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 

 " Isomerism," from the Greek word 

 iffofiepris, which signifies " having 

 equal parts." The term was intro- 

 duced by Berzelius in 1830, after 

 he had satisfied himself that com- 

 pounds existed, differing widely 

 in their properties, which contain 

 the same constituent elements in 

 the same proportions, and which 

 combine with other bodies in the 

 same proportions to form neutral 

 salts. This he found to be the case 

 with " racemic" and "tartaric" acid. 

 Up to that time he had hesitated 

 in accepting the growing evidence 

 that equal constituents in equal 

 proportions did not constitute 

 identity of compounds. Wohler in 

 1823 and Liebig in 1824 had found 

 the same numerical composition for 

 "cyanate" and "fulminate" of 

 silver. In 1825 Faraday found two 

 hydrocarbons which contained the 

 same proportions of carbon and 



hydrogen, but showed totally differ- 

 ent properties, such as unequal 

 density in the gaseous state. Two 

 oxides of tin, having the same com- 

 position, were also known, and two 

 modifications of " phosphoric acid." 

 The explanation of these anomalies 

 caused Berzelius much difficulty. 

 He resorts to the notion of a 

 difference of grouping of the con- 

 stituent atoms. " The isomerism 

 of compounds," he says, "in itself 

 presupposes that the positions of 

 the atoms in them must be differ- 

 ent " (see E. von Meyer, ' History 

 of Chemistry,' p. 238). A. Rau in 

 his ' Theorien der modernen Chemie' 

 (3 parts, Braunschweig, 1877-84) 

 gives in the appendix to the third 

 part a detailed history of isomerism. 

 He denies that Berzelius refers to 

 the different position of atoms in 

 order to explain isomerism ; he 

 attributes this suggestion to Dumas 

 in 1833. 



