94 



ESSAY V. 



last calcination and solution, as much selenite as after the 

 first. It therefore seems as if it was entirely changeable 

 into calcareous earth, if the same operation was long enough 

 continued. Mr. Westfeld found it easy to fix his opinion 

 about the constituent parts of manganese ; but how near he 

 advanced to the truth, those may determine who shall make 

 experiments in the method just described. How this change 

 of manganese into calcareous earth is produced, I dare 

 not undertake to explain, having been, notwithstanding all 

 possible trouble, never able to unite phlogiston with calcareous 

 earth. I shall add but one observation, really remarkable 

 in itself, and very well adapted to be inserted here. Having 

 once abstracted muriatic acid from minium, I found that the 

 acid had not only the smell of aqua regia, but that it also 

 was capable of dissolving gold. If finely pounded minium 

 be dissolved in pure nitrous acid, diluted with a triple 

 quantity of water, a black powder remains, which is not 

 soluble without the addition of a little sugar, upon which a 

 clear solution is immediately obtained. If this black powder 

 be digested with diluted vitriolic acid, no change happens ; 

 but on adding some sugar the powder grows white, and 

 contributes to produce vitriol of lead. If muriatic acid be 

 poured upon the black powder, an effervescence arises in a 

 warm place, and the acid grows yellowish ; the colour 

 afterwards disappears, and a strong smell of aqua regia 

 rises ; but the black powder grows white, and is changed 

 into muriatic lead (plumbum corneum). If the black powder 

 be distilled by itself in a glass retort, it grows yellow again, 

 but not till it comes near the degree of heat at which it 

 melts. This yellow powder shows in every respect the same 

 properties as common yellow calx of lead, is entirely soluble 

 in nitrous acid, and, on being mixed with muriatic acid, 

 yields no further smell of aqua regia; a proof of the 



