wmn ilii' ija|iir is piirtlv dried. The size and
number of driers determine how fust a paper
can ho run. With a given machine tliin papers
ean be run (and dried) very fast; thick ones
slowly.
G. The Calenders. — After being thoroughly dried the web of paper is pa.ssed throngli a 'stack' of .smooth chilled iron rolls, which by their own weight, and |)rcssure api)lied by screws or weights, sniiHJths the paper and produces what is called 'machine finislied' paper, as contrasted with 'supercalondereil' paper, described farther on. Tt is now wounil on a reel.
H and 1. The Red and tilitter.—AiteT being wound on a reel the paper is passed through the slitter, the rough outside edges trimmed, and if necessary the single web slit into any required widths. It is then rewound and is ready for shipment, if intended for juinting in the roll or for coating; or for supercalcndering, sheeting, and i)acking.
The Fourdrinier machine makes automatically an endless web of paper from 00 to 100 inches wide at a speed of 10 to 400 feet per minute. The plate shows the reels, calenders, and driers of one of the largest machines in the world, 160 inches wide, belonging to the International Paper Company at Rumford Falls, Maine. It can run at a speed of 300 feet per minute and produces 04,000 jjounds of paper in '24 hours.
SupERCALENDER.s. JIuch book paper requires a high finish, that is, a very smooth surface, and this is given by passing it between alternate iron and compressed paper rolls luider great pressure. These machines are c.nlled the super- ealenilers. It is then sheeted, eoiuited into reams of 4S0 or .900 sheets, and packeil in cases or bundles.
Animal Sizing and Loft Drying. Tlie finer grades of writing papers are not finished ■ as here described, but when partly dried are passed through a vat of gelatin (glue) in solution, the ex'cess squeezed off by rollers, and either slowly dried by Jiassing over a large number of hollow drums with fans inside, or cut in sheets, and hung in lofts to dry in the manner employed for hand-made paper.
The following are the main differences in the preparation of rag substitutes from that given above :
Esparto prass conies from Spain and Africa, and is very largely used in England. The grass is cleaned, dusted, and boiled with caustic soda under pressure, a so-called vomiting boiler being usually used; it is then washed and bleached in much the same manner as rags. It gives a white fibre of fair strength.
S'traw is used largely in the United States, chiefly for strawboard, and not reduced to a pure fibre. Its characteristics are similar to esparto, but it is more difficult to reduce to pure cellulose, owing to the silica it contains, requiring a stronger alkali and higher pressure in boiling.
Wood Pulp. There are two kinds of wood pulp used in paper-making, mechanical pulp or ground wood, and chemical fibre. Of the latter there are three processes of manufacture, the soda process, the sulphite, and the sul- phate.
dround wood is made by pressing blocks of wood obliquely (across the grain) against rapidly revolving grindstones, a stream of water carrying off the product, which is not chemically changed, and has very little fibre or strength. It is used very largely, however, for cheap newspaper, chielly in connection with chemical filire to impart greater strength. The plate ( Fig. 1 ) shows a pulp-grinder at Kuniford Falls, Maine, the stone being coupled directly to a turbine water wheel. It will be seen that there are three 'pockets,' in which blocks of wood are placed and pressed simultaneously against the stone. The pulp is then screened to remove lumps, bleached if necessary, and eitlicr run directly into the beaters if made into paper at the same mill (as at Rumford Falls; see plate, Fig. 2), or made into thick sheets by a machine similar to the cylinder paper machine described below. It is usually sold in a moist state. Paper containing ground wood turns yellow when exposed to the light, and becomes brittle. . solution of sulphate of aniline turns ground wood fibre a bright yellow, the intensity of the color giving a rough guide to the percentage of ground wood in the ]iaper.
Chemical Wood Pilp. The oUlest process of freeing cellulose from the incrusting woody mat- ter, producing a material for making white pa- per, is the soda process, patented by Watt & Bur- gess in England in 18.54. A soft wood, usually poplar in America, pine in Europe, is barked, chipped across the grain into small pieces, and cooked under steam pressure with a solution of caustic soda. The alkali dissolves everything but the cellulose, and after washing and bleach- ing a soft white fibre of good ((uality is pro- duced, of little strength, but very useful to supplement other fibres.
The sulphite process is apparently an Ameri- can invention, the first patent being granted in 18G7 to B. C. Tilghmann. He used sulphurous acid to produce pure cellulose, and while this is the base of the modern process, it was not brought to a practical success till bisulphite of magnesium or ealciuni was used instead.
Mitschelieh in Germany brought the process to a commeieial basis, and of late years it has developed to very large proportions. Various modifications of the process are used, but in all of them the wood, properly barked, chipped, and dusted, is digested under steam pressure in a solution of the bisulphite, washed, and bleached if necessary. 'Sulphite' fibre has good strength and color, and much of it is used unbleached. The sulphate process is not used in America, but produces a very good pulp at a higher cost than sulphite. It is similar to the soda process in theory, but sulphate of soda is used. An objection to it consists in the offensive odor of the by-products.
In the different processes of treating wood various forms of boilers are used, stationary, rotary, cylindrical, and spherical. They have to be lined to resist the action of the chemicals, and lead or cement is commonly used for this purpose. A large factor in the successful con- duct of pulp manufacture lies in recovering the chemicals from the spent liquor. In the soda process the liquor is evaporated and finally incinerated in a furnace from which nearly all the caustic soda used is recovered. There are similar economies practiced in the other processes which not only save valuable chemicals, but prevent the pollution of streams.
The Cylinder Machine. While almost all pa-
