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vin DEVELOPING AND PRINTING PICTURES 79 are on every hand, together with adequate supplies of running water. Everything, of course, is carried out in semi-darkness, the only light available being that emitted from ruby lamps. The fixing solution after it has served its purpose is not thrown away, but is subjected to a chemical treatment to recover the bromide of silver which the hyposulphite of soda has dissolved from the sensitised emulsion on the film. The silver in suspension is pre- cipitated by chemical action in. a thick sediment. In large works this recovery process is profitable, several pounds of this metallic silver being secured every week. The solution employed for development is either a com- bination of hydroquinone and metol, or a bath of rodinal, developing agents which are familiar to the amateur photographer, while the fixing bath is a solution of hypo- sulphite of soda. The developing formula is modified by various firms as a result of individual investigation. The drying operation is one that has to be carried out very carefully; the temperature of the chamber must be evenly maintained, and the air which is circulated through the room must be filtered before admission, in order to arrest all particles of dust which otherwise might settle upon the gelatine surface and wreak appreciable damage. In the early days the fickle character of the film was a serious difficulty. If it were dried too rapidly it evinced a tendency to curl, and severe shrinkage often ensued. To guard against this trouble the film was glycerined . before being dried, by being passed through a bath containing a solution of glycerine and alcohol. The improvements effected in the manufacture of the film, however, have enabled this subsidiary treatment to be dispensed with. In cases where a topical film must be rushed out quickly to catch the public in the height of its interest, however, drying is accelerated by subjecting the film to a bath of alcohol in some form or other. Although a spool of film, measuring perhaps 300 feet in length, is handed over for development, possibly that 300 feet carries two, four, or more exposures, i.e., different sections were exposed at different times, on different days,