636 PEINOIPLE9 OP CHEMISTRY 



with an aperture. On heating, first of all the moisture contained- in 

 the various substances is given off, then carbonic anhydride and the 

 products of the dry distillation of the charcoal, then the latter begins 

 to act on the, sodium carbonate, and carbonic 

 oxide and vapours of sodium appear. It is easy 

 to observe the appearance of the latter, because 

 on issuing from the aperture in the stopper 

 they take fire spontaneously and burn with a 

 very bright yellow flame. A pipe is then in- 

 troduced into the aperture 0, compelling the 

 vapours arid gases formed to pass through the 

 condenser B. This condenser consists of two 

 squard cast-iron tfays, A and A', fig. 71, with 

 wide edges' firmlv : screwed together. Between 

 these two trays there is a space in which tho condensation of the 

 vapours of sodium is effected, the thin metallic walls of the condenser 

 being cooled by the air but remaining hot enough to preserve the 

 sodium in a liquid state, so that it does not choke the apparatus, but 

 continually flows from it. The vapours of sodium, condensing in the 

 cooler, flow in tlie shape of liquid metal into a vessel containing some 

 non- volatile naphtha or hydrocarbon. This is used in order to prevent 

 the sodium oxidising as it issues from the condenser at a somewhat 

 high temperature. In order to obtain sodium of a pure quality it is 

 necessary to distil it once more, which may-even be done in porcelain 

 retorts, but the distillation must be conducted in a stream of some gas 

 on which sodium does not act, for instance In a stream of nitrogen j 

 carbonic anhydride 19 not applicable, because sodium partially de- 

 composes it, absorbing oxygen from at. Although the above described 

 methods of preparing sodium by chemical means have proved very con- 

 venient in practice, still it is now (since 1893) found profitable in 

 England to obtain it (to the amount oi several tons a week) by Davy's, 

 classical method, i.e. by the action of an electric current at a moderately 

 high temperature, because the means for producing an electric current 

 (by motors and dynamos) now render this quite feasible; This may be 

 regarded as a sign that in process of time many other technical methods 

 for producing various substances by decomposition maybe profitably 

 -carried on by electrolysis. 



3?ure sodium is a lustrous metal, wnite as silver, soft as wax ; it 

 becomes brittle in the cold. In ordinary mpist air it quickly tarnishes 



two new uses ; (1) for the manufacture of peroxide of sodium (see later on) which is used 

 in bleaching works, and (2) in the manufacture of potassium fl&d sodium cyanide fron> 

 y&llpw prussiate (Chapter XIII., Note 12). 



