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THE PHOTOGRAPHIC NEWS. Vol. XXVII. No. 1299.—July 27, 1883. CONTENTS. PAGE 25 ounces of emulsion as intended, we had 50 ounces. The silver nitrate is this time mixed with only 4 ounces 465 465 466 467 469 470 470 . 471 Silver nitrate ... Potassium bromide Potassium iodide ... Nelson’s No. 1. gelatine Hard gelatine Silver nitrate Potassium bromide Potassium iodide .. Nelson’s No. 1 gelatine Hard gelatine 400 grains 340 „ 15 „ 100 „ 500 „ On attempting to coat plates with this, we had an alto gether novel experience. The levelling shelf was cooled with ice, and plates coated were left on it for twenty minutes. At the end of that time, on tilting them up, a clear liquid was poured off, the silver bromide having, in fact, precipitated itself on the glass. The only expedient was either to throw down the emulsion with alcohol, or to add gelatine to it. We chose the latter, and as a consequence image totally wants pluck. The same has resulted in our hands in experimenting with Mr. Henderson’s lucine. Working exactly as specified by him, we have got plates of fair sensitiveness and ex cellent quality, the emulsion being as opaque as could be desired. On pushing the process to get extreme sensitive ness, either by high temperature or the addition of more ammonia, we have got a very thin emulsion. An examination of the film through a short focus eye-piece shows very distinctly what is the cause of the thinness ; it arises from a great enlargement of the grains of silver bromide. The reason for this appears evident: the small quantity of gelatine present loses all its viscoscity atthe high temperature, and does not prevent the cohesion or running together of the particles, which consequently aggregate themselves into comparatively large masses. From this it would appear evident that a larger quantity of gelatine is desirable in the emulsion whilst digestion goes on. In some recent experiments we reverted to what is practically the original formula of Dr. Eder, using, however, much higher temperature. It is pretty well known that the limit of temperature laid down by Dr. Eder—namely, 100° Fahr.—may be exceeded with safety ; but to how great an extent it may be exceeded is not generally understood, we believe. In our first experiment, we made up an emulsion as follows. We took— The silver was dissolved in eight ounces of water, and the bromide iodide and No. 1 gelatine in another eight ounces. The solutions were then emulsified together at a high temperature, and the emulsion was boiled for twenty i minutes. The hard gelatine was added with the smallest । quantity of water necessary to soak it—about six ounces. The temperature now was about 160“ Fahr.—a degree or two above it, if anything. An ounce and a quarter of the strongest ammonia was added, and the whole was stirred for several minutes, then put on one side to cool slowly. At the end of an hour it had cooled to about 400 grains 340 „ 15 „ 100 „ 300 „ Ammonia in Emulsions Hot W eather and Gelatino-Bromide W ork Stained Sensitive Films The Tourist Photographer On the Use of Partial Photographs for Studying the Move ¬ ments of Men and Animals. By M. Marey Review Stellar Photography at Harvard Notes AMMONIA IN EMULSIONS. The emulsion processes in which ammonia is used to give sensitiveness have a great advantage in the ease with which a fair degree of rapidity combined with good quality can be gained. It is also well known that it is possible to gain by these processes a very high degree of sensitiveness, although many have been unable to do this, and still more have found it unattainable without great loss of quality. In working in strict accordance with the formul given by 100° Fahr. The emulsion was neither very thin nor granular. It was left for twenty-four hours before washing was attempted, and here came the first difficulty: the ammonia at the high temperature had so far softened the we got an emulsion very thin, simply on account of dilution, but otherwise showing good qualities. Elates coated with it were at the best somewhat transparent, but there was no granularity ; and, far from giving a thin image, as do plates coated with emulsion prepared by digestion with ammonia in presence of a very small quantity of gelatine, they gave on development an image of exceeding density. The sensi tiveness was very great—229 to 23° of the sensitometer. We modified our formula to avoid the difficulty we have mentioned, and, as modified and here given, we can recom mend it to those who wish to make rapidly an emulsion of excessive sentitiveness. The formula is — FAQE Patent Intelligence u 473 Lessons in Optics for Photographers. By Capt. Abney 473 Dry Plates verius Wet. By E. E. Cadett. 272 A Dictionary of Photography wwu 476 Solid and Liquid Illuminating Agents. By L. Field, F.C.S 477 Correspondence 278 Proceedings of Societies 138 Talk in the Studio 480 To Correspondents 480 worked the process strictly as described. One of the most popular ammonia processes in this country has been that originated by Mr. Cowan, in which the digestion with ammonia is performed in the presence of a very small quantity of gelatine only, the bulk being afterwards added. This is an admirable process when a fair amount of sensitiveness—say that of an average com mercial plate, or about 17° of the sensitometer—is con- . - sidered sufficient. This can be got by the use of a com- I gelatine that it would not set stiff. It appeared stiff paratively low temperature—not much above 100°Fahr. enough, however, not to dissolve away in cold water, and Avery much higher degree of sensitiveness may be obtained we washed it. It took up so much water that, instead of by the use of a higher temperature, but it is at a sacrifice °5 """2" " om"lein" "" int ded hn3 5 of quality. The emulsion becomes thin and transparent, and unless very thick coating of plates be resorted to, the Dr. Eder in his earlier writings, keeping to the temperatures and periods of digestion which he prescribes, we have | failed to get anything above a moderate sensitiveness, and the same is the experience of such of our friends as have