warm weather the formaline bath is always advisable, and if signs of frilling appear may be introduced before fixing. The alum clearing bath is sometimes employed to prevent frilling after development and before fixing ; but, if so, careful washing is necessary, as alum in contact with hypo produces an insoluble precipitate.
Celluloid films require a deep dish owing to their habit of curling up and becoming unmanageable. Some films behave so shamefully during development that they must be enclosed in metal or ebonite rims to prevent uneven markings.
Roll Films.—Attach a strong spring clip to each end of the roll for the purpose of handling. Pass the film backwards and forwards through a tray of cold water for about a minute, rendering it equally wet and supple all over without any traces of bubbles or missed edges. Now the strip of film may be transferred to a deep developing dish ready filled with solution, where the same process is repeated, taking care that the film is drawn through with an even motion from end to end and I covered. When the images begin to appear each picture may be cut apart with a pair of shears and developed separately, but, except in cases of obstinate under exposure or over-exposure, we prefer to keep the roll intact until development is complete, as shown by the appearance of the image at the back or any other test, when the film may be washed in a trough and transferred to the hypo bath to fix at leisure. Most films frill and blister terribly in warm weather, when the first soaking should be in a bath of formaline t oz., water 20 oz. Formaline does not interfere with development, but rather increases brilliance and crispness.
Choice of a may accept the conclusion of modern investigators that all developers tend ultimately to reach the same relative gradation of density. But they do not travel by the same road. Some are much slower than others ; in some the half-tones appear simultaneously with the high lights ; in others the high lights appear long before any other detail is visible. Experience teaches that with certain particular developers it is more easy to secure the result we happen to be aiming at. Sometimes we wish for a very hard negative, at other times softness is more im portant ; and special printing processes require a special variety of negative to be successful. We are not always
content with a scientifically correct negative. The art of photography consists, as Mr. A. J. Anderson points out in a recent work, in its power of expressing with delicacy the effects of light ; and with some developers the gradations necessary for that expression cannot possibly be gauged.
Developing Solutions.--A number of formulae are appended to the notes on developing agents, but of these we would like to remark that the developing formula recommended by the makers is generally to be preferred, unless the worker has experience with these plates. Each maker has his own emulsion, differing in some peculiarity from his rivals, and the presumption is that he has provided for this in the formula printed upon the lid of the box of plates. We very frequently hear an amateur disparaging some excellent brand of plates, and find on enquiry that he thought a ready made up developer must be good enough, because it answered well with another kind of plate used by him.
The water used for these solutions should in all cases be either distilled or boiled. In all developing formula, meta bisulphite of potash S2 may be substituted for sulphite of soda, and the greater purity of this chemical, as well as the reduction of matter in solution, are points in its favour. The amount necessary will only be one-quarter by weight of that directed for sulphite of soda, or, if for immediate use, one eighth. The sulphite should be dissolved first, preferably in hot water, and the developer added to the solution when cool.
Stock Solutions.—In most of these formulx the proportion of water advisable during actual development is indicated. Nearly all the agents will keep for a few weeks, and in practice it may be well to make them up in more concen trated form. For example, with the pyro-soda developer, instead of two solutions of twenty ounces each, the chemicals may be mixed in two five-ounce bottles, and watered down to the proper consistency immediately before using.