it, is to decompose sulphuric acid by the mixture of any combustible matter capable of taking from it a part of its oxygen. In exact experiments of the laboratory, when the chemist is desirous of having great purity, it is obtained by means of metallic substances, and particularly by mercury; but for the purpose of which we are treating, where great economy is required, we would recommend the most common substances. We shall therefore give the following process.

Take chopped straw, or saw-dust, and introduce it into a mattress ; pour over it sulphuric acid, applying at the same time heat, and there will be disengaged sulphureous acid gas (vapour of sulphur), which may be combined with water in the apparatus.

The pieces are rolled upon the reels, and are drawn through the sulphureous acid, by turning them, until it is observed that the whiteness is sufficiently bright. They are then taken out, and are left to drain on a bench covered with cloth, lest they should be stained in consequence of the decomposition of the wood by the sulphureous acid; they are next washed in river water, and Spanish white is employed, if it should be judged necessary. This operation is performed by passing the pieces through a tub of clear water, in which about eight pounds Spanish white have been dissolved. To obtain a fine whiteness, the stuffs, in general, are twice sulphured. According to this process, one immersion and reeling two or three hours, is sufficient. Azuring or blueing is performed by throwing into the Spanish white liquor, a solution of one part of Prussian blue to 400 parts of water, shaking the cloth in the liquid, and reeling it rapidly.

The operation is terminated by a slight washing with soap, to give softness and pliability to the stuffs. The final operations of drying, stretching, pressing, &c. are foreign to our present subject.

Bleaching of Silk.-Silk is a semi-transparent matter, spun by a caterpillar, and formed of a substance contained in its body, which becomes hard in the air. This insect inhabits warm climates, being indigenous in Asia: it was naturalized in Europe about the time of the downfal of the Roman empire.

The filaments prepared by the silk-worm are rolled up in a cod or ball. In this state, in which we find it, it is covered with a yellow varnish which destroys its brilliancy and renders it rough. Silk by chemical analysis gives carbonate of ammonia and oil; water at a boiling heat produces no effect upon it; alcohol makes it experience no change; but concentrated alkaline leys attack and dissolve it.

To give splendour to silk, it must be freed from its varnish. This covering is soluble in alkaline leys. Silk is generally scoured by means of soap, by which it loses one-fourth of its weight. The matter disengaged from it is very fetid, and if the silk be not rinsed in plenty of water, putrid fermentation will take place. Even when the best soap is used, it is generally suspected that it injures the whiteness of the silk. The splendour of the Chinese silks is brighter than that of the European; and the Chinese employ no soap in their operations. A slightly alkaline ley will dissolve the varnish of the silk without using soap, and this has also been effected by the action of boiling water at a very high temperature.

The method which has been used successfully Take a very weak solution of caustic soda, of the apparatus for bleaching with steam.

in France, is as follows: and fill with it the boiler Charge the frames with

skeins of raw silk, and place them in the apparatus until it is full; then close the door and make the solution boil. Having continued the ebullition for twelve hours, slacken the fire, and open the door of the apparatus. The heat of the steam, which is always above 250°, will have been sufficient to free the silk from the gum, and to scour it. Wash the skeins in warm water, and, having wrung t'em, place them again on the frames in the apparatus, to undergo a second boiling. Then wash them several times in water, and immerse them in water somewhat soapy, to give them a little softness.

Notwithstanding the whiteness which silk acquires by these different operations, it must be carried to a higher degree of splendour by exposing it to the action of sulphureous acid gas, in a close chamber, or by immersing it in sulphureous acid, as before recommended for wool.

Bleaching Prints, and Printed Books.-An application has been made of the new mode of bleaching, to the whitening of books and prints that have been soiled by smoke and time.

Simple immersion in oxygenated muriatic acid, letting the article remain in it a longer or shorter space of time, according to the strength of the liquid, will be sufficient to whiten an engraving. If it be required to whiten the paper of a bound book, as it is necessary that all the leaves should be moistened by the acid, care must be taken to open the book well, and to make the boards rest on the edge of the vessel, in such a manner that the paper alone be dipped in the liquid: the leaves must be separated from each other, in order that they may be equally moistened on both sides.

The liquor assumes a yellow tint, and the paper becomes white in the same proportion; at the end of two or three hours, the book may be taken from the acid liquor, and plunged into pure water, with the same care and precaution as recommended in regard to the acid liquor, that the water may exactly touch the two surfaces of each leaf. The water must be renewed every hour, to extract the acid remaining in the paper, and to dissipate the disagreeable smell.

By following this process, there is some danger that the pages will not be all equally whitened, either because the leaves have not been sufficiently separated, or because the liquid has had more action on the front margins than on those near the binding. On this account, the best way is to destroy the binding entirely, that each leaf may receive an equal and perfect immersion; and this is the second process recommended by M. Chaptal.

"They begin," says he, "by unsewing the book, and separating it into leaves, which they place in cases formed in a leaden tub, with very thin slips of wood, or glass, so that the leaves, when laid flat, are separated 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 workman judges, by the whiteness of the paper, that it has been sufficiently 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 the 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 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 between the slips. When the paper was whitened, I lifted up the frame with leaves, and plunged them in cold water, to remove the remains of the acid as well as the smell: this process I prefer 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 greese; but it has been long known that a weak solution of potass will effectually remove stains of that kind.

"When I had to repair prints so torn that they exhibited only scraps pasted upon other paper, I was afraid of losing these fragments in the liquid, because the paste became dissolved. In such cases I inclosed the prints in a cylindric glass vessel, which I inverted on the water in which I had put the mixture proper for extricating the oxygenated muriatic acid gas. This vapour, by filling the whole inside of the jar, acted upon the print, extracted the grease as well as ink spots, and the fragments remained pasted to the paper."

Easy Method of preparing the Oxygenated Muriatic Acid.-To oxygenate the muriatic acid, nothing is necessary but to dilute it, and mix it in a very strong glass vessel with manganese, in such a manner that the mixture may not occupy the whole contents of the glass. Air bubbles are formed on the surface of the liquor; the empty space becomes filled with a greenish vapour; and at the end of some hours the acid may be farther diluted with water, and then used. It has an acid taste, because the whole is not saturated with oxygen; but it possesses all the virtues of the oxygenated muriatic acid. This process may be followed when there is not time to set up an apparatus for distilling, in order to procure the oxygenated acid.

Method of bleaching Straw.-Dip the straw in a solution of oxygenated muriatic acid, saturated with potass. (Oxygenated muriate of lime is much cheaper.) The straw is thus rendered very white, and its flexibility is increased.

Efficacy of Horse Chesnuts in bleaching Linen and clearing Woollen Stuffs, and a Ley for preparing Hemp.-The manner of making this ley is to peel the chesnuts, and rasp them as fine as possible into soft water. This is done ten or twelve hours before the mixture is to be used; and in the meanwhile, it is stirred from time to time, the better to dissolve these raspings and impregnate the water. The last stirring is given about a quarter of an hour before the water is drawn off from the thickest part of the raspings, which subside; and this is done either by inclining the vessel and pouring off the ley gently, or by Ladling it out by hand, while the water is yet white and froths like soap-suds. In order to use this ley, it is made rather hotter than the hand can well bear, and the hemp is then steeped and washed in it as in soap-suds. Linen may also be washed in this ley, and even when very dirty, much less soap will be required than is commonly used, it being sufficient to rub the dirtiest parts only with soap.-The raspinga

of the chesnuts, which sink to the bottom of the ley, are good for fowls and pigs. Hemp, as above prepared, may be dyed like silk, -wool, or cotton, and may be made into stuff and garments of all kinds; a great advantage attending the use of this material is, that it will not be destroyed by those insects which devour woollen cloth.

To bleach Bees-Wax.-Melt your wax, and while hot throw it into cold water to reduce it into little bits, or spread it out into very thin leaves, and lay it out to the air, night and day, on linen cloths, then melt it over again, and expose it as before: repeat this till the sun and dew have bleached it; then, for the last time, melt it in a kettle, and cast it with a ladle on a table covered over with little round hollows, in the form of the cakes sold by the apothecaries; but first wet your moulds with cold water, that the wax be the easier got out; lastly, lay them out in the air for two days and two nights, to make it more transparent and drier.

CHAP. XVII.

INK-MAKING..

INKS are fluid compounds, intended to form characters, or some other kinds of figures, on proper grounds of paper, parchment, or such other substance as may be fit to receive them.

There are two principal kinds of inks-writing and printing ink. Writing Ink.-When to an infusion of nut-galls some solution of sulphate of iron (green copperas) is added, a very dark blue precipitate takes place. This precipitate is the gallic acid of the galls united to the iron of the green vitriol, forming gallat of iron, which is the basis of writing ink. If galls and sulphate of iron only were used, the precipitate would fall down, leaving the water colourless; and, in order to keep it suspended in the water, forming a permanently black, or rather very dark blue fluid, gum-arabic is added, which, by its viscid nature, prevents the precipitate from falling down.

Various receipts have been given for the composition of writing ink, but very few have been founded upon a knowledge of it real nature. Though so important an article, it is but lately that it has been studied with any attention; and even still the principles and theory of its formation do not appear to be so thoroughly understood as might be wished. The receipt given by M. Ribancourt is as follows: Take eight ounces of Aleppo galls, in coarse powder; four ounces of logwood, in thin chips; four ounces of sulphate of iron (green copperas); three ounces of gum-arabic, in powder; one ounce of sulphate of copper (blue vitriol); and one ounce of sugar-candy. Boil the galls and logwood together in twelve pounds of water for one hour, or till half the liquid has been evaporated. Strain the decoction through a hair sieve, or linen cloth, and then add the other ingredients. Stir the mixture till the whole is dissolved, more especially the gum; after which, leave it to subside for twenty-four hours. Then decant the ink, and preserve it in bottles of glass or stone-ware well corked.

Another Receipt to make One Gallon of Black Writing Ink.-Into a glazed stone jar or pitcher put one pound of Aleppo galls, slightly bruised; then add one gallon of rain water, nearly of a boiling heat; let these stand together for fourteen days upon the kitchen hearth, or moderately warm; after that time add four ounces of green copperas or sulphate of iron, four ounces of log wood chips.or shavings, one ounce of alum, one ounce of sugar-candy, and four ounce of gum-arabic or senegal. Let the whole remain ten or twelve days longer in a moderate heat, the mouth of the vessel slightly covered with paper. Stir the ingredients well with a stick twice a day during the whole time; then strain off the ink through linen or flannel, bottle it, pour a little brandy on the top of the ink in each bottle, then cork them well, and keep them for use in a place of temperate heat.

This ink may be depended upon as excellent, durable, and preserving the writing all a deep black.

N. B. The best galls for the purpose are those which are dark coloured, heavy, and free from grub holes.

Red Writing Ink is made in the following manner: Take of the raspings of Brazil-wood a quarter of a pound, and infuse them two or three days in vinegar. Boil the infusion for an hour over a gentle fire, and afterwards filtre it while hot. Put it again over the fire, and dissolve in it, first, half an ounce of gum-arabic, and afterwards of alum and white sugar each half an ounce.

Another Method to make Red Ink.-Take a quarter of a pound of the best Brazil-wood (get it in the log if possible, and rasp or shave it yourself), one ounce of cream of tartar, and one ounce of alum; boil these ingredients in a quart of clear water till half is consumed, then add to the ink, when filtered hot, one ounce of gum-arabic and one ounce of fine sugar.

A little salt added will prevent it from becoming mouldy.

To prevent Ink from moulding.-Half a dozen cloves, bruised with gum-arabic, are to be put into the bottle. If a very fine ink is wanted, white wine, or vinegar and water, should be used instead of water alone.

To make Indian Ink.—Put six lighted wicks into a dish of oil; hang an iron or tin concave cover over it so as to receive all the smoke; when there is a sufficient quantity of soot settled to the cover, then take it off gently with a feather upon a sheet of paper, and mix it up with gum-tragacanth to a proper consistence.

N.B. The clearest oil makes the finest soot, consequently the best

ink.

To make China Ink.-Take dried black horse beans, burn them to a powder, mix them up with gum-arabic water, and bring them to a mass; press it well, and let it dry.

Substitute for Indian Ink-Boil parchment slips, or cuttings of glove leather, in water, till it forms a size, which, when cool, becomes of the consistence of jelly; then having blackened an earthen plate, by holding it over the flame of a candle, mix up, with a camel-hair pencil, the fine lamp-black thus obtained, with some of the above size, while the plate is still warm. This black requires no grinding, and produces an ink of the very best colour, which works as freely with the pencil, and is as perfectly transparent as the best Indian ink; it possesses the advantage of furnishing artists with a substitute for that