DR T. THOMSON'S Analysis of some Minerals. 449 



When exposed to a red heat, it gives out water, and nothing 

 else, and loses 29.866 per cent, of its weight. 



I subjected it to analysis ; but, as the quantity of it in my 

 possession only amounted to 5.3 grains after ignition, it will be 

 necessary to state the steps of the analysis, to enable the reader 

 to judge of the degree of confidence to which my experiments 

 are entitled. 



The 5.3 grains of the ignited mineral, after having been re- 

 duced to a fine powder, were intimately mixed with 30 grains 

 of carbonate of barytes, in a platinum crucible, and the mixture 

 was exposed to a strong red heat, and kept at that temperature 

 for an hour. The whole was then dissolved in dilute muriatic 

 acid. The undissolved portion having the appearance of hydro- 

 lite undecomposed, was mixed with 30 grains of carbonate of ba- 

 rytes, and kept in a strong heat for two hours. It was then 

 dissolved in dilute muriatic acid. A few flocks remained undis- 

 solved ; but they were light and loose, indicating that they had 

 been acted upon by the barytes. The two solutions were mixed 

 together, and evaporated to dry ness in a porcelain basin. The 

 dry mass was digested for some time in water acidulated with 

 muriatic acid. The whole was then thrown on the filter, to se- 

 parate the undissolved silica from the solution. The silica on 

 the filter being washed, dried, and ignited, weighed 4 grains. 

 It was laid aside for examination. 



The muriatic acid solution was neutralized by caustic am- 

 monia added slightly in excess. A brown precipitate fell, weigh- 

 ing, after ignition, 1.08 grains. Being digested in muriatic acid, 

 it left undissolved 0.055 grains of a grey matter, which, tested 

 by the blowpipe, proved to be silica very slightly tinged with 

 iron. 



The muriatic solution thus freed from silica was mixed with 

 potash-ley in considerable excess, and heated in a flask. There 

 was precipitated a quantity of peroxide of iron, weighing, af- 



