534 PRINCIPLES OF CHEMISTRY 



negative pole and oxygen at the positive pole. Davy showed that the 

 metal formed volatilises at a red heat, and this is its most important 

 physical property in relation to its extraction, all later methods being 

 founded on it Besides this Davy observed that sodium easily oxidises, 

 its vapour taking fire in air, and the latter circumstance was for a 

 long time an obstacle to the easy preparation of this metal. The 

 properties of sodium were subsequently more thoroughly investigated 

 by Gay-Lussac and The"nard, who observed that metallic iron at a high 

 temperature was capable of reducing caustic soda to sodium. 36 Brunner 

 latterly discovered that not only iron, but also charcoal, has this 

 property, although hydrogen has not. 37 But still the methods of ex- 

 tracting sodium were very troublesome, and consequently it was a great 

 rarity. The principal obstacle to its production was that an endeavour 

 was made to condense the easily-oxidising vapours of sodium in vacuo 

 in complicated apparatus. For this reason, when Donny and Maresca, 

 having thoroughly studied the matter, constructed a specially simple 

 condenser, the production of sodium was much facilitated. Further- 

 more, in practice the most important epoch in the history of the 

 production of sodium is comprised in the investigation of Sainte-Claire 

 Deville, who avoided the complex methods in vogue up to that time, 

 and furnished those simple means by which the production of sodium is 

 now rendered feasible in chemical works. 



For the production of sodium according to Deville's method, a 

 mixture of anhydrous sodium carbonate (7 parts), charcoal (two parts), 

 and lime or chalk (7 parts) is heated. This latter ingredient is only 

 added in order that the sodium carbonate, on fusing, shall not separate 



36 Deville supposes that such a decomposition of sodium hydroxide by metallic iron 

 depends solely 'on the dissociation of the alkali at a white heat into sodium, hydrogen, 

 and oxygen. Here the part played by the iron is only that it retains the oxygen formed, 

 otherwise the decomposed elements would again reunite upon cobling, as in other casea 

 of dissociation. If it be supposed that the temperature at the commencement of the dis- 

 sociation of the iron oxides is higher than that of sodium oxide, then the decomposition 

 may be explained by Deville's hypothesis. Deville demonstrates his views by the follow- 

 ing experiment : An iron bottle, filled with iron borings, was heated in such a way that 

 the upper part became red hot, the lower part remaining cooler ; sodium hydroxide was 

 introduced into the upper part. The decomposition was then effected that is, sodium 

 vapours were produced (this experiment was really performed with potassium hydroxide). 

 On opening the bottle it was found that the iron in the upper part was not oxidised, 

 but only that in the lower part. This may be explained by the decomposition of the 

 alkali into sodium, hydrogen, and oxygen taking place in the upper part, whilst the iron 

 in the lower part absorbed the oxygen set free. If the whole bottle fee subjected to the 

 same moderate heat as the lower extremity, no metallic vapours are formed. In that 

 case, according to the hypothesis, the temperature is insufficient for the dissociation of 

 the sodium hydroxide. 



57 It has been previously remarked (Chapter II. Note 9) that Beketoff showed 

 the displacement of sodium by hydrogen, not from so'dium hydroxide but from the oxide 

 Na 2 ; then, however, only one half is displaced, with the formation of NaHO 



