PARAGUTTA, A NEW INSULATING MATERIAL 137 



Even so, vulcanized rubber is very inferior to gutta percha for 

 submarine insulation as the necessary manufacturing operations are 

 more difficult and likely to lead to defects. The removal of mechanical 

 impurities is by no means simple because the raw stock is not plastic 

 enough for thorough straining. The lack of plasticity also interferes 

 with multiple covering of conductors, and the process of heating to 

 bring about vulcanization is liable to result in deformation of the 

 insulating layers. The joining and repairing of core lengths insulated 

 with rubber is also more of a problem than with gutta percha, which 

 can be so readily remolded in case imperfections appear in the course 

 of the process. 



The methods of electrical stabilization of vulcanizable rubber 

 compositions are only partially effective in the absence of vulcanization 

 and it was therefore necessary to extend the study in an effort to 

 secure the desired electrical properties in rubber in the raw state. 

 It might be supposed that mere admixture of raw rubber with gutta 

 hydrocarbon would produce the necessary stability. This is true 

 only to a limited extent. When the proportions of rubber are high 

 enough to meet the mechanical and economic requirements, the 

 electrical stability is impaired. 



Effect of Proteins on Electrical Stability of Crude 

 Rubber Immersed in Water 



It has been previously shown that crude rubber contains consider- 

 able water soluble impurities and that their removal results in a 

 large reduction in water absorption. i- ^ Rubber so prepared absorbs 

 no more water than good cable gutta percha but in a raw state when 

 immersed in water, it fails sooner or later as an insulator, often sud- 

 denly and completely. 



To determine the reason for this electrical instability of crude rubber 

 in water, samples of very pure rubber hydrocarbon completely freed 

 from proteins, resins and other impurities were prepared and tested. 

 It was found that this material not only absorbed very little water 

 but showed practically no change in electrical characteristics as a 

 result of prolonged immersion in water. The impurities natural to 

 rubber therefore seem to be responsible for its instability. 



It has been known for many years that crude rubber contains 

 proteins, ordinary plantation rubber containing about 3 per cent. 

 Previous investigators have postulated and shown considerable 

 indirect evidence to the effect that the rubber globules in rubber latex 

 have an adsorbed film of protein around them and that this condition 



2 Lowry and Kohman, Jour. Phys. CJtem., 31, 23 (1927). 



