of the double
sulphocyanide of copper, but the color disappears by washing in water.
Red coloration is due to decomposition into ferrocyanide of copper.

L. LIESEGANG'S PROCESS (1865).

Pour ammonia into a nitrate of uranium solution, wash the precipitate of
uranate of ammonia in distilled water, then dissolve in citric acid.

Mix this solution of citrate of uranium and a little of a solution of
chloride of gold with a paste prepared by dissolving tapioca in hot water.
The quantity of chloride of gold must be small and the heat not too great,
otherwise the gold would be reduced.

Spread the mixture with a sponge on the paper, which takes a brilliant
yellow color, and expose when quite dry; the proofs have the delicacy and
vigor of albumen prints.

The proofs come from the frame with a bluish-black color; they should not
be toned, but merely fixed by washing until the yellow color of the paper
has disappeared.

The color of the picture can be changed to a purple by a solution of
chloride of tin.

GUARBASSI'S PROCESS (1867).

The paper is floated in the dark for four or five minutes on a saturated
solution of bichromate of potash. When dry, it is printed a little longer
than for silver prints and afterwards floated, face upwards, on a water
bath until all the unaltered bichromate is dissolved. It is then immersed
in the following solution, which improve by use and tones the pictures to
a reddish color:

Saturated solution 4 parts
nitrate of mercury, as
free from acid as
possible
Saturated solution 1 part
bichromate of potash
Distilled water 28 parts

This solution should be prepared, filtered and allowed to stand for some
time before use. The print is left in the bath until it has assumed an
intense red color, the whites remaining perfectly pure. It is then washed
and put in another bath to obtain a brownish tint. This bath is thus
composed:

Conc. aqueous ammonia 2 parts
Distilled water 100 parts

The print must be immersed at once, and when, in a short time, it has
assumed the proper color, it should be washed immediately.

The picture is toned in a very diluted solution of chloride of gold,
1:7,000, in which the color passes from a light brown to a deep black or a
violet black tone, when it is washed in two changes of water.

A. POITEVIN'S PROCESS (1870).

"I use a paper prepared with iron sesquioxide rendered sensitive to light
by tartaric