134 Dr. Thomas Thomson s 



exposed to a heat gradually increased to redness, and kept 

 in that temperature till all the excess of sulphuric acid had 

 been driven off. The white matter in the crucible (chiefly 

 of lime) was now lixiviated with water, till every thing 

 soluble was taken up. The water thus employed, was mixed 

 with some carbonate of ammonia, and filtered to separate 

 the lime which it had dissolved in the state of sulphate. 

 The water, thus nearly freed from lime, was reduced to a 

 small quantity, by evaporation, and, while still hot, was 

 mixed with a few drops of solution of oxalate of ammonia, 

 to throw down a little lime which had either escaped the 

 action of the carbonate of ammonia, or had been afterwards 

 supplied by the filter. The mixture was allowed to stand 

 till it became clear, the liquid was then drawn off with a 

 sucker, evaporated to dryness, and the saline residue ex- 

 posed to a red heat. A salt remained, which weighed 0*2 

 grains, and which proved, on examination, to be sulphate 

 of potash, equivalent to 0*11 grain potash. 



5. Ten grains of tabasheer in the state of a fine powder 

 were intimately mixed with 20 grains of anhydrous car- 

 bonate of soda, and the mixture exposed in a platinum 

 crucible to a red heat, raised at last sufficiently high to bring 

 the whole into a state fusion. The colour of the fused mass 

 was yellowish brown. It was dissolved in muriatic acid 

 the solution evaporated to dryness, and the residue, after 

 being digested a sufficient time in muriatic acid, was thrown 

 on the filter. The silica edulcorated, dried and ignited 

 weighed 9 grains. 



6. The muriatic acid, in which the silica had been digested 

 being concentrated, was mixed with caustic ammonia. Yel- 

 low flocks fell, which were separated by decantation : these 

 flocks, when ignited, became dark brown, and weighed Ol 

 grain ; they dissolved readily in muriatic acid. The solu- 

 tion was super-saturated with caustic potash, and digested 

 on the sand bath for 24 hours. By this means 0*01 grain 

 of alumina was dissolved. The rest consisted of peroxide 

 of iron. Thus, the yellow flocks thrown down by caustic 

 ammonia consisted of Peroxide of iron, . 0*09 



Alumina, .... 0*01 



0-1 

 The liquid from which this precipitate had fallen was not 



