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BELL SYSTEM TECHNICAL JOURNAL 



contains about one per cent water when at equilibrium with sea water 

 whereas paragutta contains somewhat less than this amount. These 

 values have been determined by testing samples made up with various 

 water contents below and above equilibrium values and determining 

 the water content after prolonged immersion in 3.5 per cent NaCl 

 solution, as seen in Figure 9. The equilibrium value is practically 

 the same when equilibrium is approached from either direction. 



Fig. 8- 



5 10 15 20 25 30 35 



CONCENTRATION NaCl IN IMMERSION SOLUTION-PER CENT 



-Relation of water absorption to salt concentration in immersion solution. 



The overall quantity of water absorbed, however, cannot be used 

 as a final criterion by which to judge insulation for it has been pre- 

 viously shown (Figs. 1 to 4) that washed crude rubber completely 

 fails as an insulator after absorbing less than one per cent water. The 

 mode of distribution of water absorbing impurities in an insulating 

 material has been found to be of utmost importance as regards the 

 magnitude of the effect of moisture in various insulating materials. 

 Examples where large effects on insulating properties are caused as a 

 result of moisture absorption by localized impurities are found in the 

 above case of proteins in crude rubber, water soluble salts associated 



