kes out the greater part of the loose dust and dirt. Later, they
are sorted more carefully by hand into several grades, according to
their colors and cleanliness. All the woollens, gunny, buttons, hooks
and eyes, silks, and foreign materials are thrown aside. As the rags
are usually too large to be thrown into the boilers to be cooked, they
are cut into very small pieces by means of sharp revolving knives, to
which they are fed rapidly from an endless belt. When cut, they are
packed into a revolving kettle or boiler, called a "rotary," and
cooked with caustic soda and lime for several hours, to disintegrate
the fibres, separate the cellulose matter, and "start" the colors. The
rags, after coming out of the boiler, look very dark, and are all
mashed together. They are then thrown into a tub of water and revolved
horizontally by means of a large wheel fitted with radial knives,
which tear and bruise them while water continually runs in and out,
carrying away the dirt. In a few hours the rags look much cleaner, and
a small amount of chlorate of lime and sulphuric acid is run in to
bleach them white. After having been thoroughly stirred for a while,
the stock is run into what is called a drainer, where it is allowed to
stand for several hours to drain off as much water as possible. Liquid
chloride of lime, which is used for bleaching, and sulphuric acid is
then run over the fibre, which in turn is drained and washed off
again. By this time the pulp is white enough to be sent to the
beaters, to be prepared for the paper machines, and is called
"half-stock."

Wood fibres for book papers are usually treated in the same general
way as rags. First, the logs are peeled and are cut into suitable
lengths to be thrown into a wood chopper and cut up in very small
pieces. If the wood is treated by sulphurous acid or bi-sulphite of
lime fumes, it is called the "sulphite process"; if by caustic soda,
the "soda process." This wood is cooked in large upright kettles
called "digesters." In one case the sulphite fumes are allowed to
permeate through the wood under a high pressure, and in the other the
caustic soda is put in "straight," and the wood is cooked under a high
pressure of steam. This is done to dissolve out all the gum and
resins, in order to leave the pure cellulose matter. After the cooking
is done, the stock has to be bleached in very much the same way as
the rags and washed thoroughly before it is ready for the "beaters."