340 HERMANN VON HELMHOLTZ 



' Nernst has thrown himself zealously into the newest appli- 

 cations of physical chemistry, as worked out by the Dutchman 

 Van't H off, and advocated with great vigour by Professor Ostwald 

 of Leipzig in his Journal. These theories have already proved 

 to be of great practical utility, and have led to a multitude of 

 demonstrably correct conclusions, although they imply some 

 arbitrary asumptions which do not seem to me to be proven. 

 The chemists, however, make use of this hypothesis (of the 

 dissociation of a portion of the compound molecules of the dis- 

 solved salts) in order to form a clear conception of the processes, 

 and they must be allowed to do this after their fashion, since 

 the whole extraordinarily comprehensive system of organic 

 chemistry has developed in the most irrational manner, always 

 linked with sensory images, which could not possibly be 

 legitimate in the form in which they are represented. There is 

 a sound core in this whole movement, the application of thermo- 

 dynamics to chemistry, which is much purer in Planck's work. 

 But thermodynamic laws in their abstract form can only be 

 grasped by rigidly trained mathematicians, and are accordingly 

 scarcely accessible to the people who want to do experiments 

 on solutions and their vapour tensions, freezing points, heats 

 of solution, &c/ 



In a sketch which was probably designed in 1883 to be the 

 Introduction to the Third Part of his ' Thermodynamics ', 

 Helmholtz set forth clearly and intelligibly the reasons that led 

 him to adopt the expressions ' free ' and ' bound ' energy, show- 

 ing at the same time how he had plotted out the continuation of 

 his investigations, had he not been led by the generalization of 

 all these considerations to far more comprehensive problems. 



' Thermo-chemical researches have till now been directed 

 almost exclusively to the quantities of heat evolved during 

 chemical processes, when the forces of chemical affinity are 

 given free play, so that the association of the combining 

 substances usually takes place with more or less disturbance. 

 In such cases heat is as a rule the only work-equivalent of the 

 chemical forces produced, or at best there is only an insignificant 

 proportion of other forms of work, among which the over- 

 coming of atmospheric pressure plays, relatively at least, the 

 most frequent part. In thermochemical researches the attempt 

 is usually made to show how much heat has been given off, or 



