386 Different Msdes in which [Book V. 



the aerial acid, becaufe it could be obtained only in a 

 pure or uncombined ftate in an aerial form ; and from 

 its exifdng in confiderable quantity in chalk, &c. it 

 \yas denominated by other chemifts the cretaceous or 

 chalky acid. I have preferred the name which has 

 been adopted by the judicious Lavoifier, as more im- 

 mediately expreilive of its characleriftic, and peculiar 

 bafis, which is undoubtedly the matter of coal. 



The proportion of the materials which enter into 

 this kind of air is about eighteen parts of oxygen and 

 feven parts of that matter which the French philofo- 

 phers denominate carbon, or t coal. If, for example, 

 charcoal is burnt in a clofe veflel with oxygen gas, the 

 air which remains after combuftion is carbonic acid 

 gas. By the experiments of Lavoifier and De la Place 

 it appeared, that one ounce of charcoal required for 

 its combultion three ounces and one-third of vital air, 

 and produced three ounces and an half of fixable air. 



There are feveral methods of procuring fixed or 

 ftxable air, or carbonic acid gas firft, by the /ermen- 

 tation of liquors, in which operation its formation is 

 owing to the combination of the carbon of the facharine 

 matter with the o>:yr:n of the water. 



It is evident that a great -quantity of fixed air is pro- 

 duced, when vegetable or animal fubilances (efpecially 

 the former) are in a ilate of vinous fermentation. In 

 breweries there is always a ftratum of fixed air on the 

 furface of the fermenting liquor, reaching as high as 

 the edge of the vats; and it is owing to the produc- 

 tion and ekfticity of fixed air, that fermenting liquors, 

 when put into clofe veffels, often are known to burft 

 them with great violence. 



DF. Prieftley, in order te determine the quantity of 



fixed air contained in feveral fpecies of wine, took a 



glafi phial (fitted with a ground ftopple and tube) ca- 



6 pable 



