EMULSIONS RIPENED WITH AMMONIA.
Fairly rapid plates may be made without employing the boiling process at all, by treating them with ammonia. Such plates, although not extremely sensitive, are con siderably quicker than collodion plates. They may be prepared by treatment at a temperature of about 1000 F., or the emul sification and subsequent treatment may take place at ordinary temperature. The former does not appear to possess any ad vantage over the usual method of boiling, but the latter certainly gains much as re gards simplicity. The following solutions may be made up :•—No 1. Silver nitrate, 175 grs. ; water, 1 oz. No 2. Potassium bromide, 140 grs. ; water, 1 oz. No. 3. Gelatine, 45 grs. ; water, 1 oz. Add to No. 1 solution a little ammonia, and a pre cipitate of silver oxide is formed. Con tinue to drop in ammonia and shake the solution until the silver oxide, which is soluble in ammonia, is re-dissolved. It makes the operation a little. simpler if the ammonia is diluted with a small quantity of water. This solution is added to No. 3,
and shaken vigorously. When an intimate mixture is assured, the bromide solution, No. 2, may be added, a little at a time, with much shaking. Two hundred grains of gelatine are then dissolved in 2 oz. of water, and when cool added to the solution in the same manner. As in the prepara tion of other emulsions, the more complete the mixture the better. When this has been properly done, the emulsion should be set aside for twenty-four hours to ripen, Before doing so, it is best to pour it out into a flat glass dish, so that it may be in a convenient form for breaking up and washing. This is done as described on p. 64. The emulsion may be made with the whole of the gelatine at once, but in this case the temperature of the solution wili have to be raised, or it will be too thick to allow of proper mixing.