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123 carefully on to it. The paper is allowed to float on the gelatine solution for about half-a-minute, and then hung up to dry. The earliest coated papers will have the thin nest coating, and will be suitable for the finest class of work ; the later, and more thickly coated, will be better adapted for coarser subjects. The coated paper is thoroughly dried, and may then be stored away or coated with albumen. The preparation for albumenizing is made as follows :— Six ounces of albumen are thoroughly beaten to froth, and then mixed with 15 ounces of water, and 20 drops of ammonia are added. The mixture is allowed to subside for two or three days, when the clear part is poured off and carefully filtered into a flat dish. The sheets of gela tinized paper are floated on the albumen solution in the some manner as on the gelatine, and, in drying, special care must be taken to avoid dust. This paper is sensitized on Husnik’s alkaline alcoholic sensitizer given above. The hardened gelatine papers have rather a tendency to stick fast to the zinc plates in transfer, and in that case are difficult to remove without damaging the transfer. Kruger, in his work Die Zincogravure, gives the following formula for a paper which he says allows itself to be very easily re moved from the zinc plates. Good photographic plain paper is floated from two to four minutes on a solution of Albumen of four eggs beaten and filtered Dextrine ... ... 1 ounce Water 15 ounces and dried; then sensitized by floating again on the same solution with the addition of Alcohol 3 ounces Bichromate of ammonia ± ounce well mixed and filtered, and sufficient liquor ammonia to make it smell strongly. The coated paper is floated on this for about two minutes, dried, and is fit for use. At the Military Geographical Institute in Vienna, the paper used for photo-lithographic transfers, inked-in with a velvet roller, is prepared in the following way. A sheet of well-sized paper (usually fine drawing paper) is soaked in water till it is quite supple, and then laid down on a levelled glass plate, and all bubbles smoothed out with an india-rubber or flannel squeegee. The edges of the sheet are now turned up for about } inch all round, and supported by iron rods. A warm solution of gelatine con taining 1 part of gelatine to 30 parts water is poured on to the paper in the proportion of about 5} ounces to an ordi nary sized sheet 22 by 18. As soon as the gelatine is set, the sheet is laid on a stringed frame to dry, which requires about one and a-half to two days. The day before use, the gelatinized paper is soaked in a cold solution of bichromate of potash containing 1 part of bichromate to 15 of water for about three minutes, air bubbles being removed with a brush. The paper is then squeegeed down, gelatine side downwards, on a piece of plate-glass, previously cleaned and rubbed over with a piece of French chalk, and dries in from three to twelve hours. The dry sensitized paper may be kept in the dark for eight or ten days without spoiling. It is removed from the glass plate in pieces as required, and has a fine glassy surface. In the early process of photo-lithography by transfer, published by Asser, of Amsterdam, the transfer paper was prepared by coating unsized paper with starch paste, and when dry it was sensitized in a bath of bichro mate of potash. After exposure, printing ink was applied with a roller. The process never came into extended use, as gelatine was found more suitable than starch. Mr. Bolas has, however, recently published a modification of Asset’s method, which he particularly recommends as giving better results than the gelatine processes for a certain class of difficult subjects with ill-defined grey lines in the finer parts. To produce the best results, a very fine smooth paper must be used. Thin Rives paper is suitable. A sheet of this paper is immersed in a dish of water, smooth side uppermost. A piece of glass plate, rather larger than the paper, is slid under the floating sheet, avoiding air-bubbles between the paper and the glass. The paper and glass are then lifted out of the water together, laid on a table, and the paper having been covered with another sheet of paper or a piece of waterproof cloth, the excess of water is squeegeed out from between the paper and glass. The wet paper is next to be coated with a very weak flour paste, made by boiling together 4 parts of wheat flour and 100 parts of water, avoiding lumps. The mixture is carefully strained through muslin, and a few drops of ammonia may be added with advantage to prevent acidity. The plate bearing the paper, having been placed nearly level, is flooded with the warm paste, about 14 ounces being required for an ordinary demy sheet The plate is then gently inclined so as to run off the excess of paste at one corner, the plate being rocked meanwhile as in pour ing off collodion. The plate with the paper is now reared up on one edge to drain, and after a short time the paste will be seen to divide itself into little granular patches. The surface of the paste must now be smoothed with a long haired badger hair-brush, an operation which requires some little practice. The brush should be held loosely in the hand, working from the wrist, and the ends of the hairs should pass lightly and rapidly over the surface of the paper, till an even and satisfactory surface is produced. The paper may then either be stripped off the glass and hung up to dry, or it may be allowed to dry on the glass plate, in which case it is as well to lightly wax the surface of the glass beforehand. When dry, the paper may be sensitized by soaking for a few minutes in Husnik's alkaline alcoholic sensitizer given above, or in a 3} per cent, solution of bichromate of potash to which a few drops of ammonia have been added. It is hung up to dry in a warm place. As before noticed, gum, though it would have many conveniences from its cheapness and easy solubility, is not much used for the preparation of ordinary photolitho graphic paper. It has, however, been used with consider able success by Toovey, of Brussels, in what may be termed an indirect transfer process, in which, instead of ink, the soluble gum is transferred to the stone, and forms the reserves, so that ink, afterwards applied, fixes itself on the lines of the drawing. This process will be described in detail in a subsequent chapter. Herr Leth, of Vienna, gave me the following formula for a preparation of the paper in which gum is mixed with gelatine:— Gum arabic part Gelatine ... ... > „ Bichromate of potash 3 parts Water 48 „ The bichromate of potash is in large excess, and, according to Herr Leth, this is useful in printing from weak nega tives, because the ground can be rubbed clean without injuring the lines. According to Martin (Ilandbuch der Emailphotograpbie und der Phototypie, another formula of Leth's is as follows :— 1} ounces of gum arabic are dissolved in 48 ounces of water ; 4} ounces of bichromate of potash are added, and when dissolved, the albumen of 40 eggs is mixed in, and the whole beaten to froth. When settled, it is filtered into a dish, and paper floated on it, and dried. A gum process was formerly used at the Military Geographical Institute, in Vienna, the transfer paper being prepared by coating ordinary albumenized paper with a filtered mixture of solutions of—