288 Dr. Thomas Thomson [April 



solved in muriatic acid. This solution was mixed with a 

 great excess of caustic potash, and boiled for two hours in 

 a porcelain vessel ; the whole was then passed through a 

 filter. The liquid which passed through was colourless ; 

 the matter remaining on the filter was dark red. 



6. The potash solution which thus passed through the 

 filter, together with the washings of the filter, was evaporated 

 to dryness in rather a strong heat, and the dry residue being 

 mixed with water, was digested (in the cold) in muriatic 

 acid. A white powder remained undissolved, which, being 

 separated and ignited, weighed 13*04 grains. It possessed 

 the following characters : 



(1.) When heated before the blow-pipe with nitrate of 

 cobalt, it assumed a beautiful blue colour. 



(2.) It dissolved by heat in sulphuric acid, and the solu- 

 tion being mixed with a solution of sulphate of ammonia, 

 yielded crystals of alum. The powder then was alumina. 



7. The muriatic acid solution being supersaturated with 

 carbonate of ammonia, a white precipitate fell, which being 

 separated and ignited, possessed the characters of alumina, 

 and weighed 17*45 grains. 



Thus, the whole alumina extracted from the mineral was 

 30.49 grains. 



8. The dark red precipitate which was collected on the 

 filter (in paragraph 5) being dried and ignited, weighed 

 50*53 grains. 



9. It was digested in muriatic acid. The whole dissolved 

 except a white powder weighing 0*996 grains. It was silica 

 slightly impregnated with iron. 



10. The muriatic acid solution was mixed with carbonate 

 of ammonia till it was rendered as neutral as possible ; in- 

 deed a few flocks had precipitated. It was then heated in 

 a flask. Carbonic acid gas escaped in abundance, and the 

 whole peroxide of iron was precipitated. The whole was 

 thrown on a filter, the oxide of iron was collected on the 

 filter and washed ; the colourless solution which passed 

 through being mixed with carbonate of ammonia, a white 

 precipitate fell, which became brown by strong ignition, 

 and possessed the character of oxide of manganese. It was 

 equivalent to 7*76 grains of protoxide of manganese. 



11. The peroxide of iron remaining on the filter being 

 dried and ignited, weighed 41*774 grains. 



