482 Additional Notes. 



The great Importance of this discovery, and the extensive 

 application which has been since made of it, in explaining 

 fluidity^ congelation, evaporation, animal heat, and many- 

 other phenomena, render the period of Its annunciation to the 

 world one of the most Interesting seras in the history of che- 

 mical science. 



Fixed Air, or Carbonic Acid Gas. p. 81. 



The numerous and Important relations of this chemical 

 compound render Its original discovery, and the subsequent 

 additions to our knowledge of it, worthy of particular notice 

 in detailing the progress of the last age in this branch of sci- 

 ence. 



Paracelsus and Van Helmont were acquainted vAxh 

 the fact, that air is extricated from solid bodies during certain 

 processes, and the latter gave to air thus produced the name 

 of gas, by which word he meant to express every thing 

 which Is driven off from bodies in the state of vapour by 

 heat. Boyle called these kinds of air artificial airs, and 

 suspected that they might be different from the air of the at- 

 mosphere. Hales ascertained the quantity of air that could 

 be extricated from a great variety of bodies, and showed that 

 it formed an essential part of their composition. Dr. Black 

 proved that the substances called lime, magnesia, and 

 alkalies, are compounds, consisting of a peculiar species of 

 air, and pure lime, magnesia, and alkali. To this species of 

 air lie gave the name oi fixed air, because It existed in these 

 bodies in a fixed state, though he knew not the materials of 

 which It is composed. This air or gas was afterwards Investi- 

 gated by Dr. Priestley, and a great number of its pro- 

 perties ascertained. From these properties Mr. Keir first 

 concluded that it was an acid; and this opinion was soon con- 

 firmed by the experiments of Bergman, Fontana, and 

 others. Dr. Priestley at first suspected that this acid en- 

 tered as an element into the composition of atmospherical air; 

 and Bergman, adopting the same opinion^ gave it the name 

 of aerial acid. Mr. Bewly called it mephitic acid, because 

 it could not be respired without occasioning death. Mr. Keir 

 called it calcareous acid; and, at last, M. Lavoisier, after 

 discovering that it is formed by the combinaiion oi carbon ?ind 

 oxygen, gave It the name of carbonic acid gas, which It novr 

 generally bears. — Thompson'^^ Chemistry, 



