for, if the mould be not held perfectly level, one part of the sheet will be thicker than another. The water runs out through the interstices of the wires, and leaves a fibrous coating, in the form of a sheet, upon the bottom of the mould. The sheets, thus formed, are subjected to pressure, first between felts or woollen cloths, and afterwards alone. If intended for writing-paper, they are then sized, by dipping them in a thin solution of gelatin, or glue, obtained from the shreds and parings of animal skins. The use of the size is to increase the strength of the paper, and, by filling its interstices, to prevent the ink from spreading among the fibres, by capillary attraction. In blotting-paper, the usual sizing is omitted, and in printing-paper less is used. The paper, after being dried, is pressed, examined, selected, and made into quires and reams. Hot-pressed paper is rendered glossy, by pressing it between hot plates of polished metal.

Paper is also manufactured by machinery, and one of the most ingenious methods is that invented by the Messrs. Fourdrinier. In this arrangement, instead of moulds, the pulp is received in a continual stream, upon the surface of an endless web of brass wire, which extends round two revolving cylinders, and is kept in continual motion forwards, at the same time that it has a tremulous, or vibrating, motion. The pulp is thus made to form a long, continual sheet, which is wiped off from the wire web, by a revolving cylinder, covered with flannel, and, after being compressed between other cylinders, is finally wound into a coil, upon a reel prepared for the purpose. From this reel it is again unwound, by means of machinery, and cut into sheets of uniform

size.

The machine-made papers possess many advantages; they can receive, so to speak, unlimited dimensions ;* they preserve a perfectly uniform thickness, throughout all their length; they may be fabricated in every season of the year; nor do they require to be sorted, trim

* Pieces have been made, twelve hundred yards long.

med, and hung up in the drying-house, operations which occasioned great waste, amounting to no less than one defective sheet out of every five. The continuous paper, at one time, retained the impression of the wire-wove web, on its under side; a defect from which it has been freed, by a pressure apparatus of Mr. Donkin.

The greatest difficulty, formerly experienced in the paper manufactured upon the continuous system of Fourdrinier, was to remove the moisture from the pulp, and condense it with sufficient rapidity, so as to prevent its becoming what is called water-galled, and to permit the web to proceed directly to the drying cylinders.* Hitherto, no invention has answered so well, in practice, to remove this difficulty, as the channelled and perforated pulp-rollers, or dandies, of Mr. J. Wilks, the ingenious partner of Mr. Donkin.

III. Chemical processes, employed in the manufacture of Cloth.-These are, Bleaching, Scouring or Cleansing, Dying, and Calico Printing.

1. Bleaching is the process, by which certain animal and vegetable products, and especially such as are used as articles of clothing, are rendered white. The principal substances of the animal kingdom, which are subjected to the operation of bleaching, are wool and silk; those of vegetable origin are chiefly cotton and flax. These bodies contain a quantity of coloring matter, which, though natural to them, is not an essential constituent; it appears, also, that the coloring matter is more readily acted upon by chemical agents, and suffers decomposition with greater facility, than the animal and vegetable matters with which it is united. On these accounts, it is removed by operations, producing little or no injurious effect upon the texture or durability of the articles from which it is separated, and thus, not

*These are large, hollow, polished copper cylinders, heated from within by steam, and round which the moist sheets are carried, in order to be dried. Less than two minutes is required to transform the pulp into sheets of dry finished paper.

only is their beauty increased, but they are fitted for the reception of the colors of the dyer, and the ornamental designs of the calico-printer.

The destruction of the coloring matters, attached to the bodies to be bleached, is effected, either by the action of the air and light, of chlorine, or of sulphurous acid; which may be considered the three bleaching powers employed for manufacturing purposes.

Bleaching, by the influence of air and sunshine, is the most ancient, and still the most common, method, in several civilized countries; it is also supposed, by many, to be the least injurious to the texture of yarn and cloth. The operations it involves are very simple, consisting in the exposure of the goods upon a grassplat, to the sky, with their occasional aspersion with moisture, if necessary, in addition to the rain and dew. The atmospheric air effects the bleaching, by means of its oxygenous constituent, which combines with the coloring matter, or its elements, carbon and hydrogen, and either makes it nearly white, or converts it into a substance, easily soluble in water and alkaline solutions. This natural process is too slow, to suit the modern demands of the cotton and linen manufacturers. Fortunately for them, a new bleaching agent, unknown to our forefathers, has been discovered, in chlorine, formerly called oxymuriatic acid, an agent modified by chemistry so as to give an astonishing degree of rapidity, economy, and perfection, to this important art. It is, however, not a little surprising, that the science, which has so greatly advanced its practical part, should have left its theory far from complete, and should afford no satisfactory answers to the two following questions: What is the action of the solar rays upon the coloring matter? How do air and chlorine operate upon this principle?

Chlorine was first used in the state of simple solution in water; afterwards, in order to lessen its destructive action, when used in too concentrated a state, it was proposed to add potash to it. This compound,

however, was not found to answer the purpose; and the chloride of lime, generally known by the name of bleaching-powder, is now almost universally employed, especially in the bleaching of cotton; it is a compound, which answers the purpose, with economy, celerity, and safety.

The coloring matter of cotton, flax, and hemp, is insoluble in water, and appears to be of a resinous nature; it is partially dissolved by heated solutions of lime and potash, or soda; and by their use, and the application of a solution of bleaching-powder and diluted sulphuric acid, the coloring matter, which is not dissolved, is destroyed. Cotton is more readily bleached than flax or hemp; and these, more readily than wool: indeed, this last-mentioned substance, as well as silk, is generally bleached by the fumes of burning sulphur, or sulphurous acid gas, after they have been properly cleansed. Straw and feathers are also bleached by sulphurous acid gas. Wax is generally deprived of its color by mere exposure to air, light, and moisture.

With respect to the theory of bleaching, it may be. observed, that the action of lime, and the alkalies potash and soda, appears to be that of mere solvents; they probably dissolve the coloring matter, without effecting much alteration in its properties. The action of atmospheric air, and of chlorine, seem to be similar to each other, and very different from that of lime and the alkalies; the oxygen of the air, aided by the action of light and moisture, apparently combines with and destroys the coloring matter; and the chlorine, decomposing water, one portion of it forms muriatic acid, with its hydrogen, and another portion, with its oxygen, probably gives rise to a compound of easy decomposition, the nascent oxygen of which, acting like that of the air, though more powerfully, produces the same oxidizing effect upon the coloring matter, but more perfectly, and in a much shorter period.

That water is necessary to the action of chlorine upon vegetable coloring matter is shown, by immers

ing dry coloring matter in the dry gas, in which case, no decoloration whatever is effected, but it ensues immediately on the introduction of water. The bleaching of rags, for paper-making, is effected by the agenof chlorine. Paper, also, when written on or printed, may be bleached by the same means.

cy

There are some operations, in which the removal of color is hardly referrible to the process of bleaching; such, for example, is the decoloration of sugar, which derives its color, not from any natural cause, but the partial decomposition effected by heat. This is removed by what is usually termed animal-charcoal, or ivoryblack; this powerful decolorant is also used in some chemical operations, for the same purpose.

2. Scouring and Cleansing.-Wool, in its preparation for dyeing, requires to be cleansed from a fatty substance, called the yolk, which is contained in the fleece. This is done by means of a weak alkaline solution, which converts the yolk into soap. Putrid urine is commonly employed, on account of its cheapness ; the ammonia it contains being sufficient to remove the grease.

Silk, when taken from the cocoon, is covered with a kind of varnish, which, because it does not easily yield, either to water or alcohol, requires also the aid of a slight portion of alkali. Much care is necessary, however, in this operation; since the silk itself is liable to be corroded and discolored. Fine soap is commonly used; but even this is said to be detrimental; and the white China silk, which is supposed to be prepared without soap, has a lustre superior to the European.

3. Dyeing is the art of staining textile substances with permanent colors. To cover their surfaces with coloring matters removable by abrasion, would be to apply a pigment, rather than to communicate a dye. Dye-stuff can penetrate the minute pores of vegetable and animal fibres, only when presented to them in a state of solution; and they can constitute fast colors, only by passing afterwards into the state of insoluble