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276 CRABTRBK, SANDVIK, AND IVES [J. S. M. P. E.
film is no longer held flat but oscillates in and out of the focal plane with the well-known "in and out" of focus effects. Also, since the film is in a condition of varying strain between the intermittent sprocket and the projection aperture, the projected picture is unsteady. A similar action at the sound aperture causes a flutter in the volume and frequency of the sound.
Effects of Wrong Lubrication. — -A large quantity of paraffin or other wax applied to the edges of the film prevents adhesion between the film and gate surfaces but the wax falls off in flakes when the roll is rewound after being wound up in a warm condition. Particles of wax then lodge on the sound track with deleterious effects and accumulate in the reproducer slit or aperture, diminishing the volume of reproduced sound and in some cases cutting off the sound completely. Some treatments to which film is subjected for the supposed purpose of lubricating it have still worse effects and actually introduce noise and shorten the useful running life of the film.
A Satisfactory Method of Lubrication. — Previous work on the lubrication of motion picture film has shown that a suitable application of paraffin wax gives the best lubrication. In an earlier communication2 on this subject a process of application of wax over the entire emulsion surface was described which required the use of a combined wax applicator and buffing machine. A mixture of paraffin and carnauba wax dissolved in a non-inflammable solvent was applied to the film surface which was then buffed, for otherwise the waxed surface remained dull and diffusing. This treatment was found to give a satisfactory degree of lubrication together with protection of the whole surface against abrasions and oil markings.
This treatment is not ideal for sound prints, because, in order to obtain a high degree of lubrication, it is necessary to use a large proportion of paraffin and this produces a surface which is rather susceptible to finger markings and which collects dust particles readily. It resists scratching, however, and dirt and scratches are largely confined to the wax layer which can be removed by a cleaning solvent.
The present method of applying a thin line of molten wax along the edge of motion picture film is open to the following objections:
1. The quantity of wax applied is not readily capable of control.
2. The wax is applied in a narrow, but thick ridge, which must be spread out by the pressure pads in the projector.
3. The method is subject to certain accidents in operation which render its use less dependable than could be desired. If the waxer is used before the wax is sufficiently warm or if a draft of cold air strikes