140 Dr Turner's Analysis of a Mica from Corntoall. 



of ammonia, proved to be sulphate of lime. The pure alka- 

 line sulphates, when again fused, amounted to 4.8 grains, 

 which dissolved completely in water. Muriate of platinum 

 was then added, and the solution evaporated to dryness, to se- 

 parate the muriate of platinum and potash as perfectly as 

 possible. The dry mass was digested in a little cold water, 

 and the soluble portion examined for lithia. After separating 

 the excess of platinum, I found that the residual salt was com- 

 posed almost entirely of potash, which had passed over with 

 the washings, and that the quantity of lithia was too small to 

 be appreciated correctly. I have, in consequence, been unable 

 to ascertain its presence with absolute certainty, though the 

 following circumstance renders its existence highly probable. 

 The supposed sulphate of Lithia was decomposed by acetate 

 of lead, the excess of lead removed by sulphuretted hydrogen, 

 and the filtered solution brought to dryness. The acetate 

 thus obtained was decomposed on platinum foil, and an alka- 

 line carbonate procured, which, though potash could still be 

 detected in it, was far more fusible than the carbonates either 

 of soda or potash, and discoloured the sm-face of the metal. 



To determine fluoric acid and the other constituents of the 

 mica, 28.11 grains were ignited with four times their weight of 

 sub-carbonate of soda, and the method recommended by Ber- 

 zelius in his analysis of the topaz was adopted. The alkaline 

 solution, when neutralized by muriatic acid, gave a white pre- 

 cipitate with muriate of lime, which yielded 2.73 grains of dry 

 fluate of lime, corresponding to 0.76 grains, or 2.706 percent, 

 of fluoric acid. That it was fluate of lime, was proved by its 

 corroding glass when the acid was set free by concentrated 

 sulphuric acid. 



The matter which was not soluble in water, together with a 

 small quantity of silica separated from the alkaline solution, 

 dissolved completely in dilute muriatic acid. The solution 

 was evaporated to dryness, and after due digestion in diluted 

 acid, the silica was collected, ignited, and weighed. It yielded 

 36.54 per cent, of pure silica. 



The peroxide of iron and alumina were precipitated in the 

 cold bv sub-carbonate of soda, and were separated from one 



4 







