31. C. Lea — Image Transference. 33 



Art. IV. — Image Transference; by M. Carey Lea, Phila- 

 delphia. 



By the term, Image Transference, I propose to denote cer- 

 tain effects produced on sensitive films, effects curious in them- 

 selves, and of interest in connection with the subjects of papers 

 which have appeared in the May and June numbers of this 

 Journal. 



In those investigations it was shown to be possible to take a 

 film of a silver haloid — chloride, bromide or iodide, and after 

 making marks upon it with sodium hypophosphite to obtain a 

 development of these marks, precisely as if they had been im- 

 pressed by light, but quite independently of any exposure to 

 light. I now propose to show that it is possible to develop 

 on a film of silver haloid a complete image — a print from a 

 negative for example, without either exposing the silver haloid 

 to light, or to the action of hypophosphite, or subjecting it to 

 any treatment whatever, between the moment of its formation 

 and that of its development. The film of silver haloid comes 

 into existence with the image already impressed upon it. 



For this purpose almost any silver salt is selected ; citrate, 

 benzoate, tartrate, pyrophosphate, etc., answer perfectly. (Some 

 silver salts, the phosphate especially, undergo a slight reduction 

 spontaneously in the dark ; these are less suitable.) A film of 

 the silver salt selected is formed on paper by the ordinary meth- 

 ods, and this is exposed under the negative to a few seconds of 

 sunshine. 



The next step is to convert this film into one of silver chlo- 

 ride or bromide, by plunging it for a few minutes into dilute 

 acid. Ordinary hydrochloric acid may be diluted with six 

 times, commercial hydrobromic with two or three times, its bulk 

 of water; the exact strength is unimportant. After a short im- 

 mersion, the acid is to be washed out, and it only remains to 

 put the film, now consisting of silver haloid, into a ferro-oxa- 

 late developer, when the image appears at once. The chloride or 

 bromide of silver into which the salts above mentioned are rap- 

 idly converted by the halogen acid, comes into existence with 

 the image already impressed on it at the instant of its forma- 

 tion. 



So that although the substance which received the image is 

 completely broken up and destroyed, the image is not, but is 

 transferred in all its details to the new film of silver haloid. 



It is therefore evident that the action of light on all silver 

 salts that can thus transfer an image, must be similar in all its 

 essentials to the action of light on the silver haloids. An im- 

 portant conclusion follows, that all such silver salts must be 



Am. Joue. Sol— Third Series, Vol. XXXIV, No. 199.— July, 1887. 

 3 



