339. In the manufacture of the emulsion, sufficient importance is not given to the kind of bromide used. All bromides do not give the same
339. A few hints: Should there be any signs of frilling at any stage of developing or fixing, which will rarely or never be the case with these plates, flood the plate with a saturated solution of alum, wash well, and proceed. Trays for developing may be made of ordinary back-board, nailed with small finish nails, and covered inside and out with a composition made by melting together equal parts of yellow beeswax and common rosin. Trays and measures should be rinsed out after developing each plate. Care must be taken to wash the plate very free from the hypo, and for this purpose it is well to immerse the plate for a few minutes in a saturated solution of alum, after the washing, which will decompose any hypo remaining. The following is a better mode of intensifying: Flow the plate with a twenty-grain solution of bichloride of mercury till the intensity appears right; wash well and flow with ammonia, about one part to ten of water. Repeat, if necessary, with thorough washing. A yellow or brown discoloration of the film under the mercury indicates the presence of hypo. Alum has been much used in working gelatin plates, but hitherto simply to harden the film and prevent frilling. But recently it has been found that alum removed the traces of hypo which appear to escape the usual washing. It is therefore well to immerse the plate in a saturated solution of alum, after fixing and washing well. The British Journal advocates intensifying with silver and pyro after the use of the alum; but it is best not effects. The most rapid and the beat seems to be that of ammonium; but used alone, it has sometimes a tendency to produce gray prints. Bro-mide of zinc has precisely the opposite qualities. Bromide of lithium gives a certain adherence to the film, and the bromide composed of potassium, cadmium, and zinc, used by Mr. Chardon in the collosion emulsion, gives the gelatin negative, specially when developed with pyro-gallii- acid, a very rich tone; strengthened by bichloride of mercury cyande of silver, it produces results of remarkable beauty.
Transparancies for lantern use, collodion transfers, and other enlarging processes, are rapidly and easily made by the bromo - gelatin proto be too sanguine of silver intensification even after alum, as the mercury and ammonia method is simple, and gives permanent results, and there is at least a liability of the silver combining with the gelatin and bringing about a gradual discoloration. C. F. Richardson.
Be very careful as to any actinic light in your dark-room, and use a ruby - colored lantern or lamp (the top well covered with a dark tinned cone), if necessary. Before putting away the negative to dry, place the plate in a dish of water, film down, one end raised, and allow to soak for half an hour, and, lastly, rub with a tuft of cotton to remove any sand or sediment that may have remained on the film. Should you desire to dry the plate quickly, soak in alcohol from ten to fifteen minutes, and set aside to dry. Heat may be employed in varnishing the negative, which must be perfectly dry. Make a proof-print before varnishing, to see that the negative is of proper strength. Keep your hands free from hypo while developing, or fog will be the result If your negatives have too much contrast, weaken the developer by adding water. Over - exposure is preferable to under - exposure, and we invariably recommend a second sitting where the latter has occurred. Keep your solutions cool, as heat, while the plate is moist, will dissolve the film. The strengthening, reducing, fixing, and alum solutions can be repeatedly used, but require changing when they become too much discolored. - F. W. Guerin.
340. For a dense gelatin emulsion suitable for printing transparencies, the following formula has given me better results than any I have yet tried, and I give it in the hope that it may be useful to others who are en traced in this class of work. Formula for three ounces of emulsion
Bromide of Potassium,........................................
Iodide of Potassium,............................
Nitrate of Silver,............................
Nelson's No.1 Gelatin,............................
Dilute Nitric Acid,............................
The beer in the above formula is composed of four ounces of ordinary bitter beer with two ounces of alcohol added to make it keep, and the dilute nitric acid by adding one drachm of strong nitric acid to one ounce of distilled water. To make the emulsion, place the bromide and iodide in a beaker of suitable size, and then add one drachm of beer, three drachms of water, and ten grains of gelatin. Now weigh sixty grains of gelatin and completely immerse it in any vessel of cold water; let it remain for two or three minutes (not longer, or it would absorb too much water), and then turn it out on to a hair sieve to drain.
cess. The film being so delicately soft and structureless makes them particularly beautiful and desirable. The preparation of the emulsion for such work must be attended with unusual care as to material and temperature. But if good results are desirable, then all the care they need to produce them is reasonable.
By the time this has been done the gelatin and bromide in the beaker will be ready to dissolve. To effect this take a tin saucepan or can of about the capacity of one quart; fill it two-thirds full with water, and in this place the beaker, which must have something put for it to rest upon in order that it may not sink too deeply in the water. Now place the saucepan over a Bunsen burner, or even on an ordinary fire, and raise the temperature of the water to 140° F. Whilst this is being done weigh out the silver, dissolve it in half an ounce of distilled water, and add five drops of diluted nitric acid. When the water in the saucepan has reached the required temperature remove it from the gas, and then add the silver solution to the bromized gelatin. This can be best effected by one of the well-known spray producers, and as this is a little contrivance that any one may easily make for himself, the operator will do well to provide himself with one. Should, however, one of these be not at hand, a dropping - tube will do nearly as well. In either case the silver must be added a little at a time with constant stirring, and for stirring, a flat slip of glass from half to three-quarters of an inch broad will be found better than a round rod. When all the silver has been added the pan must be again put over the gas and the water brought to boiling-point. This will take about five minutes, and during this time the emulsion must be pretty constantly stirred. As soon as the water boils, the gas may be put out and the pan removed. Now add the remaining sixty grains of gelatin, stir for half a minute, and then drop in, with constant stirring, fifteen drops of strong ammonia. After this the emulsion must be immediately poured into a six- or eight-ounce bottle and be thoroughly shaken. Now pour cold water very carefully into the pan until the thermometer registers 140°. It is a matter of the greatest importance that the temperature be nicely regulated at this point, because if higher than that stated fog is pretty sure to be the result, and if much lower the emulsion will probably be very slow. The bottle of emulsion must then be returned to the warm water and set aside for an hour or longer to cool gradually. If the bottle be enclosed in a canister with a perforated bottom, it will be found a great convenience, as light may then be admitted into the operating-room without any fear of its injuring the emulsion. At the expiration of an hour or an hour and a half the temperature will have sunk to 80°. If it have not done so a little cold water may be poured into the pan until the thermometer registers that degree, or even a little lower. The emulsion must be left for ten minutes longer, and then it will be ready for the next operation, viz., the removal of the soluble salts. This may be most conveniently effected by precipitating it in alcohol. To succeed in this operation, three points should be particularly attended to: 1. The emulsion must be tolerably concentrated; "that is to say, no more water than necessary should have been used in its composition. 2. The temperature must be low. 8. The alcohol must not be used too sparingly. The temperature, then, having sunk sufficiently low, put five ounces of methylated alcohol into a glass beaker, and into this pour the emulsion in a thin, continuous stream, stirring at the same time with a round glass rod. When all has been poured in stir a few moments longer, pressing the rod against the sides and bottom of the beaker, and the emulsion will then be found to have collected as a compact mass round the end of the stirring-rod, from which it plates are put in a grooved box necessarily heavy, supplied with an auto-matic slide which opens as the holder, is drawn through a slot in the box. Then the boa is turned upside down, and the plate falling into the holder if there made fast, ready for exposure. Upon the holder being withdrawn, the slot is closed, and the plates remaining in the changing - box are protected from light. Sometimes such a method is a bother some one, should the plate be a trifle large, it will not come out from the box, or enter the holder. and then has to be passed over, no matter how much shaking and display of temper is given in the effort to make it work right. The second figure represents the changing - box as arranged when about to receive or discharge a plate. The brass registering plate at the side is nmbered so that account can always be made of the plate which has been exposed.