Chapter I: BLEACHING of =Cotton=:--Cotton is more easily bleached, and appears to

suffer less from the process than most other textile substances. On the old plan it was first (1) thoroughly washed in warm water, to remove the weaver's paste or dressing; then (2) 'bucked' or 'bowked' (boiled) in a weak alkaline lye, or in milk of lime, to remove colouring, fatty, and resinous matters, insoluble in simple water; and after being (3) again well washed, was (4) spread out upon the grass, or bleaching ground, and freely exposed to the joint action of light, air, and moisture (technically called 'crofting'). The operation of 'bucking' in an alkaline lye, washing, and exposure was repeated as often as necessary, when the goods were (5) 'soured' or immersed in water acidulated with sulphuric acid, after which they (6) received a final thorough washing in clean water, and were (7) dried, finished, and folded for the market. From the length of the exposure upon the bleaching ground this method is apt to injure the texture of the cloth; and from the number of operations required is necessarily expensive and tedious. It is therefore now very generally superseded by the system of chemical bleaching briefly described below.

In the CHEMICAL SYSTEM of bleaching the goods are 'washed' and 'bucked' as on the old plan, then submitted to the action of a weak solution of chloride of lime, and afterwards passed through water soured with hydrochloric or sulphuric acid, when they have only to be thoroughly washed, and to be dried and finished, for the entire completion of the process.

The new or continuous process, before referred to,[211] is the method of chemical bleaching at present in the most general use; and, indeed, it has nearly superseded all other methods. In this system the pieces, previously tacked together endwise so as to form a chain, are drawn, by the motion of rollers, in any direction, and any number of times, through every solution to the action of which it is desired to expose them, and this entirely and completely under the control of the operator.

[Footnote 211: See 'Hist.' (_antè_).]

The following _Table_ exhibits an outline of the several operations in the improved form of the continuous process as practised by Messrs McNaughten, Barton, and Thom, at Chorley, and in most other large bleach-works:--

1. Preliminary operations:--_a_. The 'pieces'[212] are separately stamped with the printer's name, a solution of silver, or sometimes coal-tar, being employed for the purpose.

[Footnote 212: Usually about 30 yards each.]

_b._ They are tacked together endwise either by hand or a machine, so as to form one continuous piece of 300 to 350 yards in length, according to the weight of the cloth.

_c._ They are singed.[213]

[Footnote 213: Generally on one side only; but for goods to be subsequently finely printed, on both sides. For very fine printing the nap is sometimes removed by shearing instead of 'singeing,' an ingenious and effective machine being employed for the purpose.]

_d._ They are crushed into a rope-like form by drawing them through a smooth aperture,[214] the surface of which is generally of glass or porcelain--the rope-form being given them to enable the water and other liquids to penetrate the goods more easily, and to allow them to be laid in loose coils in the kiers.

[Footnote 214: Such apertures are also used instead of pulleys, in the transfer of the rope from place to place.]

2. The pieces are bucked or boiled in milk of lime[215] for 12 to 14 hours,[216] followed by rinsing or cleansing in the washing-machine.

[Footnote 215: The common proportions are about 1 lb. of quick-lime slaked and reduced to milk, with 2 galls. of water, for every 14 or 15 lbs. of cloth.]

[Footnote 216: This is done in a large iron boiler furnished with a perforated false bottom of wood, and technically termed a 'kier.']

3. They are soured in water acidulated with hydrochloric acid,[217] and again washed; similar machines being employed for each.

[Footnote 217: This dilute acid or acidulated water has usually the sp. gr. 1·010 or 2° Twaddle.]

4. They are bucked or boiled for 15 or 16 hours in a solution of resinate of soda,[218] and then washed as before.

[Footnote 218: Made with about 17 _lbs._ of soda-ash and 3 _lbs._ of resin, with water, 50 galls., to every 20 or 21 _lbs._ of cloth.]

5. They are chemicked by being laid in a wooden, stone, or slate cistern, when a solution of chloride of lime[219] is pumped over them, so as to run through the 'goods' into a vessel below, from which it is returned on them by continued pumping, so that the cloth lies in it for 1 or 2 hours; it is then washed.

[Footnote 219: Technically called 'chemick.' The strength of the solution is usually of the sp. gr. 1·0025, or 1/2° Twaddle.]

6. They are bucked or boiled, for 4 or 5 hours, in a solution of 1 _lb._ of crystallised carbonate of soda, dissolved in 5 galls. of water, to every 35 _lbs._ of cloth; and washed.

7. They are again 'chemicked,' as before; and washed.

8. They are soured in very dilute hydrochloric acid;[220] and then left on 'stillages'[221] for 5 or 6 hours.

[Footnote 220: Sp. gr. 1·0125, or 2-1/2° Twaddle.]

[Footnote 221: Low stools or props to keep them from the ground.]

9. They are, finally, thoroughly washed, well squeezed between rollers, dried over steam-heated tin-cylinders, starched or dressed, and finished.

This is the usual process for good calicos, Muslins, and other light goods, are handled rather more carefully; whilst for commoner ones the sixth and seventh operations are generally omitted. The whole usually occupies 5 days; but by using Mr Barlow's high-pressure steam kiers, it may be performed in two days. Yarns, &c., may be bleached in a similar manner by first looping the skeins together.

_Obs._ According to the most reliable authorities, the strength of cotton-fibre is not impaired by its being boiled for two hours in milk of lime, under ordinary pressure, out of contact with the air; nor, according to the bleachers, even by sixteen hours boiling at the strength of 40 _lbs._ per 100 galls. It is said that lime is less injurious than 'soda.'

Solution of caustic soda, sp. gr. 1·030, does not injure it, even by boiling under high pressure; but, in practice, soda-ash, or carbonate of soda, is used, and this only in the second bucking, and in the third, if there be one. The strength now never exceeds 25 _lbs._ of the crystals to the 100 _galls._, and is usually less.

Experiments have shown that immersion for 8 hours in a solution of chloride of lime containing 3 _lbs._ to the 100 galls., followed by souring in sulphuric acid of the sp. gr. 1·067, or for 18 hours in acid of 1·035, does not injure it.

By the improved method of previously treating the goods with lime or alkalies, little chloride of lime is required. Indeed, it is said that where 300 _lbs._ were formerly employed, 30 to 40 _lbs._ only are now used. At the same time it is right to mention, that though a solution at 1/2° Twaddle is usually regarded as the best and safest strength, yet in some bleach works, particularly for inferior and less tender goods, this is greatly increased, even up to 5°, the period of immersion being proportionately reduced, as it is not safe to expose the goods long to the action of such powerful solutions. With the higher strengths they are passed rapidly through the liquid with the calender, sufficient time only being allowed to soak them thoroughly; then immediately through the acid or souring, followed by washing as before.

In Scotland and Ireland the washing is generally performed by wash-stocks; whilst in Lancashire, dash-wheels, or washing machines with squeezers, are almost always used for the purpose.

Cotton loses about 1-20th of its weight by bleaching.