3 J 4 HISTORY OF CHEMISTRY. [LECTURE XV. 



most valuable. The theory has so thoroughly permeated the 

 whole of chemistry, that investigations of the elements and 

 of their compounds have gained a new significance. As a 

 result of the bond which it establishes between the individual 

 elements, it lends to every such special investigation the charm 

 of a research of universal interest. 



Investigations which deal with the subject of affinity, pre- 

 senting this subject in a mathematical form and combining it 

 with Berthollet's doctrine of affinity, are of equal importance. 91 



We possess investigations of this kind, in a finished state, 

 which have been tested in the most different directions and 

 have been found accurate ; so that in this respect also great 

 results have been attained. 



An investigation by Guldberg and Waage 92 constitutes a 

 new departure for advancement in this direction. In place 

 of Berthollet's notion of chemical mass, these investigators 

 introduced that of active mass, by which they understand the 

 quantity of a substance contained in a unit of space. The 

 chemical energy with which two substances act upon one 

 another is then equal to the product of their active masses 

 multiplied by the affinity coefficients ; and by the latter Guld- 

 berg and Waage understand values which are dependent upon the 

 chemical nature of the substances and upon the temperature. 93 



When the substances A and B are transformed, in a chemical 

 operation, into A' and B', and where, conversely, A and B' can 

 be transformed into A and B, equilibrium is established when 

 the forces acting between A and B are equal to those acting 

 between A and B'. If the active masses A and B are repre- 

 sented by / and ^, and those of A and B' by /' and q', and 

 further, if the affinity coefficients are k and &', then in order 

 that equilibrium may be established we must have 



kpq = k '/ q' 

 In applying this equation it is advisable to introduce. 



91 Compare p. 37. m Etudes sur les affinites chimiques. Christiania 

 1867 ; J. pr. Chem. [2] 19, 69. 93 Compare also Van 't Hoff, Berichte. 

 10, 669. 



