264 METALS AND THEIR COMBINATIONS. 



the products in the first reaction. Ammonium bicarbonate 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 monohydrated sodium car- 

 bonate, Sodii carbonas monohydras, Na 2 CO 3 .H 2 O = 123.19, which 

 should contain about 85 per cent, of anhydrous sodium carbonate. 



Sodium bicarbonate, Sodii bicarbonas, NaHCO 3 = 83.43 (Bak- 

 ing-soda). Obtained, as stated in the previous paragraph, by the 

 ammonia-soda process. It can also be made by passing carbon 

 dioxide over monohydrated sodium carbonate. 



Na,CO 3 .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 12 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 bicarbonate is a constituent of the various baking-powders, the action 

 of which depends on the gradual liberation of carbon dioxide in the dough. 

 This is brought about through a second constituent, generally an acid salt such 

 as potassium bitartrate or calcium acid phosphate, which decomposes the 

 bicarbonate. 



Sodium sulphate, Sodii sulphas, Na 2 SO 4 lOH 2 O = 319.91 (Glau- 

 ber's 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. 



Experiment 23. Dissolve about 10 grammes of crystallized sodium carbonate 

 in 10 c.c. of hot water, add to this solution dilute sulphuric acid until all effer- 

 vescence ceases and the reaction on litmus-paper is exactly neutral. Evaporate 

 to about 20 c.c., and set aside for crystallization. Explain the action taking 

 place, and state how much H 2 S0 4 , and how much of the diluted sulphuric 

 acid, U. S. P., are needed for the decomposition of 10 grammes of crystallized 

 sodium carbonate. 



Sodium sulphite, Sodii sulphis, Na 2 SO 3 .7H 2 O -- = 25O.39. 

 Sodium bisulphite, Sodii bisulphis, NaHSO 3 = 1O3.35. By 



