796 Prof. A. LI. Hughes on Dissociation of 



Discission. 



Strutt * found that nitrogen from a discharge-tube had 

 active properties, and concluded that it was atomic nitrogen 

 rather than a more complex type of molecule. He mentions 

 that no reduction in pressure was observed when the dis- 

 charge-tube was immersed in liquid air during the passage 

 of the current. Wendt and Grubb f have shown that N 3 

 exists in a stream of nitrogen drawn through a discharge- 

 tube. (As in Wendt's experiments on hydrogen, the gas 

 was at a higher pressure than in these experiments, a con- 

 dition which favours collisions of atomic nitrogen with 

 molecular nitrogen to form N 3 .) No temperature dissocia- 

 tion of nitrogen such as Langmuir found for hydrogen has 

 been observed. Hence we have nothing to give us an idea 

 of how much the clean-up method underestimates that amount 

 of dissociation of nitrogen (should this be the explanation 

 for the clean up). 



The strongest evidence for the view that nitrogen is 

 dissociated in these experiments is that, the " non-recon- 

 densible" effect was obtained. Thus, after a thorough 

 outgassing, the ratio of the non-recondensible gas to the 

 amount cleaned up was 16 per cent. ; after admitting more 

 nitrogen without outgassing, and repeating, the ratio rose 

 to 31 per cent. ; and on repeating the procedure for a third 

 time the ratio amounted to 67 per cent. Less nitrogen was 

 recovered as a rule than in the corresponding experiments 

 on hydrogen. In one experiment, with both the tubes 

 surrounded by liquid air during the clean up, 25 cu. mm. 

 (referred to atmos. press, and temp.) were "lost" after a 

 considerable clean up, on warming up to room temperature. 

 On warming the tubes to 180° C. for 20 minutes, 7*1 cu. mm. 

 were recovered (nearly all of which came off in the first five 

 minutes). On warming to 265° C. for 20 minutes, 2*9 cu. mm. 

 came off, and on further \\ arming for 20 minutes to 390° C, 

 6*1 cu. mm. came off. In both the latter cases, as in the 

 first, the evolution was about complete in the first five 

 minutes. Thus, in all, 17*1 cu. mm. were recovered, out of 

 the 25 cu. mm. which had disappeared. These results show 

 that the nitrogen disappearing during a clean up clings 

 rather tenaciously to the walls of the apparatus even at 

 fairly high temperatures. 



Attention is called to the large values of "6" for runs 

 S and T, where there was no liquid air around the experi- 

 mental tube to accelerate the clean up, as was thought 



* Strutt, Proc. Roy. Soc. lxxxv. p. 219 (1911). 

 t Wendt and Grubb, Science, iii. p. 159 (1920), 



