Hi ESSAYS AND OBSERVATIONS 



ounce and a half of fait of tartar with three 

 ounces of black-lead, a fubftance of any the 

 moft unchangeable by chemical operations. 

 This mixture I expofed, for feveral hours, 

 in a covered crucible, to a fire fomewhat 

 ftronger than what is neceffary to keep fait of 

 tartar in fufion. When allowed to cool, I 

 found it ftill in the form of a loofe powder ; 

 and taking out one half, I diluted it with wa- 

 ter, and by filtration obtained a ley, which, 

 when poured into a folution of white marble 

 in aqudfortiSy precipitated the marble under 

 the form of a weak quick-lime : for the tur- 

 bid mixture gave a green colour to the juice 

 of violets, and threw up a cruft like that of 

 lime-water ; and the precipitated powder coU 

 leded and mixed with fait ammoniac imme-r 

 diately yielded the fcent of the volatile alkali. 

 Lest it (hould here be fufped:ed, that the 

 alkaline qualities of this mixture, and of the 

 precipitated marble, wero not owing to a lime 

 into which the marble was converted, but to 

 the alkali itfelf which was added, it is pror 

 per to obferve, that I mixed fo fmall a propor- 

 tion of the ley with the folufion of marble as 

 made me fure, from certain experiments, that 

 the whole of the alkali was fpent in perform- 

 ing 



