Page:Encyclopædia Britannica, Ninth Edition, v. 3.djvu/835

case of print bleaching is done with a solution of soda-ash and rosin. For a pair of Barlow kiers boiling 12,000 Ib of cloth, the quantities used are 350 Ib of soda-ash and 200 Ib of rosin dissolved with 30 gallons of caustic soda at 70 TV. The boiling is carried on for ten hours, in a like manner and at the same pressure as in the case of the lime boiling. The soda-ash and rosin form a soap, which dissolves out the free fatty acid in the cloth, and acts on the calcareous soap remaining by forming carbonate of lime and a soluble soda soap. In the white bleaching of 2700 Ib of cloth, the boiling solution is 8 gallons of caustic soda at 70 Tv., but by some bleachers soda-ash is employed in the proportion of 80 Ib to 2700 Ib of cloth. From this boil the cloth is passed on to the washing-machine, and then squeezed, when it is ready for "chemicking" with the bleaching-

powder solution.

Chemicking.—When the previous processes have been efficiently carried out, the cloth will, at this point, have attained a considerable appearance of whiteness and purity. The " chemicking" or liquoring with bleaching-powder which it now undergoes is conducted in a similar manner to the souring already described. The chemick is used as weak as possible, the solution varying from to ^ Tw. (sp. gr. 1 000625 to 1 - 00125) according to the weight and condition of the cloth under treatment. It is run through this liquor, gently squeezed, and piled up for four or six hours. It is then squeezed and washed ; and at this stage the bleacher has to judge whether the cloth requires to be chemicked a second time, which, in the case of heavy goods, is frequently necessary. If a repetition of the process is required, the cloth is again passed into the kiers, boiled with a solution of soda-ash, and the other processes repeated as before.

White Sour.—After lying in the chemick the goods are again washed and squeezed, and afterwards soured in machine with sulphuric acid, used at a strength of about 4 Tw. (sp. gr. 1 - 020), and piled up for a period of at least three hours. Thereafter, in order thoroughly to expel all acid the goods are twice washed, and finally squeezed, which concludes the operation of bleaching proper. The calico should now present a snow-white aspect, and should be fit to take the most delicate shades of colour when it is to be used for printing purposes.

Opening.—In passing through the numerous processes detailed in the foregoing statement, the cloth has been always in the form of a coil cr loose rope. In the drawing from one machine to another it has been also pulled some what to the length at the expense of breadth, and in places it is likely to have become a little twisted. The pieces have therefore now to be opened out to their full width, and, if necessary, evened. The opening out is effected by passing the pieces to a winch placed at a considerable height when the weight of the cloth itself in passing upwards unfolds it, and the selvedges are caught and extended by a boy just before it passes on to the winch. When necessary it is caught beyond the winch by an opening-machine, such as that patented in 1871 by Mr Wm. Birch of Salford. It is a complex apparatus, working by endless bands, on which are toothed projections, and these, travelling from the centre to the sides in opposite directions, open and .spread out the cloth before it passes over the roller which is mounted on the machine. From the opener the cloth passes at once to the drying-machine (hereafter described), after passing over which cloth intended for printing is folded or batched on rollers, and its further treatment belongs to the art of calico-printing.

Finishing.—So far as regards bleaching proper the pro cess is now at an end, and the further operations which white calicoes undergo have only for their object the improvement of their appearance for the market. But although the finishing adds in no way to the quality of the material, it is regarded as of great value by the merchants, and the finish of a bleacher is of more import ance than his bleaching. A great variety of finishing operations have to be employed, according to the different qualities of textiles, and the purposes to which they are devoted. Finishes are "beetled," "calendered" (either "stiff," "medium," or "soft,"or "glazed,") and,fordress muslins, etc., "elastic." As the processes and appliances for these finishing operations are very numerous and varied, they cannot here be described in detail. In most cases they are the same as used in the finishing of calico prints, and more information will be found under that head. We shall here confine our remarks chiefly to the finishing of ordinary white beetled calicoes.

Water Mangle.—The cloth, when brought into the finish ing-room, is passed over a stretching rail into a trough of boiling water and between a series of calender rollers, in which it is powerfully pressed. A common arrangement of the cylinders of the water mangle is to have a series of four, two of small diameter being made cf copper, and two larger of condensed cotton ; but wooden bowls are also sometimes employed with only a single intermediate copper cylinder. By this mangling process the water is equalized throughout the whole piece, the threads are flattened, and the cloth stretched, smoothed, and wound upon a roller, and thus rendered fit for receiving the starch.

Starching.—It is in this stage that so much is done by some bleachers to give cloth a factitious appearance of weight and bulk by filling up the interstices between the fibres with compounds which have no other object than to please or deceive the eye, and some of which have a decidedly deleterious influence on the tissue they are intended to improve in appearance. A great variety of mixtures, both cheap and nasty, are used by some finishers in place of starch with a view to produce weight and appearance, but, naturally, as little information as pos sible on this point is permitted to leak out to the public. What ought to be, and by reputable bleachers really is, used is pure starch, either of Indian corn or wheat, or both, made up into a stiff mucilage and blued with ultramarine or indigo. The cloth passes over a stretching rail into u trough of this starch, in which a roller is mounted. As it comes out of the starch it is caught between a pair of bowls, by which the superfluous starch is squeezed out and thrown back into the trough, the cloth passing on to the drying machine. The starching mangle and drying-machine are seen together in fig. 10.

FIG. 10. Starching Mangle and Drying Cans.

Drying.—The drying-machine (fig. 10), consists of a

number of cylinders made of tinned iron or copper, and filled with steam of low pressure. The cloth passes alter nately back and face over one and the other, and emerges to be placed down at the end perfectly dry. This system of drying was introduced among the first mechanical appli ances used in calico-printing, and has not as yet been superseded by any other plan. Various improvements in detail, we learn from Mr William Mather, as to the con struction of the cylinders and the mode of applying steam to them have been recently introduced, but the machine

remains the same. One important defect has been recently