of the Theory of Solutions. 



487 



one half of the normal value. These exceptions are explained 

 at once by the formation of double molecules; and this expla- 

 nation has been confirmed by the fact that such solutions on 

 dilution often lead to normal values, as if a dissociation of 

 the double molecules took place. 



Secondly, it has long been known that some acids, e. g. 

 formic and acetic acids, seem to have a bimolecular structure 

 even in the gaseous condition. 



Finally, and quite recently, Ramsay and Shields have, by 

 a method which is not far removed from osmotic pressure, 

 come to the important conclusion, similar to the above, that 

 alcohols and acids, in contradistinction to the hydrocarbons, 

 possess a polymolecular constitution ; and I have grounds for 

 suspecting that, if Ramsay slightly altered his method of 

 calculation, a still better agreement would be obtained. 



There is still another case, where small lowerings of the 

 freezing-point are observed, which cannot be explained by a 

 polymolecular constitution because simple halving is not 

 shown and because even a rise in the freezing-point often 

 occurs, as in solutions of antimony in tin, naphthol in naph- 

 thalene, carbazol in phenanthrene. 



Then the idea occurred to me that the dissolved substance 

 as well as the solvent were frozen out together. 



Fig. 5 represents the vapour-pressure of ice and water 

 near the freezing-point, a, and also the vapour-pressure of a 



Fig. 5. 



Sfl/* ief 



is 



T 



solution whose freezing-point lies at h. If now the ice 

 able to carry down some of the dissolved body, its vapour- 

 pressure diminishes, and the freezing-point correspondingly 

 rises to c, and can even lie to the right of a. As a matter of 

 fact, experiment has repeatedly confirmed this assumption, 

 as e. g. with solutions of lead, cadmium, tin, and gold in 



