MAGNESIUM. 131 



Analytical reactions. 



1. Add to magnesium solution carbonate of potassium or 

 sodium : a white precipitate of magnesium carbonate is pro- 

 duced. 



2. Add to magnesium solution carbonate of ammonium (or 

 hydrate of ammonium) : part of the magnesium will be pre- 

 cipitated as carbonate (or hydrate). These precipitates, how- 

 ever, are soluble in ammonium chloride and many other ammo- 

 nium salts ; if these latter had been added previously to the 

 magnesium solution, ammonium carbonate (or hydrate) 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 crystal- 

 line precipitate of magnesium-ammonium phosphate, MgNH 4 P0 4 , 

 is produced. 



4. Salts of magnesium are white and soluble, except the car- 

 bonate, phosphate, and arseniate ; the oxide and hydrate are 

 also insoluble. 



QUESTIONS. 



211. How is magnesium found in nature? 



212. By what process 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 composition and properties of the officinal 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 could the presence of magnesium be demonstrated in a 

 mixture of magnesium sulphate and sodium sulphate? 



