Fig. 79.

328 Preparation Of The Emulsion 101

For washing the emulsion many plans are recommended, but they all are on the same principle - a means whereby the emulsion can soak awhile and then drain and again soak and drain. The finer the emulsion is broken up the less washing is needed, and excess of washing certainly causes a thin image, although a very sensitive plate is produced. During the summer, a difficulty is found by many in obtaining water sufficiently cold. An apparatus like Fig. 81 then becomes an absolute necessity. A zinc cylinder and lid fitting into a groove or rebate and some ordinary "compo," one-fourth or three-eighths piping twisted into coils, crushed ice, and nitrate of potash is thrown into the cylinder. The water enters from the top and is considerably reduced in temperature before it passes out at the other end. I do not know that it matters which way the water enters. The washing-trough containing the emulsion should be close to the cooler.

For filtering, a good wash-leather well cleaned from "dressing," a china funnel, a jar, and a tin or zinc cylinder (Fig. 82) to hold hot water are required. It is advisable to filter twice and have two leathers and two funnels. The lip is for the purpose of adding more hot water, and the tap to take off the chilled water. The tin is made to fit the funnel, and has a rim at the bottom to rest on the shoulders of the jar, long enough to prevent the end of the funnel coming in contact with foreign matter when placed on the table.

After filtration, it is well to put the emulsion aside for twenty-four hours (or it can be used at once). A good plan is to have a series of ten-ounce, lipped stoneware bottles, using a ten- or twelve-ounce measure and a funnel to fill the bottles. By this means of measuring, none of the emulsion is lost. The bottles are then covered with a piece of tough, non-actinic paper, kept in position with an India - rub. ber band, taken into a cool place, and when thoroughly set, about half an ounce of methylated spirit is poured on (this can be used over and over again if kept from the light). The emulsion will now remain good for a considerable time, but if it be intended to keep the emulsion, it is better to make it into pellicle & la Kennett. You and the pellicle can then defy summer and winter, heat and cold. - Archer Clarke. My emulsion filter is very simple and easily made, and is illustrated by the annexed of water into the sieve until the whole of the gelatin is covered. Throw away the water in the vessel, renew three times this trashing operation, and drain carefully; now take the gelatin with a horn - spoon and put it in a precipitating glass two - thrids filled with methylic alcohol. Continue this washing until the fragments of gelatin are completely hardened, which it from the peculiar noise which they make when stirred. Now with a horn - fork spread these small emulsion pearls on a glass plate, which has previously rubbed with a tuft soaked in diagram, Fig. 83. B is a tin funnel, with its spout cut off to about an inch in length; A is a glass funnel, with quite a long spout, so as to reach nearly to the bottom of the bottle, or dish, filtered into; a rubber bottle - stopper, c, that fits the neck of the tin funnel, h, is perforated with a hole to fit the spout of the glass funnel, A, and they are all put tightly together, as shown in the diagram. When in use, the spout of the glass funnel, a, is fitted quite tightly with a wad of filtering-cotton previously wet with alcohol, and rinsed with distilled water, and the space between the tin funnel, B, and the glass funnel, x, is filled with water at 110° F. - Jay Densmore.

Fig. 80.

328 Preparation Of The Emulsion 102

Fig. 81.

328 Preparation Of The Emulsion 103

Fig. 82.

328 Preparation Of The Emulsion 104

Bromide of ammonium should be as nearly as possible neutral. It is usually more or less acid, even though otherwise pure, and frequently becomes strongly acid by keeping. It is then quite unfit for use, and will not give good results unless almost neutral. Since further extensive experiment, the writer has arrived at the conclusion that on the whole it is better to use bromide of potassium. The latter is often alkaline, but may, without much difficulty, be obtained neutral, and is free from tendency to alter. Nelson's No. 1 photo, gelatin unfortunately varies much in different samples. It should be absolutely free from the faintest smell or taste, and should dissolve clear, bright, and nearly colorless. Samples good for this purpose usually contain a very slight trace of Hc1. Nitrate of silver is usually (if good) slightly acid, with excess of nitric acid. It may be soused, but the writer has recently found that better results are obtained if the silver solution be neutralized with carbonate of soda. A slight excess does no harm, as the resulting trace of carbonate of silver is converted into bromide; indeed, an emulsion may be made by mixing washed carbonate of silver with a soluble bromide. The uses of neutralizing the silver are twofold. One is, that as the amount of acidity of AgNo3, varies with different samples, it insures the same conditions in all cases; the other is, that the presence of nitric acid in emulsion produces a tendency to green and pink discolorations in the finished negative. - W. Wilson.

When the gelatin emulsion is (lowed over a glass plate, and does not set for a long time, though the temperature of the air and of the plate is not very high, place the plate on a cold metal or stone slab (10° C). If that produces no effect, the emulsion has been spoiled, either by continued cooking at a great heat (60° to 100° 0.), or by repeated alternately melting and solidifying, the latter being specially injurious when the gelatin is of inferior quality. For this reason it is better not to keep the stock of gelatin emulsion warm, but to plunge the flask at once into cold water. When gelatin is heated continuously for a long time with ammonia, it loses its property of solidifying, and the same happens to an emulsion digested with more than five per cent, of ammonia. The best means to put it right again is to add about half its quantity of the original gelatin. By long keeping, the gelatin will benzole and wax; thoroughly dry without using heat; this requires about twenty hours. At the end of this time detach the emulsion from the plate with a paper-knife, or simply with the palm of the hand, place it on a sheet of black paper, and then in small pasteboard boxes, in which it may be kept for an indefinite time if not exposed to dampness or light.

Fig .83.

Fig .83.