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March, 1930] SURFACE TREATMENT OF SOUND FlLM 279
No method of lubrication has been found which gives longer projection life before complete breakdown of the film than the molten paraffin treatment used for comparison in these tests but the projection life is as great with the paraffin solution treatment as with the molten wax method.
A small amount of wax accumulated in the projector gate when a film treated with a solution which applied 0.3 gram of paraffin per 1000 feet of film was projected. This amount was therefore considered somewhat excessive even though no evidence was given that any interference with sound reproduction might come from it. There
T ABLE I Results of Wear and Tear Tests
Method of Lubrication
Wearing Properties
None Molten paraffin test No. 1 Molten paraffin test No. 2 Paraffin solution 0.15 gram wax per 1000 ft. film 0.30 gram wax per 1000 ft. film
100% 408% 380%
407% 423%
fore, the safe limit was considered to be 0.15 gram per 1000 feet of film. It will be seen from the table that the degree of lubrication given by this quantity of paraffin is equal to that given by 0.3 gram within the error of measurement.
Control of the Rate of Application of Wax. — The concentration of the wax solution to be used depends largely upon the quantity to be applied, although there are definite practical limits to the useful concentration. When using the applicator as first built, that is, with the disks running at the same peripheral speed as the film, a rather large volume of liquid was applied so that it was necessary to use a dilute solution (0.25 per cent). This method was discarded because the liquid accumulated in drops which dried slowly and showed some tendency to run out of the perforation area. When the apparatus was so modified that the peripheral speed of the disks was less than the speed of travel of the film, less liquid was applied and it was necessary to use a stronger solution (one per cent). With the more even distribution of the liquid produced by the rubbing effect where slippage occurred between the film and disks, the coating dried very easily. With the hot air tube three feet long and the cold air tube