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complementary colour and thus the impression of white is presented to the eye; this process is known as 66 tinting" of papers.

After bleaching and dyeing the pulp is ready to be conducted to that part of the mill in which its conversion into paper actually takes place.

From the beater it is allowed to flow into the stuff chest (a, Figs. 21 and 22), a large vessel made of wood or built in bricks and cement, provided with either a vertical or a horizontal stirring arrangement. The quantity of pulp which comes from the stuff chest and which is required to produce a paper of certain thickness and at a certain speed has to be carefully regulated. To achieve this the pulp is generally first pumped to the so-called

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regulating box," from which a continuous stream under a constant pressure is conducted to the paper machine.

Another arrangement in very common use, especially in Continental mills, has been devised for regulating the flow of pulp from the chest to the sand tables and is the following:The horizontal stirring arrangement in the stuff chest is provided at one end with a circular rim which carries on its circumference a series of small beakers or buckets. During their downward journey these beakers are filled by tipping into the pulp. On reaching the highest position the pulp is discharged into a channel connected with the sand tables; this channel may be widened or narrowed according to the amount of pulp required, the excess of pulp flowing back into the stuff chest.

Special pulp regulators, consisting of two or three pumps, as well as arrangements in which the flow of pulp is regulated directly from, and in accordance with, the speed of the paper machine, are used in some mills.

In the manufacture of heavily-sized, loaded and coloured papers, it is essential to the production of uniformity of shade and quality to use the so-called "back water" for the thinning down of the pulp in place of fresh water. The mixing is usually accomplished in a small mixing chest placed above the level of the sand tables to which pulp and back water are conducted; the pulp then travels over the "sand tables" (b, Figs. 21 and 22), which consist of shallow troughs varying in length considerably according to the quality of paper made on the machine. Ribs are fixed cross-ways on the bottom of these troughs and during their passage over the sand tables heavy particles, such as sand,

contained in the pulp as impurities, settle behind these ribs.

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The pulp still contains fibre bundles which have escaped the action of the knives and also small knots consisting of felted fibres, as well as other impurities, which, if allowed to pass along to the paper machine would show as "specks." To free the pulp, as far as possible, from these impurities, it is necessary to pass it through one or more 'strainers," c (Figs. 21 and 22). The operation of "straining" is accomplished by the aid of brass plates provided with very fine V-shaped slits which are narrower at the top and are wider towards the other side of the plate. These slits which vary in width for the different qualities of pulp are, however, only just wide enough to allow the single fibres to pass through whilst all the coarser particles are retained on the top of the plate. A number of these plates securely bolted together form a strainer. By means of rapidly revolving ratched wheels, which support the axle of the strainer, a shaking motion is produced which greatly assists the passage of the pulp through the slits. A strainer in which the plates are bolted together so as to form a flat surface is called a "flat strainer." The other types in which the plates form a rectangular box or a slowly revolving cylinder, are termed " revolving strainers."

Flat strainers have been introduced in which the passage of the pulp is considerably accelerated by a vacuum produced underneath the strainer plate.

Automatic cleansing devices, consisting of endless bands provided with india-rubber scrapers or brushes which move over the surface of the plates and carry away the knots, are also in use with flat strainers. In other self-cleansing strainers the knots are carried along with the pulp into channels from which they are conducted to "patent knotters."

The rotating strainer invented by Wandel (Fig. 23), consists of a revolving cylinder (a) placed horizontally in a trough; this cylinder is formed of a number of plates bolted securely together the narrower parts of the slits being on the inside. The pulp enters through the hollow journals (6), and finds its way through the slits into the trough, whilst knots and other impurities are lifted by ribs between the plates inside the cylinder whence they ultimately fall into, and are conducted away through, a channel (c) situated above the channel through which the pulp enters. A spurt pipe (d) fixed above the cylinder directs

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a piece of fine wire gauze supported by coarser wires, and the deckle," a narrow frame which fits closely on to the top of the wire gauze screen. The deckle serves the purpose of preventing the pulp from flowing away over the sides of the mould; the amount of pulp removed from the vat, and therefore the thickness of the finished paper, are, to a certain extent, determined by the height of the deckle.

The workman who handles the mould is called "the vatman"; he takes from the vat the quantity of pulp required to form a sheet of paper by dipping the mould into the pulp and lifting it out whilst holding it horizontally. As the water passes away through the sieve the vatman gives the mould a peculiar shaking motion by means of which felting or intertwining of the fibres is ensured; the strength of the resulting paper depends to a very considerable extent upon the skill with which this part of the process is performed.

As soon as the water has drained sufficiently the mould is passed by the vatman to the "coucher," who, after the deckle has been removed, presses the wet sheet on to a felt. The mould is then removed and the sheet of paper covered with another felt. Paper and felts are thus placed carefully alternately one on the other until a so-called "felt post has been obtained; this is then removed to a press by means of which a large portion of the water is slowly pressed out. The sheets having obtained sufficient strength by the treatment are separated from the felts and placed one on the top of the other and are once more taken to the presses; the felt marks are thus removed and the surface of the paper is considerably improved.

In the case of some papers this pressing is repeated, the sheets being separated and again placed in contact between each operation. The pressed papers are next conveyed to the drying-room where they are placed on ropes, usually made of cow-hair, and slowly dried. A mould, the covering gauze of which consists of wires of uniform thickness placed at equal distances lengthways and crossways, is called a" wove mould." If the wires are arranged closely together in the one direction but are placed further apart in the other direction, the mould is termed a “laid mould." Papers made on the two kinds of moulds are called "wove" and "laid" papers respectively. Water-marks are produced by wires sewn on the top of the wire on the mould. The paper is thinner and therefore more transparent at these parts, owing to fewer fibres

having been deposited. By using wires of varying thickness, and also by sewing on to the mould patterns produced by pressing very flexible wire gauze between steel dies, most elaborate water-marks may be produced.

No size having been used with the pulp, the sheets, as they come from the drying-rooms, are absorbent, and therefore unsuited for writing and for some printing purposes; the next operation through which hand-made paper has to pass is the so-called " tub sizing," and is accomplished by passing the sheets through a solution of glue or gelatine. This is generally done by hand, although some mills are provided with special sizing machines in which the sheets travel through the size on endless bands.

The glue, as used in the tub sizing, is either prepared in the mill by treating clippings of hides, bones, horn, &c., with water, thus extracting the gelatine; or very pure gelatine, which dissolves readily in water, is bought and used by the paper-maker. A certain amount of alum is always added to the gelatine solution in the manufacture of highly-finished papers and soap is frequently used in conjunction with the tub size.

The sheets are freed from excess of size by pressing in screw or hydraulic presses; they are then separated and conveyed to the drying chamber for the final drying. Hand-made papers are finished either by repeated pressing in hydraulic presses, by calendering, or by plate glazing.

Miscellaneous.

MOTORS.*

Speed in locomotion appeared to be the first consideration, whether as regards mails, passengers, or goods; and three or four classes of machines appeared to be ambitious to drive pedestrians, horsemen, and horse-drawn vehicles off the road. The first practical steam carriage was used by Trevithick in the year 1802. The points of importance in con. nection with traction engines and their trailers are their speed, weight, and width. Mr. E. R. Calthrop, M.Inst.C.E., one of the founders of the Liverpool Self-propelled Traffic Association, was opposed to any weight restriction, but it was to be remembered that the momentum of heavily laden waggons drawn by a powerful traction engine at the maximum speed

Extracted from the Presidential Address by Mr. Charles Hawksley to the Engineering Section of the British Asso ciation at Southport.

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