106 HISTORY OF CHEMISTRY. [LECTURE VI. 



majority of ihe elements. And how did it fare with the other 

 generalisations upon which his system rested ? The hypothesis 

 of Dulong and Petit was not without exceptions in its appli- 

 cability, as I have already stated. The numbers deduced 

 from it for silver, cobalt, and tellurium were not in harmony 

 with Berzelius' determinations, that is, with the atomic weights 

 required by the chemical analogies, and by isomorphism ; so 

 that even this hypothesis was not tenable when rigidly con- 

 sidered. Mitscherlich's law still remained, and the majority 

 of chemists believed that it permitted of an unerring conclusion 

 as to the atomic constitution. Other voices were heard, how- 

 ever, which indicated doubts, especially after Mitscherlich had 

 shown that there are dimorphous substances, i.e. substances 

 which can occur in two crystalline forms. 54 Attention was 

 drawn to the fact that, as the occurrence of dimorphism 

 proved, the crystalline form of a substance was not determined 

 solely by the number of its atoms. 55 



Of all the physical laws that had been applied to the 

 determination of atomic weights, there thus remained not one 

 upon which full reliance was placed. The conception of the 

 atom was looked upon, in consequence, as uncertain and 

 hypothetical. Chemists believed they would have to be 

 contented with the combining weight or the equivalent, the 

 latter of which had gained new support from Faraday's 

 electrolytic law. 56 At the end of the fourth decade of the 

 century, we thus find the atomic theory the most brilliant 

 theoretical achievement of chemistry abandoned and dis- 

 credited by the majority of chemists, as a generalisation of 

 too hypothetical a character. A new school had arisen, which 

 had adopted Wollaston's equivalents, and which sought, 

 successfully, to supplant the system of Berzelius. 



At the head of this movement there stands L. Gmelin. 

 The views of this chemist are of all the more importance from 

 the fact that he expounded them in his excellent Hand-book 



54 Ann. Chim. [2] 24, 264. 55 Ibid. [2] 50, 171. ** Experimental 

 Researches in Electricity, Series 3, 377, Series 7, 783 et scq. 1833-34. 



