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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 Bu ^ 
Rubber Co. This chamber is at work successfully, the mana 
reporting that the sheets or biscuits are dried in the Vacuum Cham- 
beCin about a hours. Some samples sent to London are favourably 
reported upon ; a consignment of vacuum dried sold in bmgap , 
l am Informed, secured" the top price. The vacuum dr, ed rubber 
is of a slightly lighter colour than when air-dned. 
The. Rubber sheets or biscuits or washed rubber towels as ; the 
case may be are placed in equal quantities upon per or 
which are put between the heating shelves of the drying chamber. 
The swing-hinged door closed, and the small air pump set o , 
“Site the chamber, for the first few moments the pump 
requires about horse-power but in 4 or 5 minutes when a vacuum 
of Is' Ld upwards is Secured f of a horse power suffices for the 
pump, in the case of the Bukit Rajah plant, the a, r pump is fitted 
with a steam cylinder of 4* dia. x6* 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 1 a most economica 
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 9 o° to ioo° F., then on account of 
the atmospheric pressure having been removed, evaporation sets 
in 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 I i 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 arrant „ient 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 ioo having been supplied for the 
latter works. 
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