488 MM. C. Lea—Identity of the Photosalts of Silver, ete. 
expose it to light uuder a screen such as a piece of opaque stiff 
pasteboard with openings cut in it: then apply potassio-ferrous 
oxalate, we shall obtain a very remarkable eftect: all the parts 
exposed to light take a reversed development and appear as 
lighter spaces on a dark ground. And this goes so far that we 
may expose till we get a visible and quite strong image, darker 
than the ground and yet in development this darker portion 
will come out lighter than the ground. Indeed I have one 
specimen which shows almost white figures on an intensely 
black ground. Before development these light figures were 
brown, “by exposure to light, on a rose-purple ground., I have 
seen few more curious results than this. 
From the foregoing it follows that red bromide, notwith- 
standing its intense coloration is in the same condition respect- 
ing light as normal silver bromide that has received an impres- 
sion of light so strong that any further influence of light would 
cause reverse action, only that a vastly larger proportion of its 
molecules are affected. In the case of the latent image formed 
by light on normal bromide it would seem that the particles 
affected, although numerous enough to serve as a basis of 
development are still too few and too scattered to be visible or . 
affect the color. The photobromide on the contrary has its 
mass made up of them. ‘Then if exposed to light, the hght 
carries them a stage farther—brings them to the reverse or 
‘“solarized” condition and the parts affected by light develop 
less strongly than those not exposed. 
So light can act the part of hypophosphite and hypophos- 
phite that of light, interchangeably ; each can produce a direct 
action, each a reverse and each can reverse the other. 
It then appears that in all the numerous ways in which it is 
possible to compare the photosalts with the material of the 
latent image they are found to be identical. The proofs based 
on development generally, and especially on the reversal of the 
latent image seem very strong and these receive additional sup- 
port from the exact identity of reactions shown by the photo- 
salts and by the material of the latent image. 
The question of the identity of the photosalts with the pro- 
ducts of light on the silver haloids might perhaps be left with 
some confidence to the cumulative proofs here offered. But I 
hope to be prepared to give in the next number of this Journal 
additional evidence from a new direction. | 
Philadelphia, March 21, 1887. 
