| Picked white Gum Arabic | 75 grains |
| Bromide Ammonium | 200 |
| Gelatine | 150 |
| Water | 10 oz. |
| Nitrate of silver | 300 grains |
| Water | 7½ oz. |
Dissolve in two jars in a vessel of water heated to 140 degrees F., stir each solution well with a separate rod or strip of glass, and when equally heated to 140 p42 degrees the silver may be poured in a gentle stream into the gelatine gum solution by the aid of a safe light.
When all has been mixed and thoroughly stirred, cover the top of the dish and allow the temperature to be at 140 degrees for eight hours, occasionally stirring the emulsion during that time, which should be done in the dark.
At the end of that time there should be weighed out, of Nelson's soft gelatine 250 grains, and of French hard gelatine 150 grains.
This 400 grains of gelatine must now be added to the emulsion, and occasionally stirred until all of it is thoroughly dissolved and incorporated with the emulsion, which will take about a quarter of an hour; it is then poured out in a clean 12×10 deep porcelain dish to set, and should be allowed to set for forty-eight hours, when it may be wrung through a piece of coarse canvas and allowed to fall into a solution of
| Common salt | ½ lb. |
| Water | 1 gallon |
Let it remain in this for five minutes, then strain through a horse hair sieve and wash it well for an hour and a half. Allow the shreddy emulsion to drain well in the sieve for about a quarter of an hour; at the end of that time place it in a clean stone-ware jar to melt, with the addition of four drachms of saturated solution of nitrate of potash upon melting, which may be done by setting the jar into a dish of water at a temperature of about 120 degrees F.
It will be found on measurement to be nearly 25 ounces of emulsion; as soon as it is ready for filtering four ounces of methylated spirit may be mixed with it, p43 to which have been added four drachms of an alcoholic solution of tannic acid, made by mixing ten grains of tannic acid with one ounce of alcohol; this is to prevent frilling.
The rapidity of the plates will be about eight times that of a wet collodion plate, which for all ordinary purposes will be as rapid as could be desired.
Dr. Eder, the distinguished German scientist (who is a great authority on gelatine emulsions, and has published a book on this subject), gives the two following formulæ: