226 BELL SYSTEM TECHNICAL JOURNAL 



faithfully reflect the moisture supplied from the air. A one or two 

 per cent increment of moisture affects gutta percha scarcely at all 

 but an equal amount has a most profound effect on the textiles. 



The phenolized fibers, the impregnated papers, the cellulose esters, 

 insulating varnishes and enamels, as well as glass and porcelain, are 

 intermediate between the "waterproof" insulations and the textiles 

 in their sensitivity to atmospheric moisture. We refer to these 

 insulations, of course, in the forms in which they are ordinarily used, 

 for brevity neglecting distinctions which might properly be made as 

 to relative importance of surface and volume characteristics in the 

 several cases. 



Diverse as are the insulators in use, they have another common 

 property of importance. They often contain, or have deposited on 

 their surfaces, electrolytic material which dissolves in the absorbed 

 water to form conducting solutions which are injurious to the insulating 

 qualities of the material. This fact seems to be second in importance 

 only to the prevalence of water in insulating materials. These 

 electrolytic substances may be present as part of the natural con- 

 stituents of the insulating material or as accidental contaminants; 

 they may consist of the saline or organic constituents of the vegetable 

 tissues which furnished the raw material, of by-products of the 

 processes of manufacture, of degradation products of the insulating 

 substances resulting from atmospheric oxidation or hydrolysis, or 

 of atmospheric dust. Illustrative of the diversity of electrolytic 

 material in commercial insulating materials are the natural ash 

 constituents of textiles, pulp woods and other materials of vegetable 

 origin ; saline diluents of dyes used in fibrous materials; the quebrachitol 

 of the latex of the rubber tree; acid resins produced by the atmospheric 

 oxidation of rubber and gutta percha; and the free phenol present in 

 phenol condensation products. 



While the importance of moisture and of electrolytic contaminants 

 in practical insulations has long had some recognition by electrical 

 engineering opinion, especially in the telephone field, the foregoing 

 general philosophy has been emphasized in the minds of the authors 

 and their associates by the results of extended experimental studies 

 of submarine insulation ^ and of textiles.^ 



^Williams, R. R. and Kemp, A. R., Jour. Frank. Inst., 35 (1927). Lowry, H. 

 H. and Kohman, G. T., Joicr. Phys. Chetn. 31, 23 (1927). 



'^ a. Murphy, E. J. and Walker, A. C, "Electrical Conduction in Textiles. I. 

 Dependence of the Resistivity of Cotton, Silk, and Wool upon Relative Humidity 

 and Moisture Content," Jour. Phys. Chem. 32, 1761 (1928). 



/;. Murphy, E. ]., "Electrical Conduction in Textiles. II. Alternating Current 

 Conduction in Cotton and Silk," Jour. Phys. Chem. 33, 200 (1929). 



c. Murphy, E. J., "Electrical Conduction in Textiles. 111. Anomalous Properties 

 of Conduction in Textiles," Jour. Phys. Chem. 33 (1929). 



