

Strlation of Rarefied Gases by tlie Electric Discharge* 203 



filled with a mixture of hydrogen and carbon dioxide and 

 exhausted. At a pressure of 24 millim. the current was 

 passed ; instead of a negative glow appeared a little bunch of 

 light about \ inch below the negative point. If this bunch of 

 light impinged on the'side of the tube, the glass became strongly 

 phosphorescent. At 4 millim. there was no bunch of light or 

 negative glow ; there was no sign of any striae, the tube 

 giving a spectrum of hydrogen and carbon dioxide, and no 

 evidence of separation. I then reversed the current ; imme- 

 diately striae formed, separation began and became well- 

 marked. 



I tried various mixtures of gases and always obtained the 

 same result, viz., that when the negative glow was avoided by 

 the use of the minute electrode point, neither striae nor sepa- 

 ration occurred, but in reversal of the current strongly 

 marked striae and good separation. 



My next step was to experiment with a pure vapour, 

 which, if my contention be correct, should not striate. It is 

 known that a tube of pure mercury vapour does not stratify. 

 I prepared a tube for the purpose, one end of which was con- 

 nected with the pump and the other with a bulb containing 

 mercury. After exhaustion, I strongly heated the tube and 

 boiled the mercury, which thus distilled through the tube. 

 On passing the current, as I expected, no striae appeared, 

 but simply a beautiful phosphorescence throughout the tube, 

 giving a spectrum of pure mercury only. On ceasing to boil 

 the mercury and allowing the tube to cool, a small quantity of 

 other gas was necessarily drawn in from the pump. Immedi- 

 ately striae began to appear, beginning at the end of the tube 

 connected with the pump; the negative glow changed at the 

 same time and gave a spectrum containing other lines in 

 addition to those of mercury, thus strongly confirming my 

 previous conclusion. 



Thinking that possibly the absence of striae might arise, 

 not from the purity of the mercury vapour, but from its 

 molecules being monatomic, I repeated the experiment with 

 pure vapours of iodine, sulphur, arsenic, and mercuric iodide, 

 which are not monatomic. The result was in each case pre- 

 cisely the same — the tube while heated showing no stria?, but 

 on cooling both striae and separation. 



Wishing if possible to obtain a pure gas which did not 

 stratify at ordinary temperatures, I made many attempts to 

 prepare a tube of pure hydrogen. The nearest approach to 

 success was with hydrogen prepared from pure caustic potash 

 and aluminium. The gas was then absorbed by red-hoi 

 palladium, which was re-heated in the vacuum. On passing 



P2 



