DISCUSSION OF RESULTS. 209 



curves, is probably due to an increase in the molecular aggregation of the solvent. 

 This increase is not necessarily caused by an increase in the association of 

 either of the pure solvents. Indeed, the association of the pure solvents is 

 in all probability less in the mixtures. The increase in molecular aggregation 

 above referred to may simply be due to a molecular combination of the un- 

 associated parts of the pure solvents. The view that is now generally held 

 with regard to chemical combination is that such combination usually takes 

 place between the ions and not between the molecules. We may, in a sense, 

 regard a molecule that is broken down into its ions as in a state of diminished 

 atomic aggregation, just as we regard the diminution in association, when 

 two pure solvents are mixed, as a state of diminished molecular aggregation. 

 The ions, to be sure, are in a different physical condition from the undis- 

 sociated molecule, in that they carry equal and opposite electrical charges ; 

 and we have no experimental reason whatsoever for supposing that the un- 

 associated portions of the solvent molecules, in the mixed solvents, are in the 

 same condition. It is, however, the difference in energy relations between the 

 ions that is at the basis of our present views of chemical combination. Rea- 

 soning from analogy, it is not unthinkable, to say the least, that a similar, 

 although not identical difference in energy relations is the cause of molecular 

 aggregation or association. If such an energy relation as has been referred to 

 does exist, then we have an explanation of the formation of complex mole- 

 cules, such as hydrates, double salts, etc. If the above reasoning is correct, 

 the explanation of the fluidity maximum is simple. According to Ramsay and 

 Shields l the molecular complexity of the four solvents is as follows : 



From these data we see that the molecules of methyl alcohol and the mole- 

 cules of ethyl alcohol are much more complex than the molecules of acetone. 

 For the sake of simplicity we shall limit our discussion to the case of mixtures 

 of acetone and methyl alcohol. The maximum in fluidity occurs in the 75 

 per cent mixture of the two solvents. We should expect the effect of the 

 acetone upon the methyl alcohol to be greatest in about this mixture, because 

 of the relatively large mass of the acetone present ; and, consequently, in such 

 a mixture we should have the largest number of unassociated molecules of 

 methyl alcohol. This is shown to be the case by reference to the temperature 



'Ztschr. phys. Chem., 12, 433 (1893). 



