But, though these nations appear to have early acquired some knowledge of the art of bleaching, the progress of improvement which they made in it, when compared with the advantages which some.of them enjoyed, was very inconsiderable. The same practices seem to have been handed down from one generation to another, without any material improve ment. In India, it would appear, that the art of bleaching, as well as that pf staining cloths of vari ous colours, are not in greater perfection at present, than they are described to have been in the days of Herodotus. Even in Europe, where the arts, after they have been once introduced, have generally made rapid progress, the art of bleaching made very slow advances till towards the end of the 18th cen tury., At this period, the oxymuriatic acid, and its ef fects, were discovered by the justly celebrated Mr Scheele ; and its application to the art of bleaching, by Mr Berthollet, has given it an impulse towards perfection unknown in the history of any other art.* It now became evident, that oxygen had an affinity • with the colounng matters with which cotton and li ' nen manufactures are stained ; and that, by a proper use of the alkalies, along with the oxymuriatic acid, these colouring matters could be removed, and the goods rendered white, in a space of time almost in stantaneous, when compared with the fdrmer method of bleaching.
Upon these discoveries the present improved state of bleaching is founded. And, when the vast ex tent of the cotton and linen manufactures of Great Britain and Ireland is considered, every improve ment in it must be admitted to be of the highest na tional importance. To exhibit the present state of this art, by giving a succinct statement of the late improvements, is the subject of the following article, which, for the sake of method, shall be arranged under the following chapters, viz. : 1. A. description of the machinery used in the modern bleachfields.
2. Of the detergent and other substances used.
3. An account of the manner in which these sub stances are applied.
Of the Machinery used in Modern BleacVelds.
The machinery and utensils used in bleaching are various, according to the business done by the bleacher. Where linen or heavy cotton cloths are whitened, and the business is carried on to consider able extent, the machinery is both complicated and expensive. It consists chiefly of a water-wheel suf ficiently powerful for giving motion to the wash stocks, dash wheels, squeezers, &c. with any other operations where power is required.
Figures 6. and 7. Plate LV. represent a pair of wash stocks. AA are called the stocks or feet. They are suspended on iron pivots at B, and re ceive their motion from wipers on the revolving shaft C. The cloth is laid in at D, and, by the al ternate strokes of the feet, and the curved form of the turnhead E, the cloth is washed and gradually turned. At the same time, an abundant stream of
water rushes on the cloth through holes in the upper part of the turnhead. Wash stocks are much used in Scotland and in Ireland. In the latter country, they are often made with double feet, suspended above and below two turnheads, and wrought with cranks instead of wipers. Wash stocks, properly constructed, make from 2• to 30 strokes per mi nute.
This mode of washing is now entirely given up in Lancashire, where a preference is given to what are called dash wheels and squeezers. The dash wheels are small water wheels, the inside of which are di vided into four compartments, and closed up, only leaving a hole in each compartment for putting in the cloth. There arc, besides, smaller openings for the free admission and egress of the water emPloyed in cleansing. The cloth, by the motion of the wheel, is raised up in one part of the revolution of the wheel ; while by its own weight it falls in an other. This kind of motion is very effectual in washing the cloth, while, at the same time, it does not injure its strength. This plan, however, where the economy of water is an object of any importance, is very objectionable, because the wheel must move at by far too great a velocity to act to advantage as a water wheel.
Fig. 1. Plate LV. represents a dash wheel structed to receive its motion from a shaft A, connected either with a water wheel or steam engine. The dash wheel, CD, is fixed on a separate axis, and is engaged or disengaged from the rest of the mill work by a very simple contrivance. On the end of the the shaft AB is a face wheel FG, with teeth made to correspond with those of a similar face wheel HI. The axis of the dash wheel is made moveable endways ; by sliding it forward, the teeth lay hold of one another, and the dash wheel is thus carried round by the mill ; by the sliding it backward, the teeth are disengaged, and the dash wheel -eases to move. LM represents the lever for this purpose. NNNN (Fig. 3.) are the holes for introducing the cloth into the four com partments ; the partitions are equidistant from holes. 0 (Fig. 2.) is the pipe which supplies the wa ter for cleansing the goods. PQ is an open circle in the back of the wheel for introducing the water from the pipe 0. The circle has a number of wires set all around to prevent any part of the cloth from escaping through the circle PQ. Near the cir cumference of the wheel are other holes, through which the water finds its way after passing from the cloth. Dash wheels are made to engage and disen gage by various other modes than that which is de scribed above. Circumstances make it necessary to vary these ; and a judicious millwright will be at no loss how to adapt the mode of throwing the wheel in and out of gear to the rest of the mill work.