124 SALTS OF MAGNESIA. 



of the blowpipe, and it will become pale-red, and deepen in 

 color by fusion. 



Specific gravity of the species in this family, below 3. 

 Hardness of some species as high as 7. 



epsom salt. — Sulphate of Magnesia. 



Trimetric. In modified rhombic prisms, (fig. 8, page 26.] 

 M : M =90° 34'. Cleavage perfect parallel with the shorter 

 diagonal. Usually in fibrous crusts, or botryoidal masses, 

 of a white color. Luster vitreous— earthy. Very soluble, 

 and taste bitter and saline. 



Composition : magnesia 16*3, sulphuric acid 32*5, water 

 50*2. Deliquesces before the blowpipe. Does not efTer- 

 vesce with acids. 



Dif. The fine spicula-like crystalline grains of Epsom 

 salt, as it appears in the shops, distinguish it from Glauber 

 salt, which occurs usually in thick crystals. 



Obs. The floors of the limestone caves of the West often 

 contain Epsom salt in minute crystals mingled with the 

 earth. In the Mammoth Cave, Ky.,it adheres to the roof in 

 loose masses like snow-balls. It occurs as an efflorescence 

 on the east face of the Helderberg, 10 miles from Coeymans. 

 The fine efflorescences suggested the old name hair salt. 



At Epsom in .Surrey, England, it occurs dissolved in min- 

 eral springs, and from this place the salt derived the name 

 it bears. It occurs at Sedlitz, Aragon, and other places in 

 Europe ; also in the Cordilleras of Chili ; and in a grotto in 

 Southern Africa, where it forms a layer an inch and a half 

 thick. 



Uses. Its medical uses are well known. It is obtained 

 for the arts from the bittern of sea-salt works, and quite 

 largely from magnesian carbonate of lime, by decomposing 

 it with sulphuric acid. The sulphuric acid takes the lime 

 and magnesia, expelling the carbonic acid ; and the sulphate 

 of magnesia remaining in solution is poured off from the sul- 

 phate of lime, which is insoluble. It is then crystallized by 

 evaporation. 



magnesite.— Carbonate of Magnesia. 



Rhombohedral ; R:R = 107°29. Cleavage rhombohe- 

 dral, perfect. Often in fibrous plates the surface of which 



Of what does Epsom salt consist? Where does it occur'.' Whence 

 the name Epsom 1 



