Disappearance of Gas in the Electric Discharge. 701 



^VN 2 ; it approached more nearly that corresponding to 

 WN 3 . Bat once more, according to § 11, it is probable that 

 some nitride is formed. 



24. The absence of " constant proportions /' — Avery large 

 number of observations have been made with the object of 

 determining whether the amount of gas that disappears under 

 the influence of phosphorus is proportional to the amount of 

 phosphorus present. It is clear that, of the gases mentioned, 

 hvdrogen alone is suitable for the investigation, because it 

 alone shows a definite limit to the disappearance. The 

 following experiments appear conclusive : — 



(a) If the law oE constant proportions were true, the 

 pressure of hydrogen which would disappear when mixed 

 with the vapour of phosphorus at a definite temperature 

 should be independent of the size or shape of the vessel. On 

 the contrary, it was found to depend considerably, and in a 

 very complex manner, on both the size and shape. 



(/>) In a lamp of a certain type the pressure of hydrogen 

 which would disappear when mixed with one charge of 

 phosphorus vapour was 0'039 mm. If hydrogen was filled 

 to a greater pressure than this, together with a ciiarge of 

 phosphorus, and the discharge passed, the pressure could be 

 reduced by about 0'039 mm. If, now, a second charge of 

 phosphorus was mixed with the hydrogen left, the amount 

 that could be made to disappear was much less than 

 O039 mm. ; and if further charges of phosphorus were 

 added, the decrease of pressure due to each charge appeared 

 to decrease still further. The subsequent charges do not 

 cause the absorption of as much hydrogen as the first. 



(c) The same experiment can be repeated in rather a 

 different form. If, instead of mixing the phosphorus vapour 

 with the hydrogen, we first introduce a charge of the 

 vapour, pass the discharge through this vapour, depositing it 

 on the walls as a yellow film, and then introduce hydrogen; 

 the amount of hydrogen that can be made to disappear is 

 the same as that which would disappear if the phosphorus 

 had been in the form of vapour, i. e. 0039 mm. If, how- 

 ever, we introduce initially and deposit on the walls, not one 

 charge of the vapour, but many charges, the amount of 

 hydrogen subsequently introduced that will disappear does 

 not seem to change. When the phosphorus is introduced in 

 this manner, the amount of hydrogen that can be made to 

 disappear seems independent of the amount of phosphorus 

 present, so long as it is above a certain limit. 



Phil. Mag. S. 6. Vol. 41. No. 245. May 1921. 3 A 



