This cylinder is made of wood, and furnished with a number of parallel blades, fixed longitudinally around its circumference. Immediately beneath this cylinder is a block of wood extending its length, and of the breadth of the space between the two dotted lines represented. The upper surface of this block conforms to the curvature of the cylinder, and it is provided with teeth or blades, placed close together, so as to present so many acute cutting angles, which present themselves constantly to the teeth on the revolving cylinder, not in contact, but so near as to cut, chop, and tear the rags as they are forced between them by the action of the machine. The distance between these opposed series of teeth is always susceptible of regulation, by turning screws at f f, which raise or lower the bearings gg of the axis of the cylinder, which bearings are levers turning upon fulcrums at h h. The engine is served with water by a pipe i from a reservoir supplied by the pumps, which it delivers into a small cisternj, communicating with the engine. This pipe is provided with a cock, to stop or regulate the quantity of water; and to prevent any extraneous matter passing with the water into the engine, it has a hair or wire strainer k placed across it.
When the engine is filled with water, and a quantity of rags put in, they are, by the revolution of the cylinder, drawn between its cutters and those on the block underneath. This cuts them into pieces; then, by the rapid motion of the cylinder, the rags and water are thrown upwards over a breasting, which rises in the same curve with the toothed block, up to about the middle of the cylinder; from this point they descend an inclined plane, whose length is represented by the dotted line l, and take a course round the vat, as indicated by the arrows; the whole contents of the vat are thus put into motion, which continues as long as the cylinder revolves; that being of course determined by the uniform reduction of the rags into a pulpy consistency The cutter block is made so as to slide into or out of its place from the outside of the machine, for the convenience of sharpening its teeth, etc. The cutters of the cylinder are fixed into grooves made in the wood of the cylinder, at equal distances from each other around its circumference, in a direction parallel to its axis; the number of these grooves is twenty; and for the washer, each groove has two cutters or blades put in it; then a fillet of wood is driven fast in between them, to hold them firm, and the fillets are nailed fast into the solid wood of the cylinder.
The beater is made in the same manner, except that each groove contains three bars and two fillets.
In the operation of this cylinder, it is necessary it should be inclosed in a case, or its great velocity would throw all the rags and water out of the engine. The case is a wooden box, inclosed on all sides except the bottom; one side of it rests on the edge of the vat, and the other upon the edge of the partition b. Inside this case are two hair or wire strainers, through which the foul water passes as it is dashed against them, and on the opposite side of these strainers the case is formed so as to conduct the foul water into two flat lead pipes, seen in section at o o, out of the machine. When the water is not required to be carried off, as in the beating engines, there are sliding shutters provided to these sieves, which pass through grooves on the top, and at the sides of the case, by which the water as well as the rags are returned into the engine.
When the rags have been about an hour in the first engine, if they require it, according to the modern practice, they are bleached. There are two ways of bleaching used at present; one by the oxymuriatic acid gas, the other by the acid combined in the dry way with quicklime. In the first way, the rags are boiled in an alkaline solution of potash and lime for four or five hours, or if very coarse, for eight hours. The purpose of this is to destroy the coarse part of the hemp, commonly called shon or sheave, and which exists in a great degree in coarse linens, especially German rags. The solution is then washed out in the washing engine; the water being pressed out, they are exposed to the acid in the gaseous form, as linen is; (see the article Bleaching.) The gas is then washed out as carefully as possible; this is of great importance, as, if any acid remain in the rags, it causes the paper, after some time, to putrefy and change its colour. In the other way, the oxymuriate of lime is diffused in water by agitation, the insoluble matter is thrown out, and the liquid, when clear, is diluted and put in the engine; being thoroughly mixed with the rags, it in allowed to stand for an hour or more, and the acid carefully washed out.
Bleaching is not now quite so much practised as formerly, on account of the low price of rags; indeed, we understand that unbleached papers are entirely used in the Oxford. University Press, for the printing of bibles, testaments, etc, on account of their great durability. After the bleaching, (if that process is used at all,) the stuff is reduced for an hour or more in the washing engine, and is then put into the beating engine. When it has been beat, as it is called, for about three hours and a half, it is generally fine enough, and a valve placed in the bottom of the engine being opened, the stuff escapes into the chest, or general reservoir, which supplies the vat or other machinery.
We shall now proceed to describe the mode of making paper by hand, without the aid of machinery, (in the common acceptation of that term.) The vat is made of wood, and generally about five feet in diameter, and two and a half in depth. It is kept at the required temperature by means of a grate, introduced by a hole, and surrounded on the inside of the vat by a case of copper. For fuel to this grate, charcoal or wood is used; and frequently, to prevent smoke, the wall of the building comes in contact with one part of the vat, and the fire has no communication with the place where the paper is made. Every vat is furnished on the upper part with planks, inclosed inwards, and even railed in with wood, to prevent any of the stuff from running over in the operation. Across the vat is a plank, which is called the trepan, pierced with holes at one of the extremities, and resting on the planks which surround the vat. The moulds are composed of wire cloth, and a movable frame. The wire cloth is varied in proportion to the fineness of the paper, and the nature of the stuff. A laid mould consists of a frame of wood, neatly joined at the corners. Wooden bars run across it, about an inch and a half distance from each other.