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268 HANDBOOK OF PROJECTION FOR
The Film
THE film is a strip of celluloid !>>£ inches wide by from 5^2 to 6 one thousandths of an vnch in thickness. In the process of making the celluloid is originally in strips about 2 feet wide by 250 to 300 feet in length. These wide strips are passed through a machine which spreads upon one side a coating (negative or positive, according to the use to which the stock being treated is to be put) of photographic emulsion. The emulsion is a part of the thickness of the film as above given.
Having received its emulsion coating the film is passed through another machine which splits it into ribbons 1^ inches wide, and these ribbons become the film stock which is purchased by the photoplay producer.
The negative stock is first perforated, then it is placed in a camera having an intermittent movement, a revolving shutter and a lens, the whole mechanism being very similar in its action to that of the motion picture projector, except that the mechanism and film are enclosed in a light tight box, or casing. Each $4 of an inch of the negative is successively exposed to the light by the camera mechanism, and what is nothing more nor less than a "snapshot" photograph is impressed thereon. The exposures are supposed to be at the rate of 16 per second, but in practice camera speed varies over a rather wide range, running as high as 80 feet of film to the minute in some instances.
After exposure the negative is removed from the camera, developed, fixed and dried by much the same chemical process as is any ordinary Kodak negative, though the mechanical methods necessarily differ widely from the Kodak process, since the negative film will be anywhere from ten to 300 feet in length.
The negative is then projected to a screen, so that the director may check up his work, make the scene over again if necessary, or cut out any undesirable portions. When the negative is finally in acceptable form it is placed in a printing machine in contact with a strip of positive film (positive and negative film are precisely the same, except that a different grade or kind of photographic emulsion is