PARAGUTTA, A NEW INSULATING MATERIAL 133 



result of this investigation an insulation called paragutta has been 

 developed which, as the name suggests, is derived essentially from 

 rubber and gutta percha. It is the purpose of this paper to describe 

 this material and give an account of the tests to which it has been sub- 

 jected to determine its suitability for the purpose. 



By virtue of its superior electrical properties, the use of paragutta 

 in place of gutta percha for the insulation of telephone and telegraph 

 cables offers advantages either from the standpoint of improved trans- 

 mission or the economies in materials of construction which can be 

 made as a result of modified design. 



Gutta percha and balata have been the standard materials for the 

 insulation of deep sea cables since the inception of the submarine 

 cable industry some seventy-five years ago. Although these sub- 

 stances are inadequate for modern telephone needs as regards their 

 electrical characteristics, their mechanical properties are peculiarly 

 adapted to submarine insulation. This is so much the case that gutta 

 percha can fairly be taken as a model which must be closely imitated 

 in respect to mechanical characteristics by any successful substitute. 

 This is fortunate since the use of any substitute which differs radically 

 from gutta percha would mean discarding large existing investments 

 in special technique, equipment and trained personnel, and would 

 involve serious risks as to the integrity of cables made with the new 

 material. It may be remarked in passing that no manufacturing 

 process requires a higher degree of insurance against occasional defects 

 than does the submarine insulation art, a fact that has engendered a 

 strong conservatism in the industry. 



Because of its almost ideal mechanical properties, the requirements 

 for submarine cable insulation may conveniently be described by 

 reference to gutta percha. Gutta percha insulation, which often 

 includes more or less balata in its composition, is made of raw materials 

 carefully selected for quality, which are thoroughly washed and 

 extremely uniformly blended. The thermoplasticity of the material 

 is of great service in these operations and further permits it to be 

 readily extruded onto a conductor in multiple layers in a continuous 

 sheath with great exactness and freedom from mechanical defects. 

 After being forced around the conductor the material quickly sets to 

 a hard, tough covering when drawn through cold water. Its firmness 

 and toughness are essential to resist subsequent handling operations in 

 the factory, as well as those involved in laying, picking up and re- 

 pairing. The warm, soft material adheres readily to the conductor 

 and is well adapted to the making of joints in the insulation between 

 core lengths both in the factory and on the cable ship. 



