BLACK. 9 



written by D'AIembert himself. It is, as might be 

 expected, able, clear, elaborate. He assumes the sub- 

 stance of the atmosphere to be alone entitled to the 

 name of air, and to be the foundation of all other per- 

 manently elastic bodies : " L'air elementaire, ou 1'air 

 proprement dit," he says. He describes it as " homo- 

 gene," and terms it " 1'ingredient fondamental de tout 

 Fair de I'atmosphere, et qui lui donne son nom." Other 

 substances or exhalations mix with it, he says, but these 

 he terms " passageres," passing vapours, and not per- 

 manent : the air alone (that is, the atmospheric air) he 

 calls " permanent," or permanently elastic (vol. i. p. 

 225). So little attention had the observation of Van 

 Helmont respecting the Grotto del Cane excited, that 

 we find a conjecture hazarded in the article * Grotte 7 

 (vol. vii. p. 968), which appeared in 1756. "peut- 

 etre respirent ils (les chiens), au lieu d'air, des vapeurs 

 minerales ;" but this was some time after Black's dis- 

 covery had taught us to distinguish such permanently 

 elastic vapours from atmospheric air. In the article 

 'Fermentation' (vol. vi. p. 523) we find Van Hel- 

 mont's doctrines of the connection between fermenta- 

 tion and digestion treated with ridicule, and those who 

 adopted them jocularly called the " fermentateurs." 



A few years later, however, the face of things 

 changed. In the 'Supplement,' published in 1776, 



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we find an article on ' Fixed Air,' and a reference to 

 Dr. Black's discovery ; but nothing can be more indis- 

 tinct than the author, M. Morveau's, ideas respecting 

 it ; for he leaves us in doubt whether it be the atmos- 

 pheric air or a separate substance, and yet he states 

 that the phenomena of fermentation and putrefaction 

 are explained by the evolution or absorption of this 

 air, and that mineral waters derive from its presence 

 their flavour. An abstract of M. Venel's book had in 

 1765, under the head of 'Mineral Waters,' given this 

 explanation ; but instead of representing the air com- 

 bined with the water as a different substance, he calls 



