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appeared to have solved the old difficulties associated with drying. 

 There had been, however, suggestions and proposals to introduce 

 vacuum drying on estates, and consequently I paid special 

 attention to the modes of drying washed rubber in use in Great 

 Britain. In a few manufactories only I found vacuum drying 

 had been introduced, but the great bulk of washed rubber is 

 still dried by hanging it up in dark warm rooms. A vacuum 

 drying chamber is a large iron box, of from 100 to 200 cubic 

 feet capacity, fitted inside with shallow iron trays with per- 

 forated bottoms, and heated with steam pipes. The interior is 

 connected by an iron pipe with an exhaust pump. Wet rubber is 

 placed in the iron trays, the doors are closed, and the temperature 

 raised to 120 to 130 degrees F., and the pump started. The air 

 and water vapour that are drawn out of the chamber are passed 

 through a condensing cylinder, fitted with a glass front, and the 

 condensed vapour is seen falling as a stream of drops of water. 

 After two or three hours this stream of drops of water ceases, and 

 the rubber or whatever material is being operated upon is then 

 regarded as dry and ready for removal. Rubber dried in this way 

 is always softened by the heating which is necessary if the drying 

 is to be rapid, and in the opinion of manufacturers who have not 

 adopted the process the nerve and quality of the rubber are injured, 

 though with those who have adopted vacuum drying this is not 

 regarded as very important, chiefly because the cause of softening 

 is known, and it is regarded as only an anticipation of the softening 

 which always occurs in mastication of the rubber, the next step in 

 the process of manufacture. On the other hand, some forms of 

 rubber — such as very soft African rubbers — cannot be dried in this 

 way at all because the softening in their case proceeds too far. 

 The sheets of rubber dried in this way adhere to one another when 

 packed and stored away, this is of no importance in the factory, 

 because the rubber is known to be clean and dry and ready for use, 

 but if plantation rubber were offered in the same soft and adhesive 

 masses, objection, and serious objection, would naturally be made. 

 It would be necessary to maintain a lower temperature in the 

 vacuum chamber than is in common use if this softening of the 

 rubber is to be entirely avoided, and this would seriously interfere 

 with the efficiency of the machine. The rate .of the evaporation of 

 the water and drying of the contents depends upon the difference 

 between the temperature of the vacuum chamber and the tempera- 

 ture of the condensing chamber, as well as upon the absolute 

 temperatue of the vacuum chamber. In the tropics it will not be 

 possible to maintain the condenser below 80 deg. F., which is 20 

 degrees above the temperature of the condenser in England. This 

 diminished difference, together with the necessary lowering of the 

 temperature of the vacuum chamber itself, will seriously impair the 

 efficiency of the vacuum drier, the only advantage of which is the 

 rapidity of drying. Taking into consideration the further fact that 

 plantation rubber is always inclined to be soft, I should certainly 

 not recommend any form of drying in which artificial heat is 

 necessary, and which involves the elaboration of machinery and 



