Molecular Theory of Solution. 703 



workers. Since, however, the intrinsic pressures o£ organic 

 liquids are not very different, the small change in internal 

 pressure on mixing v\ 111 not greatly affect the molecular 

 volumes, and, as Eolmes and Sageman [1906, 1909, 1913] 

 assumed, such liquids must mix together in the same way as 

 inelastic spheres. From this assumption they were able to 

 deduce the molecular complexity of a number of liquids. 

 Although molecular association may indicate strong mole- 

 cular attraction, this extra affinity will have been satisfied 

 in the aggregated molecules and they will have a smaller 

 resultant field of force. Moreover, in any case, the mole- 

 cular volume is the resultant of molecular forces. It seems, 

 therefore, that molecular volume may be taken as indicating 

 the weakness of the surrounding field of force whether the 

 molecule is simple or complex. 



No cases are known of solid substances which have an 

 infinite solubility without previous melting. With liquids 

 the condition of complete miscibility is of importance. 

 From (2) and (3) it is obvious that liquids will be completely 

 miscible when the average energy of their particles is able 

 to overcome the force opposing solution. It follows that, at 

 low temperatures, liquids will be completely miscible if their 

 relative molecular volumes fall within certain narrow limits, 

 which will increase as the temperature is raised. If liquids 

 are arranged in order of their molecular volumes, having 

 regard to their degree of assoc ; ation, they should be in order 

 of their solubilities. Liquids which are adjacent should be 

 mutually miscible. Liquids remote should be immiscible. 

 Holmes and Sageman found this to be the case, without 

 exception, for a large numl er of different liquids belonging 

 to all clashes of organic compounds. 



This suggests that the closed solubility curves found by 

 Rothmund for certain substances may be due to a change in 

 the relative degree of association of the two liquids, or to 

 some intramolecular rearrangement causing diminution of 

 molecular volume. If the aggregated molecules of one of 

 the liquids were to break up with increasing temperature 

 more rapidly than those of the ether, or if, in any way, the 

 difference in molecular volumes increased, the smaller 

 molecules would become immiscible until their energy had 

 increased sufficiently to overcome their increased mutual 

 attraction. 



Coming to the solubility of gases, the first two columns in 

 the following table are usually quoted in text-books from 

 Bunsen's figures for the solubility of different gases in water 

 and alcohol, accompanied bv a remark to the effect that, 



3C2 



