he making of bags and suitcases.

Here, however, we are not so much interested in manufactures of
cellulose itself, that is, wood, paper and cotton, as we are in its
chemical derivatives. Cellulose, as we can see from the symbol,
C_{6}H_{10}O_{5}, is composed of the three elements of carbon, hydrogen
and oxygen. These are present in the same proportion as in starch
(C_{6}H_{10}O_{5}), while glucose or grape sugar (C_{6}H_{12}O_{6}) has
one molecule of water more. But glucose is soluble in cold water and
starch is soluble in hot, while cellulose is soluble in neither.
Consequently cellulose cannot serve us for food, although some of the
vegetarian animals, notably the goat, have a digestive apparatus that
can handle it. In Finland and Germany birch wood pulp and straw were
used not only as an ingredient of cattle food but also put into war
bread. 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.

Another step was taken when Cross of London discovered that when the
mercerized cotton was treated with carbon disulfide it was dissolved to
a yellow liquid. This liquid contains the cellulose in solution as a
cellulose xanthate and on acidifying or heating the cellulose is
recovered in a hydrated form. If this yellow solution of cellulose is
squir