McClelland and M'Henry — Uncharged Nuclei. 293 



Pringal (Ann. der Physik, 26, 1908) verified the effects of oxides of 

 nitrogen upon the condensation of water vapour, and examined Barkovs^'s 

 supposition that the condensation brought about by ozonized oxygen is 

 really due to traces of nitrogen in the oxygen used. The question was a 

 difficult one, owing to the task of obtaining oxygen entirely free from 

 nitrogen; bat Pringal set himself to examine the effect of successive 

 purifications of the oxygen used. Oxygen prepared electrolytically was 

 used, and after passing through the ozonizer was passed through a solution 

 of ISTaOH to remove oxides of nitrogen. The spontaneous condensation still 

 took place, and Pringal was led to believe that the ozone, even when free 

 from oxides of nitrogen, was able to oxidize the traces of nitrogen in the 

 cloud-chamber. Using a series of seven ozonizers, each fitted with a NaOH 

 tube, he partially exhausted the cloud-chamber, and drew the ozonized 

 oxygen, from which the last traces of nitrogen should have been removed, 

 into the cloud-chamber. He repeated this process of exhaustion and re- 

 placement by ozonized oxygen, the gas in the cloud-chamber becoming freer and 

 freer from nitrogen. The process was repeated 400 times, and the spontaneous 

 condensation gradually decreased, and finally disappeared. Still a cloud could 

 be formed with expansion, but even the condensation with expansion dis- 

 appeared gradually. The ozonized oxygen now had no effect on the condensation 

 of the water vapour, and the previously observed condensation was attributed 

 to the oxides of nitrogen. Barkow and Pringal suggest that nuclei formed in 

 moist air by ultra-violet light are similarly due to the production of oxides of 

 nitrogen, and not to hydrogen peroxide. 



In this connexion also Miss Saltmarsh examined the production of nuclei 

 in moist nitrogen. When traces of oxygen are present nuclei are readily 

 formed ; but when the residual oxygen is removed by sparking for twenty 

 minutes and absorbing the oxides of nitrogen in i^aOH, the ultra-violet 

 light produced no nuclei in the pure moist nitrogen. 



The case for hydrogen peroxide, being the parent substance, rests upon a 

 test by Bieber (Ann. der Physik, 39, 1912). He passed moist oxygen 

 exposed to ultra-violet light through a vessel at the low temperature of 

 - 79° C. The condensation products were then subjected to the following 

 tests for hydrogen peroxide : — 



(1) Potass, iodide and starch, which, in the presence of ferrous sulphate, 

 gives a blue colouration with hydrogen peroxide. 



(2) Mixture of potass, ferricyanide and ferric chloride, which gives a blue 

 colouration with HgOj. 



(3) Dilute solution of titanium dioxide in strong sulphuric acid, which 

 turns brown in the presence of HjOj, 



