482 MM. C. Lea—Ldentity of the Photosalts of Silver 
a few minutes with dilute nitric acid, to a beautiful copper 
shade. 
Silver acetate was singularly little affected by sunlight, it 
looked blackish, but on cleser inspection was found to be very 
little altered. By the same treatment as above it yielded a pale 
pink photochloride. 
So fa as examined, all silver salts thus treated yielded pink 
or red photochloride. 
These facts may serve to show the identity of the photochlo- 
ride with the principal product of the continued action of light 
on silver chloride and on other salts of silver, subsequently con- 
verted into chloride. J should wish, however, to use this word 
identity in asomewhat limited sense. When the photochlorides 
are formed by different methods without the aid of light hardly 
any two forms can be considered absolutely identical: they 
differ in color and in proportion of subchloride, as already often 
mentioned, but they also differ in other respects, especially in 
resistance to reagents. Some forms are far more easily de- 
stroyed by nitric acid: those obtained by the action of sodium 
hypophosphite (as presently to be described) are amongst the 
most easily destroyed by nitric acid. There is variation, too, 
in the degree of their resistance to ainmonia. 
Very similar differences are found in the stability of the pho- 
tochlorides obtained by the action of light: some are much 
more readily attacked by nitric acid than others. The product 
obtained by the action of light on silver chloride resists ammo- 
nia more strongly than that obtained by the action of HC! on 
exposed silver oxalate. This last is quickly attacked. Gener- 
ally,.I think the dark colored forms are the most stable. 
Ata future time it may perhaps be possible to distinguish 
more exactly between these varieties. 
I next pass to the consideration of the identity existing be- 
tween the photosalts and the material of the latent image. 
Before entering, however, on that matter, it is necessary to 
describe a reaction leading to the formation of these photosalts, 
somewhat differing from the reactions already mentioned, and 
which has important bearing on the subject. 
The remarkable action which an alkaline hypophosphite ex- 
erts on salts of copper was described many years ago by M. 
Wurtz. Its action on silver salts, though there is no parallel- 
ism between the two, has enabled me to find a key to some 
of the great difficulties of the latent image. 
A dilute solution of sodium hypophosphite if poured over a 
mass of chloride, bromide or iodide of silver formed in the 
absence of light, produces no visible effect, but has the property 
of bringing those substances into the condition in which they 
