Metallic Materials in the Telephone System* 



By EARLE E. SCHUMACHER and W. C. ELLIS 



TN the development of electrical communication, metals and alloys 

 -*• have played a noteworthy part. To emphasize specifically the 

 utilization of metallic materials the telephone handset serves as an 

 admirable example. The assembly of intricate parts in this small 

 piece of apparatus, shown sectionalized in Fig. 1, contains seventeen 

 metallic elements, either alone or in combination as alloys. 



The Bell System has therefore conducted extensive metallurgical 

 researches, and the discoveries and developments have been numerous. 

 Space permits a discussion of only a few of the developments relating 

 to the more extensively used materials. These comprise the alloys of 

 lead, copper, zinc and aluminum, and the precious metals, and mag- 

 netic materials. 



Lead and Alloys of Lead 



Lead alloys are used principally as sheathing for cable, and as 

 solders for joining cable sheath and making electrical connections in 

 apparatus. 



Cables represent one of the largest single items of investment; 

 approximately ninety-five per cent of the Bell System's total wire 

 mileage is contained in lead or lead alloy sheath and this sheath requires 

 an enormous amount of lead annually in its production. The largest 

 size cable made by the System contains 4242 copper wires. The same 

 number of open wires on telephone poles would take 70 rows of poles 

 each carrying 60 wires. Under one street today in New York City 

 there are 282 cables containing about 560,000 wires. 



Since the wires in the cable are insulated from one another only by 

 the paper or textile wrappings or sheaths and by the dry air contained 

 in the cable, the presence of even a slight amount of moisture will 

 interfere with transmission by drastically reducing the insulation 

 resistance. A positive pressure of dry nitrogen is maintained in some 

 cables as additional protection against moisture entrance and to dis- 

 close sheath breaks. Continued efforts are made, therefore, to im- 

 prove cable sheath so as to keep sheath failures to a minimum. 



* Based upon a paper published in Metal Progress, November 1939. 



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