396 SCIENCE PROGRESS 



way." We had almost begun to shudder when our fears were 

 calmed by a sudden cessation of superlatives and the author's 

 adding mildly, " such an occurrence is not impossible." Our 

 peace is not of long duration, for " we may find some day that 

 all the units of the solute are potentially active." When we 

 ponder a little time over the phrase " potentially active," we are 

 brought to a frame of mind in which it would cause us no 

 surprise to find "some day" that the units of the solute were 

 continuously distributed in discrete portions throughout the 

 solvent, in the form of microscopic, hard, spherical, soft cubes of 

 immense size. The author has in fact fallen in that last 

 paragraph — perhaps by reason of some unconscious psychical 

 process of suggestion due to the fact that the din of the last 

 " terrific downfall" is still ringing in his ears — into a trap which 

 one would think by this time had lost its deadliness. As this 

 does not appear to be the case, it may not be wholly useless to 

 repeat what has previously been said elsewhere in connexion 

 with the subject : 



" The real fundamental proposition of the thermodynamic 

 theory of solution is contained in the assertion that the osmotic 

 pressure of a solution and every other property conditioned 

 solely by it, depend simply on the number of solute molecules 

 scattered through a given volume of solution and not at all on 

 the chemical nature of either solute or solvent or on the 

 relation between the latter, provided only that the solution is 

 dilute. The chemical properties of solutions, on the contrary, 

 depend not only on the number but also on the nature of the 

 dispersed particles and so are to a large extent conditioned 

 by the exact mode of connexion between the solvent and 

 solute." 



" It seems necessary to emphasise this point because of the 

 fallacy, which unfortunately appears to be widely spread, that 

 there is some fatal incompatibility between the old qualitative 

 hydrate theory of solution and the new quantitative thermody- 

 namic theory of which van't Hoff was the pioneer. This view 

 has resulted from the one-sided outlook of the champions of 

 each theory and is certainly not a necessary consequence of the 

 fundamental basis of either. It is greatly to be desired that 

 writers of the theory of solution should distinguish clearly 

 which aspect of the subject belongs properly to their own 

 investigations and should refrain from attacking, on the basis 

 of irrelevant experiments, a theory which is quite immune from 

 the criticism which may reasonably be levelled against any 

 particular hypothetical view of the nature of solutions." 



