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BLEACHING.
Art. III.

PRESENT METHODS.

We come now to describe the present mode of bleaching. The weaver,1 fn preparing his work, after stretching the warp, gives consistency to the yarn, by smearing it with a paste made of flour, or potatoes, boiled with water into a pap. This paste is applied with a brush; and, when dry, in order to make the warp smoother, the weaver then uses some greasy matter: generally, he employs tallow, which he rubs on the yarn in an unequal manner. It has been recommended, that the weavers should employ soft soap for this purpose, which would save the bleacher a great deal of trouble, and, of course, make the cloth wove without the addition of tallow of more value to him. There is a great deal of dilliculty in getting this grease thoroughly out of the cloth; and very often it remains in spite of every exertion, and causes spots, to the great injury of the cloth. It is obvious, that the weaver has no interest in using soap instead of tallow, unless the bleacher gives him some more money for cloth, in weaving which soap has been employed in preference to tallow; and it is, therefore, his business, if this suggestion be an improvement, to encourage the weaver in carrying it into effect. The first operation of bleaching is to remove from the cloth the substances added to it

by the weaver, which is partly done by washing it for some hours. In the large manufactories, both in Scotland and Lancashire, this is done by a mechanical contrivance, of which there are two sorts: one is called the wash-stocks; the other consists of a dash-wheel and squeezers. The latter method is now most generally adopted. In the wash-stocks the cloth is alternately beaten by stout pieces of wood, and turned round till the whole has received sutficieatcleansing. The dash-wheels are waterwheels, the inside of each of which is divided into four compartments, with a hole in each for putting in the linen, and several smaller holes for the free admission and egress of the water. As the wheels revolve, the cloth alternately rises and fells, while it is exposed to the action of a running stream. This method is found to answer very well, but cannot be adopted where water is not plentiful,as the wheel revolves much too fast to be used as amoving power. After the cloth has by washing been freed from any loose dirt it can carry off', it is put into a circular vat, called a kieve, which is filled with alkaline ley, at & blood heat, that has been already used for bucking linen. In a few hours a motion takes place in the liquid; its temperature increases, bubbles of air rise to the surface, and a thick scum is thrown up. This process is a species of acetic fermentation, and is completed in from 12 to 18 hoars, according to the state of the weather. After it is over, the cloth must be instantly removed, and again washed, or the putrefactive fermentation would begin, which would injure its texture, and would fix the colouring matter beyond the power of art to remove it. The bleacher must, therefore, take great care to watch this part of the process, and not allow the steeping to be continued too long. After the cloth has been steeped and washed, it undergoes the process of bucking, as described in our last Number.ever, that it did not part with the oxymuriatic acid gas so readily to the atmosphereas the water did, while it did give up the gas to the cloths; and thud it bleached them w:thout being disagreeable to the workmen and injurious to their health. In a short time the oxymuriate of potash was generally used, and continued in use till it was superseded by a cheaper article. In 1798, Mr. C. Tennant, of Glasgow, discovered that the alkaline earths, such as barytes, lime, and others, might be united with the oxymuriatic acid as well as potash, and serve the same purpose. At first be effected this union in water; but afterwards succeeded in combining the gas with the lime in a dry state, and thus made it portable at a small expense. The oxymuriate of lime is the substance now principally employed in bleaching; and lime is preferred to potash because the' former is a much cheaper commodity. The mode of preparing either is this :— Our plate represents a leaden retort, A, set on a tripod of iron, D, in a cast iron boiler, B, which is built into brick work, and has a common furnace and ash pit, E F. The top of the retort is closed by a leaden cover, with screws and nuts; loose ilax dipped in white lead, which has been ground in oil, is spread about the joinings, and the whole ean be firmly screwed together. In the top of the cover there is a hole fitted with a leaden plug, adapted for putting the materials into the retort; and when the apparatus is prepared for working, the plug is hammered into the cover, and is luted with a little soft clay, to prevent the escape of the gas. C is a leaden tube to convey the gas, and H is a vessel from 12 to 18 inches in diameter, intended to prevent any impurity from descending by the tnbe, I, into the receiver, KLL, which is made of lead, or wood lined with lead; when much work is to be done. It is covered at top, having a hole at M, for introducing water, and a stop-cock, N. Fill K, supposing it to contain 120 gallons, with a

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After it has been bucked six, seven, or eight times, the practice being different at different places, and washed and exposed as often on the field, it is soured, or allowed to remain for one night in diluted sulphuric acid; it is then again bucked, washed, and exposed on the fields, and aftervi ards immersed for twelve hours in oxymuriate of potash, or of lime. This is the most important part of modern bleaching, the part in which it most differs from former practices, and which is considered to be the greatest modern improvement. The remainder of the present Article will, therefore, be confined to a description of this part of the process.

Oxymuriatie acid gas was discovered, as we stated in our last Number, (Art. Chlorine) by Mr. Scheele; but it was the celebrated French Chemist, M. Berthollet, who first thought of applying it to bleach cloth. In 1785 and 1786, he made a number of experiments with this view, and explained to the world, in several papers, its effects on colours, and in what manner it might be employed in the arts. In the year 1787, a knowledge of these experiments, and of their application, was obtained in England; and Messrs. Milne, of Aberdeen, and the celebrated Mr. Watt, were the persons, particularly the latter, who introduced the use of this substance into our bleaching-fields. There is some doubt as to which of these gentlemen was the first to import this art from the continent; but a difference of a few weeks or months cannot depredate the

solution of caustic potash; or, if the oxymuriate of lime is to be prepared,'with water, in which 28 pounds of common salt have been dissolved, and add to it 56 pounds of quick lime, in an impalpable powder; put 21 pounds of common salt, mixed with 14 pounds of black oxide of manganese, the mixture being moistened with water till it is of the consistence of moist dough. The top of the retort must then be carefully screwed on. Then pour 81 bs of diluted sulphuric acid with as much water into the retort, by the hole at C, and plug it up immediately; oxymuriatic gas is instantly disengaged, and passes into K, where it is absorbed by the caustic potash, or by the lime-solution. This distillation is usually begun in the evening, and the work is permitted to go on through the night without any interference. In the morning, the same quantity of sulphuric acid, diluted with the same quantity of water as before, is added, when more gas is disengaged. As soon as it is observed that the production of gas diminishes, the water in the boiler, B, is heated, which again promotes the separation of the gas, and it is kept boiling as long as any gas passes into the receiver. The bubbling noise which it there makes is the mark the workmen have for guiding their operations. When finished, the solution of the oxymuriatic acid and potash, or lime, may be drawn off at the cock, N. If Jime be employed instead of potash, the liquid in the receiver is kept constantly agitated during the whole process. The liquid thus obtained is the bleaching liquid, into which we have stated, as the last step in our description, the cloth was immersed for 12 hours; it is afterwards boiled twice and washed, and then soured and washed. The linen is then rubbed over with strong black soap, and is afterwards well washed in pure spring water. It is then carefully examined, and if found fully bleached, is blued and made up for the market; and if not fully bleached, is again dipped in the oxymuriatic acid, again soured, boiled, and washed till it is perfectly white.

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CHEMISTRY AS A SCIENCE. Art. V.

IODINE.—fLCORrNE;

Iodine was accidentally discovered in 1811 or 1812, by a Mr. de Courtois, a manufacturer of saltpetre at Paris. In the course of his operations for procuring soda from the ashes of sea weeds, he found his metallic vessels much corroded, and in endeavouring to find out the cause of this, he discovered iodine. After ascertaining some of its properties, he gave a quantity of it to Mr. Clement, a celebrated Chemist, who undertook to examine it, and in December 1813, communicated the result of his researches to the French Institute. The inquiry into its real nature and properties was immediately prosecuted with great ardour in France by M. Gay Lussac, and in England by Sir Humphrey Davy and other celebrated Chemists. From their numerous experiments, it has been concluded that iodine is a simple substance, resembling chlorine in many particulars. Like it, certainly it has no other claim to the character of a simple substance but the fact of its having hitherto resisted all the eflorts of the most celebrated Chemists to decompose it. We know of no important part it performs in nature's works. It seems of no value to art, and is not necessary to life. It is made by the Chemist, though it is beyond his art to unmake it, and there are only a very few substances from which he can make it. "But," says an eloquent and enthusiastic Chemist, "for a circumstance nearly accidental, one of the most curious of substances might have remained for ages unknown, since nature has not distributed it either in a simple or compound state through her different kingdoms, but has confined it to what the Roman satirist considers as the most worthless of things, the vile sea weed." This is 'no longer a very correct assertion,

for iodine has been lately found by Mr. Fuchs in the water of a salt spring at Junthal, in the Tyrol, which discovery has been, confirmed by M. Buchner. M. Angelini alsp has detected iodine in large quantities in the mineral water of Sales, in the province of Voghera, in Piedmont.—{Bulletin desSciences, Physique, et Mathematics, Jei.,1824.) It is probable also that it is contained in several, and perhaps in all saline waters; but even admitting that it is much more diffused than we are at present aware, we must repeat that its only claim to the character of an elementary substance is, that it has hitherto resisted all the efforts of the Chemist's art to decompose it.

Iodine may be obtained in the following manner: — Reduce a quantity of kelp to powder, and digest it in water till every part of the kelp which is soluble in that liquid is dissolved. Filter the solution, and evaporate it till it no longer deposits crystals of salt. Pour the remaining liquid into a clean vessel, and drop into it .a little sulphuric acid, to separate the sulphuretted hydrogen and muriatic acid, which are often present. It is then to be evaporated till a dry mass only remains, which is to be put into a retort, and half its weight of sulphuric acid ppured upon it. A purple coloured vapour arises, which becomes more abundant on applying a moderate heat, and a black substance, in scales or in minute crystals, condenses on the neck of the retort or in the receiver; this substance is iodine. It may be rendered quite pure by again distilling it from a little weak solution of potash. If kelp be used for making soap, the waste ley of the soap-makers affords iodine in as large quantities as a solution of kelp.

Iodine thus procured is a solid substance of a greyish black colour, and of metallic lustre, having some resemblance to black-lead. It is usually in the form of scales, but it may be obtained in crystals. It has a disagreeable smell, similar to that of chlorine, bat not so strong. Its taste is acrid, and leaves a pungent hot sensation in the mouth. When swallowed by M. Orfil& it produced heat, constriction 6/the throat, nausea, and salivation'; and dogs were killed by a dose amounting to 70 grains. It possesses, therefore, poisonous qualities. Like chlorine, it destroys vegetable colours; bat it acts with much less intensity. It stains the hand' yejllOw., but the stain soon disappears. It melts at the temperature '6f 2244 of Fahrenheit's thermometer, and rises in vapour at the'temperature 6f 351 J. In the s^aftd of vapour, A has a very beaulifplf 'violet colour, from which it was named iodine, or, like, a violet. It is nearly insoluble in water, more soluble in alcohol, and still more in sulphuric ether.1 It can be made'to combine with various other substances, and these compounds Will be afterwards mentioned.

Flvorinil — In 1771 Scheele published a set of experiments on fluor spur, a well-known beautiful mineral, called, in this country, Derbyshire spar, in which he showed that'this mineral was a compound of lime and a peculiar acid,'to which he gave the name of fluoric acid. It was long supposed that this acid was a compound of oxygen with an unknown base; but in lfilO'an opinion was started, that it was like the muriatic acid, having hydrogen for its base, and combihed'with some unknown substance, which is a supporter of combustion; and this unknown substance, from its supposed analogies to chlorine, has received the name$ fluorine. This supposition is now .generally adopted by Chemists,, Under the authority of some experiments ^nade by Sir Humphr'ey: Davyi'from which he drew this conclusion. All attempts, however, to obtain fluorine in a separate state have been quite fruitless, and no evidence whatever but suppositions can be offered of its existence. As' V? do not conceive this to be the place to make our readers acquainted with the singular properties of fluoric acid, the

only substance in which fluorine is supposed to exist, we must necessarily be silent, for we. hold it a most vain employment, and a'mere waste of our time and the time of our readers, to oceupy ourselves in describing the properties of subStances which are only supposed to exist.

NEW WATER MORTAR. It has been announced in all the scientific journals and daily papers, that a Mr. Yicat, a Frenchman, has discovered, that powder of chalk heated, between six, and not above thirty minutes, on a plate of iron red hot, acquired the property of hardening under water, when mixed into a stiff paste. It would appear, from the experiments of Mr. Vicat, that this property, as far as it goes, js the consequence of only half burning the chalk. He adds, in a late Number oi" the Annates de Chlmie et de Physique, that chalk beingrich lime-stone, he might have generalized his conclusions and extended them to all lime-stones; but the number of failures he has met with in the course of his, experiments, has made him more cautious; and the facts which he proceeds' to detail justify his forbearance. "It is now four months," he says, " since my specimens of chalk, prepared in this way, were immersed in water, and placed in ray laboratory, where the temperature never falls below 52°, and they are now in the same state as they were twelve days after the immersion. A. blunt knitting-needle does not produce any sensible effect on them, but a sharp one, pushed with a slight degree of force, easily penetrates them without bending. An excellent water mortar, of the ordinary species,placed under the same circumstances..as the chalk, was not penetrated by the needle, which bent in place of entering it. But water mortar cannot be called good, which, at the end of four, months, is in a state resembling that of chalk." He goes on to recount other experiments which he has made, and which by no means warrant the. interpretation. put oa

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