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Ap 162 THE PHOTOGRAPHIC NEWS. veeK8, 1 nitered the already black ; I let I ion of silver, which water standing over the luna cornua, grown some of this water fall by drops in a solution was immediately precipitated into horn silver.” rd. That the degree and rapidity of reduction is influent PHOT AMMONIA NITRATE FOR ALBUMENIZED PAPERI $ v— I have noticed in the Journal some remarks regarding whal whenc are pa escone into t] See the old pidatic and ga three c effect. amoun be stat Filter; If, ii should so alke num, acidity certail the ar by ke gives i it fine dissolv frozen Smoot From these extracts it will be seen that Scheele, as early by the state of division of the particles, and by the presence i .1.1 i .. r v hi \ < agents capable of absorbing the chlorine when liberated I- as 1777, showed that the action of light upon chloride of its combination with silver/’ and C Remain lection ant for warrio: silver was to separate a black powder from it; by digesting this in ammonia, the excess of undecomposed chloride of silver was dissolved away from the black powder, which was shown to be metallic silver, by its dissolving in nitric acid, with evolution of red vapours, and formation of ordinary nitrate of silver. He also showed that when pure chloride of silver was decomposed by light, under water, chlorine was given off, which could be detected in the supernatant liquid by the usual tests. mixture I poured into a white crystal phial, exposed it to the beams of the sun, and shook it several time each day; the other half I set by in a dark place. After having exposed the one mixture during the space of two weeks, I filtered the * “ Dr. Faraday showed that the red gold precipitated from solutiopo phosphorous became violet merely by the addition of chloride of soda Notices of the meetings of the Royal Institution, June 13, 1856.—J. S f From the American Journal of Photoaraphy. One goodly above land, i Rummi majest the ga: view t( the wl visible Emaphe toups banks fear of pic-nic as man or two -and adopt. Caster lofty p Youse from ■ and trouble, is the best. Your correspondent recommends alcohol; I have been Us ether for five or six months for the same purpose, with the S These are stated to be in conformity with the previous it suits obtained by Dr. Guthrie, MM. Girard anti Davannl and generally also with those of M. Van Monkhoven, and F a certain extent opposed to the views advanced by Mess Hadow, Hardwich, Llewellyn, and Maskelyne in their joi report upon this subject, recently presented to the meetivs of the British Association. This subject appears to be one of considerable intere judging from the correspondence which has reached us. the subject; but, notwithstanding the assistance with whi we have been favoured by many correspondents, and 02 own inquiries into the matter, we are unable to find that t clear and satisfactory explanation given by Spiller, refert to in our previous article, has been de facto anticipated!! any previous writer. As a fitting sequence to the above tracts, we will quote the entire paragraph in which Spiller views are stated: — “Passing in review the results obtained in the foregoing^ periments, it will probably be considered that the weight 11 evidence tends to show that the metal is the ordinary product* the chemical action of light upon chloride of silver ; and th’ the principal difficulty which has stood in the way of accepts this conclusion has, in great measure, to bo accounted for byt often varying shades of colour presented by the reduced met and more especially the transition observed at the moment 0 removing the unaltered portion of material by the applicati, of the fixing agent. If, in these several stages, the change physical condition bo considered in its proper connection, 00 duo allowance be made for the very important influence kno" to be exercised over the light-reflecting capacity of these 2 nutoly divided particles by very slight modifications in t state of aggregation (quite irrespective of change in chew constitution), there will then bo no longer any difficulty in F ring these results, with others of the same class—e.g., the e ral varieties of gold prepared and examined by Professor E day,®—to a series, all of which are capable of similar explat' tions. [April 4,1862. “ 1st. That chloride of silver, when decomposed by light,” separated into its elements. J “ 2nd. That this change does not usually extend to the whon bulk of the material operated upon, on account of the opaci of the darkened product mechanically protecting a certain pi tion of unaltered chloride of silver from the action of the ligtt The matter since appears to have attracted little attention from philosophers until it was taken up by Robert Hunt, one of the earliest and most diligent workers on the subject of the chemical action of light, and an experimentalist, to whom photographers will always owe a debt of gratitude, for the valuable light ho has thrown upon these obscure phenomena. In the first edition of his “ Researches on Light,” published in 1844, are given his first experiments on this subject. A long series of experiments were subse quently published by him in the Philosophical Magazine, and at the meetings of the British Association. These were all collected together, and their results given at pp. 79-80 of the second edition of his “ Researches,” published in 1854. He here states that many experiments were tried in order to ascertain the condition of the chloride of silver, after it had been darkened by exposure to light, but he only gives the details of the most satisfactory. He prepared pure chloride of silver with great care, and then, after it was perfectly washed, dried it. “ Five grains of this were put into a long test-tube full of distilled water, and placed in the sunshine to darken, the powder being frequently moved, that every part might bo acted upon by the sun’s rays. It was found, oven after an exposure of a few minutes, that the water contained chloride; it became opaque on the addition of nitrate of silver, and this very gra dually increased as the chloride darkened. The darkening process was continued for several hours, after which tho solu tion was filtered to free it from chloride of silver, and nitrate of silver added to the silver solution ; this precipitated chloride of silver, which, when connected, dried, and weighed, gave 1’4 grains on one occasion, 1'0 grain on another, and 1’5 grains on a third trial.” Mr. Hunt states that " it is evident from this that chlo rine is liberated during the process of darkening.” Experiments were next tried in which the chloride of silver was formed on the surface of paper, to ascertain the effect of organic matter in modifying the action of light; the result being stated that “ we have hence very satisfactory proof that metallic silver is eventually formed on the surface of the chloridated photographic papers, and that the under sensitive surface is preserved in the condition of a subchloride of silver by the opacity of the superficial coat.” From other experiments, Mr. Hunt states that he is inclined to believe that “ the first action of the solar ray is to libe rate one half of the combined chlorine, which is very readily, moisture being present, replaced by oxygen. By the con tinued action of the exciting cause the oxide is decomposed, and metallic silver, in a state of fine division, is formed over the surface.” An experiment is subsequently given to prove that oxygen is absorbed by the decomposing chloride. It will be of interest to compare the results obtained by Spiller with the above experiments of Scheele and Hunt. In a paper published in the Philosophical Magazine for March, 1800, the first-named gentleman sums up his results in the form of three propositions: — called an ammonia-nitrate process for albumen paper. I do • think there has been any such yet, if it is possible to use 002 Some two years ago I made some albumen prints from vi3 <w negatives by a so-called ammonia-nitrate process, suggested' to your journal at that time. . dehly That process was an ammonia-nitrate solution of sixty, look/ more grains to the ounce in the ordinary manner, then maki eng n it strongly acid with nitric acid, silvering the paper in V t) 8 4 ordinary way with a fillet of cotton; and after printing, befo 1 toning, carefully removing all the acid by soaking in carbon the of soda water. Tho theory was, I believe, that the 20 10 sue] coagulated tho albumen before tho ammonia could act, t GVer, preserving the surface intact. I have one print of a view tha - North Carolina, made there in June, 1860, by that proc which will compare favourably with any we make now; b i do not think the ammonia improved the quality, for 1 thinos the hil did not play any part in tho production. I think that coagulat "1 the albumen before or rapidly at the time of silvering 18 advantage, and the means by which it can be done at least c
