Page:Paper and Its Uses.djvu/33

Rh in. Alum serves to mordant or fix the colour, and also serves to precipitate the resin size which is next added.

There are various prepared sizes on the market to take the place of the size prepared by the papermaker from resin and a solution of soda. The resin is melted and added to the soda solution, and boiled until the solution is complete. The size solution is added to the pulp in the beating engine, and thus we get a clue to the meaning of E.S., or engine-sized paper.

The pulp now consists of innumerable fibres, to which and in which are fixed small particles of china clay, colouring matter, and resin. In many writing papers a small amount of starch paste is added, and that also adheres to the tiny fibres. The engine is emptied by gravity into the stuff-chest, where the revolving arms keep the fibres in the mixture from precipitation. Then there is a short journey to the machine, during which the pulp undergoes great tribulation, first being diluted with a large quantity of water, then passing over sand traps which intercept grit, metallic fragments, and such matter that is heavier than the pulp and so tends to sink, and then through strainers, which retain foreign matter, unbeaten particles, and knots of fibre. The flow of pulp is governed by a system of valves, which can be quickly manipulated to alter the substance of the resulting paper.

The wet end of the machine consists of an endless band of woven wire, some 40 to 80 meshes to the inch, from 48 to 205 inches wide, and a total length of 40 feet or more. The length of wire in use at one time as a paper mould is less than half its total length. This woven wire corresponds to the mould of the vatman in hand-making. Deckle straps, the substitutes for the vatman's deckle, are thick endless rubber bands, square in section, which rest on the wire cloth, and, following