THE HYDRATE THEORY OF SOLUTIONS 207 



ionising power. Similar considerations may invalidate to a 

 large extent the analogous criticisms of Schlundt {Jour. Phys. 

 Chem. 1 90 1, 5, 168), who has shown that the conductivity of 

 silver nitrate is four times as great when dissolved in pro- 

 pionitrile as when dissolved in benzonitrile, in spite of the fact 

 that the specific inductive capacities of the two solvents are 

 practically equal, and that the same salt conducts better when 

 dissolved in pyridine, s. i.e. 12, than when dissolved in butyro- 

 nitrile, s. i. c. 20 ; it is quite possible that these differences may 

 be due to a special ionising power of certain solvents when 

 acting on particular salts {e.g. to a specific interaction between 

 silver nitrate and pyridine which might not occur between 

 silver nitrate and butyronitrile, or between potassium iodide 

 and pyridine), but in the absence of data in reference to the 

 ionic mobilities it is impossible to say how far the cases quoted 

 may or may not constitute exceptions to the Nernst-Thomson 

 rule. 



The recent extensive experiments of Walden {Zeit. phys. 

 Chem. 1906, 54, 131-230) on the electrical conductivity of tetra- 

 ethylammonium iodide, N(C 2 H S )J, in a series of fifty organic 

 solvents do not suffer from this limitation, as the observations 

 were such that in almost every case the coefficients of ionisation 

 could be calculated. The most important result of the investi- 

 gation was to show that in a large range of instances the dilution 

 required to produce a given coefficient of ionisation in the iodide was 

 inversely proportional to the cube of the specific inductive capacity of 

 the solvent. This result may be expressed mathematically as 

 e vi = constant, where v = volume containing one equivalent. 



and the following table shows the degree of concordance attained 

 in one typical series : 



H,0 . 

 CH 3 N0 2 . 



C 4 H 4 



CH3CN . 

 CH3SCN . 

 CH30H . 



C 2 H 5 CN . 



CH,(CO.CH 3 )., 



0(CO.CH 3 ), 



C 6 H 5 .CH,CN 



CH 3 O.C 6 H 4 .CHO 



C 6 H 5 .CHO 



