CHAPTER XXXVIII 

 MAGNESIUM AND ZINC. IONIC EQUILIBRIA 



WE shall now return to a consideration of the metallic elements. 

 We can most easily remember magnesium and zinc by the facts 

 that they are silver-white metals with a markedly crystalline 

 structure, and that they displace hydrogen from dilute acids. In 

 these respects they resemble aluminium, but the latter is trivalent 

 in all its compounds, while the present two elements are bivalent 

 exclusively (see Periodic System). 



MAGNESIUM Mg 



Occurrence. Magnesium carbonate is found in dolomite^ 

 CaC0 3 ,MgCO s , a common rock, and in small amounts as mag- 

 nesite MgC0 3 . The sulphate and chloride are found at Stassfurt. 

 Several natural silicates of magnesium, such as meerschaum, 

 asbestos, talc or soapstone, and olivine, are familiar minerals. 



Asbestos, a fibrous material, is used in making fireproof cloth 

 and cardboard. Soapstone is made into sinks and table tops for 

 use, for example, in laboratories. 



The Metal Magnesium. The metal is made by electrolyzing 

 a molten mixture of magnesium, potassium, and sodium chlorides. 

 A carbon rod forms the anode, and the iron crucible the cathode, 

 on which the metal collects in globules. The mass, when cold, 

 is broken up and the metal is recast in bars. The metal can be 

 drawn, through a die, into ribbon or wire. 



Magnesium rusts in the air, gradually crumbling to a white 

 powder of a basic magnesium carbonate. It burns in air, with a 

 brilliant white light, producing a mixture of the oxide MgO and 

 nitride Mg 3 N2 (see argon, p. 297). Magnesium filings, mixed 



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