LECTURE VII.] HISTORY OF CHEMISTRY. 117 



so backward a state of development, experiments were made 

 in order to obtain some information as to the constitution, or 

 mode of arrangement of the atoms, of compounds. A pursuit 

 of this kind may be regarded as idle speculation, and yet scien- 

 tific chemistry was directed, at an early period, towards such 

 considerations. This was owing to the phenomena of isomerism, 

 into which, therefore, I must here enter with some detail. 



After chemists had begun to pay attention to the quanti- 

 tative composition of substances, and especially after they had 

 learned to regard constant proportions by weight of their con- 

 stituents as a real characteristic of chemical compounds, it was 

 assumed as a matter of course that the same composition per 

 cent, always postulated the same properties. It was, of course, 

 known that very many, and indeed most, substances occurred 

 in several states : solid, liquid, and gaseous ; crystalline and 

 amorphous; etc., but the sensation that the discovery of dimor- 

 phism made, shows us how great the tendency was at that 

 time to regard physical and chemical properties as functions of 

 the composition per cent, (and of the temperature). It must 

 naturally have created much surprise to see that sulphur can 

 appear in two crystalline forms ; to hear that arragonite is 

 pure calcium carbonate, and is therefore dimorphous with 

 calc-spar ; etc. 21 



It was to be shown, however, in the same year as that in 

 which the dimorphism of sulphur was recognised (1823) that 

 even the chemical properties can change without alteration of 

 composition. In the analysis of fulminic acid, Liebig obtained 

 numbers which agreed exactly with those established for cyanic 

 acid. 22 This was at first believed to be an error, but subse- 

 quent examination confirmed the observation, and the great 

 difference between the two substances seemed wholly inex- 

 plicable. Two years later, Faraday discovered another fact of 

 the same kind. 23 He was engaged in the examination of oil 



21 Ann. Chim. [2] 24, 264. ** Ibid. [2] 24, 294 ; 25, 288 ; 

 Schweigger's Journal. 48, 376. 23 Phil. Trans. 1825, 440; Ann. Phil. 27, 

 44 and 95 ; Schweigger's Journal. 47, 340 and 441. 



