4 Holt, TJie Action of Hydrogeyi on Sodiuvi. 



At the same time the solution NaH.Na dissociates 

 more and more rapidlj^ as the temperature rises. 



About 380 C, the NaH.Na dissolved in the sodium is 

 very largeh' dissociated, and at about this temperature the 

 compound NaH begins to sublime. 



This would explain experiment (4), for at the tem- 

 perature to which the sodium was heated, very little of 

 the dissolved hydride would remain undissociated. Troost 

 and Hautefeuille failed to obtain the compound NaH since 

 they heated their hydrogenised sodium in a closed vessel 

 in order to determine the dissociation, whereas in Moissan's 

 experiments the vapour of the hydride was condensed at 

 the moment of its formation, and so removed from the 

 equilibrium of H, Na hydrides. It would appear to be an 

 analogous case to the dissociation of CaCO^. Very little 

 COj or CaO is obtained unless one of the decomposition 

 products is removed as fast as it is formed. 



The formation of an easily dissociating compound 

 Na„H or NaH.Na as described by Troost and Haute- 

 feuille is quite consistent with the sublimation of the 

 compound NaH. 



The finest crystals of the hydride (NaH) were 

 obtained when the glass tube in which they were formed 

 was about one inch internal diameter, and when the 

 sodium was heated to the lowest temperature at v/hich 

 the hydride would sublime. The current of hydrogen 

 should be at rather more than atmospheric pressure, as 

 otherwise the crystals of hydride are found to be mixed 

 with particles of metallic sodium. 



The reactions of the compound have been studied in 

 detail by Moissan, and the author has also repeated most 

 of them. The action of a concentrated solution of hydro- 

 chloric acid produces a somewhat curious result. If a 

 mass of the hydride is dropped into a test tube containing 



