181-187] TESTS FOR THE METALS 59 



This precipitate is slightly soluble in water, but less so in 

 alcohol. If the precipitate is not formed on boiling, it will 

 come down on cooling and adding excess of alcohol. 



181. Flame Coloration (26).— If a clean piece of 

 platinum wire is dipped into the liquid, and then held in 

 the Bunsen flame, a bright reddish-yellow colour will appear. 



MAGNESIUM (Mg). — Use magnesium sulphate 

 (MgS0 4 .7H 2 0) solution. 



182. Sodium Phosphate (Na 2 HP0 4 ) added after 

 ammonium chloride (NH 4 C1) and ammonium hydrate 

 (NH 4 OH) gives a white crystalline precipitate of magnesium- 

 ammonium phosphate (MgNH 4 P0 4 .6H 2 0), soluble in acids. 



183. Potassium Hydrate (KHO) gives a white pre- 

 cipitate of magnesium hydrate, Mg(OH) 2 , soluble in acids. 



184. Ammonium Hydrate (NH 4 OH) gives the 

 same precipitate as potassium hydrate ; but if ammonium 

 chloride (NH 4 C1) be added previously, this precipitate will 

 not form. 



185. Ammonium Carbonate (NH 4 ) 2 C0 3 gives a 

 white precipitate of basic magnesium carbonate in strong 

 solutions. Ammonium chloride (NH 4 C1) prevents the for- 

 mation of this precipitate. 



SODIUM (Na). — Use sodium chloride (NaCl) solution. 



186. Flame Coloration (26). — Intense yellow. This 

 colour is almost invisible when viewed through the indigo 

 prism or a thick piece of cobalt-blue glass. 



187. Solid sodium chloride heated in an ignition-tube 

 generally decrepitates and flies out of the tube ; but if it is 

 perfectly dry it will fuse, giving off no fumes. 



