COMPOUNDS OF SODIUM AND POTASSIUM 367 



heated, it rapidly gives off carbon dioxide and water, and leaves 

 sodium carbonate: 



Skeleton: NaHC0 3 <= NaaCO* + H 2 C0 3 * H 2 O + CO 2 . 

 Balanced: 2NaHCO 3 + Na 2 C0 3 + H 2 O + C0 2 . 



Like all carbonates, when treated with an acid, it gives carbonic 

 acid and this, in turn, gives water and carbon dioxide. 



NaHC0 3 + HC1 * Nad + H 2 CO 3 + H 2 O + CO 2 1 . 

 This property leads to its use in fire extinguishers. 



Sodium Carbonate Na 2 CO 3 . This salt is manufactured by 

 heating sodium bicarbonate. It is made also by the Le Blanc 

 process. Sgdium chloride is treated at a red heat with an equiv- 

 alent amount of sulphuric acid, giving sodium sulphate Na 2 S04. 

 The latter is roasted with powdered coal and limestone. The 

 coal reduces the sulphate to sodium sulphide NasS, and the latter 

 interacts with the limestone giving sodium carbonate and calcium 

 sulphide CaS. The carbonate is separated by solution in water. 

 The solution, when concentrated, gives crystals of the decahy- 

 drate, washing soda Na 2 CO 3 ,10H 2 0. The latter, when heated, 

 leaves " soda-ash " or " calcined soda 



NaCl + H 2 S0 4 - Na 2 S0 4 + 2HC1 | 

 +2C -Na2S + 2CO 2 f 

 Na,S + CaC0 3 r* NaaCOs + CaS. 



Sodium carbonate Na 2 C0 3 is used in making sodium hydroxide 

 (p. 166) and glass (p. 361), and to soften water (see p. 389). As 

 about two-thirds of washing soda is water, it is cheaper to ship 

 the anhydrous form, except when the hydrate is wanted, as for 

 washing. 



Properties of Sodium Carbonate Solution. The solution 

 is not neutral to litmus, as we might expect, but distinctly alkaline. 

 The explanation by the ionization theory is of general interest. 



