antichlor
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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