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278 CRABTREE, SANDVIK, AND IVES [J. S. M. p. E.
with the emulsion side down and then carried through the air for a sufficient distance to permit the carbon tetrachloride to evaporate completely before the wind-up was reached. The applicator rollers were driven by the film passing over them. No other roller was permitted to touch the edges of the film, where the paraffin had been coated, until the solvent was completely evaporated. A photograph of this equipment is shown in Fig. 1. The film is held by the idler rollers against the applicator disks (A) which dip into the solution in tank (T). The film travels from left to right and passes directly into the drying tube (D) through which a stream of warm air is passed in the direction opposite to the film travel. In this tube the carbon tetrachloride is evaporated rapidly. The film next enters a similar tube through which cold air is forced, in order to solidify the paraffin which is soft when it leaves the hot tube. Disks of various widths were tried and a width of 0.15 inch was finally chosen. It was considered advisable to apply the lubricant to as much of the area requiring lubrication as is possible without encroaching on the sound track. If the applicator roller extends 0.15 inch inward from the edge of the film these conditions are satisfactorily fulfilled.
When this equipment was first tried the disks were so mounted as to turn freely on the shaft and were driven by the film, which was drawn through the device by a drive roller located after the drying tubes. With this method of driving some difficulty was experienced as a result of the application of too much solution. Experiments were made with other applicator surfaces and means for driving the applicator disks. The preferred method of application was by means of the above steel disks so driven that their peripheral speed was onehalf to one-quarter of the film speed.
Satisfactory disks were also constructed by clamping a disk of leather or other porous fibrous material between two thin metal disks of slightly smaller diameter.
Quantity of Paraffin Applied. — Concentrations of paraffin in carbon tetrachloride varying from 10 to 0.5 per cent were applied to developed positive motion picture film. If the solution was applied in considerable quantity, concentrations of one per cent or greater dried very slowly. If the concentration was less than one per cent drying was not difficult, a few feet of drying tube being sufficient.
Table I shows the results of wear and tear tests made on film lubricated by the method described above in comparison with an untreated sample and two samples lubricated with molten paraffin.