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JULy 24, 1885.J THE PHOTOGRAPHIC NEWS. 471 The great drawback to this is the trouble in changing the water; otherwise the plan is a good one. Another arrangement is that suggested by Dr. Fol. and illustrated in the Photographic News Year-Book. This is decidedly good, but perhaps more costly than the case really demands. With the exception of the vertical position of the plates, the most mechanically complete and theoretically correct design is that recently illustrated in this paper (page G28) suggested by Mr. Charles Stortz, and after many experi ments, I have adopted a modification of this which seems to meet every necessity. V-shaped troughs are constructed in lengths and numbers to suit the amount of work done. Three feet is a useful size, and they can either be made of stout zinc or of wood. I prefer the latter, well painted outside and in with bitumen varnich or ordinary Brunswick black. The two sides form an angle of 120 degrees, and each is five inches deep inside. This allows for whole, half, and quarter plates to rest on two edges across the bath. At one end the arrangement is similar to that illus trated at page G28 ; that is, at 2 inches from the end, a V-shaped partition is fixed from the top to witbin J inch of the bottom, and at the extreme end adjoining the par tition an overflow pipe is placed. The troughs do not take up much room, as ihey can be placed against a wall or under a table or bench, and are stacked one over the other, the partition and overflow of one being arranged over the opposite end of the one under it, and so on alter nately. A supply pipe to the top one with tap completed the simple apparatus. Earthenware would be a good material, but is too expen sive and heavy. Wood is cheap and light, and if joints are made with brass screws and white lead, the black var nish will ensure water-tight work. I have bad one such trough in use for years without re-blacking. It is made of -inch deal. Lead pipes can be fitted in woodwork easily, either with that common cement known as “Prout’s glue,” or, perhaps better, with so-calledelcctiical cement, a mixture of resin 5 parts, beeswax 1 part, and red ochre 1 part; the latter thoroughly dried, and sifted through fine muslin before mixing. Here there is a washing apparatus readily and cheaply constructed, which affords every facility for the rapid eli mination of crystalloids from the gelatine film, by dialysis •and gravity, with a constant change of water. The plates are easily and quickly placed, or taken out to examine, and loose covers protect from injury. One precaution alone is necessary. In putting the plates, film downward, under water, slant them until submerged, and then let them rest horizontally, otherwise the presence of air-bells is just possible. In my case, before the water enters the first trough, it is made to perform the duty of turning the table on which the vignetting frames are printing. '1 his is done by means of a water-wheel, consisting of a 12-inch disc of sheet zinc, around which are soldered sixteen little shallow tinplate trays, 1 inch by 1} inch in size. Two fine jets of water fall on these trays just as they are nearly horizontal, and sufficient speed is obtained on the axis of such wheel to be converted into power by the intervention of a wheel and pulley of 12 inches and 1 inch, and the necessary straps in the shape of stout tape. This has been going daily for months, the water in the troughs being always ready for negatives at any moment. THE NEW DOUBLE-COATED SENSITIVE NEGATIVE PAPER. DV LEON WARNERKE.* The more photography becomes popular, so the more is felt the necessity of some good substitute for glass upou which to take a negative. It will be superfluous to assert that glass, being bulky, heavy, and brittle, is a very inconvenient material for out-door • Bead before the Photographic Society of Great Britain. work. A few more or less successful expedients have been pro posed and tried for this purpose since collodion made glass the almost exclusive material for negatives. The question of a sub stitute for glass has received, however, more development since the introduction of the dry plate process, and especially after that of collodion emulsion. I myself have been the originator of one of the systems, in which a collodion film, prepared on paper, was used as a temporary support. The introduction of gelatine emul sion for general use, with its great sensitiveness and different physical properties of the vehicle employed, naturally necessi tated a different method ; and such was provided, either in the shape of a gelatine film pure and simple, or in the shape of a film temp rarily attached to the paper, to be stripped off after deve lopment when dry, or in the shape of paper covered with emul sion, the image being developed and treated with hot water, as in my patent process. But the gelatine process has made the practice of photography very popular, and added a great con tingent of new adepts. These use ready prepared glass plates, and get their pictures by a very simple process of development and subsequent fixing, and they naturally object to the smallest addition to the number of operations involved in the process of obtaining a negative on any substitute for glass. For such persons ordinary plain paper, covered with sensitive gelatine emulsion, answers the purpose, the number of the operations being the same as when glass plates are used. However, prints from such negatives show the grain of the paper, and the printing is very long. My new sensitive negative paper, which I have patented, is designed to obviate these imperfections, and to render the quality of the print even superior to one obtained from a glass negative. I take the paper and cover it with gelatine emulsion on both sides. When exposing such double-coated paper in the camera, in the first instance, light will act on the front surface next to the lens, then penetrating the piper, it will act also on the back surface. When this exposed sheet is immersed in the developer, two nega tives, one on each side of the paper, will bo produced. But now let us suppose that the paper itself had some spots, both opaque and transparent ; these will have no influence on the front image, but the back image will be influenced by the spots, and in the exact ratio of its opacity. In other words, all the im perfections of the paper will be corrected by the back image, rendering the composite negative perfectly smooth, no matter how coarse or imperfect was the texture of the paper employed. I now pass round for examination a negative produced on this paper bearing some printed matter. The back image had corre sponding transparent characters, and very distinct impression of the texture of the paper ; but upon looking through the negative all appeared smooth, and such was also the print. Now it will be intelligible that a print from such a negative composed of the two will be also superior as regards roundness and pluck. If the paper used for the purpose be the ordinary photographic paper, Rive or Saxe, the objection to the slow printing remains in full force; but I use instead, paper rendered so transparent by a special preparation, that a print from the image I send round for examination did not occupy more time to print than one from a glass negative of the same density. This special paper offers other advantages. It does not curl when dipped into water, and even after' very protracted washing it remains exceptionally strong, bearing an enormous amount of handling, without crack ing. It appears as if it was not affected by water at all; in fact, if you examine this wetted negative you will observe that to the touch it does not seem at all like paper, but rather like oil-cloth or leather. Now as to the details of using it. In single sheets it can be used in ordinary carriers, provided they are fitted with rabbets instead of wire corners. Any rigid plate put behind will press it close to the rabbets, holding it perfectly flat. One thing must be taken into consideration. At the back must be a dead black sur face (velvet), otherwise, the paper being transparent, reflections from any light object behind will affect the back sensitive surface. However, the most legitimate use of the paper is in the roller slide. The new improved form I will now explain on this model [here Mr. Warnerke showed and explained the new form of his roller slide]. The development of this paper is precisely like that of ordinary glass plates, preferably with ferrous oxalate, in order to avoid any pyrogallol stain. After fixing and washing, it is advisable to pass the negative through an alum bath, to which has been added a few drops of sulphuric acid. Hydrochloric acid must not be used. This will bleach the paper if it has become discoloured with the iron oxide after long development. The finished negative can be dried on glass previously rubbed with talc, or simply by suspending it; but in this last case it will not
