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.
[220] Sp. gr. 1·0125, or 21⁄2° Twaddle.
[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.