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celluloid, but in the event of large quantities of film being set alight, it should be borne in mind that it is a very dangerous thing for the layman to attempt to put out the fire. Suffocation with blankets or by the exclusion of air should therefore only be applied to small conflagrations and in the case of more serious outbreaks, all concerned should be ordered to leave the room as quickly as possible and to do all they can by shutting doors to confine the fire to the one room. To try to extinguish a large film fire by means of water is generally quite useless.
Violent external accidents such as fire, however, are not the only causes of the destruction of valuable films. Defective storage and clums y handling during projection, rolling and joining may gradually destroy a film.
The coating of a photographic film is made of gelatine, which contains about 10-15 % of water, and for the good preservation of film it is important that this percentage of water content should not vary in either direction. If the film is kept too moist, the gelatine decomposes and the picture is destroyed; if on the other hand the film is over-dry, the layer of gelatine and with it the whole film becomes too brittle. The next time it is projected and rolled, it will break or split at the perforations. Film is therefore best kept in rooms of normal humidity, and, in winter especially, care should be taken that heating does not extract too much of its moisture from the air. The practice of dipping film in a glycerine bath after use, so that it remains constantly damp, is dangerous. In the absence of a change of air the gelatine is liable to decompose. No less mistaken is the placing of bowls of glycerine solution near the film-store; the glycerine absorbs moisture from the air, the film is thereby dried up, becomes brittle and tends to break. The temperature of the film-store should, of course, be kept as low as possible.
The basis of celluloid or acetyl cellulose undergoes as a rule much less change during storage. As we know, celluloid film contains as a softening and strengthening agent a certain quantity of camphor, which undergoes sublimation, especially under the influence of a rise in temperature. It is therefore a good idea to put some camphor in the enclosed space containing the film in order to prevent the evaporation of the camphor and the consequent tendency 01 the film to become brittle. The camphor is best hung in little porous packets in the film boxes. Flexibility, too, demands a certain content of the volatile solvents of nitro or acetylcellulose, and the over-evaporation of these substances must therefore be prevented.
To sum up, then, all that can be said about storage is that an endeavour should be made to preserve that humidity, solvency and solidity content which the film in the fresh state possesses. The temperature of the room should be kept as low as possible, the film, as far as is practicable, excluded from contact with the outside air and wrapt tight in paraffin paper within a close-shutting iron box — whenever possible, without unnecessary air-space — which should be made air-tight with some kind of insulating material and in which a little camphor has been put.