We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
Demineralization of Photographic Wash Water by Ion Exchange*
BY HARRY P. GREGOR AND N. N. SHERMAN POLYTECHNIC INSTITUTE OF BROOKLYN, BROOKLYN, NEW YORK
Summary—An ion exchange system has been developed to purify photographic wash water and allow its re-use. The effluent from a print-washing machine is cycled through a cation and then an anion exchange resin bed, and returned to the machine. The purity of the water obtained approaches that of distilled water.
This unit was developed for the United States Signal Corps, to be used in mobile photographic units, and is designed to reduce the amount of water required for print-washing. This process is applicable not only to circumstances where water is scarce, but also to processes where wash-water purity and temperature control are important, as in color photography.
THE ION EXCHANGE PROCESS
CATION EXCHANGE RESINS are insoluble, high molecular weight poly acids. They are prepared either by treatment of formed resins to produce acidic groups in the structure, or by having one of the substances used in the resin synthesis already contain the acidic group. An example of a cation exchange resin is shown in Fig. 1, where the resin has been prepared using phenol and formaldehyde (the normal constituents of Bakelite-type resins) and phenolsulfonic acid.
Cation exchange resins contain either phenolic, carboxyl, or sulfonic acid groups. Phenolic groups dissociate only in strongly alkaline solutions. Carboxyl groups dissociate at pR values above 7 to 8, while sulfonic acid groups are completely dissociated at virtually all pH. values. The identification and chemical reactivity of these types of exchange resins are described by Gregor and Bregman.1
In a dissociated acidic group, the hydrogen ion is held in the immediate vicinity of the fixed anionic group by electrical forces, for the system must be electrically neutral. The hydrogen ion can, however, be displaced from the resin if another cation diffuses into the structure to take its place. Thus, if a solution of sodium chloride is placed in
* Presented October 28, 1948, at the SMPE Convention in Washington.
AUGUST, 1949 JOURNAL OF THE SMPE VOLUME 53 183