ON THE PHYSICAL VIEW OF NATURE. 157 



" energy " has become a commercial commodity as it had 

 before become a scientific measure. 



That chemical reactions are connected with mechan- 

 ical, gravitational, optical, caloric, and electric phenomena 

 has been known for a long time. Each of these mani- 

 festations has therefore been studied as affording a 

 measure of the energy of chemical reactions, and these 

 have in turn been looked upon as results of attrac- 

 tions, or of mass actions, or of thermal conditions, or 

 of electrical polarities. We have thus mechanical, 

 thermo- chemical, electro -chemical theories of affinity. 

 Valuable discoveries and important suggestions have 

 also been arrived at by these special researches : we 

 have the laws of mass-action suggested by Berthollet 

 and revived in modern times by Guldberg and Waage ; 

 the all-important electrolytic law of Faraday and the 

 so-called third law of Berthelot in thermo-chemistry ; 37. 



Berthelot 



further, the important researches of Kopp and Hess, ando 

 None of these discoveries, however, seemed really to 

 grasp the whole subject of chemical reaction, and ac- 

 cordingly they remained for a long time unknown, or 

 fell, after a short life, into oblivion and disrepute. It 

 has been one of the greatest performances of the last 

 twenty years of the century to have approached the 

 all-important question, " What is chemical affinity, and 

 how is it to be measured ? " in a comprehensive spirit, 

 and to have brought it to the verge of solution. The 

 merit of having done this belongs the more incon- 

 testably to Prof. Wilhelm Ostwald, 1 because no one 



1 Prof. Ostwald's principal work Chemie,' of which the first edition 

 is the 'Lehrbuch der allgemeinen appeared in two volumes (Leipzig, 



