and a revolving screen which drives
out part of the water by centrifugal force. In a great vat of pulp a
drum covered with wire cloth revolves, and on it a thin sheet of pulp
settles. Felting, pressed against this sheet, carries it onward
through rolls. The sheets are pressed between coarse sacking. Such
paper is very poor stuff. In its manufacture the fiber of the wood is
so ground up that it has little strength. It is used for cardboard,
cartons, and packing-papers. Unfortunately, it is also used for
newspapers; and while it is a good thing for some of them to drop to
pieces, it is a great loss not to have the others permanent. When we
wish to know what people thought about any event fifty years ago, we
can look back to the papers of that time; but when people fifty years
from now wish to learn what we thought, many of the newspapers will
have fallen to pieces long before that time.

[Illustration: _Courtesy S. D. Warren Co._

WHERE RAGS BECOME PAPER

The vat where the rags cook and turn over, and the big room where the
web of finished paper is passed through rollers and cut into a neat
pile of trimmed sheets.]

There is, however, a method called the "sulphite process," used
principally in treating the coniferous woods, by which a much better
paper can be made. In all plants there is a substance called
"cellulose." This is what gives strength to their stems. The wood is
chipped and put into digesters large enough to hold twenty tons, and
is steam-cooked together with bisulphite of magnesium or calcium for
seven or eight hours. Another method used for cooking such woods as
poplar and gum, is to boil the wood in caustic soda, which destroys
everything except the cellulose. Wood paper of one kind or another is
used for all daily papers and for most books. Whether the best wood
paper will last as long as the best rag paper, time only can tell.

The Government of the United States tests paper in several ways
before buying it. First, a single sheet is weighed; then a ream is
put on the scales to see if it weighs four hundred and eighty times
as much. This shows whether the paper runs evenly in weight. Many
sheets are folded together and measured to see if the thickness is
regular. To test its strength, a sheet is clamped over a hole one
square inch in area, and liquid is pressed against it from below to
see how much it will stand before bursting. Strips of the paper are
pulled in a machine to test its breaking streng