The effect of pneumatic pressure on photographic sensitivity for yellow and violet light is investigated. Three different gases, namely, N2, CO2, and H2, were used in the experiment to produce the pressure. In the case of N2 and CO2, all the films show a lower sensitivity when they are subjected to pneumatic pressure during exposure. On the other hand, the application of pneumatic pressure before exposure increases the sensitivity of the films. No appreciable modification of sensitivity is observed when pressure is applied after the exposure. In the case of hydrogen, the result is somewhat different: All the films show generally higher sensitivity when they are subjected to pressure either during or before exposure. In all cases, the effect of pneumatic pressure on photographic sensitivity, as interpreted by the mean value of the variation of density from the portion of normal exposure on the characteristic curves is found to be independent of the wave-length of light. The abnormal behavior of hydrogen on photographic sensitivity is considered to be due to the chemical activity of the gas on the silver bromide of the emulsion. Certain differences between the effects produced by pneumatic and mechanical pressures on photographic sensitivity are pointed out and discussed.
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