COMPOUNDS OP MAGNESIUM. 205 



Chlormagnesite. A magnesium chloride from Vesuvius. 

 Carnallite. A hydrous magnesium-potassium chloride. 

 Tachydrite. A hydrous magnesium-calcium chloride. 



Epsomite. — Epsom Salt. Magnesium Sulphate. 



Trimetric. I/\ 7=90° 34'. Cleavage perfect parallel with 

 the shorter diagonal. Usually in fibrous crusts, or botry- 

 oidal masses, of a white color. Lustre vitreous to earthy. 

 Very soluble, and taste bitter and saline. 



Composition. Mg 0< S + 7aq = Sulphur trioxide 32*5, mag- 

 nesia 16*3, water 51*2 = 100. Liquefies in its water of crys- 

 tallization when heated. Gives much water which has an 

 acid reaction, in the closed glass tube. B.B. on charcoal 

 fuses, but finally gives an infusible mass that turns pink 

 when moistened with cobalt nitrate and ignited. 



Diff. 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 snowballs. It occurs as an efflores- 

 cence in the galleries of mines and elsewhere. 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. 



Its medical uses are well known. It is obtained for the 

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

 from magnesian calcium carbonate, by decomposing it with 

 sulphuric acid. The sulphuric acid takes the lime and 

 magnesia, expelling the carbonic acid ; and the sulphate of 

 magnesium remaining in solution is poured off from the cal- 

 cium sulphate, which is insoluble. It is then crystallized by 

 evaporation. 



Polyhalite. A brick-red saline mineral, with a weak hitter taste, 

 occurring in masses which have a somewhat fibrous appearance. A 

 hydrous calcium- magnesium sulphate. 



Kieserite. A hydrous magnesium sulphate ; from Stassfurt. 



Picromeride. A hydrous potassium - magnesium sulphate ; from 

 Stassfurt. 



