SODIUM 541 



All three oxides form sodium hydroxide with water, but only the 

 oxide Na 2 O is directly transformed into a hydrate. The other oxides 

 .liberate either hydrogen or oxygen ; they also present a similar dis- 

 tinction with reference to many other agents. Thus carbonic anhydride 

 combines directly with the oxide Na a O, which when heated in the gas 

 burns, forming sodium carbonate, whilst the: peroxide yields oxygen in - 

 addition. When treated with acids, sodium and all its oxides onjy 

 form the salts corresponding with sodium oxide* that isv.s> the formula or 

 type NaX. 'Thus the oxide of sodium, Na 2 O, is the only salt-forming 



considerably heated. Davy and Karsteu obtained the oxides of potassium, K 2 O, and of 

 sodium, NaaO, by heating the metals with their hydroxides, whence NaHO 4-Na^Na 2 O+ H, 

 but N. N. BeketofE failed to obtain oxides by this" means. "He prepared them by directly 

 igniting the metals in dry air, and afterwards heating with the metal in order to destroy 

 any peroxide. The oxide produeedjj^ajjO, -when-heated in an atmosphere of hydrogen, 

 gave a mixture of sodium and its hydroxide,: NaaO + H=NaHO + Na (see Chapter II., 

 Note 0). If both the observations mentioned are accurate! then the reaction is reversible. 

 Sodium oxide ought to be formed during the decomposition of sodium carbonate by oxide 

 of iron (aeeJSTote 26), and during the decomposition of sodium nitrite. According to 

 Karsten, its specific gravity is 2'8, according to Beketoff 2*8. The difficulty in obtaining 

 it is owing to an excess of sodium forming the suboxide, and an excess of oxygen the 

 peroxide. The grey colour peculiar to the suboxide and oxide perhaps shows that they 

 contain metallic sodium. In addition to this, in the presence of water it may contain 

 sodium hydride and NaHO. 



49 Of the oxides of sodium, that easiest to form is the peroxide, NaO or Naa0 8 ; this 

 id obtained when sodium is burnt in an excess of oxygen. If NaNO 3 be melted, it gives 

 Na 3 2 with metallic Na. In a fused state the peroxide is reddish yellow, but it becomes 

 almost colourless when eold. When heated with iodine vapour, it loses oxygen : Na.jO 2 + 1^ 

 s-Na-jOIa+O. The compound Na-jOLj is akin to the compound Qu-jOClj obtained by 

 oxidising CuCl. This reaction is one of the few in which iodine directly displaces 

 oxygen. The substance NaaOIa is soluble in water, and when acidified gives free iodine 

 and a sodium salt. Carbonic oxide is absorbed by heated sodium peroxide with formation 

 of sodium carbonate : Na-jCOs^Na-jOa+CO, whilst carbonic anhydride liberates oxygen 

 from it. With nitrous oxide it reacts thus: Na2O 2 + 2NaO=2NaN0 8 -f N 2 ; with nitrio 

 oxide it combines directly, forming sodium nitrite, NaO + NO = NaNO 3 . Sodium peroxide, 

 when treated with water, does not give hydrogen peroxide, because the latter in th 

 presence of the alkali formed (N8^Pi+2H 2 O~2NaHO+HaO 2 ) decomposes into water 

 and oxygen. In the presence of dilute sulphuric acid it forms H 2 O 2 (Na2O 2 +H 2 SO 4 

 = NaaSO 4 + HaO 2 ). Peroxide of sodium is now prepared on a large scale (by the action of air 

 upon Naat 800) for bleaching wool, silk &c. (when it acts in virtue of the HsO-j formed). 

 The oxidising properties of Na 9 O 3 under the action of heat are seen, for instance, in the 

 lact that when heated with I it forms sodium iodate ; with PbO, Na-jPbOs 5 with pyrites, 

 eulphates, &o. When peroxide of sodium comes into contact with water, it evolves much 

 heat, forming H 2 2 , and.eoomposing with the disengagement of oxygen ; but, as a rule, 

 there is no explosion. But if Na-jOa be placed in contact with organic matter, such as 

 sawdust, cotton, &c., it gives a violent explosion when heated, ignited, or acted on by 

 water. Peroxide of sodium forms an excellent oxidising agent for the preparation of the 

 higher product of oxidation of Mn, Cr, W, &c., and also for oxidising the metallic 

 sulphides. It should therefore find many applications in chemical analysis. To prepare 

 f*aaO 2 on a large scale, Castner melts Na in an aluminium vessel, and at 800 passes 

 fitt* air deprived of a portion of its oxygen (having been already once used), and then 

 ordinary dry air over it. 



