Molecular Thermodynamics, 625 



It is to be noted that 2<'i represents the range of variation 

 of the total concentration of solutes present, not of the 

 concentrations of the reactants, which latter alone, however, 

 are required to behave as perfect solutes. 



There seems, therefore, good reason to believe that in a 

 few well-chosen cases this effect might be demonstrated 

 beyond doubt, and the quantity m found with some 

 approximation in each case. Agreement between the several 

 values of m thus found would justify some confidence in this 

 estimate of the mean molecular weight of the solvent. 



It seems probable, however, that measurements of the 

 solubility of a moderately soluble gas would be the most 

 hopeful first approach to this inves ligation, — the theoretical 

 treatment being perfectly obvious from what has gone 

 before. Experimental investigation of this question is contem- 

 plated. 



Y. A Special Application. The Theory of 

 Electrolytes. 



It was pointed out in section II. that, the " molecular " 

 treatment of thermodynamics opens up the way for the use 

 of: dynamical theory. The calculation of the general energy 

 terms will be complex, however, in the general case and only 

 rough ideas and indications may be obtainable at first. 



The' idea put forward by Sutherland in 1902, that strong- 

 electrolytes are completely ionized, at any rate in dilute 

 solution, is of great interest in this connexion. 



For in a solution of ions we have forces at work which are 

 amenable to relatively simple dynamical treatment, and 

 which are considerable in dilute solutions where other inter- 

 solute forces are negligible. 



The credit of first showing that this is so is undoubtedly 

 due to Milner *, and the full value of Milner's calculation of 

 what he calls the "Yirial" of a mixture of ions has perhaps 

 scarcely been realized. Milner calculated X%rcf)(r), the sum 

 of all the electrostatic forces <f>(r) in a chaos of equal 

 numbers of oppositely charged massive points, each force 

 being multiplied by the distance (r) over which it acts. 



Calling this the " virial " of a mixture of ions he proceeds 

 to apply to the osmotic pressure of a solution of ions the 

 Yirial theorem established by Clausius for a gas. He points 

 outf that because the law of force is that of the inverse 



* Phil. Mag. ser. 6, xxiii. p. 551 ; xxv. p. 742. 

 t Loc. cit. xxv. p. 747. 



Phil Mag. S. 6. Yol. 43. No. 255. March 1922. 2 S 



