368 BELL SYSTEM TECHNICAL JOURNAL 



Submarine Insulation with Special Reference to the Use of Rubber.^ 

 R. R. Williams and A. R. Kemp. (1) Soft vulcanized rubber, though 

 not well adapted to some of the processes of manufacture of submarine 

 cable, can be so made as to be mechanically and electrically suitable 

 and to withstand the action of sea water in a manner comparable 

 with that of gutta percha over a period of a few years. Whether 

 such rubber will retain these characteristics for decades remains to 

 be demonstrated, but it seems probable that it will. 



(2) The principal factor to be controlled in producing this result is 

 the amount of water absorbed by the rubber. 



(3) Osmotic pressure of internal and external fluids is of prime 

 importance in governing the in-flow of water into rubber and gutta 

 percha. 



(4) Lowered water absorption is achieved by removal of water- 

 soluble matter from the rubber, the choice of an insoluble, non- 

 reactive filler of suitable particle size and having a minimum of 

 adsorbed gases or other contamination on its surfaces. 



(5) The electrical characteristics of rubber compounds and of gutta 

 percha are clearly related to their water content but are not simple 

 futnctions of the water content. 



(6) It appears that the mode of distribution of water is also ex- 

 tremely important. 



(7) Most fillers for rubber compounds are not suitable for submarine 

 insulation, either because of undesirable intrinsic electrical properties 

 or because they are conducive to changes incident to water absorption. 

 Hard rubber dust, silica and zinc oxide are the best fillers from these 

 standpoints so far as known. 



An Efficient Apparatus for Measuring the Diffusion of Gases and 

 Vapors through Membranes* Earle E. Schumacher and Lawrence 

 Ferguson. An efficient dilTusion measuring apparatus, embodying 

 a mechanical clamp and a mercury seal, is described. This apparatus 

 can be used for measuring the rate of diffusion of gases and vapors 

 through materials such as rubber, waxes, leathers and certain types 

 of paper. 



Investigation of the Thermionic Properties of the Rare Earth Elements.^ 

 Earle E. Schumacher and James E. Harris. Thermionic emission 

 measurements over a range of temperatures were made on samples 

 of pare Ce, La, Pr, Nd, Sa and the aluminum alloys of Yt, Eu, Ga, 



' Jr. of the Franklin Inst., Jan. 1927, Vol. 203, pp. 35-61. 



4 J. Amer. Chem. Soc, VoL 49, 427 (1927). 



•' /. Amer. Chem. Soc, VoL 48, pp. 3108-3117 (1926). 



