516 Rev. W. V. Harcourt on Lord Brougham's statements 



»* 



Black had certainly very little ambition, and apparently 

 little of the activity of an ardent curiosity : for here he rested, 

 after drawing from the facts before him some pregnant infer- 

 ences, as to the production, for instance, of this fixed air from 

 charcoal, and its diffusion through the atmosphere *. He did 

 not even measure, or collect, the air extricated in his experi- 

 ments, still less did he try its density ; he did not extend his 

 inquiries at all into its elastic condition: and the consequence 

 was that on that point which you take for the stress of his dis- 

 covery, he rather retrograded from the inferences of his pre- 

 decessors than advanced beyond them : for he went no further 

 in his conclusions than this — " Quick-lime therefore does not 

 attract air when in its most ordinary form, but is capable of 

 being joined to one particular species only, which is dispersed 

 through the atmosphere, either in the shape of an exceedingly 

 subtile powder, or more probably in that of an elastic fluid f. M 

 He did more, it is true, than discover the chemical affinity of 

 one substance only which floats in the air, or is fixed in many 

 earths and alkalies; forthat discovery, as it limited thenumber of 

 such substances, so it extended to the rest the probability of a 

 like chemical constitution : but whether these substances are or 

 are not elastic, Black, like Daniel Bernoulli, declined to decide. 

 The demonstration of this fact — that there exists more than one 

 species of elastic fluid permanent at a common temperature 

 and pressure when not acted upon by a condensing attraction 

 — was reserved for Cavendish; being the consequence of that 

 determination of its specific gravity of which you speak so 

 slightingly. — And here again, you see that in your haste you 

 have denied this great philosopher his due. 



And now that we have not only walked together over a part 



pendue, puisque lorsqu'on l'en chasse brusquement en secouant 1'eau mi- 

 nerale, la terre se depose aussi promptement, et qu'au contraire elle ne se 

 depose que tres-lentement lorsque l'eau est bouche et que l'air ne s'eva- 

 pore que lentement ; que ce meme principe contient aussi une portion de 

 la terre ferrugincuse qui exisle dans ces eaux, puisque lorsqu'elles sont de- 

 pouillees de lew air et qu'elles ont forme leur depot, on ne remarque plus 

 aucun indice de matiere ferrugineuse ; qu'on doit encore a ce meme air 

 mele avec la terre et le bitume, et qu'on peut en cet etat regarder, suivant 

 la pensee de Lister, comme une espece d'esprit, la saveur acidule qu'ont 

 ces eaux a leur source et qu'elles perdent avec leur air sur-abondant; enfin 

 que ce meme principe aerien est la cause d'une partie de l'effervescence 

 qui ces eaux font avec tous les acides." — Hist, de l' Academie, 1753, p. 174. 



* Black also ascertained that the peculiar matter of fixed air combines 

 with other bodies in more proportions than onej and Cavendish, subse- 

 quently, that that gas combines in proportions of which one was about 

 double the other, — a fact which proved of great importance to chemical 

 theory. 



f Essays, Phys. and Lit., vol. ii. p. 198, 1765 j Experiments on Magnesia, 

 &c, 1777. 



