Distilled water . . 20 Oz. 1,000 ccs.
heated to 15o° F. Digest for ten minutes, and pour out into a dish to set.
Valenta's Formula No. I. :— Ammonium bromide . 48o grs. so g.
Ammonium chloride . 48 ,, 5 Nitric acid . . io drops zo drops Hard gelatine . • 1,615 grs. 168 g.
Distilled water . . 26 oz. 1,333 ccs.
Heat to 13o° F (54-4° C.), and add— Silver nitrate . . 96o grs. roo g.
Distilled water . . 26 oz. 1,333 ccs.
also at the same temperature. Allow to digest one hour, and then pour out and set.
No. II., for greater contrasts :— The above formula with— Ammonium bromide so grs. 5.2 g.
Ammonium chloride . 300 „ 3o „ In mixing both the Wellington and Valenta formulm the same procedure may be adopted as for Wratten's.
The ratio of the silver haloids in these three emulsions is as follows :—Wratten—chloride bromide 2'1 ; Wellington—chloride 1, bromide 1.7 ; Valenta No. x, bromide 8.7 ; Valenta No. 7, bromide I. Welling ton's gives very warm tones more easily than the others with increased exposures.
Lantern Plate and Bromide Paper Emulsions These may be pure bromide emulsions, but it is preferable to use bromo-iodide, as the iodide tends to keep the whites free from fog. Some commercial bromide papers are also chlorobromide emulsions. The following gives
a very satisfactory but slow emulsion, either with or without the iodide.
Ammonium bromide 672 grs. 70 g.
Potassium iodide . 15.3 „ 1.6 „ Hard gelatine. . 2 oz. 150 „ Hydrochloric acid (io% solution) . . 144 mins. 15 ccs.
Distilled water . . 3o oz. 1,500 „ Heat to 110° P. (about C.), and add— Silver nitrate . . 96o grs. loo g.
Distilled water . . 10 oz. 50o ccs.
also heated to iio°. Digest at this temperature for one hour. If a more rapid paper is required, then after digestion cool the emulsion down to 95° F. (35° C.) and add— Liquor ammonia' . 96 mins. xo ccs.
Distilled water _ . I oz. )7 then set and allow to stand for twenty-four hours.
For enlarging, when a much more rapid paper is required, a slow negative emulsion, such as given below, may be used. For coating bromide paper the proportion of gelatine should not be too high, although this depends upon the sur face required and the method of coating, about : 18 or 20 being generally sufficient. For matt emulsions, rice starch may be added as already advised for gelatino-chloride paper. For lantern plates a little more gelatine is required, say about I :