The Predominating Influence of Moisture and Electrolytic 

 Material Upon Textiles as Insulators ^ 



By R. R. WILLIAMS and E. J. MURPHY 



The insulating qualities of textiles vary with the amount of moisture 

 present in them from hour to hour and are also strongly influenced by the 

 amount of electrolytic material (salts, etc.) which the textiles contain. 

 Electrolytic material may be washed out producing a commercially realizable 

 increase in insulation resistance of the order of 50 times the original value. 



The resistance of the animal fibers, silk and wool, is far greater for a 

 given moisture content than that of cotton or of cellulose acetate, a deriva- 

 tive of cotton. It appears probable that the distribution of water as well 

 as the quantity is important and that the two classes of fibers are charac- 

 terized by different space patterns according to which the water is dis- 

 tributed. It is suggested that the space distribution patterns are associated 

 with the colloidal structures of the materials and in turn with their chemical 

 classification as proteins and celluloses respectively. Cellulose acetate ab- 

 sorbs little water as compared with cotton and is correspondingly superior 

 electrically. However its resistance varies with moisture content in the 

 same way as that of cotton. 



A GREAT diversity of materials is used for insulating purposes. 

 No simple descriptive term includes them all as the term 

 "metals" includes commercial conducting materials. Yet in spite of 

 this diversity it is to a great extent the quantity and mode of dis- 

 tribution of water in all insulators that determines their relative 

 excellence. Were it not for the accumulation of moisture in it or on 

 it the cheapest and mechanically most convenient material could, 

 with rare exceptions, be used for the most exacting service. 



At first glance it might seem possible to select insulating materials 

 very simply according to moisture content, but a few illustrations will 

 serve to show that wide contrasts exist in the response of insulations 

 to a given amount of moisture. At one extreme is gutta percha, the 

 classical insulation of submarine cables. If dry at the outset, it 

 very gradually absorbs one or two per cent of moisture from the sea, 

 but undergoes only a slight change in electrical characteristics in the 

 process. Thereafter its water content and electrical properties are 

 extremely stable in use. Rubber insulations used in air partake of 

 these properties to some degree. Fluctuations in their electrical 

 behavior never are large or sudden so long as they are mechanically 

 intact. At the opposite extreme are the textile insulations which, 

 especially if unimpregnated, are subject to every whim of the weather. 

 Their water contents rise suddenly with corresponding changes in the 

 relative humidity of the atmosphere, and the dielectric qualities 

 1 Presented at the Winter Convention of the A. I. E. E., Jan. 28-Feb. 1, 1929. 



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