124 METALS AND THEIR COMBINATIONS. 



by the action of sulphuric acid, which removes two-thirds of 

 the calcium, forming calcium sulphate, while acid phosphate of 

 calcium is formed and remains in solution : 



Ca 3 2PO 4 + 2H 2 S0 4 = 2CaSO 4 + CaH 4 2PO 4 . 



The solution is filtered and sodium carbonate added, when 

 cabium phosphate is precipitated, phosphate of sodium, carbon 

 dioxide, and water being formed : 



CaH 4 2PO 4 + Na 2 C0 3 = CaHPO 4 + H 2 O -f CO 2 + Na 2 HPO 4 . 



The filtered and evaporated solution yields crystals of phos- 

 phate of sodium, which have a slightly alkaline reaction. 



Sodium nitrate, Sodii nitras, NaN0 3 = 85 (Nitrate of sodium, 

 Chili saltpetre, Cubic nitre}. Found in nature, and is purified by 

 crystallization. 



Other sodium salts which are officinal are the sodium bisul- 

 phite, NaHS0 3 ; borate (borax), ]S"a 2 B 4 O 7 .10H 2 ; bromide, NaBr; 

 iodide, Nal; chlorate, NaC10 3 . The three latter salts may be 

 obtained by processes analogous to those given for the corre- 

 sponding potassium compounds. 



Tests for sodium. 



1. As all the salts of sodium are soluble in water, we cannot 

 precipitate this metal in the form of a compound by any of 

 the common reagents. (Potassium antimoniate precipitates 

 neutral solution of sodium salts, but this test is not reliable.) . 



2. The chief reaction for sodium is the flame-test, compounds 

 of sodium imparting to a colorless flame an intensely yellow 

 color. (The spectroscope shows a characteristic yellow line.) 



3. Sodium compounds are white and not volatile at or below 

 a red heat. 



Lithium, Li = 8. Found in nature in combination with silicic 

 acid in a few rare minerals or as chloride in some spring waters. 

 Of inorganic salts, the bromide and carbonate of lithium are 

 officinal. The hydrate, carbonate, and phosphate of lithium 

 are much less soluble than the corresponding compounds of 

 potassium and sodium. Lithium compounds color the flame 

 beautifully crimson or carmine-red. 



