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884 TranmcUons of S.M.P.E., Vol XIII, No. 38, 1929
ing, it may be removed by bathing the film in a dilute (1.0%) solution of sodium carbonate. This must be done at a relatively low temperature (not above 65° F.) because the carbonate solution destroys the hardening, permitting the gelatin to soften and swell which may be followed by subsequent reticulation at higher temperatures.
EFFECT or DEVELOPER on HARDENING PROPERTIES
OF A
EDGING BATH
POTASSIUM ALUM O.S%
ACETIC ACID l.OM
SODIUM SOLPMITC 0-*V.
HVPO 30?4
PCRCENT OCvei-OPCR AOOCO
Figure
Effect of the addition of developer on the hardening properties of a fixing bath.
It has also been considered that excessive hardening of the gelatin film increases the brittleness of motion picture positive film thus shortening its projection life. In order to check this, samples of positive and negative motion picture film were treated with an acid alum fixing bath so as to give melting points of 125° F. and 180° F. respectively. These films were stored for six months at 115° F. and at a relative humidity of 80%, and then stored for one year at 70° F. and 60% relative humidity. The films were tested for brittleness and the tendency of the emulsion to strip from the base at intervals during the keeping tests, and in no case was there any tendency of the emulsion to strip, while the films at no time were unduly brittle.
It is therefore considered that provided motion picture film is properly processed and thoroughly washed and stored under suitable conditions of temperature and humidity, moderate hardening with potassium alum does net materially impair the keeping properties of gelatin films.