2 Holt, The Action of Hydrogen on Soditini. 



was then allowed to cool. Almost at once it became 

 covered with a layer of h}'dride. 



When cool it was reheated in the current of hydrogen. 

 The white film of hydride round each globule of molten 

 metal remained unaltered until about 370° C, when it 

 disappeared, only to reappear on the cooler parts of the 

 tube. 



3. Some of the pure crystalline hydride (free from 

 sodium) was heated in a current of h\'drogen. It decom- 

 posed almost completely at a temperature below that at 

 which it begins to sublime. The sodium arising from its 

 decomposition became at once covered with a film of 

 hydride, and at about 370° C. sublimation of the hydride 

 began as in the previous experiments. 



From this experiment, it appears that the hydride 

 decomposes at a lower temperature when heated alone 

 than when it is present as a film on the surface of molten 

 sodium. 



4. Some sodium was heated in a current of hydrogen, 

 as in the previous experiments, until the hydride was 

 subliming. It was then allowed to cool as rapidly as 

 possible. When cold the sodium was analysed. The 

 volume of hydrogen which it gave when treated with 

 absolute alcohol was only slightly in excess of that which 

 would result from an equal weight of pure sodium. As 

 in this experiment the metal was heated to about 400° C, 

 the amount of hydride dissolved in the sodium at this 

 temperature cannot be very large. 



5. A piece of sodium was heated in hydrogen in a 

 vessel standing over mercury. At a temperature of about 

 450 C. the metal began to volatilise and attack the glass, 

 but the absorption of hydrogen was extremely small, and 

 there was no visible sublimate of hydride. 



