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Oct., 1944 PROPERTIES AND BEHAVIOR OF FILM 233
and safety base, both at 50 per cent RH and after soaking in water, is given in Table 1. The ratio of the concentration of moisture in the emulsion to that in the base is much larger than the ratio of the quantity of moisture in the emulsion to that in the base. This, of course, is due to the approximately ten-fold greater thickness of the base and the difference in density. It may be seen that there is little difference in the moisture content of the regular and fine-grain emulsions at 50 per cent RH, but after soaking in water the regular emulsion absorbs more moisture than the fine-grain emulsion. The safety base has a higher concentration of moisture than the nitrate base at 50 per cent RH, although the quantity of moisture per unit area is about the same because of the difference in density of the 2
TABLE i
The Approximate Moisture Content of Eastman Motion Picture Positive Emulsion
and Film Base
Equilibrium Moisture Moisture Content After Content at Soaking in Water
50 per cent at 70 F (approximate RH at 70 F equilibrium)
Concen Quantity Concen Quantity tration of tration of
of Moisture, Moisture, of Moisture, Moisture,
Material per cent gm per ft2 per cent gm per ft*
Regular Emulsion (Stripped)
(TypeJ302) 8.0 0.16 290.0 5.8 Fine-Grain Emulsion (Stripped)
(Type 1302) 9.0 0.18 180.0 3.6 '
Nitrate Base 1943 1.25 0.25 2.7 0.55
Safety Base 1943 1.40 0.25 6.0 1.00
types of base. After soaking in water the difference between the safety and nitrate base is much more marked. The last column of Table 1 is of particular interest in the drying of the developed film since the figures indicate the relative amounts of moisture which must be removed from the particular type of emulsion or base in question.
Brief mention should be made here of a phenomenon known as moisture hysteresis which has been found to exist in many materials such as paper,7 gelatin,9 and cellulose derivatives.10 The curves, in Figs. 2, 3, and 4 are moisture adsorption curves, that is, curves obtained by allowing very dry materials to gain moisture. However, if a moist material is dried, a desorption curve is obtained similar to that shown in Fig. 5. Hysteresis is essentially a lag in the attainment of equilibrium, so that a higher moisture content is found if a