of Mineral Substances. 267 



saturated by nitric acid, and filtered. Lime-water, added to the 

 filtered liquor, gave a precipitate having the characters of fluate 

 of lime. 



D. 

 100 parts of levigated topaz were fused in a platinum cru- 

 cible, with 400 parts of nitrate of baryta ; the fused mass was 

 powdered, diffused through water, and mixed with excess of 

 sulphuric acid ; the precipitate being separated, excess of am- 

 monia was added, and the liquor was filtered off and evapo- 

 rated to dryness ; the dry salt was wholly dissipated by heat, 

 and gave no traces of a fixed alcali. 



E. 



a. 200 grains of topaz were bruised in a steel-mortar, and 

 afierwards triturated as fine as possible in one of agate. The 

 powder had sustained an increase of 4 grains. It was mixed 

 in a silver crucible with 3 ounces of ley, (composed of equal 

 parts of pure potassa and water,) evaporated to dryness, and 

 ignited for an hour. The grey mass was then softened with 

 water, and digested in muriatic acid, which entirely dissolved 

 it, forming a clear yellow liquor. This was evaporated to dry- 

 ness, water was poured upon it, and the insoluble siliceous 

 residue thus obtained being completely washed, dried, and 

 ignited, weighed 74 grains ; deducting 4 grains derived from 

 the mortar, the quantity of Si7<ca in 100 of the topaz is thus 

 found to amount to 35 grains. 



b. The muriatic solution, heated to its boiling point, was 

 saturated by carbonate of potassa ; the edulcorated precipitate 

 weighed 218 grains. 



c. 109 grains of this precipitate were re-dissolved in muria- 

 tic acid, and the solution tested by oxalate of potassa, which 

 occasioned no change. It was then precipitated by caustic 

 potassa, which being added in excess re-dissolved the whole of 

 the precipitate by the aid of heat, with the exception of a scarcely 

 perceptible portion of oxide of iron. The alcaline liquor, super- 



T 2 



