272 



METALS 'AND THEIR COMBINATIONS. 



solution (see Index), which causes a reddish-brown precipitate or 

 coloration. (See under Water Analysis, end of chapter 38.) 



Summary of analytical characters of the alkali-metals. 



24. MAGNESIUM. 

 Mg 11 = 24.18. 



General remarks. Magnesium occupies a position intermediate 

 between the alkali metals and the alkaline earths. To some extent 

 it resembles also the heavy metal zinc, with which it has in common 

 the volatility of the chloride, the solubility of the sulphate, and the 

 isomorphism of several of its compounds with the analogously con- 

 stituted compounds of zinc. 



Occurrence in nature. Magnesium is widely diffused in nature, 

 and several of its compounds are found in large quantities. It occurs 

 as chloride and sulphate in many spring waters and in the salt-mines 

 at Stassfurt; as carbonate in the mineral magnesite; as double car- 

 bonate of magnesium and calcium in the mineral dolomite (magnesian 

 limestone), which forms entire mountains ; as silicate of magnesium 

 in the minerals serpentine, meerschaum, tale, asbestos, soapstone, etc. 



Metallic magnesium may be obtained by the decomposition of 

 magnesium chloride by sodium ; but is now made in large quantities 

 by electrolysis of the molten double chloride of magnesium and 

 potassium, MgCl 2 .KCl. The furnace used for the operation is shown 

 in Fig. 31, page 80. 



Magnesium is an almost silver-white metal, losing its lustre rap- 

 idly in moist air by oxidation of the surface. It decomposes hot 



