406 SCIENTIFIC THOUGHT. 



Berzelius united Dalton's and Davy's researches into a 

 comprehensive system of chemistry. The identity or 

 difference of chemical substances seemed in the early part 

 of the century to be fixed by the constituent elements and 

 their quantitative proportions determined by a qualitative 

 and quantitative analysis. This simple view had to be 

 abandoned when Wohler in 1823, Liebig in 1824, and 

 Faraday in 1825 found that entirely different qualities, 

 indicating a different constitution, could belong to bodies 

 having the same elements in the same numerical propor- 

 tions. 1 The composition of a compound had to be dis- 

 tinguished from its constitution, the elementary from the 

 constituent analysis and formula. It took forty years 

 before the great variety of views which were brought 

 forward with the purpose of explaining how composition 

 and constitution of the same aggregate of elements might 



1 This phenomenon is termed hydrogen, but showed totally differ- 

 " Isomerism," from the Greek word ent properties, such as unequal 

 iffofifpfis, which signifies "having density in the gaseous state. Two 

 equal parts." The term was intro- oxides of tin, having the same com- 

 duced by Berzelius in 1830, after position, were also known, and two 

 he had satisfied himself that com- modifications of ' phosphoric acid." 

 pounds existed, differing widely The explanation of these anomalies 

 in their properties, which contain caused Berzelius much difficulty, 

 the same constituent elements in He resorts to the notion of a 

 the same proportions, and which difference of grouping of the con- 

 combine with other bodies in the stituent atoms. "The isomerism 

 same proportions to form neutral of compounds," he says, "in itself 

 salts. This he found to be the case presupposes that the positions of 

 with "racemic" and" tartaric" acid, the atoms in them must be differ- 

 Up to that time he had hesitated | ent" (see E. von Meyer, 'History 

 in accepting the growing evidence of Chemistry,' p. 238). A. Rau in 

 that equal constituents in equal his ' Theorien der modernen Chemie' 

 proportions did not constitute (3 parts, Braunschweig, 1877-84) 

 identity of compounds. Wohler in gives in the appendix to the third 

 1823 and Liebig in 1824 had found part a detailed history of isomerism. 

 the same numerical composition for He denies that Berzelius refers to 

 "cyanate" and "fulminate" of the different position of atoms in 

 silver. In 1825 Faraday found two order to explain isomerism ; he at- 

 hydrocarbons which contained the tributes this suggestion to Dumas 

 same proportions of carbon and in 1833. 



