UNIVERSITY COLLEGE, LONDON 115 



such a mixture in an undissociated condition (Trans- 

 actions Chem. Soc. 1899, p. 613). This is quite consistent 

 with the results of Ramsay and Cundall. 



In 1890 the British Association met at Leeds, and the 

 proceedings of the Chemical Section were enriched by a 

 discussion in which the supporters of the older views as 

 to the nature of solutions and of the newer doctrines 

 were both present and took part. The reader may be 

 reminded that up to quite recent times the nature 

 of the process involved, when a soluble substance 

 such as common salt or sugar dissolves in water, 

 had not been studied systematically and it had been 

 very generally assumed that when a solid substance 

 dissolves in a liquid a weak kind of chemical combina- 

 tion occurs between the solid and the liquid. This 

 was usually referred to broadly as the hydrate theory of 

 solution, and there can be no doubt of the existence of 

 many hydrates in salt solutions and of compounds of 

 the solute in the solvent in other cases in which liquids 

 other than water are concerned. But the electrolytic 

 and other properties of solutions cannot be accounted 

 for by the hydrate theory, and it was not till 1887 that 

 the new view of the constitution of solutions was intro- 

 duced, by which many difficulties were explained. In 

 that year the Dutch Professor Van't Hoff published in 

 the Zeitschrift fur physikalische Chemie a theory based 

 on the analogy between the state of substances when 

 in solution and the same when in the state of gas. The 

 dissolved substance exercises a pressure, called osmotic 



