F. H. Richardson's bluebook of projection (1935)

196 richardson's bluebook of projection Measuring Film Accurately (68) To measure the length of a reel of film accurately count the rotations of the projector mechanism crank shaft. Exactly one foot of film is passed with each rotation. Film measuring devices may be purchased from supply dealers. Removal of Emulsion (69) To remove the emulsion from the film, first soak it in a bucket of warm water to which has been added all the ordinary washing soda it will absorb. Let the film soak until the emulsion has become soft, after which it may be washed or rubbed off. Afterward rinse the film thoroughly in clean, warm water. Soaking for a long time, over night, for example, will do no harm. Cleaning Film (70) Film may be cleaned with a soft cloth saturated with commercially pure carbon tetrachloride. Be careful not to scratch the film. The carbon tetrachloride must evaporate thoroughly before the film is rewound. If this is not done, the tetrachloride will bleach the emulsion away. (71) Film is often cleaned with gasoline or benzine, but for several reasons we do not advise it. For one thing the film will curl badly. It may be harmed in other ways. As a rule it is best to leave the responsibility for cleaning the film to the exchanges where it should be done. They have the proper equipment and the staff to do it properly. The theatre should insist on receiving clean film from the exchanges. Rain (72) The effect termed "rain," which appears on the screen when old film is used, is caused by scratches in the film emulsion that have filled with dirt and thus have become more or less opaque. The projectionist himself should object to receiving oil-smeared film from an exchange. It is right that he should do so, but he must remember that the oil got