Journal of the Society of Motion Picture Engineers (1930-1949)

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34 CRABTREE, EATON, AND MUEHLER [J. S. M. P. E. It is seen that an increase in pH of the wash water caused a decrease in the time required to eliminate a given quantity of hypo from a given emulsion. This fact is of practical importance, especially where an alkaline water supply is used, and is contrary to the claims of D. K. Allison12 that washing with water adjusted to the isoelectric point of the gelatin will produce the most efficient hypo removal, but it substantiates the results of Sheppard and Houck.13 The most convenient and useful alkali for this purpose is ammonia. In an experiment comparing the treatment of film in ammonia after fixation in a potassium alum bath with fixation in a chrome alum bath, the results showed that the ammonia treatment has an effect equal to that of chrome alum in permitting hypo removal. Super-^ Negative Film, Type 1232, was fixed in F-25, rinsed for 2 minutes, bathed in 0.03 per cent ammonia solution (pH — 10.2, and washed with film samples fixed in F-25 and in the chrome alum F-23 bath. The results are given in Table VI. TABLE VI Effect of Dilute Ammonia Bath After Fixing on Hypo Removal Hypo Content (Mg per Sq-In) Fixing Bath Treatment 5 Min 15 Min 30 Min Potassium alum ( F-25} 0 . 56 0 . 24 0 . 08 Potassium alum (F-25} 0.03% Ammonia Nil Nil Nil Chrome Alum (F-23} 0.005 Nil Nil When film samples were washed in the same apparatus with the /?H of the water maintained at approximately £H-9.5, the rate of removal was almost as great as indicated in Table VI. TABLE VII Effect of Ammonia on Degree of Hardening (Emulsion 1232} Concentration of Melting Point (°F) Ammonia 2 Min Bathing 5 Min Bathing 10 Min Bathing (%) 0.56 161 140 100 0.28 174 166 126 0.14 182 176 154 0.07 186 182 172 0.03 194 192 190 0.00 210 210 210 The hardness of the gelatin film is affected by this alkaline treatment but not to any serious extent if the concentration of alkali is not excessive. From Table VII it is seen that ammonia used