SODIUM. 123 



Sodium carbonate has strong alkaline properties ; it is soluble 

 in 1.6 part of water at ordinary temperature, and in much less 

 water at higher temperatures ; the crystals lose water on expo- 

 sure to the air, falling into a white powder; heat facilitates the 

 expulsion of the water of crystallization, and is applied in 

 making the dried sodium carbonate, Sodii carbonas exsiccata, of the 

 U. S. P. 



Sodium bicarbonate, Sodii bicarbonas, NaHC0 3 = 84 (Bicarbonate 

 of sodium). Made by passing carbon dioxide over sodium car- 

 bonate from which the larger portion of water of crystallization 

 has been expelled : 



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



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

 and a slightly acid reaction. Soluble in 12 parts of cold water 

 and insoluble in alcohol. It is decomposed by hot water into 

 sodium carbonate, water, and carbon dioxide. 



Sodium sulphate, Sodii sulphas, Na 2 S0 4 .10H 2 = 322 (Sulphate 

 of sodium, Glauber's salt). Made, as mentioned above, by the 

 action of sulphuric acid on sodium chloride, dissolving the salt 

 thus obtained in water and crystallizing. Large, colorless, 

 transparent crystals, rapidly efflorescing on exposure to air. 

 Soluble in 2.8 parts of water at 15, in 0.25 part at 33, and in 

 0.4 part of boiling water. 



Sodium sulphite, Sodii sulphis, Na 2 S0 3 .7H 2 = 252. Made by 

 passing sulphur dioxide into solution of sodium hydrate : 



2NaHO + SO 2 = Na 2 SO 3 + H 2 O. 



Sodium hyposulphite, Sodii hyposulphis, Na 2 S 2 3 .5H 2 = 248. 

 Made by digesting a mixture of solution of sodium sulphite 

 and powdered sulphur, when combination slowly takes place : 



Na 2 S0 3 + S = Na 2 S 2 3 . 



It is used, under the name of " hypo," in photography to dis- 

 solve chloride, bromide, or iodide of silver. 



Disodium hydrogen phosphate, Sodii phosphas, Na 2 HP0 4 .12H 2 



= 358 (Phosphate of sodium), is made from calcium phosphate 



