to considerable pressure which removes further quantities of water. The paper is then firm enough to be dried, a process effected by means of drying cylinders, a few of which are shown. The actual details of the conversion of the beaten pulp into a sheet of paper can only be described very briefly.

Stuff-chests.-The pulp from the beaters is discharged into a stuff-chest and a considerable quantity of water added in order to produce a mixture having a proper working consistency. Usually each machine is provided with two stuff-chests, so that while one is being filled from the beaters, the other is utilised for supplying the machine. In this way the danger of producing variations in the weight and substance of the paper is avoided. The mixture of pulp is kept in a state of gentle motion in the stuff-chest by means of slowly revolving agitators, an operation which is necessary since the pulp would otherwise gradually sink down into the bottom of the chest.

Feed-box.-The constant and regular supply of a thin diluted pulp of uniform consistency is a most important and essential feature of the process of paper-making. The machine is not fed direct from the stuff-chests, but from a small supply-box erected at a convenient height above the level of the endless wire, and in a position which the machine man can readily reach. This box is filled from the stuff-chest by means of a pump which

A

B

Fig. 15.-Diagram of Feed-box which regulates the Supply of Pulp to the Machine.

C. Inlet pipe, through which the pulp is pumped from the stuff-chest.

D. Supply of pulp and water in box.

B. Supply pipe to paper-machine.

4. Overflow pipe, through which surplus pulp flows back to stuff-chests.

discharges into it an amount of pulp more than the machine will take, and the surplus stuff flows away back into the stuff-chest by means of an overflow pipe fixed near the top of the box. By this means the level of the diluted mixture is kept constant, so that the rate of flow from the bottom of the supply-box through the small pipe which feeds the machine is always the same, when the tap or valve fixed to the pipe is kept open at one position.

The actual quantity of pulp discharged per minute is regulated by this valve, and the rate of flow determines the thickness and substance of the finished paper. The substance is not entirely governed, however, merely by the opening or closing of the valve, as there are other devices in use for this purpose which have to be employed according to circumstances.

Sand-traps. The pulp flows from the feed-box direct into sand-traps, which keep back any dirt, impurities, or lumps of pulp. These are simply very long,

shallow, open boxes about nine to twelve inches wide, six to eight inches deep, and of varying length. For papers of extra good quality the sand-traps exceed 100 feet in length, consisting of narrow boxes placed side by side, connected at the ends by semi-circular channels, so that the pulp flows through the entire distance. A very slow rate of flow is required to ensure a complete separation of undesirable impurities.

At the point where the pulp enters the sand-traps, it is still further diluted with backwater, as it is called, which is the surplus water falling through the endless wire-cloth of the machine. This water contains a considerable quantity of fibre and other ingredients, and is thus utilised so as to prevent a serious loss of material and avoid a reduced output of paper.

The proportion of water to air-dry pulp in the mixture flowing through the sand-traps varies greatly according to the nature of the pulp, the quality of the paper being made, and other conditions of a technical character. In the case of a cheap printing paper the dilute mixture will contain about 10-12 lb. of pulp to every 100 gallons of water.

Strainers. The pulp from the sand-traps is thoroughly strained in order to remove any dirt or lumpy pieces of fibre which have not been retained by the sand-traps.

There are many forms of machines used, but for rag pulp the so-called flat strainer is most frequently adopted. It consists of a rectangular iron box mounted on strong heavy supports, the bottom being formed out of a number of strong brass plates, in which are cut fine slits. These slits are very narrow, but the width varies according to the nature of the pulp, being governed by the diameter of the fibres. With fibres of small diameter the slits may be only seven-thousandths of an inch.

The rectangular box is kept in a state of rapid and violent motion while the pulp flows on to the surface of the brass plates, in order to promote the screening process. The metal of the under surface of the plates at each slit is cut away to prevent any stoppage, and the upper surface is kept clean by the continuous movement of rubber brushes passing slowly from one end of the box to the other. The clarified mixture flows away from the lower surfaces of the strainer-plates into an outlet pipe.

Fig. 17.-Section of a
Strainer-plate.

Machine Wire. The strained pulp runs into a long narrow box placed at the head of and across the full width of the paper-machine, and gradually overflows the front edge of the box, which is cut down to ensure an even flow of pulp. The transfer of the stream of pulp to the wire is effected by the apron, a strip of thin sheet rubber or similar material, one end of which is nailed to the box and the other left free to trail on the wire as it comes up over the first supporting roll and travels forward.

The first portion of the paper-machine, where the pulp is formed into a sheet of wet paper, is known as the wet end in contradistinction to the end section devoted to drying and finishing, usually designated the dry end.

The wire is a long endless brass wire-cloth about 40 to 50 feet in length and 70 to 90 inches wide, with a fine mesh of 60 to 70 wires per inch. It is stretched on two rolls the breast-roll, situated near the narrow box containing the pulp, and the under couch roll. The wire travels from the breast-roll over a large number of tube-rolls, or hollow brass cylinders three inches in diameter, placed very close together on a rectangular frame and then underneath the couch-roll, after which it is carried back below the frame by means of the under couch-roll, and sundry other rolls of small diameter which serve to keep the wire tight.

Deckle-straps.-The pulp flows from the strainers over the apron on to the travelling machine-wire, and then immediately underneath the slice, a flat brass bar placed on edge, which is adjustable both as to its width and height above the wire-cloth. The distance of the slice from the wire determines the thickness of the pulp flowing on to the wire and, therefore, the substance and weight of the paper, to some extent, but the actual thickness of the paper is controlled by other conditions to a greater extent, as will be seen by reference to the finishing operations.

In order to prevent the pulp spreading too much and flowing over the wire at each side deckle-straps are used. These consist of thick, heavy, endless bands of rubber, of square section, which are carried on grooved brass pulleys and which travel along the machine-wire at each side and in close contact with it.

The apron at one end of the wire, the couch-roll at the other end, with the deckle-straps on each side, all combine to form in effect an endless deckle, while the machine-wire forms the endless mould. The intermittent hand process is thus converted into a continuous machine process.

Vacuum-boxes.-Directly the pulp flows under the slices, the water begins to fall through the wire. The rapid flow of the mixture on to the wire causes all the fibres to assume a position parallel to the sides of the wire, and pointing in the direction towards which they are travelling. But this tendency has to be counteracted, for a paper made up of fibres pointing almost exclusively in one direction is generally of inferior strength. The imitation of the shake given by the vatman in producing hand-made sheets is accomplished on the paper-machine by a shaking motion imparted to the rectangular frame carrying the breastroll, tube-rolls, and wire. This shake causes many of the fibres to assume a position at right angles to the machine direction, so called, and tends to equalise

Fig. 19.-A" Wove" Dandy-roll.

the strength of the sheet of paper in the two directions. The fact, however, that the water begins to leave the pulp immediately after passing the slices prevents the fibres on the under surface of the flowing sheet of wet paper from felting properly, because there is not sufficient time for them to be affected by the shake. The fibres in the water just above are much more sensitive to the action of the shake and felt much better. This curious difference in behaviour can easily be seen by comparing the two sides of a sheet of mottled paper.

The draining of the water from the pulp is hastened by the tube-rolls which draw the water away from the wire very rapidly by capillarity, though the main purpose of the tube-rolls is to support and keep the wire in its proper horizontal position. The further removal of water is produced by a number of vacuumboxes, usually two or three, placed close up underneath the wire just in front of

Fig. 20.—A “Laid” Dandy-roll.

the couch-roll. The suction, induced by special powerful pumps, draws a large quantity of water from the wet sheet of pulp as it travels continuously over the vacuum-boxes.

Save-all. The very large quantity of water escaping through the meshes of the wire is not allowed to run away, but is carefully caught in a large shallow box or save-all, placed under the wire close up to the tube-rolls. It contains a large amount of fibre, varying from 5 to 15 lb. of air-dry fibre per 1000 gallons, and this cannot be ignored. It is pumped up and used for diluting the pulp from the stuff-chests before it flows into the sand-traps. Any surplus over and above the amount required for this is utilised in the beatingengines.

Dandy-roll. Before the pulp has travelled over all the suction-boxes it is usually submitted to the action of the dandy-roll, which carried on suitable