SODIUM 585 



from tfie charcoal. 38 The chalk on being heated loses carbonic anhy- 

 dride, leaving infusible lime, which is permeated by the sodium 

 carbonate and forms a thick mass, in which the charcoal is intimately 

 mixed with the sodiunJ carbonate. When the charcoal is heated with 

 the sodium carbonate, at a white heat, carbonic oxide and vapours of 

 sodium are disengaged, according to the equation : 



Na 2 C0 3 + 20 = Na 2 4- SCO 



On cooling the vapours and gases disengaged, the vapours condense 

 into molten metal (in this form sodium does not easily oxidise, whilst 

 In vapour it burns) and the carbonic oxide remains as gas. 



In sodium works an iron tube, about a metre long and a decimeter 



Fro. 70. Manufacture of sodium t>j Deville'e process. A C, iron tube containing a mixture ol 

 soda, charcoal, and chalk. B, condenser. 



in diameter, is made out of boiler plate. The pipe is luted into a 

 furnace having a strong draught, capable of giving a high temperature* 

 &nd the tube is charged with the mixture required for the preparation 

 of sodium. One end of the tube is closed with a cast-iron stopper A 

 with clay luting, and the "other with the- cast-iron stopper C provided 



58 Since lihe clpse of the eighties in England, where the preparation of sodium is at 

 present carried out on a large .commercial scale (from 1860 to 1870 it was only 

 manufactured in a few works in France), it has been the practice to add to Deville's 

 mixture iron, or iron oxide which with the charcoal gives metallic and carburetted iron, 

 which still further facilitates the decomposition. At present a kilqgrain of sodium may 

 be purchased for about the same sum (2/-) as a gram cost thirty years ago. Castner, in 

 England, greatly improved the manufacture of sodium in large quantities, and so 

 cheapened it as a reducing agent in the preparation of metallic aluminium. He heated 

 a mixture of 44 parts of NaHO, and 7 parts of carbide of iron in large iron retorts 

 at 1,000 and obtained about 6| parts of 'metallic sodium. The reaction proceeds 

 more easily than with carbon or iron alone, and the decomposition o the NaHO proceeds 

 according to the equation: 8NaHO + C = Na2CO 5 + 8H+Na. Subsequently, in 1891, 

 aluminium was prepared by electrolysis (see Chapter XVII.), and metallic sodium found 



