252 Profs. J. Dewar and J. A. Fleming. Dielectric Constants 



constant I), and the process of change and adjustment a third time 

 repeated. Let the variation of the sliding condenser in this third 

 case be S. It is then very easy to show that the following relation 

 holds good between D , D, S , S, and s, viz. : — 



or D=52=i(S-0 + l. 



b — S 



In order to apply this method we employed absolute ethylic 

 alcohol as the standard dielectric substance of known dielectric 

 constant, and took as its dielectric constant at 15° C. the value 25'8 

 (according to Nernst), a number closely in agreement with all the 

 best results by other observers. 



The actual capacity of the experimental condenser with air as 

 dielectric was very small, not being more than about O00001 of a 

 microfarad. Hence in the above formula D = 25*8. 



The value of s was determined to be 1*33 and 1*38 in two experi- 

 ments, and the mean 1*36 was taken as the value of s. 



The following liquids were then examined by placing them in the 

 experimental condenser and keeping them at ordinary temperatures, 

 viz., 16° C. to 20° C. 



1. Solution of Potassic Hydrate in water, 5 per cent, solution. 



2. Solution of Rubidic Hydrate in water, 5 per cent, solution. 



3. Amyl alcohol. 



4. Ethylic ether. 



5. Ethylic ether, pure and dry. 



6. Ethylic alcohol. 



The change in capacity of the sliding condenser when ethylic 

 alcohol replaced the air in the experimental condenser was 16*7. 

 Hence S = 167 and D = 25'8, also s = 1-36. 



Therefore = = 1-613. 



S — s 15-34 



The following table shows the observed values of 5 in the several cases 

 when the above liquids were placed in the experimental condenser, and 

 the corresponding calculated value of the dielectric constant D, where 

 D = 1-613 x(S-s) + l. 



