SODIUM. 263 



Sodium peroxide, Na 2 2 . is now extensively used as a bleaching and ox- 

 idi/ing agent. It is a white or yellowish-white powder, readily decomposed by 

 water into sodium hydroxide and oxygen; when dissolved in a dilute acid, 

 hydrogen peroxide is formed. It is made by heating sodium in a current of 

 oxygen. When it is brought in contact with water or dilute acids, great care 

 must be taken to have a low temperature, else violent action will take place, 

 with evolution of oxygen. 



Sodium carbonate, Na 2 CO 3 .10H 2 O (Washing soda, Sal sodce). 

 This compound is, of all alkaline substances, the one manufactured in 

 the largest quantities, being used in the manufacture of many highly 

 important articles, as, for instance, soap, glass, etc. 



Sodium carbonate is made, according to Leblanc's process, from 

 the chloride by first converting it into sulphate (salt-cake) by the 

 action of sulphuric acid : 



2NaCl + H 2 S0 4 == 2HC1 + Na 2 SO 4 



The escaping vapors of hydrochloric acid are absorbed in water, 

 and this liquid acid is used largely in the manufacture of bleaching- 

 powder. The sodium sulphate is mixed with coal and limestone 

 (calcium carbonate) and the mixture heated in reverberatory furnaces, 

 when decomposition takes place, calcium sulphide, sodium carbonate, 

 and carbonic oxide being formed : 



Na 2 SO 4 + 40 + CaCO 3 = CaS + Na,CO 8 + 4CO 



The resulting mass, known as black-ash, is washed with water, 

 which dissolves the sodium carbonate, while calcium sulphide enters 

 into combination with calcium oxide, thus forming an insoluble 

 double compound of oxy-sulphide of calcium. 



The liquid obtained by washing the black-ash, when evaporated 

 to dryness, yields crude sodium carbonate, or " soda ash" ; when this 

 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 4 C1 + NaHCO 3 . 







The sodium acid carbonate thus obtained is converted into carbo- 

 nate by heating : 



2NaHCO, == 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 



