The methods now in use for bleaching silk, wool, and all animal
fibers, such as sulphurous acid, alkalies, soap, etc., are so
imperfect that Tessie du Motay has patented the following process,
involving the use of binoxide of barium, with or without the addition
of permanganates. The binoxide of barium is pulverized and subjected
to the action of carbonic acid to remove any unconverted caustic
baryta present. It is then thrown into boiling water, and after the
bath has partially cooled the materials to be bleached are introduced
and the bath kept at a temperature of 86 deg. Fah. to 194 deg. Fah. for two
hours; silk from wild silkworms requiring a higher temperature than
wool, goat's hair, and the like. It is then taken out and washed, put
into an acid bath, then washed again. If necessary, the barium bath
is repeated, as also the subsequent washings. If this second bath of
binoxide of barium does not produce the requisite whiteness, it is
introduced into a solution of permanganic acid or permanganate of
magnesia before the last washing.
Binoxide of Barium, BaO_{2}, is made by subjecting the oxide or
caustic baryta, BaO, to a stream of oxygen or common air at a high
temperature. Its bleaching action is probably due to the formation of
peroxide of hydrogen in solution in the bath.
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