*43 



Works for the drying of India Rubber over 20,000 tons per annum 

 of the wet rubber being now treated in the Vacuum Chambers. 



A few months back a chamber of No. 3 size which receives about 

 120 lbs. of wet rubber per charge was supplied to the Bukit Rajah 

 Rubber Co. This chamber is at work successfully, the manager 

 reporting that the sheets or biscuits are dried in the Vacuum Cham- 

 ber in about 2 hours. Some samples sent to London are favourably 

 reported upon ; a consignment of vacuum dried sold in Singapore, 

 I am informed, secured the top price. The vacuum dried rubber 

 is of a slightly lighter colour than when air-dried. 



The Rubber sheets or biscuits or washed rubber towels as the 

 case may be are placed in equal quantities upon perforated trays 

 which are put between the heating shelves of the drying chamber. 

 The swing-hinged door closed, and the small air pump set to work, 

 to evacuate the chamber, for the first few moments the pump 

 requires about horse-power but in 4 or 5 minutes when a vacuum 

 of 28' and upwards is secured f of a horse power suffices for the 

 pump. In the case of the Bukit Rajah plant, the air pump is fitted 

 with a steam cylinder of 4 T 5 ¥ dia. x6 T 5 ¥ stroke and when the steam 

 has driven the pump it is passed to the heating shelves of the dry- 

 ing chamber and effects the evaporation. This is a most economical 

 system of working, practically doing away with the fuel bill for 

 drying purposes, as the steam used is so little as to be scarcely 

 appreciable. 



When the wet Rubber reaches 90 to 100 F., then on account of 

 the atmospheric pressure having been removed, evaporation sets 

 m most rapidly and the rubber remains at this low temperature for 

 a considerable time, rising slowly towards the completion of the 

 drying which takes about two hours as I am informed by the Bukit 

 Rajah Co., for their Rubber biscuits. In the Rubber factories with 

 washed Rubber the time is from ij to if hours. 



In the vacuum chamber owing to the low temperature and the 

 absence of air with its oxygen the wet surface of the warm rubber 

 does not become oxydised as happens with air-dried rubbers. 



In the Rubber factories the difference is very marked, the washed 

 Rubber sheets from the ordinary drying room being quite hard, 

 whilst the same sheets vacuum dried remain soft and pliable and 

 of a lighter colour. 



The vapour arising from the drying rubber passes to a small 

 surface condenser, where the moisture is condensed and collected, 

 the air pump being a dry one. The condenser is also fitted with a 

 patented arrangement of Mr. PASSBURG'S by which it can be told 

 when all moisture has been removed from the material in the 

 drying chamber. 



The space occupied is very small. 



Next to Rubber Works, these chambers have been most largely 

 used in explosives works, about 100 having been supplied for the 

 latter works. 



