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526 Transactions of S.M.P.E., Vol. XI, No. 31, 1927
of 8 ounces for each spring or a total of 16 ounces. The spring tensions should be adjusted individually at intervals by attaching a spring balance to the upper end of a narrow film strip placed at one side of the gate and increasing or decreasing the gate tension until the film just commences to travel upwards when the spring registers eight ounces with an upward pull.
In a like manner the tension with full width film should be adjusted to sixteen ounces.
B. The nature and smoothness of the gate surfaces. The nature of the gate material in contact with the film surface, providing it is of sufficient hardness, is of less importance than its degree of smoothness. Satisfactory materials are cast iron or stainless steel, either plain or chromium plated. Corrosion should be carefully guarded against and any gelatin incrustation removed with a wood or bone scraper so as not to scratch the polished surface.
C. The temperature existing at' the gate. As explained above, the tendency of the gelatin to incrust on the gate springs in the case of freshly processed film increases with temperature. Any means of reducing gate temperature, such as the use of heat absorbing glass, a blast of air impinging on the gate, or suitable radiating fins on the gate, is desirable.
Methods of Facilitating the Passage of Motion Picture Film through
the Projector
Even though a projector is in good mechanical condition and the above requirements are fulfilled, there is invariably a tendency for a gate incrustation to form with ''green" film. Numerous methods of treating the film to offset this have been suggested from time to time as follows:
1. By Edge Burnishing the Gelatin Surface. It was considered that if the burnishing effect of the gate springs on the gelatin coating of the film could be simulated by a preliminary treatment, the difficulty caused by incrustation might be diminished. Accordingly, a machine was constructed for burnishing the edges of the film (see Fig. 8) consisting of a highly pohshed undercut roller (Ri) working against the edges of the film and revolving above an idler roller (R2). The film was fed between rollers Ri and R2 by means of a gearing so arranged that the film advanced through a distance of l/80th the circumference of the roller Ri for every revolution of