152 PRACTICAL LESSONS IN SCIENCE. 



the existence of animal life. It is also used in glazing pottery 

 ware. 



Previous to the war of the French Revolution most of the car- 

 bonate of soda came from Spain. As the supply became scanty 

 and the prices high, Napoleon offered a premium for the discov- 

 ery of a process by which the carbonate could be made in France. 

 The chemist LeBlanc discovered the process now in use for the 

 manufacture of sodium carbonate from sodium chloride, a case 

 in which science took the lead in an economic process. By this 

 process sodium chloride is mixed with an equal weight of sul- 

 phuric acid and strongly heated, which results in the formation 

 of the sodium sulphate, called salt cake and hydrochloric acid, as 

 follows: 2NaCH-H 2 S0 4 =Na 2 S0 4 -f2HCl. Arrangements are 

 usually made so that the acid passing off as a gas is absorbed 

 by water. The sodium sulphate is then mixed with about an 

 equal weight of limestone and about half its weight of fine coal, 

 and strongly heated, when the carbon takes up the oxygen of 

 the sulphate which reduces it to sodium sulphide, Na 2 S, and this 

 acted upon by the carbonic acid liberated from the limestone, 

 forms sodium carbonate Na 2 C0 3 and sulphide of calcium CaS, 

 according to the following equations : Na 2 S0 4 -f-4C=Na 2 S+4CO, 

 and Na 2 S+CaC0 3 limestone Na 2 C0 3 +CaS. The sodium car- 

 bonate is dissolved from the mass and crystallized from the 

 evaporating solution. Sodium bicarbonate HNaC0 3 is the sal- 

 eratus or soda used in bread making, etc. 



The metal SODIUM (Na) is prepared from the carbonate by 

 heating it with coal when the carbon takes the carbon dioxide 

 from the sodium forming carbonic oxide, and the sodium passing 

 over as vapor is condensed under oil or naphtha. Equation, 

 Na2C0 3 +2C=2Na-h3CO. This metal is similar to potassium, 

 but does not decompose water as vigorously, and burns with a 

 yellow flame. It is used for the extraction of the metals alumi- 

 num, magnesium, gold and silver from their ores. 



Sodium hydroxide, formula NaOH, is prepared by treating 

 sodium carbonate with calcium hydroxide, equation Na 2 C0 3 -f-Ca 

 O 2 H 2 =CaC0 8 +2NaOH. It is a white solid somewhat similar to 



