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290 CRABTREE, SANDVIK, AND
In the absence of the surface waxing treatment with newly processed prints it is imperative either to edge-wax as recommended or to pass the film through a cleaning machine using a 0.5 per cent solution of light motor oil in carbon tetrachloride in the second tank, the first tank being by-passed. This treatment will apply a thin film of lubricating oil to the entire film surface which will assist in preventing the accumulation of ground noise although, in view of the slightly tacky nature of the oiled surface, the film will accumulate dust and dirt more rapidly than cantol waxed film and will require cleaning and retreating frequently.
The authors are indebted to Mr. D. B. Hyndman for assistance in the experimental work.
Note. — Since the above experiments were completed it has been found that sound record film may be satisfactorily edge-waxed by using a 10 per cent solution of paraffin in carbon tetrachloride and rotating the application disks so that the peripheral speed is about one-twelfth the speed of the film. With this procedure no auxiliary drying apparatus is necessary.
DISCUSSION
MR. DICKSON: Did you run samples of film through the carbon tetrachloride forty or fifty times in these tests?
DR. SANDVIK: No, we cleaned some of the samples as many as seven times.
MR. DICKSON: Does treatment with carbon tetrachloride make the film brittle?
MR. CRABTREE: If carbon tetrachloride is pure, and reputable commercial samples are pure and free from sulphur, the film is not affected. If sulphur compounds are contained in it, the image is eventually toned brown.
MR. RICHARDSON: Recently I received a complaint from a New York City exhibitor that his projectors were continually damaging film. I found that the aperture tension was abnormally high — so high that 145 feet of film per minute could be projected with no over-shooting. High tension is the primary cause of excessive film wear and of the deposition of emulsion on the tension shoes. This difficulty could be remedied by the projector manufacturer. If he would provide a tension adjustment, theaters requiring a ninety foot per minute projection speed would not abuse the film to the extent they now do.
MR. CRABTREE: I don't know whether Mr. Richardson heard the first part of the paper. The object of the treatment is to enable you to get "green" film through the projector, and this method ensures that you cannot get too much wax on it. Molten wax is all right if it is put on correctly but usually it is not. The second object is to prevent the accumulation of ground noise, which you notice could be produced by conically cinching the film. The matter of the tension of the shoes has nothing to do with this.