150 METALS AND THEIE COMBINATIONS. 



22. MAGNESIUM. 

 Mgii = 24.3. 



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 

 01 Strassfurt; as carbonate in th,e ^ineralmaqnefdte . as double car- 

 bonate of magnesium and calcium in the mmeraTHo/omife (magnesian 

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

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



Metallic magnesium may be obtained by the decomposition of 

 magnesium cHprideby sodium : 



MgCl 2 + 2Na = 2NaCl + Mg. 



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

 in moist_air - Jb^LO^dajdoji_Qf_the surface. It decomposes^IroT^water 

 with liberation of hydrogen : 



Mg + 2H 2 O = 2H + Mg(OH) 2 . 



When heated to a red heat it burns with a brilliant bluish-white 

 light forming magnesium oxide. 



Magnesium carbonate, Magnesii carbonas. Approximately : 

 (Mg-CO 3 ) 4 .Mg(OH) 2 .5H 2 O (Magnesia alba, Light magnesia). The 

 normal magnesium carbonate, MgCO 3 , is found in nature, but the 

 official preparation contains carbonate, hydroxide, and water. It is 

 obtained by boiling a solution of magnesium sulphate with solution 



the source of ammonium compounds ? 205. State the composition, mode of 

 preparation, and properties of sal-ammoniac. 206. How is ammonium car- 

 bonate manufactured, and what difference exists between the solid article and 

 its solution? 207. State the composition of ammonium sulphide and of am- 

 monium hydrogen sulphide ; how are they made, and what are they used for ? 

 208. By what process may ammonium sulphate, nitrate, and phosphate be 

 obtained from ammonium hydroxide or ammonium carbonate, and what chemi- 

 cal change takes place? 209. How does heat act upon ammonium compounds? 

 210. Give analytical reactions for ammonium salts. 



