nearly 2000 acres of forest a year. The United States grinds up about
five million cords of wood a year in the manufacture of pulp for paper
and other purposes.

In making "mechanical pulp" the blocks of wood, mostly spruce and
hemlock, are simply pressed sidewise of the grain against wet
grindstones. But in wood fiber the cellulose is in part combined with
lignin, which is worse than useless. To break up the ligno-cellulose
combine chemicals are used. The logs for this are not ground fine, but
cut up by disk chippers. The chips are digested for several hours under
heat and pressure with acid or alkali. There are three processes in
vogue. In the most common process the reagent is calcium sulfite, made
by passing sulfur fumes (SO_{2}) into lime water. In another process a
solution of caustic of soda is used to disintegrate the wood. The third,
known as the "sulfate" process, should rather be called the sulfide
process since the active agent is an alkaline solution of sodium sulfide
made by roasting sodium sulfate with the carbonaceous matter extracted
from the wood. This sulfate process, though the most recent of the
three, is being increasingly employed in this country, for by means of
it the resinous pine wood of the South can be worked up and the final
product, known as kraft paper because it is strong, is used for
wrapping.

But whatever the process we get nearly pure cellulose which, as you can
see by examining this page under a microscope, consists of a tangled web
of thin white fibers, the remains of the original cell walls. Owing to
the severe treatment it has undergone wood pulp paper does not last so
long as the linen rag paper used by our ancestors. The pages of the
newspapers, magazines and books printed nowadays are likely to become
brown and brittle in a few years, no great loss for the most part since