On phlogiston. 463 



ed in an add, or fome fubftance into which it enters as a 

 conftituent part. But mercury revived from red precipitate 

 by inflammable air, boiled in lulphuric acid gives lulphure- 

 ous gas, and when added to nitric acid, nitrous air, neither 

 of which contain inflammable air. 



It fhould alfo exhibit Ibme properties, when fuhjeiSled 

 to the adion of chemical agents, different from that which 

 is revived from a mercurial calx merely by an increafe of 

 its temperature, which is not the cafe ; and if mercury ab- 

 forbs inflammable air, that which is revived without addi- 

 tion, when heated in inflammable air, fhould abforb fome 

 of it which it will not do. 



It certainly is not probable, that an ounce of mercury 

 containing more than twelve quarts of hydrogenous gas, 

 iliould have the fame external appearance, and exhibit the 

 iame chemical properties, as that which does not contain 

 one particle of this air. 



Dr. Prieftley not only believes, that when red precipitate 

 is heated in hydrogenous gas, the inflammable air enters 

 into the metal, but that, the pure air of the metallic calx is 

 diffufed through the hydrogenous gas which remains be- 

 hind. 



As a proof of this he mentions an explofion, which 

 happened from reviving red precipitate, in inflammable air. 

 I have performed this experiment, with different propor- 

 tions of red precipitate, twenty times, and never met with 

 any accident. 



The inflammable air that Dr. Prieftley ufed, mufl: have 

 been mixed with atmofpheric air, or an explofion would 

 not have happened. That the pure air of the metallic calx 

 is not diffufed throuirh the inflammable air which re- 



o 



mains behind, appears evident from the following circum- 

 ffance. 



If one drachm of red precipitate, is revived in fixteen 

 ounce meafures of hydrogenous gas, twelve ounce mea- 



fures 



