TREATMENT FOR TEXTILE INSULATION 219 



wound with textile insulated wire. If the treatment is applied to the 

 wire before winding, the desired improvement in stability of the con- 

 stants is obtained. Coils treated after winding, however, show very 

 little improvement since the lacquer does not penetrate but merely 

 provides a superficial covering of film which does not exclude moisture 

 or break up the interlocking fibers between turns. 



It has been found that increasing the thickness of the lacquer film, 

 beyond that required to cover the fibers and provide a smooth surface, 

 results in relatively small additional improvement in the insulation. 

 This is of economic importance since, with proper methods of appli- 

 cation, a relatively thin film may be practically as effective as a thick 

 one requiring a considerably greater quantity of material, and a rapid 

 check on the quality of the product can be made by visual inspection 

 of the surface condition of the treated insulation. 



Electrical Characteristics of Treated Wire 

 The accompanying graphs show a comparison of the electrical char- 

 acteristics of untreated and treated cotton and silk insulation, respect- 

 ively, for a cycle of relative humidity ranging from 65 per cent to 90 

 per cent and back to 65 per cent at a constant temperature of 85° F. 

 The comparison is given for both commercial and purified materials 

 as a matter of general interest, although purified textiles are now used 

 exclusively in Bell System central office wire insulation. The graphs 

 are plotted from data on samples of wire insulated with silk and cotton 

 taken at random from stocks of commercial and purified materials and 

 treated with cellulose acetate under conditions of regular production. 

 The values given by the graphs should not be considered as applying 

 quantitatively to any standard type of central office wire but are 

 intended to show, on a comparative basis, the extent to which the 

 commercial and purified materials have been improved by treatment 

 with cellulose acetate, and the rather remarkable improvement in the 

 characteristics of commercial textiles by both purification and cellulose 

 acetate treatment. 



Perhaps the comparison of greatest general interest is that of insu- 

 lation resistance, Figs. 2 and 3, since it is important in any electric 

 circuit that the insulation shall be capable of preventing undue energy 

 loss from direct current leakage. From these graphs, it is seen that 

 the insulation resistance of commercial cotton may be improved from 

 100 to 300 fold by treatment with cellulose acetate and in the order of 

 500 to 2,000 fold by purification plus acetate treatment depending 

 upon the relative humidity. Thus, as indicated by insulation re- 

 sistance, acetate treated purified cotton becomes a comparatively high 



