Abstracts of Bell System Technical Papers Not Appearing in this Journal (01 April 1927)

Submarine Insulation with Special Reference to the Use of Rubber* 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 watersoluble matter from the rubber, the choice of an insoluble, nonreactive 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 fumctions of the water content. (6) It appears that the mode of distribution of water is also extremely 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.