d with perfect clear whites. To obtain the color
of silver photographs one hour's immersion is sufficient. After this
operation the proofs are washed until the water is no more tinged yellow.

By immersion in
Ferrous sulphate 100 parts
Iron sesquichloride 40 parts
Hydrochloric acid 80 parts
Water 200 to 300 parts

the proofs undergo the following gradation of colors: red, reddish violet,
blue-violet, black and greenish black. As soon as the desired color is
obtained, the proofs are washed in acidified water and dried.

The most beautiful purple violet is obtained by leaving the proofs in the
iron solution until green-black, and then washing for a moment in a dilute
solution of sub-acetate of lead.

A brown-black may be produced by treatment, after washing, with an
ammoniacal solution of hypermanganate of potash.

A weak solution of nitrate of silver also yields very fine pictures, but
the exposure should be very short, and the proofs must be fixed in water
containing a small quantity of oxalate of ammonia.

In order to impart to the proofs the gloss of silver photographs, they
should be albumenized in the ordinary manner, and the albumen
insolubilized by well known means.

The chemical actions in this process I explain in the following manner: On
the paper there are Fe2Cl3 and CuCl, the latter in excess. By the action
of light, and according to the transparency of the negative, Fe2Cl3 is
reduced to FeCl, while CuCl suffers no alteration.

If the paper be immediately placed in an _absolutely_ dry room after
exposure, the picture remains unchanged. In a moist atmosphere FeCl
attracts moisture and, with a part of CuCl, is so decomposed that Fe2Cl3
is formed together with Cu2Cl.

After this action has commenced, if the proof be not immediately immersed
in a solution of sulphocyanate of potassium, Cu2Cl passes over to a higher
combination of chlorine, and the paper is again fit to be impressed anew
by the action of light.

As long as FeCl or even Cu2Cl is present, if the print is immersed in the
sulphocyanate solution, sulphocyanate of copper is immediately formed on
the reduced parts, while on the others the sulphocyanide of copper, formed
and dissolved by the sulphocyanide of potassium in excess, becomes decom-
posed with water in soluble sulphocyanide of copper and deposited as such
on the parts already covered with the salt.

Frequently the prints appear yellow from formation