Under this title a process has been brought forward by Mr. Hunt. It
consists of the application of a solution of succinic acid to paper,
which is subsequently washed over with nitrate of silver. The image is
then to be taken either in the camera or otherwise, as required, and is
brought out by the application of the sulphate of iron in solution.
Although this process has not come into general use, its exact
description may be interesting to the general reader, and we therefore
subjoin it.
The solution with which the paper is first washed is to be prepared as
follows: succinic acid, two drachms; common salt, five grains;
mucilage of gum arabic, half a fluid drachm; distilled water, one fluid
drachm and a half. When the paper is nearly dry, it is to be brushed
over with a solution of nitrate of silver, containing a drachm of the
salt, to an ounce of distilled water. It is now ready for exposure in
the camera. To bring out the dormant picture it is necessary to wash
it with a mixture of a drachm of concentrated solution of the green
sulphate of iron and two drachms and a half of mucilage of gum arabic.
Subsequently, however, it has been found that the sulphate of iron
produces upon all the salts of silver effects quite as beautiful as in
the succinate. On the iodide, bromide, acetate, and benzoate, the
effects are far more pleasing and striking. When pictures are
produced, or the dormant camera image brought out, by the agency of
sulphate of iron, it is remarkable how rapidly the effect takes place.
Engravings can be thus copied almost instantaneously, and camera views
obtained in one or two minutes on almost any preparation of silver.
The common sulphate of copper solution has the same property.