A compound, Na₂Cl, which corresponds with the suboxide, is apparently formed when a galvanic current is passed through fused common salt; the sodium liberated dissolves in the common salt, and does not separate from the compound either on cooling or on treatment with mercury. It is therefore supposed to be Na₂Cl; the more so as the mass obtained gives hydrogen when treated with water: Na₂Cl + H₂O = H + NaHO + NaCl, that is, it acts like suboxide of sodium. If Na₂Cl really exists as a salt, then the corresponding base Na₄O, according to the rule with other bases of the composition M₄O, ought to be called a quaternary oxide. According to certain evidence, a suboxide is formed when thin sheets or fine drops of sodium slowly oxidise in moist air.

According to observations easily made, sodium when fused in air oxidises but does not burn, the combustion only commencing with the formation of vapour—that is, when considerably heated. Davy and Karsten obtained the oxides of potassium, K₂O, and of sodium, Na₂O, by heating the metals with their hydroxides, whence NaHO + Na = Na₂O + 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 produced, Na₂O, when heated in an atmosphere of hydrogen, gave a mixture of sodium and its hydroxide: Na₂O + H = NaHO + Na (see Chapter II., Note ¹³⁸). 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 ⁷⁵⁴), 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.