624 BELL SYSTEM TECHNICAL JOURNAL 



always confirmed the duct survey as to the location of anodic regions. 

 The trouble was corrected by removal of the cinder beds. 



Summary 



In summarization it may be stated that corrosion is not a primary 

 factor affecting the life of aerial cables. The tendency of lead to crack 

 as a result of repeated stressing has been minimized by alloying with 

 one per cent of antimony, and aerial cables sheathed with this alloy 

 have shown satisfactory resistance to embrittlement of this character. 

 When cable sheathing materials are buried in direct contact with soils, 

 serious corrosion develops as a result of differential aeration cell action, 

 and appears to have little or no relation to chemical composition of the 

 metallic material. In addition to corrosion cells which originate in 

 some inhomogeneity of the environment, such as the partial exclusion 

 of air, corrosion of cable sheathing may occur by means of galvanic 

 cells arising from the presence of metallic impurities or contact with a 

 more noble metal such as copper. The electrolytic operation of these 

 corrosion cells is influenced by the conductance of the surrounding 

 electrolyte and the chemical nature of its components. Such con- 

 stituents as oxygen, nitrates, alkalies, organic acids and chlorides (in 

 low concentrations) facilitate the operation of these cells, thereby 

 increasing the rate of corrosion, whereas silicates, sulfates, carbonates, 

 colloids and certain organic compounds of the soil waters exert a 

 protective action which may retard or prevent corrosion. Finally 

 mention is made of the characteristics of the most common kind of 

 corrosion, that due to stray electrical currents. This may occur as 

 anodic action when current flows from the cable to earth, or it may 

 occur as cathodic action when the current flows in the reverse direction 

 if there be sufficient concentrations of alkali or lime salts in the sur- 

 rounding electrolyte. 



From the description of the occurrence and general characteristics of 

 cable sheath corrosion in the present paper it may be concluded that 

 although there are many conditions under which cables may corrode, 

 the actual incidence of corrosion is small owing to the maintenance of 

 non-corrosive chemical and electrical environments in the cable plant. 



References 



1. "Useful Information about Lead," Lead Ind. Assn. 1931, New York. 



2. Archbutt, Met. Ind. (London), 18, 341 (1921). 



3. Gough and Sopwith, Jour. Inst. Met., 56, 55 (1935). 



4. Burns, Bell Sys. Tech. Jour., 15, 20 (1936). For fuller details see Vernon, Trans. 



Faraday Soc, 19, 839 (1924); 23, 113 (1927) from whose work the curves of 

 Fig. 1 of this reference were adapted. 



5. Pilling and Bedworth, Jour. Inst. Met., 29, 529 (1923). 



6. Vernon, Discussion, Jour. Inst. Met., 56, 84 (1935). 



