Manchester Memoirs, Vol. xlvii. {igo'^), No. II. 13 



radicles, the formation of isomers, and the substitution of 

 one element by another, were facts which strengthened 

 the atomic theory and seemed to be incapable of reason- 

 able interpretation upon other terms. Their connection 

 with one another, however, was not well understood, and 

 wearisome discussions preceded their coordination under 

 one general law. 



With the tedious controversies which distracted 

 chemists between 1830 and 1850, we have nothing now 

 to do ; they were important in their day, but they do 

 not come within the scope of the present argument. 

 Theory after theory was advanced, prospered for a time, 

 and then decayed ; and chemical literature is crowded 

 with their fossil remains. Each one, doubtless, indicated 

 an advance in knowledge, but each one also exaggerated 

 the importance of some special set of relations, and so 

 overshot the mark. During this period, however, Faraday 

 discovered the law of electrolysis which is now known by 

 his name, and the chemical equivalents were thereby 

 given another extension of meaning. The electro- 

 chemical theories of Berzelius had fallen to the ground, 

 but Faraday's law came as a permanent addition to the 

 physical side of chemistry. 



During the sixth decade of the nineteenth century, two 

 important forward steps were taken. The kinetic theory 

 of gases gave new force to Avogadro's law, and made 

 its complete recognition by chemists necessary. Atoms, 

 molecules, equivalents, and atomic weights needed to be 

 more sharply defined, and in this work many chemists 

 shared. Berzelius had proposed a system of atomic 

 weights which differed, except in the value taken for its 

 base, but little from the one now in use. This was 

 abandoned for a table devised by Gmelin, in which the 

 laws of Avogadro and of Dulong and Petit were almost 



