On phlogiston. 4^,^ 



Thirdly. If the procefs of calcination is performed in 

 a variety of gafes, containing fome oxygenous air, the ox- 

 ygen only will be imbibed by the metal, and the others will 

 be left unaltered. 



Fourthly. If any fubftance is added to a metallic oxyd, 

 and the calx is revived, a compound body will be produced, 

 formed of the agent ufed and the oxygen contained in the calx. 



Thus, if the filings of pure bar iron are mixed with red 

 precipitate, and expofed to a red heat, the iron will be 

 converted into a calx and the mercury will be revived. If 

 pure charcoal is mixed with the precipitate, carbonic acid 

 will be produced ; and if the mercurial calx is revived in 

 hydrogenous gas, water will be formed. 



The firft objection of Dr. Prieftley, to this theory of the 

 calcination of metals, is as follows. 



He fays, if turbith mineral is expofed to a red heat, a calx 

 remains which cannot be revived in any degree of heat, 

 without the aid of fome fubftance, fuppofed to contain phlo- 

 gifton. Before we proceed any further in this inveftigati- 

 on, it is abfolutely neceflary to determine the real compofi- 

 tion of turbith mineral. 



According to the French philofophers, this fubftance is 

 a pure oxyd of mercury. 



Fourcroy and Baume declare, that it does not contain 

 one particle of the fulphuric acid. Dr. Prieftley is doubtful 

 whether it is a fait or a calx ; and in the F.dinburgh Difpen- 

 fatory and London Pharmacopoeia Chirurgica, it is called 

 hydrargyrus vitriolatus flavus. 



The following experiments were made, to afcertain the 

 compofition of this fubftance. 



Firft. One ounce of pure turbith mineral was expofed 

 to a red heat, in a long glafs tube, v/hich communicated 

 with an hydropneumatic apparatus, when thirty-thi-ee ounce 

 meafures of oxygenous gas were obtained. Upon break- 

 ing the glafs, a quantity of fluid mercury was found in the 



tube. 



