134 BELL SYSTEM TECHNICAL JOURNAL 



In addition to those excellent and unique mechanical properties, 

 gutta percha possesses electrical characteristics peculiarly adapted to 

 submarine cable construction. Its outstanding electrical merit con- 

 sists in the fact that its electrical characteristics are stable under sea 

 bottom conditions over a great many years. 



Gutta percha is obtained from the latex of a large number of species 

 of trees growing wild in the forests of the Malay Peninsula and the 

 East Indian Islands. The products of the various species of trees are 

 by no means of equal value, varying as they do in the content of 

 hydrocarbon, resins, moisture and other substances. Since the ma- 

 terial is gathered and worked up upon the spot by primitive people a 

 great deal of carelessness as well as deliberate adulteration is practiced 

 and the material comes upon the market in a dirty condition and in a 

 bewildering variety of forms which almost prohibit effective inspection, 

 standardization and grading. 



The essential constituent of gutta percha is an unsaturated hydro- 

 carbon of colloidal nature which is similar in its chemistry to rubber. 

 It is this constituent which makes gutta percha plastic when warm 

 and tough when cold, and which contributes most conspicuously to 

 its electrical excellence as an insulator. The usual gutta percha in- 

 sulation is the result of blending and washing various grades of crude 

 gutta percha to remove dirt and water soluble components. The 

 hydrocarbon, resin, dirt and moisture contents as determined by 

 analysis of the crude material together with the electrical and mechan- 

 ical properties after washing are the principal characteristics used to 

 determine whether or not a particular grade of crude gutta percha is 

 suitable for use as submarine cable insulation. The hydrocarbon con- 

 tent of gutta percha insulation when applied to the conductor is usually 

 about 60 per cent, the remainder being mostly the natural resins to- 

 gether with small amounts of very finely divided dirt (humus) and 

 residual moisture. The proteins or albumens in crude gutta percha 

 and balata are almost completely removed by simple washing. 



Balata comes from two species of trees of the same general botanical 

 family as gutta percha, but is native to the forest regions of upper 

 South America and is unknown in the gutta percha producing area 

 of the Far East. The latex of the balata tree is more fluid than that 

 of gutta percha, which permits the trees to be tapped and the fluid to 

 be collected at a central point in the forest, where the product from 

 various trees is mixed for recovery of the gum. Because of the small 

 number of species involved and the transportability of the fluid latex, 

 balata is produced in a much more limited number of grades and is 

 cleaner and more dependable as to uniformity of quality. Its essential 



