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EFFECT OF THE WATER SUPPLY IN PROCESSING MOTION PICTURE FILM
J. I. Ctabttee and G. E. Matthews*
WATER is the most widely used chemical in the processing of motion picture film and it is important therefore to know to what extent the impurities present in it may be harmful to the various operations and how these impurities may be removed.
Impurities in Water
Excluding distilled water, rain water, and water from clean melted ice or snow, impurities may be present as follows:
1. Dissolved salts such as bicarbonates, chlorides, and sulfates of calcium, magnesium, sodium and potassium.
2. Suspended matter which may consist of:
(a) Mineral matter such as mud, iron rust, or free sulfur.
(b) Vegetable matter such as decayed vegetation.
(c) Animal matter such as biological growths and bacteria. The suspended particles may be of colloidal dimensions when they are difficult to remove by filtration.
3. Dissolved extracts usually colored yellow or brown from decayed vegetable matter and the bark of trees.
4. Dissolved gases such as air, carbon dioxide, sulfur dioxide, and hydrogen sulfide.
Effect of Impurities on Processing Development
1. If a developing solution is prepared with water containing calcium salts, a white precipitate consisting largely of calcium sulfite, but with some calcium carbonate, is apt to form on mixing.
In some cases a precipitate does not form immediately but a sludge1 consisting of fine needle-shaped crystals of calcium sulfite separates out on standing (Fig. 1) . Magnesium salts, unless present in excess, are not precipitated. Such a sludge or precipitate will settle out on the emulsion side of film, plates, and papers and cause spots.2 The white precipitate or sludge is harmless, however, if allowed to settle and only the clear supernatant liquid drawn off for use.
The developer, of course, is robbed of sulfite and carbonate to the extent of the quantity required to form the sludge or precipitate, but except in the case of developers of low alkalinity, this effect is negligible. Experiments have shown that the quantity of calcium or magnesium salts occurring in average natural waters in the United States is insufficient to produce any appreciable effect on the developing power of developers containing 0.3 % sodium carbonate by virtue of a lowering of the carbonate content.3
* Kodak Research Laboratories.
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