with water under pressure to
about 260 deg. C., it dissolves completely without decomposition. If boiled
with a strong solution of zinc chloride, or treated in the cold with zinc
chloride and concentrated hydrochloric acid, or with an ammoniacal solution
of copper hydroxide (Schweitzer's reagent), it dissolves to a clear
solution from which it may be reprecipitated without chemical change by
neutralizing or diluting the solution.

Cellulose has the formula (C_{6}H_{12}O_{5})_{n}. When hydrolyzed under the
influence of the enzyme _cytase_, it breaks down, first into cellobiose, an
isomer of maltose, and then into glucose. It is, therefore, chemically
like, but not identical with, starch; and structurally it is arranged in
fibrous form instead of in granules. Under the action of fermentative
enzymes, as when vegetable matter decays under stagnant water, in swamps,
etc., cellulose breaks down into carbon dioxide and marsh gas, according to
the equation

(C_{6}H_{12}O_{5})_{n} + {n}_H_{2}O = 3_{n}CO_{2}+3_{n}CH_{4}.

Cellulose is acted upon by caustic alkalies in a variety of ways. When
fused with a mixture of dry sodium and potassium hydroxides, it is
decomposed into oxalic and acetic acids. When heated with a 10 to 15 per
cent solution of caustic soda, cellulose fibers thicken and become
translucent, thus resembling silk fibers. This process, known as
"Mercerizing," is largely used for the production of commercial fabrics.

Acids also act on cellulose in a variety of ways. When heated with nitric
acid (sp. gr. 1.25), it is converted into _oxycellulose_; while dilute
sulfuric acid, under similar conditions, yields _hydro-cellulose_, a
substance having the formula C_{12}H_{22}O_{11}, which retains the fibrous
structure of the original cellulose but which, when dry, may be rubbed up
into a fine powder. Concentrated nitric acid, or better, a mixture of
concentrated nitric and sulfuric acids, acts upon cellulose, converting it
into various nitro-derivatives, several of which have great industrial
value. The number of NO_{3} groups which unite with the cellulose molecule
under these conditions depends upon the temperature, pressure, etc.,
employed during the nitration process; di-, tri-, tetra-, penta-, and
hexanitrates are all known. _Pyroxylin_, or _collodion_, is a mixture
of the tetra- and penta-nitrates, which is soluble in alcohol and is
used in surgery, in photography, and in the manufacture of celluloid,
which