522 Dr. S. A. Shorter on the Kinetic 



can only be deduced from Henry's law by kinetically obscure 

 thermodynamical methods. It is evident, therefore, that any 

 theory which claims to give a direct kinetic interpretation of 

 Raoult's law must be subject to very careful consideration. 



I wish to point out, with respect to Dr. Tinker's theory, 

 that when it is applied correctly to the special case of a dilute 

 solution, it yields a law for the lowering of the partial vapour 

 pressure of the solvent quite different from Raoult's law; 

 and that Dr. Tinker's deduction of Raoult's law from his 

 general theory is due to a mathematical error. 



Dr. Tinker first obtains expressions for what he terms the 

 internal partial liquid pressure of each of the components of 

 the binary mixture. This is the pressure which would be 

 exerted by the molecules of the component if they behaved 

 as molecules of an ideal gas and were confined in a space 

 equal to the total "free space " in the solution. Dr. Tinker 

 obtains for the ratio of the internal pressure 7Ti of the pure 

 solvent, to the partial internal pressure 7r 1 / of the solvent in 

 the solution, the following expression, 



where N and n are the number of molecules of solvent and 

 solute respectively in the solution, Y 1 and Vi — bi are the 

 molecular volume and "free space " respectively of the 

 pure solvent, V 2 and V 2 — b 2 corresponding magnitudes 

 relating to the pure solute, and ne the expansion on forming 

 the solution from its components. 



Dr. Tinker next considers the relation between these 

 partial internal pressures and the partial vapour pressures 

 of the components, arriving at the following expression for 

 the ratio of the vapour pressure p x of the pure solvent to the 

 partial vapour pressure pi' of the solvent in the solution, 



where Q is the molecular heat of dilution, T the absolute 

 temperature, and R the " gas constant." 



Let us consider now the case of an ideal dilute solution. 

 As the concentration diminishes, the quantity Q/n tends to a 

 zero limit. This follows, of course, from simple kinetic 

 considerations. Hence we have 



Pi _*[i 



Pi' V 



* Numbered equations quoted from Dr. Tinker's paper will be dis- 

 tinguished in this communication by the numbers given them there. 

 Other equations will be distinguished, when necessary, by letters. 



