120 SCIENCE PROGRESS 



value of the limiting molecular conductivity was generally found 

 to be about three times as great as for the corresponding 

 aqueous solution. If A^ represents the maximum molecular 

 conductivity, A M = U K + U A , where U K and U A are the velo- 

 cities of the kation and anion respectively. 



This therefore indicates that the ionic velocities in ammonia 

 are far greater than in water and accounts for the fact that 

 most salt solutions in liquid ammonia show a higher conductivity 

 than the corresponding aqueous solutions, in spite of the fact 

 that dissolved salts are far less ionised in ammonia than in 

 water. This high mobility of the ions is in accordance with 

 the low viscosity of ammonia solutions. The influence of the 

 viscosity of the solvent on the mobility of the ions was investi- 

 gated by measuring the conductivity of tetramethylammonium 

 iodide in various solvents. It was found that the limiting value 

 of the molecular conductivity was approximately proportional 

 to the fluidity of the solvent, fluidity being the reciprocal of the 

 viscosity determined by the ordinary physical methods (rate 

 of flow of liquid through a narrow tube, etc.). Direct measure- 

 ments of the ionic velocities in ammonia were made by Franklin 

 and Cady (22), who found that these were from 2*4 to 2"8 times 

 as great at — 33 C. as in water at 4- 18 C. 



In liquid ammonia, Ostwald's dilution formula holds approxi- 

 mately for solutions of the binary salts. This seems to indicate 

 that in ammonia solutions the conditions are more simple than 

 in aqueous solutions. 



Before leaving this branch of the subject, mention should 

 be made of the more recent work of Franklin and Kraus (23)- 

 They found that the conductivity of pure liquid ammonia is not 

 greater than 0*005 x JO -0 , a value much lower than that usually 

 given in the literature of the subject. In favour of this low value 

 they point out that the velocity of the interaction of sodium and 

 liquid ammonia is far less than that of the analogous interaction 

 of sodium and water and this in spite of the fact that in the 

 former the sodium is in the dissolved state, which — other things 

 being equal — would tend to make the action go more swiftly. 

 In the case of the metallic salts special attention has been paid 

 to the more concentrated solutions, the earlier work having 

 dealt more with dilute solutions in order to find the values for 

 the maximum conductivity. 



The conductivity values afforded by ammonium and sodium 



