508 NOTES. 



propositions, " presqu'inouies jusque la; 1'eau n'est pas un 

 element; il existe plusieurs sortes d'airs, essentiellement 

 diflerentes." He then mentions Von Helmont inaccurately, 

 as having ascertained that there were " permanently elastic 

 vapours other than atmospheric air;" and Hales, still more 

 inaccurately, as having measured these permanently elastic 

 fluids : whereas Hales considered them all as common air, 

 combined with impure exhalations, an opinion which pre- 

 vailed a century and a half after Von Helmont, and was 

 adopted by D'Alembert in his article "Air" in the Ency- 

 clopaedia, 1751. Black's discovery of fixed air, he con- 

 fines solely to its explaining the causticity of the alkalis 

 and earths. No one, he says, before Cavendish had dis- 

 tinguished it as a separate aeriform substance ; and though 

 emanations were said to proceed from bodies, no one knew in 

 what they consisted. Cavendish, he says, in 1766 first settled 

 all these questions, and showed that this air, whether from 

 chalk or fermentation, or mines, was one and the same fluid, 

 " auquel on a depuis reserve le nom d'air fixe." Finally he 

 (Cavendish) discovered that it was the air evolved from burn- 

 ing charcoal (p. cxxx). He then ascribes the application of 

 inflammable air to raising balloons in the air to M. Charles's 

 application of Mr. Cavendish's experiments on the specific 

 gravity of that gas. 



This is really somewhat astounding. That a person of 

 M. Cuvier's eminent attainments, filling the high office of 

 Secretaire Perpetuel, and charged with the delicate and 

 important duty of recording the history of science yearly, 

 should not have deemed it worth his while to read either the 

 celebrated experiments on Magnesia Alba and Quicklime 

 published in 1755, or the Lectures published in 1803, before 

 assuming to write the history of chemical discovery, is wholly 

 beyond belief. Had he read the former work, he would have 

 found that Dr. Black gave to the air which he had discovered 

 the name of fixed air; and that he did so, not because it was 

 the same with, or any modification of, atmospheric air, but 

 simply because air was a known term in common use to 

 represent a permanently elastic fluid, and because this kind 

 of air was found fixed in combination with bodies. Had he 



