" Prepare the following solution :—
" Take nitrate of silver 2 1/2 drachms ; acetic-acid 4 1/2 drachms ; distilled water 3 1/2 ounces : mix and dissolve.
" Now take four of the glasses of the paper-holders perfectly clean, and place each upon a piece of common blotting-paper to absorb any little excess of liquid. Pour about 1 1/2 drachms, or rather more of the solution just prepared, into a small glass funnel, into which a filter of white bibulous paper has been placed, and let the solution filter drop by drop upon glass No. 1, until about 1 1/2 drachms have been filtered in detached drops, regularly placed upon its surface : then, with a slip of paper, cause the liquid to be diffused over the whole surface of the glass. Take a piece of prepared paper, and place it marked, side downwards, upon a glass just prepared, beginning at the end nearest you, and thus chasing out the air. Draw it up once or twice by its two diagonal corners ; allow it to rest, and prepare glass No. 2 in a similar manner. Now look at glass No. 1, and it will be perceived that the violet tint of the paper has become mottled with patches of white, which gradually spread, and in a few seconds the paper resumes its original whiteness, which is an indication that it is ready for the camera. It will be found to adhere firmly to the glass. Do not remove it ; but hold the glass up to allow the excess of fluid to run off at one corner. It must not be touched with blotting-paper, but replaced flat on the table. Serve Nos. 2, 3, and 4, in like manner. Take four pieces of common white paper, not too much sized, free from iron spots, and cut a trifle smaller than the prepared sheet; soak them in distilled water; draw out one piece, hold it up by the fingers to drain off superfluous moisture, and place it gently upon the back of the prepared paper. With another piece of glass kept for the purpose, having the edge rounded, and large enough to act uniformly upon the paper, scrape off gently the excess of liquid, beginning at the top of the sheet, and removing with the rounded edge of the scraper the liquid to one of the corners. Repeat this operation twice. Both the excited and superimposed paper are thus fixed to the glass. - Two glasses and papers being thus prepared, take the clean glass No. 5, and place upon No. 1 : press gently : the moist paper will cause it to adhere. Take up the two glasses thus affixed and place them upon glass No. 2, in such a manner that the supernumerary glass No. 5 shall be in the centre. The whole will form a compact body, and having polished the surfaces, and wiped the edges, may at once be put in the paper-holders. * * *
With a Ross's, Chevalier's, or Lerebours' single lens, three inches diameter, and half an inch diaphragm, the object to be copied, well lighted by the sun, the paper will require from four to six minutes' exposure.
Take out the three glasses, which will still firmly adhere, separate them gently, and remove the piece of moistened paper, which must not be used again. Now lift up the prepared paper by one corner to the extent of half the glass, and pour into the centre about one drachm of a saturated solution of gallic acid, which will immediately diffuse itself. Raise also the other corner to facilitate its extension ; and serve the others in like manner. The image takes generally from ten to twenty minutes to develope. Hold up the glass to a candle to watch its intensity. When sufficiently developed remove the negative from the glass. Wash it in two or three waters for a few hours, dry with blotting-paper, and immerse each separately for ten minutes in a bath of bromide of potassium in solution : then wash and dry.
" The iodide may be removed by means of hyposulphite of soda in the usual way, twelve months afterwards, or when convenient. If," says Mr. Thomas, " the process has been carefully conducted, four beautiful negatives must be the result. I was ten days working incessantly at Pompeii, and scarcely ever knew what a failure was".
Mr. Muller, a gentleman who has been practising photography with great success at Patna, in the East Indies, has communi-cated his process to me, which is as follows:—
A solution of hydriodate of iron is made in the proportions of 8 or 10 grains of iodide of iron to 1 ounce of water; this solution is prepared in the ordinary way, with iodine, iron turnings, and water. The ordinary paper employed in photography is washed on one side with a solution of nitrate of lead (15 grains of the salt to 1 ounce of water); when dry, this paper is iodized either by immersing it completely in the solution of the hydrio-date of iron, or by floating the leaded surface on the solution. It is removed after a minute or two, and lightly dried with blotting-paper. The paper now contains iodide of lead and proto-nitrate of iron : while still moist it is rendered sensitive by a solution of nitrate of silver (100 grains to the ounce of water) and placed in the camera. After the ordinary exposure it may be removed to a dark room; if the image is not already developed, it will be found speedily to appear in great sharpness without any further application. It may then be fixed with the hyposulphite of soda in the usual manner.
In December 1852 Sir John Herschel communicated to the pages of the Athenœum a letter from his brother-in-law, Mr. Stewart, a resident at Pau, in the Pyrenees. In this he states, that, at the suggestion of Professor Pegnault, he was induced to adopt a process of manipulation which gave some charming results, and which he thus describes:—
" The following observations are confined to negative paper processes divisible into two—the wet and the dry. The solutions 1 employ for both these processes are identical, and are as follows:—
Solution of iodide of potassium, of the strength of 5 parts of iodide to 100 of pure water.
Solution of aceto-nitrate of silver, in the following proportions: —15 parts of nitrate of silver, 20 of glacial acetic acid, 150 of distilled water.