Mr Magnus's Analysis of Picrosmine. Ill 



and acetate of baryta added, so long as any precipitate appear- 

 ed. The sulphate of baryta was separated, and the remain- 

 ing acetate of magnesia, along with the superabundant acetate 

 of baryta, evaporated to dryness and ignited. The acetates 

 having thus been transformed into carbonates, those of soda or 

 potash should have been contained in the water with which 

 they were digested ; but this, having been again evaporated, 

 did leave only a slight residue, which proved likewise to be 

 magnesia, since it was soluble in muriatic acid, from which it 

 was precipitated by ammonia. The mineral, therefore, does 

 not contain either soda or potash. 



The quantity of silica was ascertained by the usual process. 

 A quantity of 0.982 gr. of the mineral, carefully prepared by 

 grinding and washing, and mixed with three or four times its 

 weight of carbonate of soda, was melted in a platina crucible, 

 the mass dissolved in water, and muriatic acid added, as long 

 as there yet appeared any effervescence. The fluid was eva- 

 porated, the residue well dried, and then redissolved in water, 

 with a few drops of muriatic acid. The silica obtained weigh- 

 ed 0.539 gr., which corresponds to 54.886 per cent, of the 

 mineral. The remaining liquid gave, with pure ammonia, a 

 precipitate, which after ignition, weighed 0.047 or 4.786 per 

 cent. Not a trace of lime could be detected by oxalate of am- 

 monia. The quantity of water I ascertained, by exposing the 

 mineral, in the state of powder, to the strongest heat that can 

 be produced by means of the spirit-lamp, with double air cur- 

 rent. Two experiments gave the following results : — 



0.740 gr. lost 0.0575 gr. equal to 7.76 per cent. 

 0.453 gr. lost 0.031 gr. equal to 6-843 per cent. 



the average of which, 7.301, gives pretty nearly the contents 

 of volatile ingredients. They consist chiefly of water, with a 

 slight alkaline action on litmus paper, owing probably to an 

 inconsiderable portion of ammonia produced by the decompo- 

 sition of that substance, which gives the black colour to the 

 mineral when heated ; a phenomenon which has been very 

 generally observed in minerals containing magnesia. I pos- 

 sessed too small a quantity of the mineral to collect the water 



