152 METALS AND THEIR COMBINATIONS. 



Kieserite, MgSo 4 .H 2 O, and by decomposition of the native carbonate 

 by sulphuric acid : 



MgCO 3 + H 2 SO 4 = MgSO 4 + CO 2 + H 2 O. 



It forms colorless crystals, which have a cooling, saline, and bitter 

 taste, a neutral reaction, and are easily soluble in water. 



Analytical reactions. 



(Magnesium sulphate, MgSO 4 , may be used.) 



1. Add to a magnesium solution potassium or sodium carbonate 

 and heat : a white precipitate of basic magnesium carbonate, 4MgCO 3 . 

 Mg(OH) 2 , is produced. 



2. Add to a magnesium solution ammonium carbonate (or ammo- 

 nium hydroxide) : part of the magnesium will be precipitated as 

 carbonate (or hydroxide). These precipitates, however, are soluble 

 in ammonium chloride and many other ammonium salts: if these 

 latter had been added previously to the magnesium solution, ammo- 

 nium carbonate (or hydroxide) would cause no precipitation. (The 

 dissolving action of the ammonium chloride is due to the tendency 

 of magnesium to form double salts with ammonium salts.) 



3. To solution of magnesium add a solution containing sodium 

 phosphate, ammonium chloride, and ammonia: a white crystalline 

 precipitate of magnesium ammonium phosphate, MgNH 4 PO 4 , is pro- 

 duced, which is somewhat soluble in water, but almost insoluble in 

 water containing some ammonia. 



4. Salts of magnesium are w r hite and soluble, except the carbonate, 

 phosphate, and arsenate; the oxide and hydroxide also are insoluble; 

 the latter is precipitated "by sodium or potassium hydroxide. 



'23. CALCIUM. 

 Caii = 40 (39.91). 



General remarks regarding- the metals of the alkaline earths. 

 The three metals, calcium, barium, and strontium, form the second 



QUESTIONS. 211. How is magnesium found in nature ? 212. By what pro- 

 cess is metallic magnesium obtained? 213. Give the physical and chemical 

 properties of magnesium. 214. State two methods by which magnesium oxide 

 can be obtained. 215. What is calcined magnesia? 216. State the composi- 

 tion and properties of the official magnesium carbonate, and how it is made. 

 217. What is Epsom salt, and how is it obtained ? 218. Which compounds of 

 magnesium are insoluble? 219.' Give tests for magnesium compounds. 220. 

 How can the presence of magnesium be demonstrated in a mixture of mag- 

 nesium sulphate and sodium sulphate ? 



