1913] on the Method of Positive Rays 599 



from it when the lead is dissolved. I have tried several samples of 

 lead : the one which g-uve the X3 Hue most distinctly was a piece of 

 lead from the roof of Trinity College Chapel, several hnndred years 

 old. A sample of Kahlbaum's chemically pure lead, which must, I 

 suppose, at no distant date have been suljjected to severe ordeals by 

 fire and water, showed the line quite distinctly, though not so well 

 as the older lead. I have tried similar experiments w-ith iron, and 

 found that iron which gave the three line very distinctly ceased to do 

 so after it had been dissolved in acid. 



As the most obvious explanation of X3 is that it is H3, bearing 

 the same relation to hydrogen that ozone does to oxygen, and pro- 

 duced in some way from the hydrogen dissolved in the metal, I tried 

 if I could produce it by charging metals with large quantities of 

 hydrogen, and then seeing if the hydrogen coming from the metal 

 gave any traces of H3. Thus, for example, I tested the hydrogen 

 given off from hot palladium, but found no trace of X3. I then 

 charged nickel at a temperature of about 355° C. with hydrogen in 

 the way recommended by Sabatier, but found no increase in the 

 brightness of the X3 over nickel that had not been deliberately ex- 

 posed to hydrogen. I tried if the brightness of the line would be 

 increased by adding hydrogen to the bulb A, in which the bombard- 

 ment took place, but found no effect. I also tried adding oxygen to 

 this bulb, thinking that if it was H3 it would combine with the 

 oxygen, and thus be eliminated, but no great diminution in the 

 intensity was produced by this treatment. The gas seems quite 

 stable, at least it can be kept for several days without suffering any 

 diminution that can be detected ; indeed, when once it has got into a 

 bulb, there is considerable difficulty in getting the bulb free from it. 

 It must be remembered, too, that by the method it is produced the 

 gas is subjected all the time to electric discharges which would 

 break it up unless it possesses very great stability. Thus if Xg is a 

 polymeric modification of hydrogen, it must possess the following 

 properties : — 



1. It must be very stable. 



2. It must resist the action of oxygen. 



3. It must not be decomposed by long-continued exposure 



to the electric discharge. 



These are properties which a priori we should hardly have ex- 

 pected an allotropic modification of hydrogen to possess. 



Mendeleef predicted the existence of an element with an atomic 

 weight 3. According to him this element should be intensely 

 electro-negative and possess the properties of fluorine to an exagge- 

 rated extent. The gas Xg can, however, be kept in glass vessels, which 

 we should not expect to be possible if it possessed more than fluorine's 



