SODIUM 531 



then does not undergo decomposition if it is in an atmosphere of hydrogen. 

 It oxidises easily in air, but not so easily as potassium hydride. The 

 chemical reactions of sodium are retained in its hydride, and, if we may 



x press it, they are even increased by the addition of hydrogen. At 

 all events, in. the properties of sodium hydride 43 we see other properties 

 than in such hydrogen compounds as HC1, H 2 O, H 3 N, H 4 C, or even 

 in the gaseous metallic hydrides AsH 3 , TeH e . But platinum, palladium, 

 nickel, and iron, in absorbing hydrogen form compounds in which 

 hydrogen is in a similar state. In them, as in sodium hydride, the 

 hydrogen is compressed, absorbed, occluded (page 141). 



The most important property of sodium is its power of easily decom- 

 posing water and evolving hydrogen from the majority of the hydrogen 

 compounds, and especially from all acid and hydrate compounds in which 

 hydroxyl ought to be recognised. This depends on the power of sodium 

 of combining with the elements which are in combination with the hydro- 

 gen. We already know that sodium disengages hydrogen, not only from 

 water, hydrochloric acid, 44 and all other acids, but also from ammonia, 

 although it does not displace hydrogen from the hydrocarbons. 45 



43 In general, during the formation of alloys the volumes change very slightly, and 

 therefore from the volume of Na 2 H some idea may be formed of the volume of 

 hydrogen in a solid or liquid state. Archimedes even concluded that there was gold 

 in an alloy of copper and gold by reason of its volume and density. From the fact that 

 the density of Na 2 H is equal to 0'959, it may be seen that the volume of 47 grams (the 

 gram molecule) of this compound = 49'0 c.c. The volume of 46 grams of sodium con- 

 tained in the Na, 2 H is equal (the density in the same conditions 0'97) to 47'4 c.c. There- 

 fore the volume of 1 gram of hydrogen in Na 2 H is equal to 1*6 c.c., and consequently the 

 density of metallic hydrogen, or the weight of 1 c.c., approaches 0'6 gram. This density 

 is also proper to the hydrogen alloyed with potassium and palladium. Judging from the 

 scanty information which is at present available, liquid hydrogen near its absolute 

 boiling-point (Chapter II.) has a far less density. 



It ought to be mentioned that sodium hydride, according to the usual equivalency of 

 H., with O, corresponds, not with the oxide Na^O.but with the suboxide of sodium, Na 4 O, 

 and if we judge the atomicity of elements by hydrogen compounds) sodium ought to be 

 counted us srmivalent. According to the law of substitution, Na ought to be taken as 

 univalent in all its ordinary combinations : Na^O, NaCl, NaHO, NaHSO 4 , &c. Therefore 

 sodium hydride belongs to the series Na. 2 X, and not NaX. 



44 H. A. Schmidt remarked that completely dry hydrogen chloride is decomposed 

 with great difficulty by sodium, although the decomposition proceeds easily with potas- 

 sium and with sodium in moist hydrogen chloride. Wanklyn also remarked that sodium 

 burns with great difficulty in dry chlorine. Probably in relation to this there is a corre- 

 spondence with other phenomena observed by Dixon, who found that completely dry 

 carbonic oxide does not explode with oxygen on passing an electric spark. 



4& As sodium does not di^phn T hydrogen from the hydrocarbons, it may be preserved 



in liquid hydrocarbons. Naphtha is generally used for this purpose, as it consists of a 



mixture of various liquid hydrocarbons. However, in naphtha sodium usually becomes 



1 with a crust composed of matter produced by the action of the sodium on certain of 



tin- substances contained in the mixture composing naphtha. In order that sodium may 



i its lustre in naphtha, secondary octyl alcohol is added. (This alcohol is obtained by 



distilling castor oil with caustic potash.) Potassium and sodium keep well in a mixture 



of pure benzene and naphthalene. 



M M 2 



