54* ON THE COMPOSITION OF EMERY. 



iron. Though this procefs was twice repeated with the re* 



maining powder, and in a ftronger heat, a great porportion of 



it remained undifTblved. 



The alkaline folution, after a red calx of iron had fubfided 



from it, was faturated with acid ; and gave a precipitate of a 



white earth, which I found to be almoii purely argillaceous. 



This refult is The refult of thefe experiments, was fo fimilar to thofe of 



fimilar to Klap- ]^j r Klaproth on diamond fpar, as to render it very probable 

 roth's with dia- ' * . .. ,/ . r . _ , , , r ,, 



rnond fpar. tr) at e mery was in reality the lame iubftance, though ulually 



mixed with a larger proportion of iron ; and the fubfequent 



experiments appear to confirm this opinion. 



Emery pulve- ^ n order to obtain a quantity of emery as free from iron as 



rized and cleared I could, I reduced to a coarfe powder, a piece which con- 



pLucf e n s ! tiC flfted of different ftrata * fome of which were of much lj g hter 

 colour than others j and afterwards feparated, by a magnet, 

 the particles which were attracted by it. The part which was 

 j not attracted by the magnet, I obferved to have the ufual de- 



gree of hardnefs (by the fcratches which might be made with 

 it on flint.) I then reduced it to a finer powder, in an agate 

 mortar ,• and, as this was principally done by preflure, and 

 not by grinding, hardly any fenlible addition was made to its 

 weight. In the fame manner, I found that diamond fpar 

 might be powdered to the fame degree of finenefs,. without 

 any material increafe of weight from the mortar. 



*o of the clear - Of the emery powder thus prepared, 20 grains were taken, 



powder fufed anc j heated in the manner before defcribed, with 120 grains 



• of foda, which had been previoufly deprived of carbonic acid, 



and boiled to drynefs in a filver pan. By nearly the fame 



procefs as that ufed by Mr. Klaproth, I obtained about 16,0 



grains of argillaceous earth, ,6 of {iliceous earth, ,8 or ,9 of 



and by the fame iron, and ,6 of a grain remained undilTolved. Thefe numbers, 



procefs as Klap- reduced to parts of a hundred, are therefore, 

 roth's the com- 

 ponent parts Argillaceous earth 80 

 oftmery Silex --- - - 3 



Iron - - - . 4. 



Undiflblved - » 3 



90. 



Mr. 



