138 Mr. D. Forbes' s Researches on the 



The Epsomite presents itself in elongated masses, consisting 

 of an aggregate of crystalline fibres, either colourless or of a 

 white colour ; streak white; hardness 1*75, scratching talc, but not 

 rock-salt, and apparently but little less hard than the last-named 

 substance. Lustre semivitreous to vitreous, occasionally earthy. 

 The specific gravity was taken by weighing the mineral in petro- 

 leum at 60° F. (15°*5 C), and calculated to be 1*636, water 

 being 1*000. 



It was readily soluble in water, leaving only a minute residue 

 of white quartz sand ; and the qualitative examination showed the 

 absence of lime, alumina, and iron, but the presence of sulphuric 

 acid, water, magnesia, and soda. 



The quantitative analysis was conducted as follows. 23*27 

 grains dissolved in water left, upon filtration, a minute insoluble 

 residue of quartz particles weighing 0*08 grain, or equivalent to 

 0*34 per cent. The filtrate was precipitated by a solution of 

 chloride of barium, and afforded a precipitate of sulphate of ba- 

 rytes amounting to 22*26 grains, equivalent to 7*62 grains anhy- 

 drous sulphuric acid, or 32*86 per cent. 



Another portion, 27*35 grains in weight, was dissolved in wafor 

 and precipitated by adding acetate of barytes in slight excess. 

 The precipitate formed was, after standing for some time, removed 

 by filtration, and the clear solution evaporated to dryness in a 

 platinum capsule, and heated to redness in order to convert the 

 acetates into carbonates. The incinerated mass was then ex- 

 tracted with water and evaporated to dryness in a tared platinum 

 crucible with the addition of a few drops of pure sulphuric acid. 

 The sulphate of soda thus obtained weighed 0*21 grain, or equi- 

 valent to 0*09 grain soda, or 0'33 per cent, soda in the mineral. 



In order to determine the amount of water, a third quantity, 

 amounting to 30*06 grains, was heated in a Rammelsberg's air- 

 bath to 300° F. (150° C), when it sustained a loss of 12*37 

 grains; upon heating farther to 600° F. (317° C.) more water 

 was evolved, and this heat was continued until traces of sul- 

 phuric acid fumes commenced to show themselves, when the 

 amount of water driven off was found to be 15*27 grains, or equi- 

 valent to 50*79 per cent. 



From the above results the following percentage composition 

 of the mineral is deduced : — 



Water 50*79 



Sulphuric acid . . 32*86 

 Magnesia .... 15*87 

 Soda ..... 0*33 

 Silica ..... 0*34 

 100*19 



