(5) Benting.—The half-stuff is next put into the beating engines, .which are similar to the washers, but hare no washing-drum, and the knives are arranged to macerate the pulp faster. At this point ilk loading materials, color, and sizing are added, and if various fibres are used, such as rag, \vocal fibre, o• esparto, they are mixed here, while the half-stuff is being reduced to the very fine condition required for making into paper. Most papers contain a filler, usually china clay (kaolin, q.v.) or sulphate of lime ('pearl hardening'). This fills the pores, giving a more even printing surface, besides adding to the weight. As paper is usually sold by the pound, the latter consideration is not without its influence, the loading sometimes amounting to per cent. An addition of 10 per cent. of mineral is not considered an adulteration. Bleached pulp has a yellowish cast, and to ob tain a pure white a little blue is added, and papers that are colored in the pulp are prepared at this point. Sizing is added to prevent the absorption of ink. Unsized (or 'water leaf') papers absorb water readily and cannot be used for writing with a pen. The sizing is of two kinds, vegetable (rosin) size, added at this stage of manufacture, and animal (glue) size, which is applied externally after the paper is made. The accompanying plate (Fig. 2) shows the beating engines in a 'news' mill at Rumford Falls, Maine. A boy is 'furnishing' the second engine, putting in chemical fibre, while the of varying lengths. When the washing is com
pleted. the washing cylinder is raised out of the beater and the supply of water cut off. The heating process is then continued a little longer till the pulp reaches the stage called half-stuff, the practice varying in different mills.
(4) Iflcuehing.—The pulp is now as white as it can be made without bleaching, and is a light gray if medium grade white and colored rags were used. The addition of a solution of chloride of lime (bleaching powder), decomposed by sul phuric acid, bleaches the pulp to a creamy whiteness. In America the is done in the washing engines, but in Europe a separate ground wood is run in from the large pipe above. On the other side is seen a man getting out china clay from a cask.
Rosin size is prepared as follows: A rosin soap is made by dissolving rosin with caustic soda o• potash; this is added to the pulp in the heating engine and precipitated on the fibres by the addition of a solution of alum o• sulphate of alumina. Paper thus sized is called engine sized or rosin-sized paper, as distinguished from `tub-sized' o• animal-sized. which will be de scribed later.
The pulp may be beaten fine enough in the beating engine, but the practice in this country is to dump it into a 'stuff chest,' a large circular receptacle, with a horizontal agitator to keep it from settling, and then to pump it through a so-called 'Jordan' or refining engine into a sec ond stuff chest, whence it is pumped to the Four drinier machine.