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426 THE PHOTOGRAPHIC NEWS [JUIY 6, 1883. Patent Jntelligence. Patents Granted in Sweden. 353. G. MEISENBACE, for " Photographic printing-plates, &c.”— Dated 3rd October, 1882. 412. L. H. Philippi, for “Apparatus for obtaining photographs on metal.”—Dated 28th November, 1882. Patents Granted in Austria-Hungary. G. Meisenbach, of Munich, for ‘ 1 Photographic plaques for relievo and intaglio negatives, &c.”—Dated 9th February, 1883. Patents Granted in Germany. 23,138. T. KoTTERITZSCH, of Pappendorf, near Hainichen, for “ Continuous regeneration of photographic oxalate developers.” Dated 17th September, 1882. Class 01. Patent Granted in United States. 278,788. Mathias FLamMaNg, of Newark, N.J., for “ A photo graphic camera.”—Application filed 26th March, 1883. No model. o- ON THE CAUSE OF THE GREAT SENSITIVENESS OF GELATINE EMULSION AS COMPARED WITH COLLODION EMULSION. BY H. W. VOGEL. Under nearly the same title as above, Mr. H. Farmer recently published a paper, and as I have worked upon the same subject during some years with definite results, and have already published details in the Photographic News about a year ago, I beg to give some remarks on Mr. Farmer’s suggestion. 1 proved by many experiments that there is a very marked difference between the silver bromide precipitated in collodion, and that precipitated in gelatine, as regards their behaviour under the solar spec trum ; the first (precipitated in collodion) has its maximum of sensitiveness in the indigo (average wave length 430), while the second (precipitated in gelatine) has its maximum in the blue (wave length 450). I pointed out, further, that the ripened and unripened silver bromide has the same spectroscopical behaviour—that is to say, the point of maximum is the same with both. Iprovedby experiments that this behaviour does not depend upon the physical character of the two vehicles. I prepared for this purpose collodio-gelatine emulsion, at first with collodion emulsion by mixing it with gelatine dissolved in glacial acetic acid, and in the second place with gelatine emulsion made with the same solvent and mixed afterwards with collodion. Here the vehicle was the same in both cases, and, in spite of that, there was the very marked above-mentioned spectroscopical difference. I have also emulsified bromide of silver precipitated in gelatine emulsion, with collodion, and have found no change in the spectroscopical behaviour. Therefore I came to the conclusion that there are two different modifications of silver bromide, called by me, after the point of spectro scopical maximum, the blue-sensitive and the indigo-sensi tive bromide of silver; and that the different qualities of silver bromide formed in gelatine and in collodion are not due to the different physical characteristics of the two vehicles, as Mr. Farmer asserts. I acknowledge that there is an influence of the vehicle, but not one which could change the general character of the different modifications. More than that, I observed that it is possible to form the two different modifications of silver bromide without the aid of any vehicle, and I stated that the blue-sensitive silver bromide is formed by precipitating silver bromide in aqueous solutions, and indigo-sensitive silver bromide is formed by precipitating it in strong alcoholic solutions. But some one may say that the spectroscopical difference between the two alleged modifications of silver bromide is not sufficient characteristically. Well, then, I beg to answer that there are other much more marked differences between the two modifications—differences which partly are already observed, and also pointed out by Mr. Farmer ; for example, that the sensitiveness of the blue-sensitive bromide of silver is very much increased by heat ; the sensitiveness of the indigo-sensitive bromide not, or, ac cording to Mr. Farmer, only a little. I will give here the other different qualities of the two kinds of bromide ot silver observed by me, and I think they are sufficient to prove that these two modifications really exist. These different qualities are— 1. The Unequal Capability of Diffusion of the tuio Bromides. —Let us suppose the case of a bromide precipitated by mixing a solution of 3 gms. of ammonium bromide iu 100 c.c. of strong alcohol, with 5 gms. of silver nitrate in 10 gms. of weak alcohol, and compare it with a silver bromide precipitated under similar conditions from aqueous solutions. In each case we obtain coarse granular masses; but on adding them to collodion on the one hand, and to' gelatine on the other hand, it will be found that the bro mide which was precipitated from alcohol refuses to thoroughly diffuse itself in the gelatinous solution ; while the silver bromide which was precipitated from water fails to diffuse itself pecfectly through collodion. 2. Unequal Reducibility of the two Bromides.—The blue sensitive bromide is reduced to the metallic state with much more difficulty than the indigo-sensitive modifica tion. If collodio-bromide plates are treated on the one hand, and gelatino-bromide plates on the other hand, with a chemical or alkaline developer, the former darkens much more rapidly than the latter. Hence it becomes possible to make use of much more powerful developers for gelatine plates than for collodion plates. That this greater reduci bility of the indigo-sensitive bromide is really due to an integral difference, and not to the greater porosity of the collodion film, is proved by the circumstance that the bromide of the collodio-gelatine emulsion is reduced with the same difficulty as the corresponding bromide in pure gelatine. Another conclusive experiment is to coat a collodio-bromide plate with gelatine, and expose it after drying; this plate is much quicker developed with the strong alkaline developer than a gelatine plate, and with out fogging, the gelatine coating increasing the sensitive ness a little ; but in general, it is far inferior to a gelatino- bromide plate. The latter develops much slower, but gives much more detail in the shadows. 3. Ihe Unlike Behaviour with Chemical and Optical Sensi tisers.—My experiments prove that the action of these agents is far more energetic in the case of the indigo sensitive bromide. 4. Behaviour of the Bromides with the Developer.—The exposed blue-sensitive silver bromide is at least twenty- five times more sensitive in relation to chemical develop ment, than in relation to physical development; while in the case of the indigo-sensitive bromide, this condition of things is so far modified that the compound is at most not more than three times as sensitive when subjected to chemical development, as when subjected to physical deve lopment. The blue-sensitive bromide and the indigo sensitive bromide are approximately equal as regards sensitiveness when the development is physical, but widely different when the development is chemical. 5. Different Behaviour when Heated.—Blue-sensitive bro mide, when prepared with an excess of alkaline bromide, is made much more sensitive when heated under water; but the indigo-sensitive bromide either increases in sensi tiveness a very little, or not at all ; or, according to Mr. Farmer, only a little. I think that these different quali ties, which are very marked, are sufficient to prove that there are two modifications of silver bromide, and that the existence of these two modifications is the cause of the different sensitiveness of the gelatine and collodion emul sions. The essential feature of the action of light is the com mencement of a reducing action, and one would from this