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Dec., 1940] COMMITTEE ON PRESERVATION OF FILM 599
(1) taking the amount of film and the size of the container as constants and the vent area as the variable, (2) taking the vent and the container as constants with the amount of film as the variable, and (3) taking the vent and the amount of film as constants and the size of the container as the variable. The sizes of the containers ranged from 197 cu-in to 38,016 cu-in or 22 cu-ft. The amount of film ranged from 8 oz to 30 Ib. A very satisfactory correlation was noted in the results obtained. The values for pressures plotted against the ratio of film to vent area formed a regular curve. The pressure rises slowly with increase in the ratio of film to vent area until a critical point is reached, above which the curve rapidly approaches the vertical. Beyond this point a slight increase in the amount of film or a slight decrease in the vent area will result in explosive pressures.
In the studies referred to it was found that 6 Ib of raw film per sqin of vent area represent a critical point above which there is danger of explosions. In view of these experiments The National Archives reiterates its recommendation of 20 sq-in of vent area per 100 Ib of film in standard vault construction. It should be noted that this discussion is based on the use of unenclosed films anoVon preliminary data furnished by the National Bureau of Standards. A final and detailed report is to be issued shortly by that agency.
(HI) PRINTERS FOR OLD AND SHRUNKEN FILM
Hitherto there has not been much demand for the reproduction of films which were too old and shrunken to pass through an ordinary printer. It is true that at various times old films have been reproduced for various commercial purposes, both by optical6 and by step printers,7 but the problem did not assume a serious aspect until the use of old films for museum and archival study and research purposes became as significant as it is today.
With the advent of sound, modern film processing became a much more precise procedure than it was in the old days before rigid standards8 for film dimensions were established. The present trend in film printing has been for the elimination of the old style step or intermittent printer and to substitute for it the much speedier and more precisely constructed continuous printer.9 However, the step printer had an advantage which the continuous printer does not have. As each frame was printed step by step in the intermittent printer any minute deviation10 of the negative was independently corrected on the copy by a slight shifting of the relation between the negative and