222 RUBBER AND 



to some extent the series of rollers in a modern flour 

 mill, although the processes of rubber washing and flour 

 milling have little other resemblance. By passing 

 repeatedly through the washing rollers under a stream 

 of water, the impurities present in most kinds of com- 

 mercial rubber are gradually washed away, and the 

 rubber finally emerges in the form of a thin crepe 

 convenient for drying. The rubber itself undergoes 

 much tearing and stretching during the process, and it 

 is important that this mechanical action should not be 

 carried further than is absolutely necessary in order to 

 ensure a sufficient degree of purity, since the " nerve " 

 of the rubber is largely destroyed by the forcible treat- 

 ment involved. 



Drying. 



The so-called "nerve" lost in washing is partly 

 recovered during the slow process of drying, which is 

 effected by hanging the strips of rubber in large 

 chambers exposed to a current of dry air. The drying 

 of the washed rubber takes place more readily than 

 in the case of rubber freshly prepared from latex, since 

 the moisture is not so closely incorporated in the 

 substance of the rubber. On the other hand many 

 commercial rubbers, for example hard Para, contain a 

 considerable proportion of the original moisture derived 

 from the latex. When this moisture in addition to the 

 water introduced during washing has to be removed, 

 the drying process takes considerably longer. 



