1913] on Active Nitrogen 657 



the emission of the yellow light which you see, and this continues as 

 long as the process of pairing off is incomplete. 



Preliminary to even considering this theory, we must be certain 

 that nothing but nitrogen is necessary to the success of the experi- 

 ment, and that no other substance intervenes. Some experimenters 

 in Germany have recently expressed the opinion that traces of oxygen 

 are concerned. I am satisfied, however, that they are entirely mis- 

 taken. The nitrogen used in the experiment you have just seen has 

 been standing in contact with phosphorus until the phosphorus no 

 longer glows in the dark. If I added a T^w(rT)tti part of oxygen to 

 the nitrogen, the phosphorus would begin glowing again quite 

 perceptibly. So we may be sure that there is not that amount of 

 oxygen present; and I do not think it is reasonable to attribute 

 these brilliant effects to a smaller amount. Again, we may enquire 

 what is the effect of adding oxygen intentionally ? I find that the 

 addition of 2 per cent of oxygen is enough to obliterate the phe- 

 nomena altogether. Much more might be said on the subject, but 

 we must pass on. 



It is convenient for some purposes to experiment in a different 

 way. We have here two similar glass globes containing rarefied 

 nitrogen. I can induce an electric discharge in them without elec- 

 trodes by putting them in this coil of wire, through which a Leyden 

 jar is constantly discharging. When I withdraw them you see that 

 they are brilliantly luminous, and that they remain so for several 

 minutes after stimulation. By holding them alternately in the 

 exciting coil we can get them about equally bright, and you see that 

 the luminosity of each decays at about the same rate. Now I stimu- 

 late them equally again, and cool one down by immersing it in liquid 

 air. It shines brightly for a moment, but soon becomes quenched. 

 I withdraw it, and you can compare it with the other, which is still 

 brightly luminous. 



This experiment shows that cooling the gas shortens the period 

 of luminosity. Let me show you next that the brilliance is increased 

 by cooling. I have exhausted this bulb to a suitable degree, and 

 cool the neck by immersion in liquid air, contained in a transparent 

 vessel (Fig. 2). You see how much brighter the cooled portion is 

 after excitation than the rest of the bulb. There is no doubt a 

 certain ambiguity in this form of experiment, because cooling a 

 portion of the vessel causes a local concentration of the gas in tliat 

 portion. I must ask you to take it from me that special experiments 

 laave proved that this cause is not enough to explain the greatly 

 increased brightness you have seen. The reunion of nitrogen atoms 

 occurs then more quickly the lower the temperature. This is a 

 unique instance of a chemical action being quickened by cooling. 

 In all other cases heating accelerates the action. Plausible objections 

 may be made to this statement, but I must content myself now with 

 saying that they admit of answer. 



