May 15, 1913] 



NATURE 



283 



ACTIVE NITROGEN. 1 



ga 



VERYONE has heard of ozone, the active modi- 

 ' fication of oxygen which is produced when this 

 ! is subjected to electric discharge. I hope to 



NITROGEN 



show you to-night that nitrogen can also be made to 

 assume an active state under suitable experimental 

 conditions. We will begin with an experiment 

 (Fig. 1) which will serve to introduce the subject. 



A rapid stream of rarefied nitrogen gas passes 

 through the tube a at a pressure of a few mm. of 

 mercury, and on its way the gas is sparked through 

 by a series of high-tension electric discharges from 

 a' Levden jar. It then issues as a jet into the large 

 vessel b, where it is seen to be brilliantly luminous, 

 the stream of gas being visible as a whirling cloud 

 of brilliant vellow light. Notice that this light is of 

 a different colour from that of the electric discharge 

 in the former vessel. 



Why does the gas remain luminous in this way 

 for an appreciable time after the electric discharge 

 has passed through it? The view which I shall 

 develop this evening is that the discharge has split 

 the nitrogen molecules into single atoms. Nitrogen 

 atoms in this condition are uneasy, and are anxious 

 to find partners again. But to do this takes time. 

 The reunion of the nitrogen atoms is attended with 

 the emission of the yellow light which you see, and 

 this continues so long as the process of pairing off 

 is incomplete. 



Preliminary even to considering this theory, we 

 must be certain that nothing but nitrogen is necessary 

 to the success of the experiment, and that no other 

 substance intervenes. Some experimenters in Ger- 

 many have recently expressed the opinion that traces 

 of oxygen are concerned. I am satisfied, however, 

 that thev are entirely mistaken. The nitrogen used 

 in the experiment you have just seen has been stand- 

 ing in contact with phosphorus until the phosphorus 

 no" longer glows in the dark. If I added a i/ioo,oooth 

 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 attri- 

 bute these brilliant effects to a smaller amount. 

 Again, we may inquire what is the effect of adding 

 oxygen intentionally? I find that 

 the addition of 2 per cent, ol 

 oxygen is enough to obliterate the 

 phenomena altogether. Much more 

 might be said on the subject, bul 

 we must pass on. 



It is convenient for some purposes 

 to experiment in a different way. 

 We have hero two similar glass 

 globes containing rarefied nitrogen. 

 I can induce an electric discharge 

 in them without electrodes by putting them 

 in this coil of wire, through which a Leyden 



1 Discourse delivered at the Royal Institution on Friday, February 28, by 

 trie Hon. R. J. Strutt, F.R.S. 



NO. 22^2, VOL. Ql] 



jar is constantly discharging. Winn 1 with- 

 draw them you see that they are brilliantly luminous, 

 and that they remain so for several minutes after 

 stimulation. Bv holding them alternately in the ex- 

 citing coil we can get them about equally bright, and 

 you see that the luminosity of each decays 

 11 about the same rate. Now I stimulate 

 them equally again, and cool one down by 

 immersing it in liquid air. It shines brightly 

 for a moment, but soon becomes quenched. 

 1 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 

 in: show vou 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 that 



portion. I must ask 



you to take it from 



me that special ex- 



periments have 



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 acceler- 



ates the action. 



Plausible objections 



may be made to this 



statement, but I 



must content myself 



now with saying 



that they admit of 



answer. 



When oxygen and 



hydrogen unite, the 



union may occur in 



two distinct ways. 



It may occur with 



luminosity throughout the volume of the mixture, as 



when the gases are exploded, or, again, it may occur 



at the surface of a solid such as clean platinum. In 



the latter case there is no luminosity. 



LIQUID 

 AIR 



Similarly, active nitrogen atoms may reunite in the 

 volume of' the gas with luminosity— this we have seen 

 alreadv— or the combination may occur without 

 luminosity at a suitable surface. Oxidised copper 



