132 AGRICULTURAL CHEMISTRY 



When heated with calcium carbonate, sodium sulfid forms 

 sodium carbonate and calcium sulfid, the latter product 

 being insoluble in water while sodium carbonate is solu- 

 ble in water, and hence is readily separated by filtration. 

 The process of manufacture usually consists in mixing 

 coal and calcium carbonate with sodium sulfate, the prod- 

 uct being known as crude soda which is refined and from 

 which calcined and crystallized soda are obtained. 



In the Solvay process, (NH 4 ) 2 CO 3 is employed, which 

 forms, with sodium chlorid, HNaCO 3 which when heated 

 yields Na 2 CO 3 , CO 2 and H 2 O. 



163. Sodium Hydroxid. This base is prepared in the 

 same way as KOH ; Na 2 CO 3 being used in place of 

 K 2 CO 3 . NaOH is extensively used in the manufacture 

 of soaps. 



164. Sodium Phosphates. Sodium forms three phos- 

 phates : primary sodium phosphate, secondary sodium 

 phosphate, NaHPO 4 , and tertiary or normal sodium phos- 

 phate, Na 3 PO 4 . Phosphates of soda are not found to any 

 appreciable extent in soils because phosphoric acid forms, 

 with iron, alumina and calcium which are always present, 

 insoluble compounds. 



165. fliscellaneous Sodium Salts. I^ke potassium, 

 sodium forms a large number of salts as Na 2 SO 4 , NaHSO 4 , 

 NaBr, NaCN, Na 2 S and Na 2 O. Sodium compounds are 

 all soluble except the silicates and a few of the more com- 

 plex, salts. 



As previously stated, salts of sodium are similar to the 

 corresponding salts of potassium. The sodium com- 



