212 MAGNESIUM CARBONATES 



MAGNESIUM AND ITS MEDICINAL SALTS 



Magnesium salts are obtained from dolomite or magnesian 

 limestone ; magnesite, a native carbonate ; talc, meerschaum 

 and other silicates, and from sea-water. 



Magnesium salts when swallowed are not rapidly absorbed, 

 and do not cause any toxic effects. The oxides and carbon- 

 ates are antacid and laxative ; the sulphate is purgative and 

 febrifuge. 



MAGNESIUM OXIDES. Magnesia. Calcined Magnesia. MgO. 



LIGHT CALCINED MAGNESIA. Magnesia levis. 



HEAVY CALCINED MAGNESIA. Magnesia ponderosa. (B.P.) 



Light Magnesium Oxide, MgO, is prepared by exposing 

 light magnesium carbonate to a dull-red heat. Heavy 

 magnesium oxide, MgO, is prepared by exposing heavy 

 magnesium carbonate to a dull-red heat. Magnesium oxide 

 is a bulky white powder differing from heavy magnesia only 

 in its greater lightness, the volumes corresponding to the 

 same weight being to each other in the ratio of three and a 

 half to one (B.P.). Magnesia is odourless, with a slightly 

 earthy taste ; insoluble in water, but readily dissolved by 

 acids. 



MAGNESIUM CARBONATES. 3(MgC0 3 ), Mg(HO) 2 , 4H 2 0. 

 LIGHT MAGNESIUM CARBONATE. Magnesii Carbonas levis. 

 HEAVY MAGNESIUM CARBONATE. Magnesii Carbonas pon- 

 derosus. 



When sodium carbonate is mixed with- a solution of mag- 

 nesium sulphate, magnesium carbonate and magnesium 

 hydrate are precipitated. The manner of preparation affects 

 the weight, but not the other properties. Diluted solutions, 

 boiled, yield the light carbonate. Tolerably concentrated 

 solutions, mixed without heat, yield the heavy carbonate, 

 which is three and a half times heavier than the other, more 

 dense, loose, and granular ; and, under the microscope, is 

 found to be partly amorphous, with intermixture of numer- 

 ous slender prisms. Both varieties are white, odourless, and 

 tasteless, sparingly soluble in water, but readily dissolve in 



