Page:Encyclopædia Britannica, Ninth Edition, v. 3.djvu/839

When necessary the processes from 10 to 14 are repeated, whole processes occupy, on an average, four weeks.

II. "WITH CROFTING. The 1. Boiled in liine. 2. Washed. 3. Soured. 4. Washed. 5. Boiled in alkali and washed. 6. Exposed on grass 3 or 4 days. 7. Boiled in alkali. 8. Washed. 9. Exposed on grass. 10. Liquored. 11. Washed. 12. Soured with sulphuric acid. 13. Washed. 14. Boiled in alkali. 15. Liquored. 16. Washed. 17. Soured with sulphuric acid. 18. Washed, and processes 14 to 18 repeated if required.

With exposure on the grass the occupies from 4 to 6 weeks. The the same as in the case of calicoes iinishing linen damasks:— bleaching of plain linens usually finishing processes are essentially The following are the stages in

1. Nipped in squeezers. ~2. Blued in ultramarine in blue ing-water mangle. 3. Starched in starching-mangle. 4. Dried on steam cans. 5. Damped with fine spray. 6. Beetled. 7. Calendered. 8. Dried on steam cans. 9. Again calendered. 10. Viewed to detect rust spots and holes. 11. Lapped. 12. Pressed in hydraulic-press.

Charles Tennant of St Rollox made some experiments in 1831 to determine by which parts of the process the chief loss was sustained during bleaching. The result was that in 1000 parts by weight, linen yarn lost—

In the now abandoned fermenting alkaline steep 57 parts. In 4 boils with caustic soda 70 ,, In 4 steeps with chloride of lime 170 ,, In 4 steeps in the sour 18 ,, Total 315 parts in 1000.

Bleaching of Paper-Making Materials.

In addition to cotton and linen rags, esparto or Spanish grass (Jfacrochloa tenacissima) is now very largely used for the manufacture of the better classes of paper. Wood, especially the wood of the aspen (Populus tremula), is also now applied as a paper-making material. Jute has been used for printing paper, and straw is very largely employed, but chiefly for brown and packing papers. These and the numerous other substances used for paper-making are all reduced to the condition of "half-stuff" before they come to undergo the operation of bleaching, and the treatment they receive in this stage varies only in the amount of whitening required, and consequently in the proportions of bleaching solution used. It is therefore unnecessary to notice more than the process followed in the bleaching of the " half-stuff," which in Great Britain is very frequently prepared from a mixture of esparto fibre and rags. The bleaching solution of chloride of lime is either prepared in specially constructed cisterns, fitted with revolving agitators and stored in a reservoir for use, or prepared for immediate use in a wooden vessel. When the solution is made up to the requisite strength, and all insoluble sediment has sunk to the bottom of the vessel, it is ready for pouring into the engine. From 4 to 1 Ib of ordinary bleaching-powder are used for every 100 Ib of rag half -stuff, but a much larger proportion is required for esparto. Sulphuric acid in not more than a proportion of 1 Ib to 4 Ib of bleaching-powder is thereafter added in a highly dilute condition, and the whole, after mixing in the engine, is turned into the drainer, which is a large tank provided with a false bottom of per forated wood covered with wire-netting or bagging. In some cases the bleaching-liquids are not added to the pulp material till it is deposited in the drainer ; and the acic solution may be poured in first, or both solutions may be alternately used in small quantities. The bleaching process is sometimes carried on in separate engines constructed of materials not affected by the corrosive action of acid sub stances. Drained half-stuff may also be bleached in a suitable apparatus by the direct application of chlorine gas.

It is of the greatest importance to free the pulpy material from the last traces of chlorine before it is made into paper, as it would react upon the manufactured product and render it brittle. To eliminate the free chlorine and acid, <tc., the pulp is washed in the beater with pure water till it ceases to redden litmus paper, or give other characteristic indications of the presence of such compounds. The pre judicial effects of chlorine and its combinations are also overcome by the addition of " antichlor," the hyposulphite of soda or of lime, which forms with them compounds that do not affect the colour of the paper, although it is desir able, as far as possible, to remove such compounds also by washing with water.

Bleaching of Straw.

The fine wheat-straw used in Tuscany and elsewhere for straw-plaiting, after being cut, dried, and tied up in bundles, is stacked for a month. It is then spread out in a meadow, and exposed to the action of the sun and air, being frequently turned during that period, The lower joint of the straw is then separated, leaving only the upper joint with the ear attached, this being the only part of the straw used. It is then steamed, and after that exposed to the action of sulphurous acid gas prepared by burning sulphur, which complete the bleaching. It is then tied up in bundles, in which state it is ready for the market. In the strawplait-niaking centres of Great Britain- Luton, Dunstable, &c., in Bedfordshire straw is bleached, chielly after plaiting, by the influence of sulphurous acid gas.

Whitening and Cleaning Prints, Maps, Books, and other Articles of Paper.

Chlorine was first applied to this purpose by Chaptal, and his method was employed with the greatest success by Yialard and Heudier, who by Chaptal s process restored several of ths most valuable books of the French .National Library. Chaptal s modus operandi is thus described in his own words:—

" They begin by unsewing the book and separating it into leaves, which they place in cases formed in a leaden tub, with veiy thin slips of wood or glass, so that the leaves, when laid flat, are separ ated from each other by intervals scarcely sensible. The acid is then poured in, making it fall on the sides of the tub, in order that the leaves may not be deranged by its motion. When the work man judges, by the whiteness of the paper, that it has been suf ficiently acted upon by the acid, it is drawn off by a cock at the bottom of the tub, and its place is supplied by clear fresh water, which weakens and carries off the remains of the acid, as well as its strong smell. The leaves are then to be dried, and, after being pressed, may be again bound up.

The leaves may be placed also vertically in the tub ; and this position seems to possess some advantage, as they will then be less liable to be torn. With this view I constructed a wooden frame, which I adjusted to the proper height, according to the size of the leaves which I wished to whiten. This frame supported very thin slips of wood, leaving only the space of half a line between them. I placed two leaves in each of these intervals, and kept them fixed in their place by two small wooden wedges, which I pushed in be tween the slips. When the paper was whitened, I lifted up the frame with the leaves, and plunged them into cold water, to remove the remains of the acid, as well as the smell. This process I pre fer to the other.

"By this operation books are not only cleaned, but the paper acquires a degree of whiteness superior to what it possessed when first made. The use of this acid is attended also with the valuable advantage of destroying ink spots. This liquor has no action upon spots of oil, or animal grease ; but it has been long known that a weak solution of potash will effectually remove stains of that kind.