with the material of the latent Photographic Image. 483 
exist in the latent image. Applied in strong solution and with 
the aid of heat, it produces brown purple photochloride, bromide 
and iodide of silver. I will here briefly describe the first of 
these compounds in order to continue the series of photo- 
chlorides, and then pass to the consideration: of the latent 
image. 
Photochloride of Silver by Sodium Hypophosphite. 
Silver chloride freshly precipitated with excess of HCl and 
well washed, placed in a flask with a strong solution of sodium 
hypophosphite and heat applied begins to darken before the 
~ boiling point is reached. Actual boiling for ten or fifteen min- 
utes gives a deep chocolate color. This product well washed 
and freed from traces of metallic silver by cautious boiling 
with very dilute nitric acid has a pink, red or brown color vary- 
ing in intensity according to the length of the action. Some- 
times a lavender shade is produced, and this is more apt to be 
the case when the silver chloride has been precipitated with ex- 
cess of silver nitrate instead of excess of HCL. 
Silver determinations of two specimens of the purified pro- 
duct were made, indicating the presence in one specimen of 
1°77 per cent of subchloride, in the other of 3°53. 
By the continued action of heat for many hours a complete 
reduction to metallic silver takes place. 
Photochloride obtained in this way has generally a brown or 
dull purple color. Boiled with nitric acid it is apt to break up 
in aS many minutes as some other forms would require hours 
for decomposition, yielding white chloride, whilst the nitric 
acid takes up small quantities of silver. 
IDENTITY OF PHOTOSALTS WITH THE MATERIAL OF THE 
LATENT IMAGE. 
It is proposed here to show : | 
1st. That in the entire absence of light, sodium hypophos- 
phite is able to affect a sensitive film of silver haloid exactly in 
the same way as does light, producing a result equivalent to a 
latent image formed by light and capable of development in the 
same way as an actual impression of light. 
2d. That these two effects, the impression produced by hypo- 
phosphite and that by light, comport themselves to reagents 
exactly the same way and seem every way identical. 
3d. That the image produced by hypophosphite on silver 
chloride always gives rise to a positive development, but on sil- 
ver bromide may give rise either to a direct or to a reverse 
image, both of these effects corresponding exactly with those of light. 
More than this, sodium hypophosphite may be made to reverse 
the image produced by light on silver bromide and conversely 
