SODIUM. 143 



is dissolved and crystallized it takes up ten molecules of water, 

 forming the ordinary washing soda. 



Sodium carbonate is manufactured also by the so-called ammonia 

 process, or the Solvay process. This depends on the decomposition 

 of sodium chloride by ammonium bicarbonate under pressure, when 

 sodium bicarbonate and ammonium chloride are formed, thus : 

 NaCl + NH 4 HCO 3 = NH.C1 + NaHCO 3 . 



The sodium acid carbonate thus obtained is converted into carbo- 

 nate by heating : 



2NaHCO 3 = Na 2 CO 3 + H 2 O + CO 2 . 



The carbon dioxide obtained by this action is caused to act upon 

 ammonia, liberated from the ammonium chloride, obtained as one of 

 the products in the first reaction. Ammonium carbonate is thus 

 regenerated and used in a subsequent operation for the decomposition 

 of common salt. 



Sodium carbonate has strong alkaline properties ; it is soluble in 

 1.6 parts of cold water, and in much less water at higher temper- 

 atures ; the crystals lose water on exposure to the air, falling into a 

 white powder; heat facilitates the expulsion of the water of crys- 

 tallization, and is applied in making the dried sodium carbonate, 

 Sodii carbonas exsiccatJis of the U. S. P., which should contain about 

 73 per cent, of anhydrous sodium carbonate. 



Sodium bicarbonate, Sodii bicarbonas, NaHCO 3 =84. Ob- 

 tained, as stated in the previous paragraph, by the ammonia- soda 

 process. It can also be made by passing carbon dioxide over sodium 

 carbonate from which the larger portion of water of crystallization 

 has been expelled : 



NajCO a + H 2 O + CO 2 = 2NaHCO 3 . 



It is a white powder, having a cooling, mildly saline taste, and a 

 slightly alkaline reaction. Soluble in 11.3 parts of cold water, and 

 insoluble in alcohol. It is decomposed by heat or by hot water into 

 sodium carbonate, water, and carbon dioxide. 



Sodium sulphate, Sodii sulphas, Na 2 SO 4 10H 2 O = 322 (Glaubers 

 salt). Made, as mentioned above, by the action of sulphuric acid on 

 sodium chloride, dissolving the salt thus obtained in water, and crys- 

 tallizing. Large, colorless, transparent crystals, rapidly efflorescing 

 on exposure to air. Soluble in 2.8 parts of water at 15 C. (59 F.), 

 in 0.25 part at 34 C. (93 F.), and in 0.47 part of boiling water. 



