604 BELL SYSTEM TECHNICAL JOURNAL 



percha and the core covered with a rubber or textile sheathin^^ The 

 first lead-covered telephone cables were made by David Brooks, Jr., 

 and were installed in the year 1880. These consisted of cotton- 

 covered wires drawn into a lead pipe — a moisture-proofing compound 

 of rosin and paraffin being forced afterward into the pipe and allowed 

 to solidify by cooling. The Western Electric Company began the 

 manufacture of lead-covered telephone cables in 1881. These were of 

 the so-called "Patterson" type and employed cotton-covered wires 

 drawn into a lead pipe after which melted paraffin charged with 

 carbon dioxide under high pressure, was forced into the pipe and 

 allowed to cool, forming thereby a solid cake of paraffin between the 

 core and the pipe. Cotton-wrapped wire alone took the place of this 

 structure in 1884 and some four years later paper began to be substi- 

 tuted for cotton. Beginning in 1882 telephone cables were sheathed 

 with an alloy of 97 per cent lead and 3 per cent tin, which continued to 

 be the standard composition for cable sheathing in the Bell System 

 until 1912. The general adoption of the present standard alloy of 

 lead with 1 per cent antimony in that year has afforded substantial 

 economies and a sheathing of high resistance to fatigue cracking. 

 Recently, a new development, lead hardened with 0.03-0.04 per cent 

 calcium, has shown in laboratory tests some promise as a cable sheath- 

 ing material. In England ternary alloys of lead with cadmium and 

 tin or with cadmium and antimony have been proposed. Unalloyed 

 commercial lead is the covering generally used for power cables. 



The lead which best lends itself to the manufacture of lead-antimony 

 cable sheathing is a high-copper, low-bismuth chemical grade of lead 

 of the following nominal composition: 



Silver 0.002 to 0.02% 



Copper 0.04 to 0.08% 



Bismuth 0.005% (max.) 



Arsenic, antimony and tin together 0.002 (max.) 



Zinc 0.001 (max.) 



Iron 0.0015 (max.) 



Lead (by diflF.) 99.90 



There is no evidence that the copper content of this lead has any 

 significant effect upon corrodibility when used in 1 per cent antimony 

 sheathing, although it does appear to be a factor in certain other uses. 

 Indeed, chemical composition appears to be of lesser importance than 

 environmental influences in the corrosion of cable sheathing. The 

 prevention of corrosion failures is mainly a matter of providing and 

 maintaining non-corrosive chemical and electrical environments. 



While the choice of lead as a cable sheathing material was dictated 

 primarily by physical requirements, notably its adaptability to extru- 



