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JUNE 8, 1883.] THE PHOTOGRAPHIC NEWS. 359 approximately an elliptical form, so that if one knew the exact time of exposure which would give the best result with any mixture, one might deviate two or three minutes either way from that time without producing a noticeable result. I have found .. 10 parts .. 1 part ... 50 parts Red prussiate of potash ... Citrate of iron and ammonia Gum-arabic Water ... 1 part 10 parts 50 ,, 2 parts 3 » 20 „ 8 parts 8 » 1 part 80 parts it good whites are seldom obtained upon porous paper. The Best Chemicals for this Work are the recrystallized red prussiate of potash and citrate of iron and ammonia. If the red prussiate has not been recrystallized, the whites will be un satisfactory, and the samples of citrates of iron and ammonia which have come to us from other chemists than those named, have all proved unreliable for this purpose. The Sensitizing Liquid.—Its Proportions.—The blue process was originally introduced from France, by the late Mr. A. L. Holley. X was indebted to Mr. P. Barnes, who was with Mr.! Holley at the time, for an early account cf it, and I had the first blue process machine that was in use in New England. Since 1875, instruction in the use of the blue process has been given to the students of mechanical engineering of the Massachusetts Institute of Technology, and they have caused its introduction into many draughting offices. The proportions of the sensitizing liquid, as originally given me by Mr. Barnes, were as follows :— printed more rapidly. This preparation I continue to use when much time may elapse between sensitizing and printing ; but, when the paper is to be printed immediately after sensitizing, I use a larger proportion of citrate of iron and ammonia. Before arriving at the conclusion that these proportions were the best to be used, I made a series of purely empirical experiments, sixteen negatives at the same time upon a single sheet of paper. This frame is interchangeable with the one that contains the plate glass. The negatives are so arranged in the frame that the sheets can be cut and bound, as in the ordinary process of book binding. The time required for exposure, when printing from glass negatives, varies with the negative ; and, in order to secure satisfactory results with the multiple frame, it is necessary to stop the exposure of some, while the exposure of others is con- I tinued. I insert wooden or cloth stoppers into the frame for the purpose of stopping the exposure of certain negatives. When paraffined manuscript is to be printed from, I find it convenient to have it written on sheets of small size, and to have these mounted upon an opaque frame of brown Manilla paper, printing sixteen or more at a time, depending upon the size of the printing-frame. Many small tracings may be similarly mounted upon a brown paper multiple frame, and may be printed together upon a single sheet. beginning with the proportion : Red prussiate of potash ... Citrate of iron and ammonia Water ... ... ... aud ending with the proportions : Red prussiate of potash ... Citrate of iron ani ammonia Water * Since this paper was read, I have seen in the ofice of the City Engi neer, of Boston, a drying case which is similar in some respects to the one that I have devised. It has been longer in use than my own, The drawers are simply the ordinary mosquito netting frames covered with cotton neiting. They have no fronts, but a door covers the front of the case, and shuts out the light. The Grades of Paper that are well adapted for Blue Process sent the intensity of the blue, the curves drawn would have Work. I have tested many grades of paper, to ascertain if they : 1-1 -n:-as—r f — *knt 3 — ‘ an- a Besults of ^Experiments.—In our use, it first appeared that the gum might be omitted from the preparation when sufficiently hard papers were used. Next, that a preparation containing I found the best plan for conducting these experiments to be : to coat a sheet of the paper with a given mixture ; to cut the sheet into strips before exposure ; to expose all the strips of the sheet, at the same time, to the direct sunlight without an inter vening negative ; and to withdraw them, one after another, at stated intervals. I found that with each mixture there was a time of exposure which would produce the deepest blue, that with over-exposure the blue gradually turned grey, and that if a curve should be plotted, the abscissas of which should represent i the time of exposure, and the ordinates of which should repre- that with the same paper, the same blue results with any good pro portions of the chemicals named, provided a sufficient weight of both chemicals is applied to the surface ; that an excess of the red prussiate of potash renders the preparation less sensitive to light, and very much lengthens the necessary time of exposure; that the prints are finer with some excess of the red prussiate ; that an excess of the citrate of iron and ammonia hastens the time Red prussiate of potash ... Citrate of iron and ammonia Water quarter of an inch below the bottom of the drawer. My case stands in a poorly-lighted room, and paper dried in this case and । removed to a portfolio as soon as it is dry does not seem to be injured by the light that reaches it. With the case in a well- lighted room, I should prefer to have outer doors to the case, made of ordinary board six or eight inches wide, hinged to one end, and arranged to swing horizontally across the front of the case. These would more completely prevent the admission of I light. The opening of any one of the doors would allow three or four of the drawers to be filled, while the rest of the case would be comparatively dark at the same time.* The Portfolio for Protecting the Sensitized Paper from Exposure to Light.—The sensitized paper is very well protected from ex posure to light, if kept in a portfolio or book, the brown paper leaves of which are considerably larger than the sensitized sheets. The sheets may be returned to such a book after exposure, and washed at the convenience of the operator. They can be washed more quickly and perfectly if two water-tanks are provided in which to wash them. A few minutes’ soaking will remove nearly all of the sensitizing preparation which has not been fixed by the exposure. If the soaking is too long continued in water that is much discoloured by the sensitizing preparation, the sheets become saturated with the diluted preparation, and they may become slightly coloured by after exposure. If the first soaking is not too long continued, and if the sheets are transferred at once to a second bath of clean water, which is kept slowly changing from an open faucet, they may remain there until the soluble chemicals have been entirely extracted, and there will be no risk of staining by after-exposure.’ Washing in two tanks is of more consequence when the ground is white and the lines blue, than when the ground is blue and the lines white. of printing materially ; • that a greater excess of the citrate causes the whites to become badly stained by the iron, while a still greater excess of the citrate in a concentrated solution causes the sensitized paper to change without exposure to light, and to produce a redder blue or purple, which does not adhere to the paper, but may be washed off with a sponge. I have found that the cheapest method of reproducing inked drawings thathave been made on thick paper is not to trace them, but to print the blues from a photographic glass negative ; and also, that the dry plate process is well adapted to such work in offices, when one has become sufficiently experienced. Printed matter can also most easily and inexpensively be reproduced by the same means, when a small issue is required on each successive year. For the reproduction of manuscript by the blue process, the best plan that I have found has been to write the manuscript upon the thinnest blue-tinted French notepaper, with black opaque ink—the stylographic ink is very good—and, afterward, to dip the paper into melted paraffin, and to dry the paper at the I melting temperature. This operation, if cheaply done, requires special apparatus. For positive printing from the glass negative, I I use a multiple frame, by the aid of which I can print from were well adapted for blue process work. Some grades of brown Manilla are very good ; others have little specks embedded in their surfaces which refuse to take on a blue tint; still others, when printed upon, have white lines that are wider than the corresponding black lines of the negative. The blue obtained upon bond paper appears to be particularly rich, and the whites remain pure ; but bond paper cockles badly, and the cockles re main in the finished print. Weston’s linen record is an excellent paper. It is strong, cockles but little, and dries very smooth. A paper that is used by Allen and Rowell, for carbon printing, is comparatively cheap, and is an excellent paper. It is not so stiff as the linen record, and the whites are quite as pure. It does not cockle, neither does it curl while being sensitized. It comes in one hundred pound rolls, and is about thirty inches wide The best papers are those that are prepared for photo graphic work. The plain Saxe and the plain Rives both give excellent results. Blue lines on a pure white ground can be ob tained on these papers, from photographic negatives, without difficulty. None of the hard papers of good grade require the use of gum in the sensitizing liquid. The liquid penetrates the more porous papers too far when gum is not used, and without