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272 THS PHOTOGRAPHIC NEWS. [June 5, 1868. SOLAR PRINTING ON CANVAS. nitrate of silver to each drachm 4 drachms a of of 1 ounce 1} ounces 20 grains applying the non-coagulated coating, allowing it to dry, then flowing the silver solution over the coating; but this method is not so economical or convenient as the process first described. The method of preparing the ammonio-nitrate of silver Ammonia sufficient quantity. " Dissolve the silver in the water ; remove a small por tion, say 1 drachm. To the larger portion add carefully sufficient ammonia to precipitate the silver and re-dissolve the precipitate, guarding against any excess of ammonia. Then add the remaining drachm of the silver solution to in sure a decided excess of silver. Lastly, add the two drachms of nitric acid, and the solution is ready for use at any time. “ After the printing process has been carried as far as may be desired, it remains only to fix the impression, which may be done in the usual way, namely, the rinsing away of the free nitrate of silver, and then pouring over the picture a solution of hyposulphite of soda for a few minutes, after wards removing the hyposulphite of soda by washing the print under a gentle stream.” diately coagulate the albumen ; take the pestle and triturate the coagulum until it becomes smooth and pulpy. It is then ready for use. Now take a flat camel’s-hair brush about two inches wide, and paint evenly over the canvas or other material with this combination, and it is ready for use when dry ; or, if it is desired to print with the solar camera, it is quite as good wet. If a very intense print is required, the coating may, when dry, be subjected to the vapour of ammonia, which will still add to the sensitiveness of the coating. “ This combination is very sensitive to light, and hence due caution must be observed in regard to it, so as not to injure the whites of the picture. It has also the quality of taking very kindly to all kinds of surfaces, oily or not, and may be therefore very easily laid quite free from bubbles or other defects. I have had quite as good results by first “ Dissolve the salt in the albumen, then grind fine on painter's slab the zme-white in a portion of the albumen, then add the remainder, and mix it uniformly; place the pigment mixture in a Wedgwood mortar, and proceed to the dark-room; then add the silver solution, which will imme- 1 ounce 1 „ 2 drachms ceeds as follows :—“ Take of— Pure zinc-white Albumen of fresh eggs Salt, or chloride of ammonium Solution of ammonio-nitrate silver, containing 30 grains rules will not supply him with imagination sufficient to enable him to perpetually invent new arrangements, he will find they aid him very materially in giving expression to his inventions, and will prevent him being extravagant or exaggerated in his arrangements of the form. He should also store his mind with incidents suitable to his sitters, and he may then, perhaps, be able to give less occupation to the eternal book we see in the hands of photographees almost as often as a roll of paper is represented in the statues of statemen. Remarks on the treatment of the single figure should also contain something on the subject of vignettes, a style of portrait usually confined to the head and shoulders, a kind of picture so simple as apparently to require very little con sideration, but I have seen them done so- badly that a few words may be of service. A vignette head should never convey the impression that the sitter was lounging in a chair or leaning on a table ; the reason being, that as the chair or table is not visible, the figure would appear out of shape and deformed. As a general rule, the shoulders should appear level, as though the subject was standing. A little variation between the direc tion of the head and shoulders will always give variety and animation. The lighting should be more delicate than that suitable for other portraits, and the background should always be light. If the white margin to the vignette be very slightly tinted in the light after printing, the delicate effect will be increased ; but, when this is attempted, it is usually overdone, and then the effect becomes heady, and worse than if the white paper had been left pure. In conclusion, make it a constant practice, before removing the cap from the lens, to first give a rapid glance at the sitter to see whether the outline of the figure composes well, that the light and shade is massive and round, and that there appears some indication of the expression you desire on the face of the sitter. If there is a lack of either of these qualities, do not waste your plate until you have got them before your lens. solution is as follows -Take of— Nitrate of silver ... Water Pure nitric acid Ma. Isaac Rehn, of Philadelphia, has recently secured a patent for a process for coating or sensitizing the surface of canvas for printing enlargements upon, by means of the solar camera, by the use of which he claims to get perfect results easily, and without injury to the canvas. He pro ON A NEW AND SIMPLE METHOD OF RECOVER ING METALLIC GOLD AND SILVER FROM RESIDUES. BY VICTOR U. BLOEDE, CHEMIST* Mercury has the property of rapidly combining with, or dissolving, as it were, metallic gold and silver, and, in fact, most other metals, forming with them a liquid or pasty mass (according to the amount of foreign metal) which is techni cally termed an amalgam or ‘‘butter." A few drops of mercury poured upon a gold dollar or silver five-cent, piece very quickly dissolves either. When the mercury has taken up a considerable amount of the precious metal from the powdered ore, it is drawn off into bags or large pieces of fine tough buckskin, and then subjected to pressure either between the hands or under a screw. The pure mercury, owing to its extreme permeability, rapidly oozes through the fine pores of the leather, finally leaving in the bag a compact, brittle mass consisting of the precious metals, with a per centage of mercury in combination. To obtain from this crude mass the gold or silver in its pure reguline state the amalgam is placed upon an iron vessel, or, better yet, in an iron retort, and subjected to a low red heat on an ordinary coal fire. The mercury, owing to its extreme volatility, very rapidly evaporates, arid, in the course of a few minutes, leaves the precious metals in a state of purity. If the process is carefully managed, as we shall presently describe, there is, however, no danger to be apprehended. To Reduce Old Baths and Nitrate of Silver Solutions. Filter the solution of silver proposed to be operated upon until it is clear, and place the filtiate into a clean white bottle of suitable capacity. To each pint of the liquid add 4 ounces or more of mercury, and allow the mixture to remain at perfect rest for a few days. In a very few hours a beautiful sparkling coruscation will be found forming upon the surface of the mercury. This shining deposit consists of perfectly pure metallic silver, and has been called Arlor Diana, or “ tree of life.” It is formed upon the surface of the mercury by what is known in chemistry as double elective affinity, and for each atom of the silver so deposited, a corresponding amount of mercury is acted upon by the nitric acid of the silver, and passes into solution as nitrate of mercury. The deposition continues until all the silver has been thrown down, when we find over it a strong solu tion of the nitrate of mercury, which may be obtained in the * Condensed from The Philadelphia Photographer.
