INFLUENCE OF MOISTURE UPON INSULATORS 239 



The reader will have been led to ask several questions. Why do 

 the several kinds of fibers differ so much in absorption of water and 

 particularly why does not a given amount of water affect them all 

 alike electrically? He will want to know if the mere fact of animal, 

 vegetable, or artificial origin is associated with a particular type of 

 electrical or hygroscopic behavior. He will wonder whether there is 

 any fundamental resemblance between the silk which is rapidly 

 extruded by a worm and the hair which grows so slowly on a sheep's 

 back. He will inquire whether there is sufftcient justification for 

 classifying other vegetable fibers with cotton. To these questions 

 only partial and to some extent speculative answers can be given. 



We are justified on chemical grounds in classifying the fibers in 

 the same way which we have found to be convenient for discussion 

 of their hygroscopic and electrical properties. How much importance 

 should be attached to this correspondence between the chemical and 

 electrical classifications cannot be determined at present. However, 

 the correspondence seems suggestive and deserving of a brief dis- 

 cussion. The first class, that of animal fibers, has a common chemical 

 nature in that they consist largely of proteins. Proteins are molecular 

 aggregates of colloidal size composed in turn of simpler substances 

 known as amino acids. Each of the constituent amino acids contains 

 both an acidic and a basic group, so that in acid solutions they behave 

 as bases and in alkaline solutions they behave as acids. This so- 

 called amphoteric property is due to the presence of an acidic oxygen 

 nucleus and a basic nitrogen atom, which are almost invariably 

 adjacent to one another. Amphoteric properties persist in the proteins 

 which are formed by union of many amino acids in a single molecule. 

 This is illustrated by the fact that either amino acids or proteins in a 

 solution which is subjected to a d.c. voltage tend to migrate to positions 

 intermediate between the electrodes where the acidity is such that 

 they are equally ionized as bases and as acids. The combination of 

 adjacent acidic and basic groups within a single molecule gives them 

 a salt-like property which may be significant. It is reasonable to 

 associate the hygroscopic quality of the proteins with these groups 

 as the molecules are usually without groups of polar character other 

 than the paired groups mentioned. 



That their common protein character is responsible in some way 

 for the properties of principal interest from the insulating standpoint 

 is rendered the more probable by the close resemblance of silk and 

 wool, as shown by the approximate parallelism of their curves in 

 Fig. 4. This resemblance is shared in considerable measure by other 

 hairs than wool. 



