extracted from the rubber without exposing it to injuriously high 

 temperatures, and the process is quite independent of climatic 

 conditions. 



Less fuel is required than by the hot air drying method, as 

 in the latter it is estimated that only about one-third of the heat 

 conveyed by the air is given up to the rubber since the air has 

 to pass too quickly through the drying-rooms to take up all the 

 moisture of which it is capable. On the other hand, if the hot 

 air be made to travel slowly with a view of taking up a greater 

 percentage of moisture, the drying of the rubber is considerably 

 retarded. The hot air likewise frequently contains dust which 

 is liable to be deposited on the moist surface of the rubber. 



Far less space is required for vacuum drying than for hot air 

 drying, as in the latter case it is necessary to leave sufficient 

 space between the rubber blocks or sheets for a free current of 

 air to pass around them. Hot air dried rubber is frequently 

 hard on the surface, whereas the reverse condition is obtained in 

 a vacuum dryer. 



The enormous economy which is effected in fuel by vacuum 

 drying will be better appreciated if it be borne in mind that 



