eristic violet metallic gold. To fix the images obtained by
the latter reactions, it suffices to wash them in a few changes of water,
and, if developed with silver, they can be toned by any of the alkaline
solutions of auric chloride used in the printing out silver process, etc.

The photographs obtained by all these processes are permanent.

DR. J.B. OBERNETTER'S PROCESS (1863).

Copper chloride 100 parts
Ferric chloride, sol. sp. 13 parts
gr. 1.5
Hydrochloric acid, conc. 12 parts
C. P.
Water 1,000 parts

Float the paper on this solution for about two minutes and hang it up to
dry. The keeping quality of the prepared paper is remarkable; it has been
kept for two years without apparent change; its sensitiveness is at least
one-third greater than that of silver albumen paper. Unless developed
within an hour or two, the vigor of the proof is much impaired; after
twenty-four hours a print can be taken over on the same.

When exposed, only a faint image is visible. It should be fixed in the
following solution:

Potassium sulphocyanate 12 parts
Sulphuric acid, conc. 1 part
Sensitizing solution 10 to 12 parts
Water 1,000 parts

A print is floated on this solution, face downward, for three or four
minutes, taking care to agitate the liquid as little as possible; the
print is afterwards immersed and another one floated in its place, thus
proceeding until all the prints are immersed or the solution can hold no
more. A fresh solution is then added to strengthen it: the older the
solution the more rapidly and better it works. In this developer copper
cyanide is precipitated on the parts acted on by light, and this exactly
in the proportion to the luminous action. The time of immersion depends
on the method selected to finish the proofs; it its from five minutes to
half an hour. If the proof is immersed for, say, twenty-four hours, the
image comes out in a relief which may bring the shadows to two lines in
depth. When well developed and thoroughly washed, the proof can be dried
and the subsequent operations made at any convenient time.

Various processes may be employed to give to these proofs the tone
required; thus: the prints well washed are placed in a solution of
ferricyanate of potassium at 6 to 12 per 100 of water, where they take a
red color increasing in intensity. If left over night the color becomes a
splendid velvet deep re