RUBBER PLANTING 231 



at a high temperature. We have already distinguished 

 in the last chapter between hot and cold vulcanisation. 

 Under hot vulcanisation again two processes may be 

 separately considered. Of these, the more important is 

 the dry process originally patented by Goodyear. In 

 this process the proper amount of sulphur is incorporated 

 with the rubber in the mixing rollers before the articles 

 are made up, and vulcanisation is effected by heating 

 either directly in steam under pressure or in steam- 

 jacketed chambers, or in hydraulic presses heated by 

 steam in various ways. 



Hancock's wet process, on the other hand, is chiefly 

 of historical interest. In this process articles made of 

 sheet rubber, without any previous admixture of sulphur, 

 are immersed in molten sulphur for a certain time and 

 at a certain temperature. 



Finally, in the cold process, patented by Parkes in 

 1848, the articles are immersed in a solution of chloride 

 of sulphur, in carbon bisulphide, or in benzene. This 

 process is exceedingly rapid, and can only be applied to 

 articles of very thin sheet. 



The Dry Process. 



The chambers used for vulcanising by the dry 

 process are often of very large size. They may take 

 the form of great iron tunnels, into which the articles 

 to be vulcanised are run on rails. Hose pipes are often 

 vulcanised in lengths of 60 feet or more. The rubber 



