Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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A substance used in removing the remaining traces of free chlorine or hypochlorite not removed from a paper pulp by washing. Typical antichlors include sodium bisulfite (NaHSO 3 ) and sodium thiosulfite (Na 2 S 2 O 3 ). The antichlor is usually added to the pulp stock near the end of the bleaching stage, and is allowed to react until no blue coloration is obtained with a potassium-starch indicator. This removes the last traces of hypochlorous acid, hypochlorite ion, and free chlorine. The reaction products are then washed out. Antichlors are seldom used in multistage bleaching operations, as they are considered to be wasteful of bleaching agents. (72 )

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