CHEMICAL THEORY OF SOLUTIONS. PART I. 3 



sider these simple cases as accidental and try to establish a 

 theory which would embrace the manifold ness of the phenomena 

 in one general consideration ? Or are we to look at these 

 simplest relations as normal and try to account for the devia- 

 tions by introducing appropriate hypotheses ? The teaching of 

 the history of chemistry leaves us no doubt on this point. The 

 anomalous behaviour of vapours, wdiicli appeared at first to en- 

 danger the universal validity of the gas laws, led to the establish- 

 ment of the chemical hypothesis of association and dissociation, 

 a hypothesis which has proved so fruitful and assisted in no 

 small degree in the development of rational views on chemical 

 affinity. Again the anomalies of the salt solutions with respect 

 to the theory of the dilute solution have found their natural 

 explanation in the chemical hypothesis of electrolytic dissociation, 

 under whose banner physical chemistry has achieved so many 

 conquests. What then could be more natural than to assume 

 the simple and regular behaviour of certain solutions as normal 

 and to consider the deviations from such as due to reversible 

 chemical reactions taking place in the solution ? And as the 

 manifoldness of chemical reactions is inexhaustible, the resources 

 of this hypothesis must be so too. It is indeed not difficult to 

 imagine that most of the complex relations actually observed 

 could be accounted for in this way. The theory of solution 

 based on such a hypothesis may be called chemical in contrast 

 to such a physical theory as that of van der Waals. 



In working out the consequences of particular hypothesis 

 there is always danger of becoming one-sided and losing sight 

 of other possibilities. Yet for the first attempts it would be 

 better not to be too circumsj^ect, lest one should be lost in the 

 maze of the variety of things which must be taken into considéra- 



