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For Washed Emulsion

water, prints, time, washing, hypo, print and placed

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FOR WASHED EMULSION (for Transparencies). Ether, s.g. .720 5 fluid ounces Alcohol, s.g. .820 3 fluid ounces Pyroxyline or papyroxyline 6o grains Bromide of cadmium and ammonium too grams or Bromide of zinc 96 grains • Hydrochloric acid, s.g. 1.2 8 minims Sensitize with twenty grains of nitrate of silver to each ounce, dissolved in a minimum of water with two drachms of boiling alcohol. Allow to stand for two or three days.

N. B.—In the three last formulae, the emulsion after being allowed to ripen for the time stated, should be poured into a dish and allowed to become thoroughly dry. The mass of dry emulsion is then washed, to remove all the soluble salts, and is then again dried and redissolved in equal parts of ether and alcohol, at the rate of from twenty to twenty-four grains to the ounce of solvents.

WASHING.—The operation of washing the negative and positive prints is performed for the purpose of totally eliminating the sodium hyposulphite and other soluble subtances. Con siderable importance is attached to this operation, as upon it depends, to a great extent, the per manency of the negative or positive print.

For negatives, the handiest contrivance is a light wire rack, holding about a dozen nega tives, and which can be placed in a suitable zinc or porcelain vessel, through which a running stream of water can be made to flow. With an arrangement of this kind, negatives should be thoroughly washed in about an hour.

In washing prints we have also to prevent them from clinging together. Several arrange ments have been contrived and placed upon the market which answer the purpose very well. The water should be emptied quite away several times, the prints drained, and placed in a fresh supply of clean water.

To lessen the time of washing many so called hypo-eliminators have been devised, but with most of these, however, another com pound is formed at least as injurious to the permanency of the print as the hypo itself.

Most authors recommend washing the prints in a running stream of water, but a little consideration will show that a number of complete changes will be far more efficaci ous. We can prove this by experiment. In a large basin of water empty a bottle of strong dye, and allow a stream of water to flow into the basin, and out over the sides. The time

taken before the water becomes perfectly color less will be astonishing. Now, if we simply empty the basin and fill it up again, and repeat this operation but twice, the water will contain no trace of the coloring matter. A similar effect takes place with the hypo, except that the latter being colorless it is not noticeable. The most perfect method of eliminating the hypo from prints is one which, although somewhat tedious and for large num bers of prints hardly possible yet for special work where great permanency is required, might be of great advantage. The prints are washed for a quarter of an hour or so in clean water. Another vessel containing clean water is then arranged near at hand, and each print laid on a sheet of clean glass and squeegeed back and front to remove all possible moisture. It is then placed in the fresh water, and another print treated in the same manner. When all the prints have been subjected to this treatment the water in the first vessel is then changed, and after about another quarter of an hour the prints are again squeegeed and placed in the fresh water. By repeating this operation, say, three or four times, using fresh water each time, the prints should be thoroughly well washed and all traces of hypo eliminated. By this method the length of time the prints are required to remain in the water is considerably lessened, and this is always an advantage, as with a too long immersion in water the albumen has a slight decomposing action which is fatal to permanency.

Regarding the length of time required in washing to thoroughly eliminate the hypo we cannot do better than give here the excellent experiments of Messrs. Haddon and Grundy, and in their own words: " In carrying out a research on the amounts of silver in hypo left in albu menized paper at different stages of washing, we had two objects in view; firstly, to determine the time the print should be washed; and, secondly, to endeavor to determine the cause of the fading of the finished print.

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