‘COMPOUNDS OF MAGNESIUM. 205 
Chlormagnesite. A magnesium chloride from Vesuvius. 
Carnallite. Ahydrous magnesium-potassium chloride. 
Tachydiitc. A hydrous magnesium-calcium chloride. 

Epsomite. Epsom Salt. Magnesium Sulphate. 
Trimetric. JA J=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 O,8+ 7aq=Sulphur trioxide 382°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 bitter taste, 
occurring in masses which have a somewhat fibrous appearance. A 
hydrous calcium. magnesium sulphate. 
Kescrite. A hydrous magnesium sulphate ; from Stassfurit. 
Picromeride. A hydrous potassium-magnesium sulphate; from 
Stassfurt. . 
