246 BELL SYSTEM TECHNICAL JOURNAL 



cotton an acceptable substitute for silk as wire insulation, as well as to 

 improve greatly the insulating properties of silk. In one instance, 

 central office distributing frame wire, of which the Bell System uses 

 about five hundred million conductor feet annually, it was found pos- 

 sible to use double silk insulated conductor of treated thread where 

 formerly triple silk insulation was required. An actual improvement 

 in insulation was effected at the same time that a considerable economy 



resulted. 



Metallic Materials 



N on- Ferrous Metals 



Telephone apparatus uses about 30,000,000 lbs. yearly of brass, 

 bronze and nickel silver as structural members, springs and bearings. 

 Because of space limitation the parts are necessarily small, many are 

 formed into irregular shapes; spring parts must maintain accurate 

 adjustment and have long fatigue life; certain other parts must resist 

 wear. Experience with commercial grades of brass indicated wide 

 variations under existing specifications and unsatisfactory means of 

 testing the quality. At first blush there may not appear to be any 

 connection between the temper of a metal spring and the grade of 

 telephone service furnished, but looking at the matter broadly we were 

 convinced that the stakes were large enough to warrant our launching 

 an investigation of non-ferrous metals with the object of arriving at a 

 better purchasing specification. Accordingly the Bell Telephone 

 Laboratories initiated a joint study with the Western Electric Company 

 and the American Brass Company which has extended over a period 

 of several years. The results of this work have been described in 

 considerable detail in appropriate papers before the American Society 

 for Testing Materials.'' •" 

 This has resulted — 



1. In a more accurate knowledge of the physical properties of brass, 



phosphor bronze and nickel silver. 



2. Development of improved methods of test. 



3. Preparation of better purchasing specifications with resulting 



improved control of the quality of the materials. 



As an instance of the benefits derived, the work on hardness testing 

 may be cited. For many years the scleroscope had been used as a rapid 

 means of controlling the quality of sheet metal but trouble was fre- 

 quently encountered because results could not be readily duplicated on 



* "Physical Properties and Methods of Test for Sheet Brass," H. N. Van Deusen, 

 L. I. Shaw and C. H. Davis, Proc. Amer. Soc.for Testing Materials, 1927. 



*" Physical Properties and Method of Test for Sheet Non-Ferrous Metals," 

 J. R. Townsend, W. A. Straw and C. H. Davis, Proc. A. S. T. M., 1929. 



