116 SALTS OF MAGNESIA. 



stone containing magnesia cannot be used for some 

 purposes, where the caustic powers thus retained are 

 objectionable (873). 



249. The carbonate of magnesia, like the carbonate 

 of lime, and indeed all other compounds of that acid, 

 is easily decomposed by any more powerful acid (117). 



250. When magnesia or its carbonate is acted on 

 by sulphuric acid, sulphate of magnesia is formed, 

 which is a salt easily dissolved by water, and distin- 

 guished by a peculiar sweet-bitter taste. It is found 

 in many mineral waters, and exists in unusually large 

 quantity in some springs near Epsom, in consequence 

 of which it is commonly called Epsom salts. A solu- 

 tion of sulphate of magnesia is readily decomposed 

 by the alkaline carbonates ; carbonate of potash, 

 soda, or ammonia, throwing down carbonate of mag- 

 nesia. 



251. The compound of muriatic acid and magnesia, 

 or chloride of magnesium, is also frequently found in 

 mineral waters, and exists in some quantity in sea- 

 water ; it is very soluble in water, and therefore, when 

 sea-water is evaporated in order to procure the com- 

 mon salt which it contains, it is never wholly evapo- 

 rated; but when the greater part has been driven off 

 by heat, and a large quantity of common salt is depo- 

 sited, the remaining liquor, commonly called bittern, 

 which contains a little common salt, and nearly all 

 the muriate of magnesia, and other easily soluble 

 salts, is drawn off. 



252. The muriate of magnesia, like the muriate of 



