Paragutta, A New Insulating Material for Submarine 



Cables * 



By A. R. KEMP 



Gutta percha and balata have proven eminently suitable for the in- 

 sulation of long deep sea telegraph cables, but their dielectric losses are too 

 high to meet the requirements of submarine telephone cables designed to 

 operate over long distances or of shorter cables employing carrier currents. 



This paper describes a new material called paragutta which has been 

 developed to meet the present needs. It consists essentially of the purified 

 hydrocarbons of balata (or gutta percha) and of rubber together with minor 

 quantities of waxes to modify the mechanical characteristics. The puri- 

 fication of rubber particularly with respect to nitrogenous constituents 

 is necessary to effect electrical stability in water, A commercially usable 

 method of purifying rubber is described. 



Evidence is furnished that paragutta has all of the desirable thermo- 

 plastic and mechanical properties of gutta percha while possessing such 

 superior insulation characteristics as to make it suitable for use on long 

 cables designed for transoceanic telephony. Its use is also advantageous 

 on shorter deep sea cables designed for carrier telephony as well as for 

 ocean telegraphs. 



FORMERLY deep sea cables were used exclusively for telegraph 

 purposes but in recent years there has been an increasing use of 

 this type of cable for telephone service. Telephonic communication 

 requires cables of very much superior transmission quality to that 

 needed for telegraph. At the higher frequencies of voice transmission 

 the energy losses in the insulating material become a serious factor 

 and a radical improvement in submarine insulation is called for. 



The longest existing deep sea cables operating at voice frequency 

 only slightly exceed 100 miles and the construction of a transoceanic 

 telephone cable with standard materials has been regarded as beyond 

 the practical limits of feasibility. 



The installation and rapid expansion of transatlantic radio telephony 

 during the past few years have created a need for a deep sea telephone 

 cable to supplement this service, particularly during periods of at- 

 mospheric disturbances. In addition the development of carrier 

 telephony offers possibilities for increasing the trafific over shorter 

 submarine cables. For the shorter cable, the still higher frequencies 

 of carrier telephony make demands upon the insulating material 

 similar to those of long cables operating at voice frequency. 



In view of these circumstances an extended study was undertaken 

 of the causes of losses and other electrical weaknesses of submarine 

 insulation and a search has been made for better materials. As a 



* Jour. Franklin Instilule, Jan., 1931. 



132 



