This method was suggested to me by Professor Maconochie, who indeed prepared the glass on which the mice were etched.
Collodion Negatives.—Allow me to communicate a sure and simple way of darkening collodion positives for printing. It was shown to me by a friend of mine; and not having seen it in your "N. & Q.," I have undertaken to lay it before your readers, hoping that it may be found useful to many beginners.
After having developed your picture, as a positive, with protosulphate of iron and nitric acid, wash it well from the developing fluid, and keep it on one end that all the water may drop from the plate. Then take three parts of a concentrated solution of gallic acid, and one part of a nitrate of silver solution, 60 grains to the ounce of water; mix together, and pour on the plate. The picture will gradually begin to blacken; and after half an hour or more, you will obtain a sufficient density for printing a positive on paper.
Every one who will take the trouble to try it will be sure to succeed. Of all the ways to blackening a picture for printing I have tried, not excepting Professor Maconochie's method with chloride of gold and muriate of ammonia, the surest I find is the one which I have laid before you. Just try it, and you will be glad with the result.
F. M. (a Maltese.)
Malta, Valetta.
Replies to Minor Queries.
"London Labour and the London Poor" (Vol. viii., p. 527.).—I beg to inform Mr. Gantillon that the above work is discontinued. The parts entitled "Those that will work" and "Those that cannot work" have been completed, and form a valuable book; but the discontinuance of the third part is no loss at all, for in commencing upon "Those that will not work," Mr. Mayhew began with a history of prostitution in ancient and modern times, a subject which did not possess the novelty or originality of his other divisions, and consequently his readers fell off so fast that he was forced first to raise the price of, and afterwards to discontinue altogether, the publication. Probably, if he had confined himself to treating the London prostitutes as he did the costermongers, the work would have been completed, and would then have formed a complete encyclopædia of London Labour and the London Poor.
Arthur C. Wilson.