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Crahtree — The Handling of Motion Picture Film 47
however, is excessively swollen at any period and especially before hardening the structure of the finally dried hardened gelatine is more or less spongy and it has, therefore, much less strength than gelatine which has not been swollen.
Apparatus: Suitable apparatus for handling motion picture film in the field at high tem.peratures has been described in previous papers.^
The Care of Developed Motion Picture Film at High Temperatures
At normal temperatures film base undergoes only a very slight change with age — so slow that no alteration of its physical properties takes place for several years, providing the film is not allowed to become excessively dry. Under certain conditions, however, the film base undergoes actual chemical decomposition depending on the conditions of processing and storing.
It has been found that small traces of impurities in the gelatine film such as residual chemicals left in the film either as the result of imperfect fixing or the use of an exhausted fixing bath, or as a result of imperfect washing, or thorough washing in impure water, very materially hastens the decomposition. Film which is to be kept for any considerable length of time should, therefore, be thoroughly fixed in two successive fixing baths and thoroughly washed in pure water.
Experience has also shown that even film which has been thoroughly fixed and washed when stored at high temperatures rapidly becomes brittle, the film base undergoes chemical decomposition and in a few years time the film image is destroyed by the decomposition products. At normal tem_peratures the rate of decomposition is negligible but with rising temperature above 80° F. decomposition takes place at a very rapidly increasing rate. It is very important, therefore, that film should be stored at a temperature not higher than 60 to 70° F. though a temperature around 40 to 50° F. is to be preferred.
^ "A Portable Apparatus for Developing M. P. Film at High Temperatures"' by J. I. Crabtree. B. J. Phot. Aug. 1918, 379.
"The Development of M. P. Film by the Reel and Tank Systems" by J. I. Crabtree, Trans. Soc. M. P. Eng. Vol. 16, 163.