360 BULLETIN OP THE UNIVERSITY OP WISCONSIN. 



wise KahlbauHi's preparation — it was prepared from the bisul- 

 phite compound. It boiled at 55.7° C. under 746 mm of pres- 

 sure. The water used had a specific conductivity of 3.6 X 10 -6 . 

 In calibrating, the "zero" of the apparatus, obtained by plac- 

 ing a straight piece of copper wire in place of the cell, was fre- 

 quently redetermined, as a change in the position of certain 

 parts of the apparatus may produce a change of the "zero" point. 

 This precaution was also taken whenever solvents of unknown 

 dielectric constants were under examination. As a check on any 

 change in the capacity of the cells, the calibrating liquids whose 

 dielectric constants were nearest in value to that found for the 

 solvent under examination were introduced into the cell and the 

 settings for maximum resonance determined. In this way any 

 change in the position of the condenser plates could be readily 

 detected. This procedure also gives all the necessary data for 

 calculating the dielectric constant according to the formula 

 given by Drude : l 



. 2 7T 1 .2*1* 



cot — j. cot — , — - 



D = D 1 + (D 8 -2> 1 )— 1 ^ f - -j^ 



COt j-= COt j-i 



A A 



in which a is the wave-length of the electric waves in air, D is 

 the dielectric constant sought, I is the setting for maximum res- 

 onance when the cell contains the solvent whose dielectric con- 

 stant is sought; D t , h and D 2 , l 2 , are the dielectric constants and 

 settings of the calibrating solutions. In working with pyri- 

 dine the dielectric constant was calculated by this formula using 

 84 cm for a. . The value found was the same as the value ob- 

 tained with the aid of the calibration curve. 



From 10 to 30 settings for maximum resonance were made 

 for each solvent examined, and the average of these was the value 

 used for obtaining the dielectric constant. 



The methods of dehydrating and rectifying the various solv- 

 ents will be found under the head of each particular solvent in 

 the statement of results given below. 



A series of trial experiments was at first made with the appa- 



1 Zeit. phys. Chem. 33, 309. (1397). 



