BLACK. 331 



the other end in a vessel filled with lime-water. 

 The air that was driven through the liquid again pre- 

 cipitated the lime in the form of chalk. Finally, he 

 ascertained by breathing through a syphon filled with 

 lime-water, and finding the lime again precipitated, that 

 animals, by breathing, evolve air of this description. 



The great step was now made, therefore, that the 

 air of the atmosphere is not the only permanently 

 elastic body, but that others exist, having perfectly 

 different qualities from the atmospheric air, and capa- 

 ble of losing their elasticity by entering into chemi- 

 cal union with solid or with liquid substances, from 

 which being afterwards separated, they regain the 

 elastic or aeriform state. He gave to this body the 

 name of fixed air, to denote only that it was found 

 fixed in bodies, as well as elastic and separate. He 

 used the term " air" only to denote its mechanical re- 

 semblance to the atmospheric air, and not at all to 

 imply that it was of the same nature. No one ever 

 could confound the two substances together ; and ac- 

 cordingly M. Morveau, in explaining some years after- 

 wards the reluctance of chemists to adopt the new 

 theory of causticity, gives as their excuse, that although 

 this doctrine " admirably tallies with all the pheno- 

 mena, yet it ascribes to fixed air properties which 

 really make it a new body or existence" ("forment 

 reellement un nouvel elre").* 



In order to estimate the importance of this dis- 

 covery, and at the same time to show how entirely it 



* Supplement to the * Encyclopedic,' vol. ii. p. 274, published 

 in 1777. 



