1902.] Electrical Conduction in Gases, and Luminosity. 107 



apply the far more delicate electroscopic test to such substances under 

 various conditions. It so happens that the property referred to was 

 first noticed in the case of saccharin in my laboratory (in 1895) by 

 Mr. Win. Jackson Pope,'* and in March last I applied to this gentleman 

 for a specimen of the substance he had prepared in 1895. He was able 

 to send me crystals, but informed me that those he had tested were 

 inactive. We found this to be true of the remainder, seventeen out 

 of thirty-six crystals being inactive, at most a very feeble glow being 

 observed on crushing the others ; but active crystals were obtained on 

 rec'rystallising the inactive material from acetone. Old specimens of 

 sugar crystals appear to be as active as new ones. — Note, added 

 May 2.] 



A class of effects attendant on radio-activity, and which have an 

 important bearing on the question previously considered, are those 

 attributed to emanations from radio-active substances. Sir Wm. 

 Crookes has brought the subject prominently under notice in his recent 

 communication. The behaviour of such emanations is strikingly 

 similar to that of ordinary gross matter ; indeed, it is difficult to 

 resist the conclusion that such is their character, and that they are but 

 secondary products engendered by radio-activity. 



[Professor Eutherford's recent observations on the " emanation " 

 from thorium compounds are very difficult to interpret. The assump- 

 tion that Mr. Soddy and he are inclined to make,t that the emanation 

 is allied in properties to the elements of the argon group is almost a 

 contradiction in terms. Such a constituent presumably would be an 

 inert substance, and if not removed by the drastic treatment to which 

 they submitted their material without permanently affecting its radia- 

 tive power, it would scarcely then escape spontaneously on mere 

 exposure of the solid. It would seem to be far more probable that the 

 " emanation " is a secondary manifestation, in some way conditioned 

 by the " straight-line radiation." 



There is a feature in Dr. Russell's experiments which has always 

 struck me as remarkable, assuming that the photographic effects he 

 has obtained are clue to hydrogen peroxide, viz., the absolute sharp- 

 ness of the images formed by a scratched zinc plate even when this is 

 placed at a relatively considerable distance above the sensitive film. 

 If the emanation passed by mere diffusion from the active surface, a 

 more or less blurred image might be expected to form. It would 



almost seem that the molecules are projected in straight lines in 



other words, that they may be electrically charged. If so, a distinc- 

 tion should perhaps be drawn between a merely vaporised substance 

 and a " nascent " substance. — Note, added May 2.] 



The production of hydrogen peroxide under such an influence at 



* ' Cliern. > oc. Trans.,' 1895, p. 9S5. 

 f ' Chem. Soc. Trans.,' 1902, p. 321. . 



