34 31. C. Lea — Image Transference. 



capable of forming subsalts, else the image could not be trans- 

 ferred. In the case of most silver salts the existence of such 

 subsalts has not before been recognized or even suspected ; in- 

 deed, if I am not mistaken, the existence or such a subsalt of 

 silver phosphate has been expressly denied. But the image 

 formed by light on silver phosphate can be transferred, there- 

 fore subphosphate must exist. 



These results have also a very direct bearing on the subject 

 of one of my papers in the last number of this Journal. 

 I there endeavored to show that the photo-salts of silver 

 as obtained by purely chemical means are identical with the pro- 

 ducts, of the action of light on the silver haloids, both with 

 the material of the latent image, and with the visible product 

 of the continued action of light, or rather with the most char- 

 acteristic constituent of that product. As respects this latter 

 identity, I showed that although the brightly colored photo- 

 chloride could not be obtained by the direct action of light on 

 silver chloride, it could readily be formed indirectly by acting 

 with light on other salts of silver, and treating the product with 

 HOI. 



It might be argued that in this proof one link was wanting, 

 viz: proof that the photo-chloride obtained by the action of 

 HC1 on silver salts, other than chloride, exposed to light, was 

 of the same nature as that obtained by the action of light di- 

 ectly on silver chloride. The results above described supply 

 that link, if it was needed, and show that the photo-chloride ob- 

 tained by the action of HC1 on silver salts, other than the 

 chloride, exposed to light, has the same capacity for develop- 

 ment as has the material of the latent image obtained on or- 

 dinary silver chloride. 



But this proof itself may be thought liable to an objection. 

 It may be said that as an image was certainly impressed upon 

 the original film, it is not completely proved that the halogen 

 acid had anything to do with the ultimate production of a de- 

 veloped image. The objection would not be well taken, and 

 the experiment may be varied to two ways, either of which 

 eliminates it. 



Most silver salts are soluble in nitric acid. After applying 

 the halogen acid, it may be washed off, and the paper may be 

 placed in nitric acid until every trace of the original salt (sup- 

 posing that any escaped the action of the HC1 or HBr) is re- 

 moved, and until it is absolutely certain that nothing is left in 

 the film but the silver haloid. When this is done, the devel- 

 opment, so far from being impeded, is rendered only the stronger 

 and brighter. Certainly therefore the silver haloid is the essen- 

 tial base of the development. 



