Souring only to pH 5.0 is usually without effect in removing iron stains. After souring to pH 5.0, it is necessary to add dilute stock solution equivalent to about 1/2 pound of Ammonium bifluoride for each 100 pounds of cloth. It is usually advisable to carry out stain removal at 140-180'F. The excess Ammonium bifluoride solution should be rinsed out at least to a pH of 5.0. If the soluble, colorless iron salts are allowed to remain in the cloth, the iron stains will show up again the next time the cloth delay is desired.
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