DEVELOPMENTS IN COMMUNICATION MATERIALS 



245 



This face is farthest from the heated ends of the terminals, is free from 

 mechanical strain and is therefore not damaged by soldering operations. 

 Since it was the practice to mold this test strip using several partially- 

 cured preforms, the veneer construction was introduced with only a 

 slight increase in cost. The cellulose acetate has nearly the same 

 molding temperature as the phenol plastic, so that the composite test 

 strip could be molded in one operation. Fig. 10 shows the appearance 



■TERMINALS IN HOLES IN PREFORMS 



PREFORM OF PHENOL PLASTIC 



PREFORM OF PHENOL PLASTIC 



PREFORM OF PHENOL PLASTIC 



PREFORM OF CELLULOSE ACETATE 



Fig. 10 — Method of molding composite 200 point test strip, 

 of the modified test strip and the method of molding. 



Textile Insulation 



Another development was in the improvement of textile insulation 

 which was recently described before the Institute.^- ^ It is mentioned 

 here only in passing, because of its great commercial importance. 



As a result of several years of study in the laboratory, it was found 

 that the insulating quality of textiles depended on (1) the kind of 

 fiber; (2) impurities present in the fiber; (3) moisture. The salts of 

 sodium and potassium were found to be highly detrimental from an 

 insulation standpoint. A very great improvement was effected by a 

 washing treatment of the textile. Thus it has been possible to make 



^ "The Predominating Influence of Moisture and Electrolytic Material Upon 

 Textiles as Insulators," R. R. Williams and E. J. Murphy, Trans. A. I. E. E., Vol. 

 48, 1929. 



^ "Purified Textile Insulation," H. H. Glenn and E. B. Wood, Trans. A. I. E. E., 

 Vol. 48, 1929. 



