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March, 1930] SURFACE TREATMENT OF SOUND FlLM
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but thorough scouring is given to the emulsion surface. At the point where the film leaves the first tank a single squeegee is located to prevent the more or less dirty liquid being carried in a large quantity into the tank B. New cleaning liquid is introduced in tank B and then transferred to tank A so that the film is finally rinsed in clean liquid.
Bach sample, except Nos. 102 and 103, was again measured and the procedure repeated after projecting for 20, 30, 40, 50, 82, and 130 times, respectively.
The results of these measurements are shown in Table IV where the ume level of a 2000 cycle constant frequency as 100. When the film
FIG. 2. Diagram of the cleaning machine.
relative ground noise volume levels are expressed in terms of the volsamples were being measured, this constant frequency was measured at frequent intervals, as a check on the constancy of the photo-cell and the amplifier.
The excellence of the different treatments included in Table IV is shown in Table V in the order of their decreasing merit.
The values in Table IV are expressed graphically in Fig. 3. From the curves and Table IV it is seen that samples Nos. 91, 93, 102, 107, and 111 were very satisfactory and much better than any of the others. Sample No. 102 (cantol wax, buffed, and solution edge-waxed) shows the very permanent protective effect found in the preliminary study. It is noteworthy that this sample was neither cleaned nor retreated. Also, a clean dry plush can be used repeatedly for cleaning this surface