On phlogiston. 455 



quits one part of it and joins to another, which fuhlimcs in 

 the form of a Avhite fait. That part which the fulphuric 

 acid leaves, is converted into a calx, is revived vrithout ad- 

 dition, and yields oxygenous gas. 



This fulphate of mercury is the fuppofed calx, to which 

 Dr. Prieftley refers. It is fometimes obtained of a red co- 

 lour, owing to fome impure matter contained in the turbith 

 mineral, which by depriving a part of the fulphuric acid of 

 its pure air, converts it into fulphur, which uniting with 

 part of the revived mercury, forms cinnabar, which gives 

 the whole of the fublimed fait a red colour. 



That it is a fulphate of mercury, we have an additional 

 proof, from an experiment of Dr. Prieftley, for he pro- 

 cured ethiops mineral, by heating this fuppofed calx in 

 inflammable air, by means of a burning lens, which he 

 could not have obtained from a pure calx of mercury, treat- 

 ed in the fame manner. 



The fize of the veifel in which turbith mineral is heated, 

 will vary the refult of the experiment. No refiduum can 

 be obtained, by expofmg it in a crucible to a red heat, for 

 the whole of it flies away, and leaves only a mark on the 

 bottom of the veffel. The fame circumftance will take 

 place, if a fliort glafs tube is ufed. 



Having thus determined, that the fubftance which re- 

 mains after expofmg turbith mineral to a red heat, is a 

 neutral fait coloured red by cinnabar, and not a metallic 

 calx, we fee that the firft obje£tion of Dr. Prieftley, to the 

 theory of the calcination of metals, adopted by the anti- 

 phlogiftic chemills, lofes all its force, for certainly it does 

 not follow, that becaufe the fulphate of mercury requires to 

 be deprived of its fulphuric acid, before running mercury 

 can be procured from it, that therefore all mercurial calces 

 require the addition of phlogifton, to be converted into 

 mercury. 



The 



