Radium rays on Mercurous Salts. 261 



To test this some mercurous sulphate was covered, both in 

 a watch-glass and in a sealed tube, with sulphuric acid and the 

 darkening occurred. Some was also covered with dilute nitric 

 acid when again the darkening was observed. These results do 

 not seem consistent with the view that free mercury, or an oxide, 

 or a sulphide is set free. 



The salt was exposed in a vacuum tube to a stream of cathode 

 rays, and in another experiment to the blue discharge in a slightly 

 exhausted tube. In both cases a darkening was rapidly produced. 



Exposure to Rontgen rays had no effect, but I now think that 

 the X-ray tube which was used at that time was one which did 

 not give out a sufficiently powerful stream of rays, nor was the 

 experiment continued long enough. 



Becquerel rays from uranium nitrate gave no result, but 

 recently I have found that the rays from 10 milligrammes of 

 radium bromide, mounted as usual under mica, produce a visible 

 result in 24 hours, whilst in 3 or 4 days they produce a very 

 marked darkening. The mercurous salt phosphoresces very slightly 

 in the presence of the rays. Mercurous bromide also phosphoresces, 

 but the darkening was not visible in the time given for the 

 exposure. This salt however is much less sensitive to light. 



What the chemical action is, is a difficult point to settle as the 

 coloration is limited to such a small mass. The facts seem to 

 prevent an acceptance of the simple view of the separation of 

 mercury with the formation of a mercuric salt. Two views seem 

 still possible (a) that a dark sub-salt is formed or (b) that a 

 polymeric modification is produced. 



In regard to the first view we may compare with this action 

 that of radium rays on sodium chloride which M. and Mme Curie 1 

 have shewn is coloured blue just as it is with cathode rays or by 

 the vapour of sodium. This has been interpreted by supposing the 

 formation of a coloured sub-salt. In accordance with this view 

 we should postulate the formation of a mercury sub-sulphate. 



With regard to the second view the polymerising action of the 

 radium rays has been observed in the case of the production of 

 ozone from oxygen 2 and of red phosphorus 3 from the yellow modi- 

 fication. 



One of these views probably explains this action on mercurous 

 salts. The action, however, is so small that its effect on the 

 electromotive force of Clark cells cannot be large even if it is 

 extensive enough for detection. 



1 Soc. Franc. Phys. Bull., 142, p. 6, 1900. 



2 Demareay, C. R., 129, p. 823, 1899. 



3 Becquerel, G. R., 133, p. 709, 1901. 



