Page:Encyclopædia Britannica, Ninth Edition, v. 3.djvu/831

imparted in the process of spinning and weaving, that is the object of bleaching. The operations, although appa rently complex and numerous, are essentially simple, though frequently repeated, and the greatest variety of detail is connected with the finishing of cloth, which is in reality a separate industry, frequently conducted in distinct estab lishments under the name of calendering and finishing works. Bleaching proper resolves itself into washing with suitable detergents, and subjecting the washed material to the influence of chlorine, whereby the colouring matter either belonging to the fibre or imparted to it is oxidized

and discharged.

FIG. 1. Ground-Plan of Bleach-House

The general arrangements of a bleach-house will be made plain from the ground-plan (fig. 1). The various pieces of apparatus, the positions of which are there indicated, will be described in connection with the sequence of opera tions through which the cloth passes in the process of bleaching. In the best arranged works, it should be mentioned, where power is required to work any machine, it is generally supplied by a separate engine attached to the machine itself, instead of by gearing carried from one engine for all the machinery. For this plan, as well as for the greater portion of the illustrations which follow, we are indebted to Mr William Mather, of the eminent firm of Mather and Platt, Salford, to whom we are also under obligation for much valuable practical information. We have also to express our indebtedness to Mr Alexander Crum of Thornliebank, for the fullest access to the impor tant works of his firm, and for the cordial assistance afforded by the managers of its various departments.

The sequence of operations in the bleaching and finishing of calico has undergone no change in its general details since the bleaching-powder process was first introduced; but the mechanical arrangements by which the operations are conducted have been the subject of frequent improvements. The ingenuity of engineers and bleachers has been chiefly directed towards the decreasing of manual labour, economy of fuel and materials, and the rapid completion of the various processes. The application of factory legislation to bleach-works by the Bleaching and Dyeing Works Act of 1860, by imposing a necessity for regular and stated hours of work, still further stimulated the production of apparatus and arrangements for prompt and certain completion of the various operations. Consequently a great part of the old machinery and arrangements of a bleach-house have now disappeared, and the processes are carried on in a continuous series of operations by machinery and appliances to a large extent self-acting. Formerly each piece of goods was separately treated and carried by hand or on barrows from one stage to the next ; now the pieces are sewn end to end, as many as 1000 pieces, measuring perhaps 20 miles, being operated on in one stretch.

FlG 2. Section of a Dash- Wheel.

As various pieces of old machinery are yet in use for certain kinds of work, it has been considered desirable to give descriptions and figures of some of them, and these, at the same time, will serve the further purpose of indicating the nature of the mechanical improvements which have been carried out, in recent years, in bleaching establishments. The important and frequently repeated operation of wash ing was formerly conducted either at the wash-stocks or washing-mill or in the dash-wheel. The wash-stocks, which are yet in use in many large works, especially where linen is the bleacher s staple, consists of a trough or box for holding the goods to be washed, through which a constant stream of water is passing. A pair or more of heavy hammer-headed wooden beams, hung by long shafts, and playing into the trough, are alternately tilted against the cloth, causing the water by their momentum to work through and squirt out of the mass. This process of washing is rather tedious, occupying on an average about half an hour, and requiring besides a great amount of manual labour. The dash-wheel (fig. 2) is a cylindrical boy revolving on its axis. Tt has four divisions, as shown by the dot ted lines, and an opening into each division. A num ber of pieces are put into each, abundance of water is admitted behind, and the knocking of the pieces as they alternately dash from one side of the division to the other during the revolution of the wheel effects the washing. The process lasts from four to six minutes. The dash- wheel is used to the present day in the bleaching of curtaiu materials and fine muslins. In nothing have greater im provements been effected than in the arrangement of the kiers or vessels in which the cloth is boiled or " bowked." An old form of kier is seen in fig. 3. It consisted of a cylindrical vessel AA, 9 feet wide, of wood or iron, having a false bot tom BB, on which the goods were placed, about 6 inches from the real one. A small A pipe E, in the cen tre of a wider one CC, conveyed the steam from the steam - boiler. When the liquid boiled at the bottom, where the steam issued, the steam forced its way up the pipe CC, carrying with it a quan tity of the lye, which was thrown back by the small cover D, spreading itself over the surface of the goods, and filter ing through them into the space below the false bottom, where it was again heated by the steam, reascended the pipe CC, and so on in constant succession, till the boil ing was completed. FF is a wooden cover which prevented the cooling of the materials below a boiling heat.

FIG. 3. Section of Kier (old form).

The bleaching of common calico is divided into two

branches 1st, print bleaching, in the case of which the goods are bleached as a preliminary to the process of calico printing ; and 2d, white bleaching, which applies to goods to be finished white or imprinted. The processes differ in

some of their details, as in white bleaching it is only neces-