Various modifications of the foregoing process have from time to time been proposed ; among others, that of softening the wood by previous soaking in water, or steaming, aeema to be valuable, as by so doing, it is highly probable that a longer fibre could be obtained, the soft wood being more readily torn away by the atones. Some inventors have proposed to replace the sandstone by an artificial atone containing a large quantity of emery.
Treatment of "Broke" Paper.—As " broke " paper has already passed through the manufac turing process, hut little is necessary to be done to it. If quite olean, it only requires to be broken up again in an engine ; but if dirty, or with much printing on it, some sort of boiling is necessary. Generally speaking, a rather dilute solution of soda is sufficient. Sometimes it is necessary to thrash and dust the waste paper much in the same way as raga.
Hand-made Paper.—The preparation of the pulp for hand-made is similar to that for machine made paper. Generally speaking, however, paper can only be made successfully by hand, when long and strong fibres are used ; with short and inferior pulp, it is difficult to form a continuous sheet of any size. Hence hand-made papers are almost exclusively manufactured from pulp pre pared from rags, or some such strong material.
A very brief description of the actual process will be sufficient, and it will at the same time facilitate the right comprehension of the machine process. The paper is made on a mould of wire cloth, with a movable edge of wood, extending slightly above the surface of the mould, called the " deckle." The wire-cloth is generally supported by pieces of thick wire placed beneath it, and these again by wedge-shaped pieces of wood, the thin end being next the wires. To form a sheet of paper, the workman dips the frame into a vat containing the prepared pulp, lifting up just so much as will make a sheet of the necessary thickness. As soon as the mould is removed from the vat, the water begins to drain through the wire-cloth, and to leave the fibres on the surface in the form of a coherent sheet, the felting or intertwining being assisted by lateral motion given to the frame by the workman. The movable deckle is then taken off, and the mould is given to another workman, called the " coucher," who turns it over and presses it against a felt, by this means transferring the sheet from the wire to the felt. A number of the sheets thus formed are piled above each other, alternately with pieces of felt, and the whole is subjected to strong pressure, to expel the water. The felts are then removed, and the sheets are again pressed. After this, they are sized by being dipped in a solution of gelatine ; again slightly pressed, and then hung up separately on lines or poles to dry.
The making of paper by hand is Comparatively little practised in the present day ; some kinds of paper, however, such as bank-notes, and different kinds of drawing-paper,.are always made in
this way.
Any pattern or name required on the paper is obtained by making the wire-cloth mould in awl a way that it is slightly raised in those parts where the pattern is needed ; consequently less pulp lodges there, and the paper is proportionately thinner, thus showing the exact counterpart of the pattern on the mould. Such are known as "water-marks." The Paper Machine.—The pulp, after leaving the beaters, passes into a large vessel called the stuff-chest, of which there are one or more to each machine. As soon as the beater is empty, water is run in to thoroughly rinse out the remaining pulp, the washings also going into the stuff-cheat. These may be made either of wood or iron, and should be provided with arms fixed on a vertical shaft, made to revolve by suitable gearing. The arms are for the purpose of keeping the pulp thoroughly mixed, and should only work at a moderate speed, otherwise they would be liable to cause the fibres to go into small knots or lumps. The pulp is drawn from the stuff-chests by means of the pump A (Fig. 1051), and is discharged into a regulating-box (not shown). The object of this box is to keep a regular and constant supply of pulp on the machine. It consists of a cylindrical vessel, having two overflow-pipes near the top, and a discharge-pipe near the bottom. The pulp is pumped in through a ball-valve in the bottom, in larger quantity than is actually needed, the excess flowing away back into the stuff-chests, through the two overflow-pipes. By this means, the box is always kept full, and therefore the stream of pulp issuing out of the bottom pipe is always under the same pressure. It flows from this pipe, the quantity being regulated by means of a cock, according to the thickness of paper required, directly on to the sand-tables. These may be of various sizes and shapes, hut should be so large that the pulp takes some little time to travel over them. They consist of long shallow troughs, generally of a sinuous form. The bottoms are partly covered with woollen felt, having very long hairs on its surface, and partly with thin strips of wood placed across the direction of the flow of the pulp, and at a slight angle. They and the woollen felt serve the purpose of retaining any particles, such as sand and dirt, that may have escaped removal in the previous treatment of the pulp, and that are heavy enough to have sunk down during the passage of the pulp over them. As the pulp, when it leaves the stuff-chests, does not contain sufficient water for the purpose of making paper, it is mixed, at the end of the sand-tables where it flows on, with a quantity of water from the "save-all " (see farther on), flowing from the box B (Fig. 1051) placed at a higher level.