376 BULLETIN OF THE UNIVERSITY OF WISCONSIN. 



resents the cyanogen group (CN) ; in Curves II and Ha, R 

 represents the hydroxyl group (OH) ; in Curve III, it repre-. 

 sents the carboxyl group (COOH) ; in Curve IV the amido 

 group (NH 2 ) ; while in Curve V, R represents the (N0 3 ) 

 group. The value 16.2 for the dielectric constant of liquid am- 

 monia is taken from the work of Coolidge 1 who measured its di- 

 electric constant at 14° C. 



Discussion of Results. 



The marked differences that exist between the physical prop- 

 erties of the first two members of any homologous series of com- 

 pounds are well exemplified by the great differences between the 

 dielectric constants of hydrocyanic acid and acetonitrile, of 

 water and methyl alcohol and of formic acid and acetic acid. 

 The difference in value between the dielectric constants of 

 liquid ammonia and liquid methylamine is not so marked 

 as in the other cases just mentioned; but it is highly 

 probable that the value found for methylamine is too high. 

 The curves show that in an homologous series the dielectric 

 constants decrease with increase of molecular weight. This 

 also holds for the aromatic amido compounds. Pyridine 

 (D. C, 12.4) and a-picoline (D. C, 9.8) also illustrate this 

 fact, as do also nitrobenzene [D. C, 35.0] and ortho-nitro- 

 toluene [D. C, 27.] 2 The primary amines have higher values 

 for their dielectric constants than the corresponding secondary 

 amines, and the values for the secondary amines are higher than 

 the tertiary, as is shown by the following examples : 



Ethylamine, D. C. = 6.17. 

 Diethylamine, D. C. = 3.58. 

 Trimethylamine, D. C. = 2.95. 



A further inspection of the values of the dielectric constants 

 of the several homologous series of liquid compounds investi- 

 gated by other observers will show that a decrease in the value 

 of the dielectric constant with increase of molecular weight is 



i Wied. Ann. 69, 130, (1899). 



1 This value was found by Turner. Zeit, phys. Chem. 35, 385, (1900). 



