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190 GREGOR AND SHERMAN August
squeegee, followed by washing all the fix out of the paper. It was found that to wash one thousand 8 X 10-inch prints, a unit having a bed volume of approximately 5 liters would be required. Prints washed in this demineralized water were compared with ones washed in distilled water; no differences were observed. The stability and clarity of the prints were unchanged, as shown by "Fadometer" tests.
Other demineralization processes were also tested. By the use of a strong-base anion exchange resin ahead of a cation resin, the normal cycle can be reversed. Thus, neutral salts in the influent are converted to their corresponding hydroxides by the anion bed, followed by base absorption in the cation bed. In this experiment the anion exchange resin Amberlite IRA-400,* which has most of its capacity in the form of strongly basic groups, was used. This bed was followed by one of Dowex 50. While this demineralization system produced a good grade of wash water, its capacity was considerably less than that of the one adopted.
The use of a weak-acid cation exchange resin was also investigated. When a carboxyl resin is used in conjunction with an anion exchange bed, demineralization can occur. The small amount of acid formed upon the first pass is absorbed by the anion bed, and the neutral effluent upon recycling can have more of its cations converted to acid and be absorbed. This system was investigated, using Amberlite IRC-50* as the weak-acid cation exchange resin, and lonac A-300 as the anion exchange resin. This system was able to demineralize wash water. However, the rate of the process was much too slow for printwashing. Also, the quality of water produced was poor.
The applicability of this method for color-process work was demonstrated by developing identical batches of Ansco color film simultaneously, one being washed in tap water and the other using the demineralization apparatus. The developing outfit was Type 2. No detectable difference in the quality of the two prints appeared. It has been observed that reticulation of film occurs in some instances where wash water of too high purity is used, due to the excessive swelling of the emulsion caused by osmotic pressure. This can be avoided for the demineralization process by adding a small amount of a nonelectrolyte, as urea, to the water, since compounds of this type are not affected by ion exchange.
* Rohm and Haas Co., Philadelphia, Pennsylvania.