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



BAKERIAN LECTURE. Further Experiments on the Action 

 exerted by certain Metals and other Bodies on a Photo- 

 graphic Plate." By W. J. RUSSELL, Ph.D., V.P.R.S. Re- 

 ceived February 10, Read March 24, 1898. 



In a paper read before this Society in June last* it was stated 

 that certain metals, alloys, and other substances such as picture 

 copal, printing ink, straw board, &c., were able to act even at a 

 distance on a sensitive photographic plate, producing effects similar 

 in appearance and developed in the same way as plates which had 

 been acted on by ordinary light. At that time sufficient 'experi- 

 mental evidence had not been obtained to determine the nature of 

 this action, or even to clearly indicate its general character, whether 

 in fact the action arose from vapour given off by the active body, 

 or whether phosphorescence was produced which acted on the plate. 

 That bodies so slightly volatile as zinc, aluminium, nickel, &c., 

 should be able to give off at ordinary temperatures in a few days 

 sufficient vapour to act strongly on a photographic plate, and that 

 such vapour should be able to pass rapidly through media, such as 

 gelatin, celluloid, collodion, &c., seemed difficult to realise, although 

 many of the earlier experiments appeared to indicate that this was 

 the kind of action which took place. Later experiments confirm 

 the view that a vapour is given off, which is the cause of the action 

 on the plate. 



Certain organic bodies, as well as metals, have been shown to act 

 on the photographic plate, and in endeavouring to ascertain the 

 nature of this action experiments with organic bodies were first 

 undertaken, as the results which they yield are more easily and 

 rapidly obtained than those with the metals, and if their mode of 

 action was determined it would probably throw light on the action 

 exerted by the metals. In the former communication it was stated 

 that printing ink and copal varnish are active substances, both when 

 in direct contact with a photographic plate and when at a distance 

 from it. Further it was found that the action which they exerted 

 was able to pass through different media. Although printing inks 

 and copal varnishes may vary considerably in composition, the 

 main constituents are constant, hence it was easy to determine that 

 boiled oil and turpentine were the bodies to which they owed their 

 activity, and that these bodies separately behaved in the same 

 way as did printing ink and copal varnish. Boiled oil that is, 

 linseed oil which has been heated with oxide of lead is an active 

 substance, and most of the following experiments have been made 



* <Koy. Soc. Proc.,' vol. 61, p. 424. 



