482 Mr. L. 0. Jackson on the Dielectric Constants 



change fairly regularly from member to member of each 

 series, and that the values for the corresponding members of 

 the two series are distinctly different. 



Methyl formate 8"87 (19°) Methyl acetate 7'03 (20°) 



Ethyl formate 8'27 (19°) Ethyl acetate 5*85 (20°) 



n-Propyl formate 7*72 (19°) n-Propyl acetate 5'65 (19°) 



n-Butyl formate — n-Butyl acetate 5*00 (19°) 



The figures in brackets are the temperatures at which the 

 determinations were made. 



The object of the present work was to determine the values 

 of the dielectric constants of the above series of esters at the 

 low temperatures obtainable with liquid air so as to rind 

 the actual values of the dielectric constants and compare 

 them with those obtaining at ordinary room temperatures, 

 and to find whether the relations holding at ordinary tem- 

 peratures between the various members of the series and 

 between corresponding members of the series of formates 

 and acetates hold also at the lower temperatures. 



The results obtained, for which great accuracy is not 

 claimed and which are intended as preliminary values, show 

 that apparently the acid radicle contributes but little, as 

 compared with the rest of the molecule, to the value of the 

 dielectric constant at the temperature of liquid air, since 

 the constants for the corresponding formates and acetates 

 are found to be approximately equal. The values for the 

 various members of either series do not apparently exhibit 

 the same relationships to each other as hold at ordinary 

 temperatures. 



Method of Experiment. 



The principle underlying the method used in the present 

 work may be stated briefly as follows : — An electric circuit 

 containing a capacity C and an inductance L will oscillate 

 w T ith a frequency determined by the relation 



T = 2tiVLC, 



where T is the time of oscillation. 



If, now, a second condenser is connected in parallel with 

 the first one, and the latter is so reduced that the frequency 

 of oscillation of the circuit is the same as in the absence of 

 the second condenser, first when the latter has air (or, more 

 correctly, a vacuum) as its dielectric, and secondly some 

 other substance, the ratio of the amounts by which the first 

 condenser had to be reduced in the two cases will give the 



