532 PRINCIPLES OF CHEMISTRY 



Sodium burns both in chlorine and in oxygen, evolving much heat. 

 These properties of sodium are closely connected with its power of 

 taking up oxygen, chlorine, and similar elements from most of their 

 compounds. Just as sodium removes the oxygen from the oxides of 

 nitrogen and from carbonic anhydride, so also does it decompose the 

 majority of oxides at definite temperatures. Here the essence of the 

 matter is the same as in the decomposition of water. Thus, for instance, 

 when acting on magnesium chloride, the sodium displaces the magne- 

 sium, or when acting on aluminium chloride sodium displaces metallic 

 aluminium. Sulphur, phosphorus, arsenic, and a whole series of other 

 elements, also combine with sodium. 46 



With oxygen sodium unites in three degrees of combination, forming 

 a suboxide, Na 4 O, an oxide, Na 2 O, and a peroxide, NaO. They are 

 thus termed because Na 2 O is a basic oxide (with water it forms a basic 

 hydroxide), but Na 4 O and NaO do not form corresponding saline 

 compounds. The suboxide is a grey inflammable substance which 

 easily decomposes water, disengaging hydrogen ; it is formed by the 

 slow oxidation of sodium at the ordinary temperature. The peroxide 

 is a greenish yellow substance, fusing at a bright red heat ; it is produced 

 by burning sodium in an excess of oxygen, and it yields oxygen when 

 treated with water : 



Suboxide: ]STa 4 O-f 3H 2 O= 



Oxide: Na 2 O + H 2 6=2NaH0 48 

 Peroxide : NaO + H 2 0==2NaHO + O 



46 If sodium does not directly displace the hydrogen in hydrocarbons, still by indirect 

 means compounds may be obtained which contain sodium and hydrocarbon groups. Some 

 of these compounds have been produced, although not in a pure state. Thus, for instance 

 zinc ethyl Zn(C 2 H 5 ) 2 , when treated with sodium, loses zinc and forms sodium ethyl, C 2 H 5 Na, 

 but this decomposition is not complete, and the compound formed cannot be separated by 

 distillation from the remaining zinc ethyl. In this combination the energy of the sodium 

 clearly appears, for which reason it reacts with substances containing haloids, oxygen, 

 &c., and directly absorbs carbonic anhydride, forming a salt of a carboxylic acid 

 (propionic). 



47 A compound, Na 2 Cl, which corresponds with the suboxide, is evidently formed 

 when a galvanic current is passed through fused common salt ; the sodium liberated dis- 

 solves in the common salt, and does not separate from the compound either on cool- 

 ing or on treatment with mercury. It is therefore supposed to be Na 2 Cl ; the 

 more so as the mass obtained gives hydrogen when treated with water : Na-jCl + H 2 O 

 = H + NaHO + NaCl, that is, it acts like suboxide of sodium. If NaoCl really exists as a 

 salt, then the corresponding base Na 4 O, according to the example of other bases of the 

 composition M 4 O, 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. 



48 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 con- 

 siderably heated. Davy and Karsten obtained the oxides of potassium, K 2 O, and of sodium. 



