250 ANNUAL KEPORT SMITHSONIAN INSTITUTION, 1908. 



characterized by the practically instantaneous nature of a certain 

 category of chemical reactions offer an almost inexhaustible series of 

 chemical equilibria. 



Here, however, the law of electrolytic dissociation comes to our aid, 

 a law derived, it is true, in principle from experiments on the electric 

 conductibility of dilute saline solutions, but which was first put on a 

 reliable experimental footing by the osmotic method of molecular 

 weight determination. 



The importance of this doctrine extends far beyond the field of 

 chemistiy proper. Briefly described, its application to chemical proc- 

 esses consists in the fact that it allows an exact application of the 

 laws of static chemistry to characteristic aqueous solutions and 

 through these to the reactions of ordinary analytic chemistry. 



The later refinement of this doctrine has resulted in a very detailed 

 theory of equilibrium in dilute solutions, and in particular in the 

 proof of the fact that when, for a certain solvent, the coefficients of 

 dissociation and solubility of those electrically neutral molecules 

 which are composed of several combined ions are known, the equi- 

 librium in this solvent can be calculated, and if the coefficients of 

 distribution are known, the equilibrium in any other solvent what- 

 ever can be derived with equal facility. 



On account of the simplicity of the gaseous state we should 

 expect that the law of mass action would be particularly profitable 

 in reference to this phase. But it was found that at low tempera- 

 tures the speeds of reactions, like many of the reactions of organic 

 chemistry, were generally very small. At high temperatures, how- 

 ever, equilibrium was established as in ionic reactions almost instan- 

 taneously. But in this simple field there are, at the lower tempera- 

 tures, difficultly controlled catalytic influences, and at the high 

 temperatures inherent experimental difficulties place themselves in 

 the way. It is nevertheless to be hoped that in this field of gaseous 

 reactions which investigators are now eagerly attacking from differ- 

 ent points, a wealth of material and a corresponding theoretical 

 profit will soon be forthcoming. 



In the application of thermodynamics to chemical phenomena lies 

 another field where the methods of theoretical physics have been 

 fruitful. There, too, the first great step in advance was taken 

 almost forty years ago. The work I allude to is that particularly 

 important proof that the chemical law of mass action should be 

 recognized as a direct application of thermodynamics, which is found 

 in volume 2 of the transactions of the German Chemical Society. 



Among the further results obtained in this way I should state that 

 the aid of thermodynamics alone has made possible the close and ex- 

 haustive study of heterogeneous equilibria, particularly those where 

 mixtures of given concentration (not only dilute solutions) enter into 



