PURIFIED TEXTILE INSULATION 255 



The foregoing is intended to show what has been accomplished on 

 a commercial scale at reasonable cost in the way of improving the 

 insulating properties of silk and cotton. There still exists a rather 

 wide margin in insulating properties between washed silk and washed 

 cotton at high humidities which further study may show can be 

 reduced. The graphs do not show the magnitude of improvement in 

 cotton which has been obtained occasionally in laboratory experiments 

 which leads us to hope that presently it may be possible to process 

 cotton in a way that will result in its having electrical properties 

 equal to those of washed silk for many practical purposes. 



The question naturally arises as to the permanence of the improve- 

 ment effected by the purification process. We have attempted to 

 answer this question by periodic tests of washed silk and cotton 

 insulated wire over an extended time, the test samples being exposed 

 to ordinary room conditions where they could accumulate the normal 

 quantity of dust. The results show no tendency for the insulation 

 to revert to the constants of unwashed insulation. This appears 

 logical since there is no particular reason to expect contamination by 

 accumulation of such impurities as sodium or potassium salts from 

 ordinary exposure to the air. Furthermore, in service, telephone 

 office wiring is protected from the effects of dust by braided textile 

 coverings or by the application of waxes or varnishes where the 

 individual wires are exposed. 



Conclusion 



The discussion has been confined primarily to telephone central 

 office cabling where silk and cotton are used in the cable core without 

 impregnation. However, it is believed that the whole subject of 

 purification of textiles becomes of general interest when it is stated 

 that the improvements obtained by washing are not nullified by the 

 supplementary use of impregnating waxes or varnishes. That is, 

 the improvement in dielectric properties and reduced electrolysis 

 obtained by washing and by impregnating are apparently substantially 

 additive. While the studies have not proceeded far enough to cover 

 comprehensively all of the better known impregnating waxes, asphalts, 

 varnishes, etc., they have proceeded to the point where we can say 

 that this is the case for the beeswax-paraffine waxes and certain 

 asphaltic compounds. These findings are in line with the generally 

 known fact that impregnation of textiles with wax compounds does 

 not prevent, though it does retard, the absorption of moisture which 

 in the presence of soluble salts causes conducting paths to be estab- 

 lished, probably through the embedded textile fibers. Consequently, 



