138 BELL SYSTEM TECHNICAL JOURNAL 



also exists in crude rubber. It is also known that latex serum contains 

 a substantial quantity of protein in solution. The preparation of 

 crude rubber from latex by addition of acid or by processes of evap- 

 oration of the water by heat undoubtedly results in the precipitation 

 of considerable quantities of this protein which becomes entrapped 

 between the globules as they coalesce. It is easy then to visualize 

 that in crude rubber there exists a continuous phase of protein or a 

 protein network which, acting like most protein matter, absorbs large 

 quantities of water, resulting in paths through which electrical con- 

 duction occurs. 



Removal of Nitrogen Containing Bodies from Rubber 



The problem of developing a suitable commercial method for 

 preparing rubber free from nitrogenous matter offered many apparent 

 difficulties. The proteins are colloidal in nature and in the presence 

 of water form gelatinous masses rather than true solutions. On this 

 account they often cannot be removed by simple washing as can be done 

 in the case of gutta percha and balata. It has been known for some 

 time that proteins can be broken down to water soluble products by 

 boiling with dilute hydrochloric or sulphuric acids. This treatment 

 did not produce satisfactory results in the case of rubber. As a result 

 of many experiments involving a variety of methods, it was found that 

 heating rubber in an autoclave at an elevated temperature in the 

 presence of water alone fairly rapidly brought about the desired hy- 

 drolysis of the rubber proteins, converting them to water soluble 

 materials. As a result of subsequent washing, it was found that the 

 nitrogenous bodies had been almost completely eliminated without 

 deleterious effect on the rubber hydrocarbon. 



Rubber either in the form of sheets immersed in water or as an aque- 

 ous rubber dispersion such as latex can be employed in the process. 

 The treatment of latex, however, results in a more rapid hydrolysis 

 of the proteins. Considerable latitude exists in the choice of condi- 

 tions, but the following example will suffice to describe one method of 

 carrying out the process: ammonia preserved latex is diluted 1 to 5 

 with pure water. The latex is then heated in an autoclave for approx- 

 imately ten hours at 150° C. After cooling it is coagulated with 

 acetic acid and thoroughly washed. As a result of this treatment 

 the nitrogen content of the rubber is found to be less than 0.10 

 per cent, which is about one fourth that of ordinary plantation crude 

 rubber. Figures 1, 2, 3 and 4 illustrate the relative water absorption 

 and electrical stability of deproteinized rubber as compared with the 

 ordinary crude product. Vulcanized deproteinized rubber was also 



