Nitrate of potash 10 grs.
Acetic acid ½ drm.
Nitric acid 2 drops.
In this mixture nitrate of potash is employed to convert the sulphate of iron into nitrate in place of nitrate of baryta in Dr. Diamond's formula, or nitrate of lead as recommended by Mr. Sisson; the advantage being that no filtering is required, as the sulphate of potash (produced by the double decomposition) is soluble in water, and does not interfere with the developing qualities of the solution.
"The above gives the bright deposit of silver so much admired in Dr. Diamond's pictures, and will be found to answer equally well either for positives or negatives. If the nitric acid be omitted, we obtain the effects of protonitrate of iron prepared in the usual way.—John Spiller."
(From the Photographic Journal.)
Photographs in natural Colours.—As "N. & Q." numbers among its correspondents many residents in the United States, I hope you will permit me to inquire through its columns whether there is really any foundation for the very startling announcement, in Professor Hunt's Photography, of Mr. Hill of New York having "obtained more than fifty pictures from nature in all the beauty of native coloration," or whether the statement is, as I conclude Professor Hunt is inclined to believe, one of those hoaxes in which many of our transatlantic friends take so much delight.
Matter-of-Fact.
Photographs by artificial Lights.—May I ask for references to any manuals of photography, or papers in scientific journals, in which are recorded any experiments that have been made with the view of obtaining photographs by means of artificial lights? This is, I have no doubt, a subject of interest to many who, like myself, are busily occupied during the day, and have only their evenings for scientific pursuits: while it is obvious, that if such a process can be successfully practised, there are many objects—such as prints, coins, seals, objects of natural history and antiquity—which might well be copied by it, even though artificial light should prove far slower in its action than solar light.
A Clerk.