Volltext Seite (XML)
numerals or other characters, to distinguish its several plate guides and the plate-carrier containing an index corresponding to such guides and numerals, substantially as and for purposes herein described. Ninth. In combination with the plate-carrier, or slide, a bar or plate containing an index, and operated from the outside of the camera by a rack-and-pinion, or other mechanical device. Tenth. In combination with a photographic camera, a remov able or portable adjuster corresponding on a reduced scale to the vision outlet or picture boundary and peep-hole of the camera substantially as and for purposes stated. Eleventh. In combination with the independent front or ex tension of the camera and the camera proper, the swinging brackets pivotted to such camera, and adapted to hold the ex tension upright in an advanced position in front of said camera, substantially as and for purposes herein set forth and described. Twelfth. The plate-carrier or slide as adapted to slide to and fro of the camera-box, and with respect to the lens. Patents Granted, in Belgium. 60,080. P. A. ArTOUT, otherwise TarLFER, and J. Clayton, of Paris, for “ Using eosine in gelatinous bromic photography.”— Dated 5th January, 1883. French patent, 13th December, 1882. 60,181. H. MADER, of Isny (Wurtemburg), for “A changing slide for photographers.”—Dated 16th January, 1883. Patent Granted in United States. 271,402. John BARNErT, of New York, N.Y., for “ A plate holder for photographic cameras.”—Application filed 7th August, 1882. No model. ZINC BROMIDE IN EMULSION, AND EXCESS OF BROMIDE. BY CAPTAIN ABNEY, B.E., F.R.S. I have noticed Colonel Dawson’s remarks about zinc bro mide in emulsion, and also Mr, Arnold Spiller’s commu nication in re the same subject. I may perhaps be allowed to give my experience with zinc bromide, as for some time past I have been working with it. About two years ago I began by adding some zinc bromide to potassium bromide in about the same proportions as adopted by Colonel Dawson, and did not find any particular advantage in it. During the last six months I experimented with bromide emulsions, using nothing but zinc bromide as the haloid salt, sometimes adding potassium iodide to it. My experi ence is of rather a varied kind. I had a certain stock of the zinc salt by me, and every emulsion was a decided suc cess when made with it, particularly when iodide was used, as given below. The plates were rapid (23 to 25 on the sensitometer) and clean, and gave unusual density, and so satisfied was I with my result, that I determined to make it the staple of my emulsions, although its cost is very much more than potassium bromide. My stock of zinc came to an end, and with it the extreme rapidity I had got. The new salt was pure enough, and acid, as must be the case, dissolving perfectly in water and alcohol, having no trace of oxide ; but boil as one would, the needful colour was got with great difficulty, five hours even being sometimes insufficient. It was curious to remark that the addition of five per cent, of potassium bromide at the end of a long boil, when the proper colour had not been obtained, was sufficient to send it to the blue state in five minutes ; but the emulsion was then slightly veiled, and did not show more than 19 on the sensitometer. These experiences were discouraging, but I am certain that when the true chemical state of the case is known, the zinc emulsions will prove to be of the same excellent quality as when I first prepared them. The addition of metallic cad mium to the emulsion helped matters to a certain extent, any free hydrobromic acid liberated being taken up by it. The great drawback to the use of the zinc is its hygroscopic character, an exposure of an unstoppered bottle for a short time to the air causing it to become moist. In weighing, this is of great consequence when a certain excess is neces sary. The zinc salt seems to preserve the gelatine from decomposition, as might be expected, and this may be of importance in hot weather, when emulsion is left to ripen. The formul I used were as follows :— I. Zinc bromide ... ... Potassium iodide Water II. Silver nitrate Water ... III. Gelatine ... Water .. ... 125 grains ... 8 grains ... 1} ounces ... 178 grains ... ± ounce ... 30 grains ... 1 ounce II. and III. are mixed together, and then I. added. The usual quantity (160 to 200 grains) of gelatine was then added, and the washing proceeded with. When the bro mide alone was used, the silver nitrate was reduced to 170 grains. I may say that zinc is not the only salt which has lately played tricks ou me. With the formulae in which potassium bromide was used in about the same equivalent proportions as above, I have often lately had to boil 2} hours, whilst with other samples of bromide one hour used to be amply sufficient. That the gelatine is not in fault is shown by the fact that the same packet was used in both cases. Now in an older formula I had used a much larger excess of bromide, and boiling then took about twenty-five minutes to complete ; for, as I have often stated, the larger the excess of bromide within certain limits, the more rapid is the con version of the silver bromide from the slow to the rapid state. The drawback to the large excess was found in the fact that the images were apt to want density. By increas ing the bromide to a mean between that formerly used, and that I had lately been using—viz., to 142 grains—I found that the conversion took place by boiling in from thirty- five minutes to forty-five minutes, and that rapid and dense plates resulted from it; in fact, similar plates to those to which I had been accustomed. It is such vagaries in tne bromides which so often baff: experimenters, and lead them to state that different results are obtained by them to those obtained by others; and it is only by knowing the results to be expected by increasing or diminishing the quantity, that “even” plates are to be obtained. There are several novel experiences in emulsion making which I have yet to describe, which also throw light on the different degrees of sensitiveness that are found on working from one formula. These I defer for the present, as there are one or two points which I wish to clear up before giving them pub licity. PHOTO-LITHOGRAPHY AND PHOTO ZINCOGRAPHY. BY MAJOR J. WATERHOUSE, B.S.C., Assistant Surveyor-General of India. Chapter VI.—The Preparation of the Photo-Transfer Paper—(continued). For the reproduction of very fine subjects by the washing-off method, Mr. Bolas prepares a paper similar to Husnik's; six ounces of an easily soluble gelatine, such as Cox’s, are dissolved in 25 ounces of warm water, and the mixture is churned vigorously for twenty minutes. At the end of this time, 75 ounces of warm water are added, and the mixture is again churned for a few minutes in order to thoroughly mix the water and gelatine solution. While the mixture is being churned, 3 drops of carbolic acid and a { of an ounce of liquor ammonia are added. The gelatine solution must now be strained through fine muslin, and poured into a dish standing in an outer metal one filled with hot water, kept hot, if necessary, with a Bunsin burner. The surface of the solution having been very carefully skimmed free from froth and bubbles, a sheet of the paper is held by two diagonally opposite corners, and lowered