Colouring.—The colouring matters usually added for the production of white paper are ultra marine and pink, the latter being either a preparation of cochineal or a coal-tar colour. Sometimes a coal-tar blue is used instead of ultramarine. The addition of a small quantity of blue and pink is requisite to complement the slight yellow colour of the pulp, and so produce a white paper. The ultramarine has to be chosen with special reference to its tinctorial power, and chiefly to its capacity for resisting the action of alum, inferior qualities being discharged by the latter. Ultra marine, being a pigment, is only mechanically held by the pulp ; aniline blue actually dyes the pulp, and is therefore more intimately combined with it.
Paper of any colour may be made either by adding some material of the colour required, or such substances as will produce it. It will not be necessary to enumerate here the different materials employed. The so-called " toned " paper is produced by adding to the pulp a solution of pernitrate of iron, from which a fine precipitate of oxide of iron deposits on the fibres, and thus the slightly brownish shade is obtained. The size, clay, and colouring materials having been added to the pulp, nothing now remains but to reduce it to a tufficiently fine state of division. In this part of the process, much care and attention are called for, as upon the proper conduct of the beating operation, the character of the paper greatly depends.
The object of the beaterman should be, by carefully adjusting the distance of the roll from the bed-plate, to thoroughly disintegrate the esparto, and to produce a pulp with as long a fibre :as possible. If the roll be lowered too much at the commencement of the operation, the fibres, instead of being drawn out or beaten, will be cut by the knives, and the paper will be proportionately weakened.
If circumstances allow of it, the pulp should be worked in the beaters for a long time, and the disintegrating process should be conducted slowly ; but the method of working depends con siderably upon the character of the paper required. Thus, if a very thin paper is to be produced, it is absolutely necessary, in order to make a strong firm sheet, to beat the pulp slowly, and preserve the fibre, whereas this is not so necessary in the case of thick papers. In this, as in many other particulars, the manufacturer has to consider not only the production of a good strong sheet of paper, but, on the other hand, the expense involved on account of the extra time and power consumed.
Though the ordinary form of beater contains only one roll, some have been made containing two, and with a special appliance for sending the pulp under the rolls in two separate streams. Engines have been made containing even four rolls. In some American mills, beating-engines are employed of a totally different construction from the ordinary form. The most important of these
are the Jordan and Kingsland beaters, so called from the names of their inventors. The former consists essentially of a conical-shaped roll, studded with knives, in the same way as the ordinary roll, revolving in an iron box of corresponding shape, and fitted with knives placed at slightly different angles in the direction of its length. The half-stuff enters at the narrow end, through a box provided with an arrangement for regulating the flow, and is discharged through two or more openings in the cover at the wide end. The Kingsland engine consists of a vertical, circular chamber, the sides of which are covered with knives, and between which a circular plate revolves; this ie also covered on both sides with knives. The pulp enters through a pipe in the centre of one of the sides of the chamber, and flows out through an opening in the opposite side.
The latest form of beater is that invented by S. L. Gould. The essential difference between it and the Kingsland is that, instead of having a plate revolving vertically against two stationary ones, its plate, which is placed horizontally, is covered with knives on one side only, and revolves upon but one fixed plate, much in the same way as a pair of mill stones.
The pulp supplied to these forms of beater is generally broken much finer than is the case with the ordinary kind, because it is necessary to make it flow easily through them ; this could not be done if the fibres were not sufficiently broken up. The chief advantages claimed for them is that they are more economical, both of time and power ; also that the pulp is more regularly beaten.
Treatment of first step in the treatment of rage is to remove, before sorting, as much as possible of the dust and other impurities which invariably accompany them. This is not absolutely necessary, though advantageous, as it renders them less unpleasant for the workers to sort subsequently. This preliminary purification is generally done in a machine, technically called a " thrasher." It consists essentially of a square wooden box, the top of which is lined inside with steel spikes about 6-8 in. long. The box is divided into two portions, by means of a piece of coarse wire gauze. In the upper portion, a shaft revolves, bearing a number of teeth, similar to, and alternating in position with, the stationary teeth at the top of the box. The rags are supplied at one end of the box, and are discharged at the other, the dust having escaped through the wire gauze into the bottom division. It is objected by some that the thrasher causes a great waste of fibre, but, on the other hand, it may be said that a less violent subsequent treatment is necessary.