SODH'M 533 



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

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

 either liberate 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 2 0, which when heated in the gas 

 burns, forming sodium carbonate, whilst in this case the peroxide 49 also 

 yields oxygen. When treated with acids, sodium and all its oxides only 

 form the salts corresponding with sodium oxide that is, of the formula or 

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

 oxide of this metal, as water is in the case of hydrogen. Although the 

 peroxide H 2 O 2 is derived from hydrogen, yet there are no correspond- 

 ing salts known, and if they are formed they are probably as unstable as 

 hydrogen peroxide itself. Although carbon forms carbonic oxide, CO, 

 still it has only one salt-forming oxide carbonic anhydride, CO 2 . 

 Nitrogen and chlorine both give several salt-forming oxides and types of 

 salts. But of the oxides of nitrogen, NO and NO 2 do not form salts, 

 as do N 2 O 3 , N 2 4 , and N 2 O 5 , but N 2 O 4 does not form special salts, 

 and N 2 5 corresponds with the highest form of the saline compounds 

 of nitrogen. Such distinctions between the elements, according to 

 their power of giving one or several saline forms, is a radical property 

 of no less importance than the basic or acid properties of the oxides 

 produced. Sodium as a typical metal does not form any acid oxides, 



, by heating the metals with their hydroxides, whence NaHO + Na = Na^O + H, but 

 N. N. Beketoff 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 Na. 2 O produced, when heated in. an atmosphere of hydrogen, 

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

 Note l)j. 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 (see Note 26), and during the decomposition of sodium nitrite. According to 

 Karsten, its specific gravity is 2'8, according to Beketoff 2'3. 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. 



49 Of the oxides of sodium, that easiest to form is the peroxide NaO or Na, 2 O 2 ; this 

 is obtained when sodium is burnt in an excess of oxygen. When heated with iodine 

 vapour, it loses oxygen: Na^Oa + I^NaaOIa + O. The compound Na^OIj is akin to 

 the compound Cu 2 OCl 3 obtained by oxidising CuCl. This reaction is one of the few 

 where iodine directly displaces oxygen. The substance Na. 2 OI 2 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: NaoCO 5 =Na. 2 O 2 + CO, whilst 

 carbonic anhydride liberates oxygen from it. With nitrous oxide it reacts thus : Na2O 2 



+ 2N 2 O = 2NaNO 2 + N 2 ; with nitric oxide it combines directly, forming a nitrite, NaO 



+ NO = NaNO 2 . Sodium peroxide, when treated with water, does not give hydrogen 

 peroxide, because the latter in the presence of the alkali formed (Na. 2 O 2 + 2H 2 O = 2NaHO 



4- H 3 O 2 ) decomposes into water and oxygen. 



