664 Mr. W. H. Gibson on Influence of Volume Change 



specific volumes vi and v 2 as found experimentally, or as 

 calculated from the formula of Batschinski : 



v — w=cF, 



where v is the specific volume of a liquid, 



w is the specific volume at zero fluidity, 

 F is the fluidity, and c is a constant. 



An hypothesis by the use of which the volume change of 

 each constituent in a mixture can be calculated is required 

 before the above fluidity formula can be used, and the values 

 obtained by it compared with experimental data. 



Lumsden * examined the change in the molecular volume 

 of solutes dissolved in organic solvents with change in 

 temperature and concentration, and found that the molecular 

 volume was affected by the temperature, concentration, and 

 nature of the solvent. 



These changes calculated on the assumption that the 

 solvent is unaffected are too small, since any change in the 

 volume of the solute will be accompanied by a change in 

 the volume of the solvent. 



Walden f considers that the molecular volume is connected 

 with the co-volume of the solvent, holding that the greater 

 the co-volume, the smaller is the solution volume of the 

 solute. 



The formula of Batschinski enables the value of iv, which 

 may be considered as the co-volume of a liquid, to be 

 calculated for liquids from fluidity data, so that the relation 

 between w, the co-volume, and v, the specific volume, for 

 different liquids, may be compared. 



The molecules of a liquid of volume H-u? are free to move 

 in the space Mv, where M is the molecular weight. On 

 mixture with another liquid of different specific volume and 

 co-volume, a rearrangement of the free space at the disposal 

 of the molecules will usually occur until an equilibrium is 

 reached ; that is to say, the specific volume of both liquids 

 will change, and the change will depend on the concentration 

 of each liquid in the mixture. 



The hypothesis adopted in the calculations in this paper 

 is that when two chemically indifferent, non-associated 

 liquids are mixed their specific volumes change until the 

 free space per unit of co-volume is the same for both kinds 

 of molecule in the mixture. This would apply for any 



* J. C. S. 1907, Trans, p. 24. 



t Zeit. Phys. Chem. lixfp. 385 (1907). 



