Since the introduction of the new process into the United States, the preparation of rapid dry plates has been and remains now in the hands of certain prominent firms, who, from the skill they have acquired and the advantages they derive from all the machinery and conveniences that large capital enables them to procure, are enabled to supply fully the demand with a much better article than could be had were each consumer to manufacture for himself. In fact, if the photographer were compelled to manufacture his own dry plates there would be a very different condition of affairs at the present time.

Gelatine is a substance so susceptible to change from the action of our climate, with its varyirig temperature, that of a large number who have attempted to make dry plates for the trade, many have completely failed, some of them after a partial success; and others after spending thousands of dollars never could make two batches of emulsion alike; and' then again the keen competition of the successful concerns has reduced the profits to not more than fair returns to a precarious business.

There are many, no doubt, who would be glad to experiment in this field, especially among amateurs, and it is for the benefit of such that certain hints and formulae are given in this connection to enable them to make, if successful, their own plates.

The' formulae herewith given are selected from a large number published in the German, English and American journals, and while good dry plates may be made by either of them, yet it is doubtful if the highest success would repay the outlay.

A careful study of the published formulae and the current literature on the subject of Gelatino-Bromide Emulsion will disclose the general principles on which they are based.

A certain amount of bromide of ammonium or potassium (preferably ammonium, on account of its greater uniformity and purity) and nitrate of silver are dissolved separately, and mixed together in a thin solu-sion of gelatine, at a moderately warm temperature. Great sensitiveness is obtained by a long exposure to the same warm temperature, or by the addition of a small amount of ammonia, and raising the heat to the boiling-point for from a half to a full hour; when it is cooled more gelatine is added and the whole allowed to congeal or set, when it is reduced to shreds, and washed in cold water to remove the excess of the preponderate salt.

The sensitiveness of the emulsion is said to depend upon the fineness of sub-division of the grain of the bromide of silver in the presence of the gelatine. This extreme fineness is secured by long emulsifica-tion, or by the use of ammonia and a boiling heat.

The strength and tenacity of the emulsion depend on the quality of the gelatine, and its freedom from deterioration during the process of emulsification and the subsequent washing. A soft gelatine is suitable for the process of emulsification; afterwards a hard quality is used to give body and resistance.

The presence of free bromide or of free nitrate of silver in the finished emulsion would be fatal to its usefulness; therefore, as both of those salts are easily soluble in water, they must be got rid of by washing; consequently, before washing, the mass of jelly should be induced by the use of a refrigerator to set firm and hard, so that it may be broken up into shreds for washing, and the smaller the shreds the less washing they will require.

Of the following formulae the first two are copied from English photographic year books, and are believed to be reliable; the others are by Dr. Eder, the greatest German authority on gelatine emulsion, and they are comparatively simple.

Gelatine Emulsion. A

Twenty minims of No. 1 solution are introduced into the whole of No. 2, and the Gelatine is left to swell.

In another glass vessel 330 grains of nitrate of silver are dissolved in 3 ounces of distilled water; a small quantity, about two fluid drachms, of the latter is poured into a test tube and diluted with an equal bulk of distilled water.

The solution of the bromo-gelatine is then rendered complete by immersing the bottle in hot water, and the dilute silver nitrate is added all at once.

The bottle is then shaken and the remainder of the strong silver solution added in quantities of half an ounce at a time, shaking the bottle as before after each addition.

The emulsion is then boiled for fifty-five (55) minutes, and when cooled down to 90 degrees F., one ounce of gelatine, which has been previously swelled and dissolved in water so as to measure four ounces, is added and put away in a cold place to set.

When set, squeeze through coarse canvas into cold water one half gallon and ¼ lb. salt; let it remain for five minutes, then wash thoroughly.

The addition of two ounces of alcohol and enough water to make up to twenty ounces completes the process.

In the preparation of this or any gelatine emulsion the work may be carried on in daylight as far as the mixing of the bromide and silver, which must be done in a dark room by the aid of a lamp or gas light shaded by orange or ruby glass. Sufficient of this non-actinic light may be admitted to enable the work of washing the emulsion, and afterwards the coating of the plates, to be carried on with ease and comfort, as the emulsion when wet is only half as sensitive as when dry.

Gelatine Emulsion. B

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 degrees the silver may be poured in a gentle stream into the gelatine gum solution by the aid of a safe light.