acid gases
Gases which may form destructive acids in paper,
board, leather, and other book materials. Sulfur
dioxide (SO 2 ), present in the air as
a pollutant, is one such gas; it can form highly
destructive sulfuric acid (H 2 SO
4 ), either by oxidizing to form sulfur
trioxide (SO 3 ), which in the presence
of water vapor, is transformed into H 2
SO 4 , or by combining directly with
water vapor to form sulfurous acid (H 2
SO), which, while a weak acid itself, reacts with
oxygen to form H 2 SO 4 . It
is suspected that the rate of conversion is
increased by the presence in the paper of metallic
catalysts, such as iron or copper, which may enter
the paper during manufacture, but as yet there is
no proof of this. (193 , 265 )
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