Properties of Sodium Vapour. 131 



Another experiment was made showing that sodium vaporizes 

 in observable quantities when just above its melting-point. In 

 the Berichte der Deutschen Ghemischen Gesellschaft, No. 1, 1905, 

 Kraft and Bergfeld showed that sodium distilled at 140° C. 

 Apparently these observers did not obtain distillation of sodium 

 vapour at a lower temperature. It seemed worth while to try 

 whether at the temperature of boiling water it would be possible 

 to notice any distillation. A bulb was taken with a little sodium 

 deposited on its upper part, the lower part being quite clear. 

 The lower part was placed in cold water and a jet of steam was 

 played on the upper part. After some hours a very distinct 

 film of sodium was observed on the lower part of the bulb, 

 showing that, at a temperature 2° above the melting-point of 

 sodium, vapour was formed in observable quantities. No dis- 

 tillation could be observed from sodium at the ordinary air 

 temperature when a clear part of the bulb was placed in liquid 

 air. Sodium apparently therefore does not sublime at ordinary 

 temperatures. 



10—2 



