424 Dr. W. J. Russell. On the Action exerted by certain 



* On the Action exerted by certain Metals and other Substances 

 on a Photographic Plate." By W. J. Russell. Ph.D., 

 F.R.S., Lecturer on Chemistry at St. Bartholomew's 

 Hospital. Received May 13, — Read June 17, 1897. 



Having some years ago prepared for the purpose of spectroscopic 

 examination several uranium compounds, it was of iuterest to make 

 further use of them by repeating some of the very important experi- 

 ments which Becquerel has made with these compounds. He has 

 shown, that if the mefal or some of its salts be placed on a photo- 

 graphic plate in perfect darkness, and allowed to remain there for 

 some days, the plate becomes acted on, the action being rendered 

 evident by the ordinary photographic process of development. This 

 action is readily produced, and belongs apparently to all the salts of 

 this metal, and, as Becquerel has shown, to uranous as w r ell as uranie 

 salts. It is very remarkable that this power belongs also to the 

 salts when in solution, and, as the action passes through glass, solu- 

 tions of the double chloride or of the nitrate contained in a thin 

 glass bottle, when placed on a photographic plate, act readily upon it. 

 While speaking of these compounds it may be well to record some 

 experiments which have been made to determine whether the} 7- lost 

 their peculiar activity on being kept in the dark. 



On the 10th Augcst last, specimens of yellow oxide, recrystallised 

 nitrate, and chloride, the latter in solution, were each divided into 

 two equal portions, and all placed in similar clean thin glass bottles. 

 One sample of each was then placed in total darkness, and the other 

 -kept im the light. These samples have from time to time been tested 

 by placing them on a photographic plate for a week and then 

 developing the plate in the usual manner. Seven such examinations 

 have been made at about one month's interval. rTo very marked 

 -difference between the samples in the light and the dark has occurred ; 

 on the whole the samples preserved in the dark have proved slightly 

 the most active, and this was decidedly the case with all three 

 ■specimens at the last examination on March 26. Another experi- 

 ment was began a little later with the black oxide of uranium, which 

 appears to be one of the most active of the uranium compounds; 

 'equal weights of a sample of this body were placed in two similar 

 pill -boxes with a glass bottom; one has been kept in the dark, and 

 the other in the light; after five months there was no difference in 

 the effect which they produced on the photographic plate (Plate 2). 

 The experiments are being continued. When repeating these different 

 uranium experiments and using a card painted with the yellow oxide, 

 perforated zinc vas made use of simply as a screen to show the 



