478 



Mr. A. P. Chattock on an 



Substance. 



s in cm. 



V max .i*E.S. 

 units. 



ds 





0015 



0-0165 



0018 



53 

 56 

 56 



3500 

 3400 

 3100 





Oil 





The potential was measured by comparing the spark in the 

 liquid with a spark in air arranged parallel with it ; the 

 assumption being made that the same potential was necessary 

 to produce the air-spark whether the potential was applied 

 suddenly or slowly. 



M for water is 2 x 10 10 . Berthelot * has succeeded 



m 



stretching water by yj^ of its whole volume. K for water 

 (calculated from fi) = 1*8. We have therefore 



q^2'6xl0~ 12 . 



In the accompanying table the values of q calculated by 

 the various methods discussed in this paper are collected for 

 convenience of reference. Their agreement with each other 

 and with the ionic charge seems to me to be quite beyond the 

 range of chance. Except in one case theory has been able 

 to anticipate any marked divergence from the ionic value, as 

 is shown by the sign > or < . 



On the other hand, it is well to emphasize what has already 

 been pointed out, that even granting the reality of the above 

 relations, the existence of initially charged molecules is not in 

 every case necessitated by the success of the method of calcu- 

 lation. It has been shown above that Method III. affords 

 equally good evidence that cohesion is due to chemical affinity, 

 to ionic charges, or perhaps to both. The order of magnitude 

 of the resulting value of q will in each case be the same. So, 

 too, Dielectric Capacity has been shown by Clausius to be 

 explicable on the hypothesis of induced charges in conducting 

 molecules ; and the ratio of the volume of the molecules to 

 the space they occupy, when determined by this theory, is in 

 close agreement with the same ratio calculated from the 

 behaviour of gases under pressure. Either this agreement, 

 therefore, or that of the results of Method IY. with the other 

 five determinations of q, must be accidental; for neither theory 

 of dielectric capacity implies the other in any way, so far as 



B.A. Report for 1888, p. 583. 



