130 PARA RUBBER. 



torn between the rollers. These impurities are loosely embedded in 

 the rubber, but if the temperature is raised too high the resins may 

 be converted into sticky substances, which will cement the rubber 

 and mechanical impurities and thus render it impossible to remove 

 the latter by this process. 



The fragments rejoin and finally form a porous sheet which, 

 when dry, is known as washed rubber to the manufacturer. The 

 rubber may then undergo various masticating, mixing, and vulcani- 

 zing processes. 



Lawrence has, according to the ' ' India Rubber Journal," Novem- 

 ber 20, 1905, brought out a patent method for cleaning crude rubber, 

 which is to some extent applicable to ordinary scrap rubber on 

 estates. The process consists of first grinding or macerating the 

 rubber, and then subjecting it to liquids or solutions having different 

 specific gravities. It is specially devised to deal with the extraction 

 of the fibrous and woody matter in crude or scrap rubber. 

 Loss in Manufacturing. 



The actual loss in these purification processes is often surprising. 

 The loss on washing some of the Para rubber collected by the 

 natives in the Amazon District varies from 10 to 40 per cent. , and 

 Biffen states that the loss in the factories is as follows for different 

 gradesof Para rubber: — (1) fine Para, 10-15 percent. ; (2) extra fine, 

 the carelessly smoked pieces, 15-20 per cent.; Sernamby, rubber 

 pulled from the cuts on the tree and cups, 20-40 per cent. Many 

 lots of fine wild Para have, during recent times,* shown a loss on 

 washing of from 15-16 per cent, in samples containing 2 - 2 to 29 per 

 cent, of resin and 0-27 to 0-29 per cent of ash. According to John- 

 son, the loss from fine Para is from 10-15 per cent., whereas that 

 from the plantation biscuit, sheet, crepe, &c, rubber is only 

 about 1 per cent. Weberj states that the fine Para rubber from 

 the Amazon District shows a loss on washing of 12 to 18 per cent., 

 and contains 1-3 per cent, of resin and 0-3 per cent, of ash in the 

 dry washed material. 



Different brands show a variation in the amount of the loss on 

 washing as indicated below, and the composition of the impurities 

 are clearly put forward by Weber : — 



Loss on Oily and Resinous 

 Brand. Washing. Substances. Ash. 



per cent. per cent. per cent. 



1 



Ceylon 



Para, hard cure 



Para, soft cure 



Ceara 



Borneo 



3-0 .. 0-5 



2-1 .. 0-5 



2-5 .. 0-3 



2-0 .. 2-74 



O . O O ■ 9 



The loss on washing is estimated by determining the yield of dry 

 washed rubber obtainable from a known bulk of crude rubber. This 



* India Rubber Trades Journal, April 28, 1902. 

 f Weber, I.e.. p. 122, 



