Metallic Materials in the Telephone System

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 magnetic 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.