102 Chemical Philosophy. [Cuap. II. 



view of the progress made in chemical science at 

 this eventful period. 



Not long after Dr. Black had published his doc- 

 trine of Latent Heat, his discovery of Carbonic 

 Acid gave additional lustre to his character, and 

 formed a new sera in the history of chemistry. 



Paracelsus and Van Helmont were acquainted 

 with 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 oft 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 atmosphere. Hales ascertained the 

 quantity of air that could be extricated from a 

 gi'cat variety of bodies, and showed that it formed 

 an essential part of their composition. Dr. Black 

 proved that the substances called //w^, magnesia, 

 and alkalies, are compounds, consisting of a pecu- 

 liar species of air, and pure lime, magnesia, and 

 alkali. To this species of air he gave the name of 

 fixed air, because it existed in these bodies in a 

 fixed state, though he knew not the materials of 

 which it is composed. The air or gas was after- 

 wards investigated by Dr. Priestley, and a great 

 number of its properties ascertained. From these 

 properties Mr. Keir first concluded that it was 

 acid; and tliis opinion was soon confirmed by the 

 experiments of Bergman, Fontana, and others. 

 Dr. Priestley at first suspected that this acid en- 

 tered as an ckment into the composition of atmo- 

 spherical air ; and Bergman, adopting the same 



