Allen — The Insulating Properties of Erinoid. 



349 



per cm. cube for fibre may range from 10 to 10,000, or somewhat higher if 

 the material is very dry. 



The value of o- obtained by Curtis 1 for red fibre at 22° C. was 5000. The 

 corresponding value from the results of Table 11 is roughly of the same 

 order. 



Eayner 5 gives 100 as the value of a at 20° C. for red fibre, a result of the 

 same order as the corresponding value in Table 10, or more nearly in agree- 

 ment with the results obtained for sheet fibre in Table 2. 



The degree of dryness of the sample is by far the chief factor governing 

 this large variation in insulation resistance of vulcanized fibre. 



3k. io 



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Ph 



V> . _ 



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at 



Logarithmic Values of the Specific Resistance. 



Fig. 3. — The relation between the reciprocal of absolute temperature and the logarithmic value 

 of specific, resistance. B is drawn for black erinoid ; W for white erinoid ; if for red 

 erinoid ; Fi and Fi for two different samples of red vulcanized fibre. 



The values of -=, and log 10 o- given in Tables 7 to 11 are plotted in Fig. 3 



for the samples of erinoid and fibre tested, and the points all lie fairly upon 

 straight lines. 



1 Bulletin of the Bureau of Standards, vol. ii, No. 3, 1915, p. 418, Table 8. 

 3 Journ. Inst. Elec. Eng., xxxiv, 1905, p. 620. 



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