ELECTROMOTIVE FORCES IN PYRIDINE 71 



dine is increased. The heats of ionization decrease with in- 

 crease of pyridine relatively more rapidly in each of the alco- 

 holic-pyridine mixtures than in the water-pyridine mixtures. 



In the last column of Table XIV are given a few dielectric 

 constants 21 . It will be observed that in this respect also, the 

 first addition of pyridine to the other solvent produces rela- 

 tively the greatest change. Are then, the electrode potentials 

 and heats of ionization functions of the dielectric constants? 



The solution pressure of silver in contact with pyridine so- 

 lutions of silver nitrate is found to be much higher than when 

 in contact with aqueous or alcoholic solutions, These calcu- 

 lations were made by substituting in (6) the electrode poten- 

 tials obtained for the 0.1 N solutions in each of the pure solv- 

 ents, and the values of = calculated from the following values 

 of the equivalent conductivities: Water, \ =99.46 22 and Xco 

 = 128.54 23 . Methyl alcohol, \ =38.575 22 and x°°=98.0. Ethyl 

 alcohol \ =13.215 22 and *°°=35.6 23 . Pyridine, \ =27.585 22 

 and x °°=71. 22 



The solution pressures in water and the alcohols are in good 

 agreement with those calculated by Farr. The values calculated 

 for water also are very close to the values 2.3xl0- 17 , given by 

 Neumann 24 . Assuming from conductivity data that silver ni- 

 trate is one-fourth as highly ionized in pyridine as it is in aqueous 

 solutions, Kahlenberg calculated the solution pressure of silver 

 in pyridine to be 3.4xl0- 10 , a value very close to the one herein 

 reported. 



SUMMARY. 



The electromotive forces of concentration cells containing so- 

 lutions of silver nitrate in the pure solvents: water, methyl alco- 

 hol, ethyl alcohol, pyridine, and in the binary mixtures of pyridine 

 with each of the other solvents have been determined at C and 

 25°. It has been shown that the Nernst equation cannot be ap- 

 plied to solutions of silver nitrate in pyridine, possibly lie- 

 cause of a change in the solution pressure of the metal with the 

 concentration of the salt or because of the association and sub- 

 sequent complex ionization of silver nitrate in pyridine solutions. 

 The equivalent conductance is not a measure of the concentra- 

 tion of the silver ions. 



"Determined by Mr. Richard Beeson. 



22 This laboratory. 



^Kohlrausch, Sitzungsber, Berl. Akad., 26, 570, 1902. 



"Zeit. physik. Chem.. 14, 193, 1894. 



