Volltext Seite (XML)
378 THE PHOTOGRAPHIC NEWS. [JUNE 12, 1885. Claim.—1. The combination, with a camera for rapid or in stantaneous photographing, of an attached sighting-tube arranged outside of or to one side of the instrument, provided with cross hairs or strips, dividing the field within it, and adjustable rela tively to the camera to properly place the object on the sensitive plate of the camera as it appears in corresponding position on the field within said tube, substantially as specified. 2. The finder or side tubular attachment, C, constructed with vertical and horizontal cross hairs or strips, d d, at or near its one end, and diagonal cross hairs or strips, d'd', at or near its oppo site end, for use in connection with a camera adapted to produce rapid or instantaneous photographing, essentially as described. 3. Th: ground glass G of the camera, having vertical, hori zontal, and diagonal pencil or other marks, d* d 3 , upon it, in combination with the tube C, adjustably connected with the camera on its outside, and provided at or near its one end with vertical and horizontal cross hairs or strips, d d, and at or near its other end with diagonal cross hairs or strips d'd', substantially as and for the purposes herein set forth. 4. In combination with the camera, the tube C, with its verti cal, horizontal, and diagonal cross hairs or strips d d', arranged as described, and the adjusting slotted bars D D' and E E', essentially as and for the purpose described. 318,908. Alvin P. Johnson, Boston, Mass. “Photograph album.”—Filed June 13th, 1884. (No model.) Claim.—1. A photographic album leaf composed of a picture supporting leaf provided with two narrow bands of tough paper or cloth secured thereto by their ends only, and adapted to im pinge upon two opposite ends of the photograph to hold the same in position, and a duplex matting in the form of an enve lope to receive said picture-supporting leaf, provided with suit able openings through which to view the pictures, and adapted to be applied thereto or removed therefrom. 2. The combination of a picture-supporting leaf provided with bands, and having its upper and lower edges made slightly con verging, and the mats secured to filling pieces arranged to form a chamber to receive the leaf and fit its taper edges, substantially as described. 3. The combination of the leaf hinged to the strip, and having its upper and lower edges made slightly converging, and the mats secured to the filling pieces arranged to form a chamber to re ceive the leaf and fit its tapered edges, substantially as described. THE PHOTOGRAPHIC IMAGE. BY CAPTAIN ABNEY, R.E., P.B.S.* When white light is allowed to act on chloride of silver for a sufficient time to blacken it, I think every one will agree that, at all events in the presence of moisture, or moist air (as is all air unless chemically purified), chlorine is given off. I think, also, it will be allowed that when bromide of silver is acted upon similarly, bromine is given off; a gelatine plate when darkened absolutely smells of bromine, or some compound analogous to it. Further, experiment has shown that the rays which are chemi cally active are confined to that region of the spectrum which the silver salt absorbs. Let us take chloride of silver as the ex ample on which to found an argument, for any reasoning which may apply to the one will equally apply to the other haloid salts of silver. I suppose I shall not be going beyond general belief, or, at all events, beyond the belief held by those to whom I care to address myself, that homogenous matter is made up of • Bead before the Photographic Society of Great Britain. molecules, all having a similar composition, and that such molecules are themselves made up of atoms. In the case of bromide of silver, for instance, the atoms are bromine and silver. Now we are told in most text-books that silver is a monad, an 1 that it requires only one atom of silver to combine with one atom of bromine, or rather, perhaps, that it requires only one atom of bromine to combine with one atom of silver ; confining myself, however, to pure chemistry, without any reference to photographic action, the evidence of this is based on the behaviour of silver when combined with certain other elements. The opinion, however, that silver is a monad, is not allowed by some chemists of the highest repute. However, we will, for the purpose of argument, take it that the old idea is correct, and that Ag requires one atom of the halogens to combine with it. The first question we have to ask is, does such a body as a sub-chloride or sub-bromide exist ? Now we will not go into photographic evidence, but confine our selves to chemical evidence simply. In 1839, the year when Daguerreotype was discovered, Wohler found that when hydro gen was passed over argentic-oxalite, mellitate, or citrate, when- heated to the boiling point of water, half the acid was set free, and a dark brown argentous salt remained. The acid can be re moved by washing, only a small portion of the argentous salt being removed, the solution of the latter forming a port-wine coloured liquid. Further, Wohler obtained argentous oxide (Ag,0) by means of repeatedly boiling soda-ley with argentic arsenite. Argentous oxide is, of course, the base of argentous citrate, oxalate, or mellitate. Again, Geuther found that argentous oxide is formed by precipitating silver nitrate with cuprous hydrate. Again, argentous oxide is produced by the action of hydrogen peroxide on metallic silver. A bright silver plate immersed in a neutral solution of hydrogen dioxide becomes covered with bubbles of oxygen, and coated with a greyish white film, while part of the silver is converted into hydrated argentous oxide, according to the equation 2Ag,+ H,0,=2HAg.0. Argentous salts are also produced by passing hydrogen into ammoniacal solutions of silver salts. Such is an outline of the chemical evidence of the existence of argentous oxide, and it would appear that such evidence is very strong ; in fact, as strong as required under any circumstances. That this is not the work of only one chemist, adds more weight to the existence of such a compound. Such being granted, the admission of the possibility of the existence of sub-chloride or sub-bromide of silver is at once apparent. Wohler describes a method by adding to the argen tous oxide a solution of hydrochloric acid, or by common salt. In this case we have .— Ag,0+21 ICL=2 Ag.C1+H,0 and Ag 1 O4-2NaCl=2Ag»Cl-|-Na J O. Argentous chloride is also formed by bringing silver in contact with a solation of sal-ammoniac, and the first action of ferric chloride or cupric chloride is the same. Argentous bromide or sub-bromide can be formed in the same way. By chemical analogy, if there is such a substance as sub-oxide or argentous oxide, there is the same reason for believing in the existence of the sub-chloride and sub-bromide. Now comes the question as to whether the same compound is produced by the action of light. When silver chloride is exposed to the action of light, we know well that a violet-coloured substance is produced, and that such a coloration is also found when exposure takes place in the presence of nitric acid. We also know that metallic silver dis solves in dilute nitric acid. Now since chlorine is evolved, one of two things must occur—either the total liberation of the chlorine from the silver salt, or else its partial liberation. Which does it do ? Under any ordinary circumstances it would be said that it was not metallic silver which was left, since it was unacted upon by nitric acid. Some years ago, Guthrie experi mented on this subject, and he put it down that metallic silver was formed, but that it was in a passive state, similar to that state which iron can take. The connection between the two is not very apparent, considering the manner in which iron loses that state. I would further mention that Thorpe found that whilst nitric acid dissolved about 2 parts per 100,090 of white silver chloride, that when darkened by light only 8 per 100,000 was dissolved. Now we have another exceedingly interesting proof that the salt formed by light and the argentous chloride are the same. If a collodion film containing silver chloride be exposed to light till it is lavender, and be exposed