Scientific American Supplement, No. 821 | Page 4

away the sand and other solid extraneous matter. The further reduction of the cut rags was formerly performed in a stamp mill, which is no longer employed, the pulp mill or rag engine being universally used.
The construction of this engine may be described as follows: A box or trough of wood, iron, or stone is by a partition divided into two parts which are connected at their ends. At one side upon the bottom of the box lies an oakwood block, called the back fall. In a hollow of this back fall is sunk the so-called plate, furnished with a number of sharp steel cutters or knives, lying alongside of each other. A roller of solid oakwood, the circumference of which is also furnished with sharp steel cutters or knives, is fastened upon a shaft and revolves within the hollow. The journal bearings of the shaft are let into and fastened in movable wooden carriers. The carriers of the bearings may be raised and lowered by turning suitable thumbscrews, whereby the distance between the roller and the back fall is increased or decreased. The whole is above covered with a dome, the so-called case, to prevent the throwing out of the mass under the operation of grinding. The roller is revolved with a velocity of from 100 to 150 revolutions per minute, whereby the rags are sucked in between the roller and the back fall and cut and torn between the knives. At the beginning of the operation, the distance between the roller and the back fall is made as great as possible, the intention being less to cut the rags than to wash them thoroughly. The dirty water is then drawn off and replaced by clean, and the space of the grinding apparatus is lessened gradually, so as to cut the rags between the knives. The mass is constantly kept in motion and each piece of rag passes repeatedly between the knives. The case protects the mass from being thrown out by the centrifugal force. The work of beating the rags is ended in a few hours, and the ensuing thin paste is drawn off into the pulp chest, this being a square box lined with lead.
From the pulp chest it passes to the form of the paper machine. This form consists of an endless fine web of brass wire, which revolves around rollers. The upper part of this form rests upon a number of hollow copper rollers, whereby a level place is formed. The form revolves uniformly around the two end rollers, and has at the same time a vibratory motion, by which the pulp running upon the form is spread out uniformly and conducted along, more flowing on as the latter progresses. The water escapes rapidly through the close wire web. In order to limit the form on the sides two endless leather straps revolve around the rollers on each side, which touch with their lower parts the form on both sides and confine the fluid within a proper breadth. The thickness of the pulp is regulated at the head of the form by a brass rule standing at a certain height; its function is to level the pulp and distribute it at a certain thickness. The continually moving pulp layer assumes greater consistency the nearer it approaches to the dandy roll. This is a cylinder covered with brass wire, and is for the purpose of compressing the paper, after it has left the form, and free it from a great part of the water, which escapes into a box. The paper is now freed of a good deal of the fluid, and assumes a consistency with which it is enabled to leave the form, which now commences to return underneath the paper, passing on to an endless felt, which revolves around rollers and delivers it to two iron rolls. The paper passes through a second pair of iron rollers, the interiors of which are heated by steam. These rollers cause the last of the water to be evaporated, so that it can then be rolled upon reels. A special arrangement shaves the edges to the exact size required.
The paper is made in different thicknesses and designated by numbers to the size and weight.
Waste paper, bookbinders' shavings, etc., can be used for making the paper. As much wool as possible should be employed, because the wool fiber has a greater resistance than vegetable fiber to the effects of the temperature. By wool fiber is understood the horny substance resembling hair, with the difference that the former has no marrowy tissue. The covering pellicle of the wool fiber consists of flat, mostly elongated leaves, with more or less corners, lying over each other like scales, which makes the surface of the fiber rough; this condition, together with the