RUBBER PLANTING 235 



a filling material with fresh rubber, but the bulk of the 

 reclaimed rubber used in manufacture goes through a 

 series of complicated processes. The discarded rubber 

 goods used for making reclaim, whether they be old 

 rubber shoes or old motor tyres, usually contain a con- 

 siderable quantity of cotton fibre. In order to remove 

 this fibre the rubber is boiled with dilute sulphuric acid, 

 and the cotton thus disintegrated can then be got rid of 

 by grinding, combined with the use of an air blast. The 

 acid process is generally followed by an alkali process, 

 in which the free sulphur is removed by boiling with 

 caustic soda. The residual rubber is then heated with 

 resin-oil, and can afterwards be manipulated more or 

 less like ordinary unvulcanised rubber. The reclaimed 

 rubber contains all the mineral substances originally 

 added, so that little further mixing is required if a 

 similar class of goods is to be remanufactured. 



In addition to the methods described above, it is 

 claimed that processes have already been perfected by 

 which the sulphur of vulcanisation can be more or less 

 completely removed from the old rubber. Schidrowitz 

 states that other processes have been recently introduced 

 by which " particles of vulcanised rubber in the shape 

 of dust or flakes can by pressure and heat be moulded 

 to a homogeneous mass, which, on cooling, is to all 

 intents and purposes indistinguishable from an ordinary 

 moulded article." 



