84 Mr. M. M. Pattison Muir on Chemical Classification. 



of classification by types leads, if logically carried out, to the 

 establishment of a number of subsidiary classes, each charac- 

 terized by its own qualities. 



4. The various systems of classification which have predo- 

 minated in chemical science may bo broadly divided into two 

 groups : — those in which chemical substances have been clas- 

 sified in accordance with the functions performed by them ; 

 and those in which chemical substances have been classified 

 in accordance with their composition. I shall endeavour to 

 give a slight historical sketch of the various systems of che- 

 mical classification. 



5. Before the time of Black, Cavendish, Priestley, and 

 Lavoisier and his associates, we find chemists paying almost 

 exclusive attention to the action of bodies without inquiring 

 into their composition. We find accounts of many experi- 

 ments upon the mutua action of salts and acids, metals and 

 semimetals, and so on ; but, because of the absence of mea- 

 surements of the quantities of the various reacting bodies, we 

 find nothing but vagueness. The mere qualitative study of 

 reactions never led to any fiir-reaching generalizations. 



Casual coincidences, vague analogies, were followed up ; 

 principles were imagined to exist in various substances ; and 

 by the supposed existence of these imagined principles sub- 

 stances were grouped together. Thus we have the principle 

 of acidity, the mercurial principle existent in metals, and many 

 other similar fantasies. 



The nomenclature of chemistry at the time preceding that 

 of the introduction of Bergman's system was a nomenclature 

 based in many particulars on the mere qualitati^-e study of 

 reactions. Such names as oil of vitriol, butter of antiuiony, 

 liver of sulphur, sugar of lead, milk of lime, &c. call attention 

 only to the outer and shallow analogies of appearance, consist- 

 ence, colour, &c. of the substances named. According as at- 

 tention was directed to this or to that reaction of one and the 

 same substance, so was a different name devised for that sub- 

 stance ; thus we meet with carbonate of potassium under the 

 names oi fixed salt of tartar, fixed vegetable alkali, chalky tartar, 

 alkahest of Van Hehnont, &c. &c. 



The study of qualitative reactions could lead to no true con- 

 ception of the essential function exerted by any substance ; 

 hence not only in the nomenclature, but also in actual prac- 

 tice do Ave find constant failure to distinguish between essen- 

 tially distinct substances. The fact that a substance effervesced 

 on addition of acid appears to have been adopted as character- 

 istic, and to have led to the confused grouping together of 

 several different compounds under the name of Alkali. But 



