120 PARA RUBBER. 



Burgess* states that the raw rubber, before it is vulcanized, is 

 very sensitive to heat, and a temperature of 150° F. may render 

 Para rubber sticky on the surface, and a higher temperature utterly 

 destroy the "nerve" of it; he declares that it is, therefore, injudi- 

 cious to use artificial heat in hastening the drying of rubber. He 

 also states that if artificial heat were absolutely necessary a very 

 carefully regulated temperature, never exceeding 120° F., would 

 probably not cause any great damage. 



Weberf asserted that certain brands of indiarubber cannot be 

 hung up to dry in the form of sheets after the washing process, as 

 they become so soft as to fall to pieces. The temperature at which 

 indiarubber begins to soften varies according to the percentage of 

 the resinous and oily substances present, and many samples of good 

 Para rubber pass into a more or less fluid state at about 170 to 180°F. 



It is, therefore, obvious that the question of drying rubber is apt 

 to be a delicate one where high temperatures are concerned. In the 

 ' ' India Rubber World " (November 1 , 1905) a suggestion is made that 

 the principle of drying rubber in vacuo might be tried. It is main- 

 tained that the drying in vacuo is accomplished rapidly, only low 

 temperatures are necessary, and a great saving in fuel, space, and 

 labour is effected. The vacuum drying chambers may be obtained 

 in rectangular and in cylindrical styles and fitted with plate shelves or 

 shelf coils inside. According to Burgess, a vacuum chamber con- 

 sists of a large iron box, of from 100 to 200 cubic feet capacit} 7 , fitted 

 inside with shallow trays with perforated bottoms, and heated 

 with steam pipes, the interior being connected by an iron pipe with 

 an exhaust pump. The temperature of the chamber is raised to 

 120 to 130° F. , and after the air has been drawn through the chamber 

 for a few hours the rubber is usually sufficiently dry for most pur- 

 poses. Most manufacturers, however, have not adopted drying in 

 vacuo, as they believe the rubber is softened by the heating and the 

 nerve and quality of the rubber injured, but prefer to dry the rubber 

 gradually in dark warm rooms, 



Dickson's Machine for Coagulating and Drying Rubber. 



Mr. Dickson has kindly supplied me with the following descrip- 

 tion of his machine : — 



"This machine consists of a small furnace, on the top of 

 which is a smoke box containing a revolving drum. Between 

 the furnace and the smoke box is a series of baffle plates to 

 divert the fumes and ensure that no flames and sparks pass into 

 the smoke box. At one side is a shallow pan for receiving the 

 latex. In this pan is a small roller partly immersed in the latex, with 

 its surface in contact with the surface of the large drum. A fire 

 is placed in the furnace, and the fumes are allowed to pass between the 

 baffle plates and round the large drum to the chimney. When the 



* Burgess, Lecture at the Agri-Horticultural Show, Kuala Lumpur, 

 1904. 



* Chemistry of India Rubber, p. 21 



