It is not likely, however, that the human stomach even under the
pressure of famine is able to get much nutriment out of sawdust. But by
digesting with dilute acid sawdust can be transformed into sugars and
these by fermentation into alcohol, so it would be possible for a man
after he has read his morning paper to get drunk on it.
If the cellulose, instead of being digested a long time in dilute acid,
is dipped into a solution of sulfuric acid (50 to 80 per cent.) and then
washed and dried it acquires a hard, tough and translucent coating that
makes it water-proof and grease-proof. This is the "parchment paper"
that has largely replaced sheepskin. Strong alkali has a similar effect
to strong acid. In 1844 John Mercer, a Lancashire calico printer,
discovered that by passing cotton cloth or yarn through a cold 30 per
cent. solution of caustic soda the fiber is shortened and strengthened.
For over forty years little attention was paid to this discovery, but
when it was found that if the material was stretched so that it could
not shrink on drying the twisted ribbons of the cotton fiber were
changed into smooth-walled cylinders like silk, the process came into
general use and nowadays much that passes for silk is "mercerized"
cotton.
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