220 PAPER forms, revolving or stationary. The most usual is stationary. It consists of an upright cylinder of cast or malleable iron (fig. 1), about 8 feet in diameter by 6 feet deep, and fitted with a perforated false bottom, on which the rags rest. The boiler is further fitted with a filling door A at the top, and an emptying door B below. After being FIG. 1. Section of Rag- Boiler. charged with rags, it is filled to about half its height with water ; a sufficient quantity of caustic soda, varying accord ing to the nature of the rags, is introduced ; the door is then shut, and steam is admitted by a small pipe C which is con tained in, and communicates at the foot with, a larger pipe D and causes a constant circulation of hot liquid, which is dispersed all over the boiler by striking against a hood E at the top. This is technically known as the "vomit." The rags are boiled in this solution of caustic soda for ten to twelve hours, when the steam is turned off and the liquid is discharged by the pipe G. After a subsequent washing with cold water in the boiler the lower door is opened and the boiled rags withdrawn into small trucks, and picked by women to remove impurities, such as india-rubber, &c. The rags are now submitted to the action of the break ing engine (figs. 2 and 3). This is an oblong trough with FIG. 2. Breaking Engine Vertical Section. lounded ends, and may be about 6 feet wide and 12 feet long by about 2 feet in depth, but the size varies greatly. It is partially divided in the centre by the midfeather A, and provided with a heavy iron roll B, fitted with knives technically called bars, which revolves at a high speed on the plate C, also furnished with knives. The engine is half filled with water and packed with the boiled rags. Water is introduced by the valve D, and is withdrawn by the washer E. The washer consists of a drum about 3 feet in diameter and 18 inches broad, covered with fine wire-cloth, and fitted inside with buckets shown by the dotted lines G. It is partially immersed in the pulp, and as it revolves discharges the water by the centre down the FIG. 3. Breaking Engine Horizontal Section. shoot H. The rags are allowed to remain in this washer, according to their cleanness, from one to two hours, and then the solution of chloride of lime by which they are bleached is introduced. After running mixed with this in the engine from one to two hours, the pulp is run down into large stone chests, where it is allowed to lie for twenty-four hours till it becomes perfectly white ; it is then drained and pressed to remove the remaining bleach ing solution as far as possible. The bleached pulp is now removed to the beating engine, which differs but little from the washing engine except that in the roll of the beater there are three bars to the bunch, while in the washer there are only two to the bunch. Here the pulp is furnished in the engine with water as before, and washed till it is free from chloride of lime, or this may be neutralized by the vise of a sulphite or hyposulphite of soda. The pulp is then submitted to the action of the beater roll for from four to six hours, the circular knives being allowed to revolve very near the plate, so as to draw out the fibres into a very fine state, while preserving their strength as far as possible. While the operation of " beating " is being proceeded with, the loading material, consisting of china clay or pearl white, is added. This is by no means to be viewed entirely as an adulteration, as it too generally is. No doubt to a certain extent it weakens the paper, but it is not added in hand-made papers, in which great strength is required. In writing papers for ordinary purposes, however, and in printing papers, the addition of mineral matter in modera tion is of positive advantage, as it closes up the pores of the fibres and enables the paper to take a much better finish than it would otherwise do. The next process is the sizing, to which all papers for writing and most of those for printing purposes are sub jected. Sizing consists in the deposition on the fibres of a substance which is comparatively waterproof, and for engine sizing a mixture of resin soap treated with alum is employed. The resin soap is formed by dissolving resin in carbonate or caustic soda, allowing the mixture to cool, when the soap floats on the surface, and the mother-liquor, containing the excess of alkali, is run off. It is of con siderable importance to get rid of this mother-liquor before using the soap, as it is of no use, and takes alum to neutralize it. The soap is now dissolved in water, and, in many mills where starch is used for stiffening purposes,
