SCHLUNDT — DIELECTRIC CONSTANTS OF PURE SOLVENTS. 359 



the apparatus employed. The reader is referred to Drude's 

 original articles, after reading which the additional remarks on 

 the method contained in the paragraphs that now follow will be 

 much better understood. 



The apparatus used for these measurements was a trifle larger 

 than the one described by Drude. The wave-length of the elec- 

 trical waves in the two parallel wires in air was about 84 cm. as 

 compared with 74 cm. of the apparatus employed by Drude. A 

 vacuum tube containing hydrogen was used to determine the. set- 

 tings for maximum resonance. It served very well indeed for 

 this purpose. 



Of the two methods described by Drude the first is the more 

 accurate, but it necessitates the use of comparatively large quan- 

 tities of substance, at least 200 cc, which, in most cases, were not 

 available. Moreover, the poisonous nature of many of the com- 

 pounds made it desirable to work with small quantities which 

 could be kept in a closed cell while under investigation. 

 Drude's "second" method, although less accurate, was therefore 

 chosen. This method enables one to operate with less than a 

 cubic centimeter of solvent and gives results accurate to within 

 two per cent. In this method the substance to be measured is 

 introduced into a small condenser which is placed in the sec- 

 ondary circuit. The length of the secondary circuit is then ad- 

 justed for maximum resonance. The dielectric constant cor- 

 responding to the length noted is found from a calibration curve 

 representing the results obtained in calibrating the apparatus 

 for the particular condenser. 



Four cells similar in form but of different capacities served as 

 condensers. The apparatus was calibrated for each cell with the 

 liquids recommended by Drude, namely : benzene, acetone, water, 

 mixtures of benzene and acetone, and mixtures of acetone and 

 water. Seventeen liquids whose dielectric constants range from 

 2.26 to 80.9 at 19° C. were prepared. The benzene used for 

 these calibrating solutions was Kahlbaum's thiophene free prep- 

 aration, purified by crystallization. Its boiling point was 

 79.2° C. under 744.6 mm of pressure. The acetone was like- 



