On phlogiston. 469 



chemifts confider this preparation as a carbonate of iron, 

 1 do not think it is entituled to this appellation, for one 

 ounce of it yields but four ounce meafures of fixed air, 

 whereas the fame quantity of the precipitate from green 

 vitriol by the common pot-afh of the fhops, yields thirty- 

 two ounce meafures, and deferves this character with more 

 propriety. 



A ftrong proof that finery cinder contains oxygen is, 

 that when it is heated in hydrogenous gas, it makes a large 

 quantity of it difappear, and I have lliewn, that when 

 metallic calces are heated in this air, that the difappearance 

 of the inflammable air, is always in ftri£l proportion to 

 the pure air which they contain. 



SECTION IV. 



Of Carbonic Acid or Fixed Air. 



According to the advocates of the antiphlogiftic fyftem, 

 the carbonic acid or fixed air, is a combination of char- 

 coal and oxygen. They are of this opinion for two rea- 

 fons. 



Firft. If charcoal be plunged in a vefTel of oxygen 

 gas, the whole of it will be confumed, and carbonic acid 

 gas will be produced. 



Secondly. It is well known, that all the calces of mer- 

 cury may be reduced without any addition, and will afford 

 oxygenous gas, but if charcoal be mixed with them, the 

 carbonic acid gas will be formed, and the charcoal will be 

 confumed. 



Dr. Prieftley in oppofition to this opinion declares, that 

 large quantities of fixed air have been procured in his ex- 

 periments, where neither charcoal nor any thing containing 

 it was concerned. 



He 



