seded by chemical liquids. A sympathetic ink, which was to show itself at a distance, was known to an apothecary of the name of Brossonius, as early as 1653. He taught the use of it to Borel, under the name of a magnetic fluid, which was to be visible only when looked on by the eyes of affection. To this ink, made of arseniated liver of sulphur, he ascribed the property of shining through many folds of paper, and even through a deal board. The German author who tells this, explains the mode in which this ink worked as follows: Sulphur is so strong that if a person writes with acetate of lead on one side of 24 sheets of paper, and exposes the other side of the 24 sheets to the vapour of arseniated sulphur, the vapour penetrates through all the sheets of paper, and makes the letters on the other side visible, and nearly black. If a strong acid is added, the effect is increased, and even a thick deal board may thus be written on one side, and the letters made visible by the application of sulphur to the other. The first person who has left in modern times any record of sympathetic magnetic ink, was Peter Borell, who wrote about 1653; and in 1669 the magnetic power of this ink was denied, and its mode of operation shown by Otto Tachen, a German chemist. Waiz showed, in 1715, how to prepare sympathetic ink from the metal called cobalt; though before that the secret of preparing green inks was known, for Paracelsus is said to have known how, by their means, to produce in winter the appearance of a garden. Since

that time the knowledge of sympathetic inks has never been lost to the world; but the Post seems so convenient a mode of conveying the secrets of lovers, without any fear of their meeting the jealous eyes of guardians or keepers, that black ink is almost the only one in general use.

PERFUMED SWORDS. We do not think it can be any ple asanter to die by a sweet scented

weapon than by one which has only the qualities of steel. There may, however, be dandies in armour as well as in dress, and to them we recommend the following method of making perfumed sword-blades:

Take eight grains of ambergris, and four grains of musk, grind them together with a little sugar-candy in a glass or an agate mortar; add to the mixture four scruples of oil of Benjamin, and mix it well together. Then hold the sword-blade over a gentle, clear charcoal fire, and when the blade is well heated, dip a little sponge in the mixture, and wipe the sword all over with it. Though this should be done only once, yet will the blade for ever retain the odoriferous scent.

RANCID BUTTER. To the Editor of the Chemist. SIR, AS I believe in the old adage, that to prevent is better preserving butter free from ranthan to cure, I subjoin a mode of cidity for a great length of time: Take two parts of good dry salt, one part of good Lisbon sugar, and one of nitre: mix them. To add one ounce of the above mixevery pound of good fresh butter ture, work it well together, and press it into jars for use. It should be kept three weeks before used; if it be sooner opened, the salts will not be sufficiently blended with it. Your obedient servant,

TO MAKE A SOLID OUT OF

TWO INVISIBLE GASES. OUR little plate shows the mode of making a very pleasing and instructive experiment. Sal ammoniac,/or muriate of ammonia, a salt generally known, is a compound of muriatic acid and volatile alkali. Both these substances exist in a gaseous form, and are invisible, like common air; but both may be combined with water, which acquires their properties, by reducing them to the liquid state. If these two substances are brought, in their gaseous and invisible state, into contact, they instantly unite to form sal ammoniac, which is a solid substance, and is usually met with in the form of a hard elastic cake. To ignorant persons this may appear something like a creation: for nothing is seen, nothing can be felt, and yet a solid matter is produced. The smell, indeed, the taste, and the deleterious effects of the gases, if breathed, and the knowledge we possess of air and its properties, though it also is invisible and unfelt, except when the storm rages, convince us that the gases are substances as well as the solid; but to those who did not know these things, the experimenter might assume the character of divinity, and man might lay

claim to the powers of creation. To make this experiment, take two glass flasks, BB, placed in brass flask-holders, which may be moved and fixed to any part of the upright stands, AA. Pour into one flask muriatic acid, and into the other liquid ammonia; connect the two flasks by means of two tubes, DD, bent at right angles, with the glass hollow cylinder, E. These tubes must enter both E and the flasks, B B, and be fitted air tight to both. The glass E is supported by two stands, CC. Apply the heat of two spirit lamps, FF, to the two flasks, and the ammoniacal and muriatic acid gases, rising in the form of invisible vapours by the action of heat, and meeting in the glass cylinder, E, form first a white flaky cloud and afterwards a dense mass, which' soon renders the glass opaque and the further progress of the experiment invisible. If, however, it be continued, there will be found, when the experiment is completed, a white solid substance deposited on the inside of the glass cylinder, which is muriate of ammonia. This experiment is instructive, as showing in a clear manner the change of form which sometimes results from chemical action.

13

THE MANUFACTURE OF COTTON.

(Continued from p. 172.) THE first thing which is done with the cotton after it is brought to England, is to pick it; and in many places this is still done by the hand, as most of the machines which have been employed for this purpose have been found to injure the staple of the cotton. When picked or cleaned by the hand, the cotton is laid on a table made of cords, and quite elastic, and it is then beaten with slender rods. This separates the fibres without breaking them, and the seeds fall through between the meshes of the cords. Some of the machines which have been constructed to save this labour, are in imitation of it, and are called batting-machines; others are called rollergins; and others again, which seem to have answered best, centrifugal cotton-pickers. These machines are too complicated for description, and we shall, therefore, pass to carding. This is conducted on the same principle for cotton as for other similar substances; and it is probable that most of our readers are acquainted with the process. The card is a kind of brush made of wire, and was originally used by the hand; afterwards cards were fixed; and now they are all cylinders, driven by steam or water. In the process of carding there has been a prodigious saving of labour, by the introduction of machinery. After the carding, the cotton is stretched, or, as some people call it, roved, which is a species of imperfect spinning, as it at the same

time receives a small twist. After the roving is complete the cotton is wound on bobbins, and is then ready to be spun, which it now is, by what is called the water method, invented by Sir Richard Arkwright, or by means of what is called a mule, the invention of Mr. Crompton,--Jennies, which were the invention of Hargreaves, having given place to these two still more efficacious methods. It is in spinning that the improvement in the mode of manufacturing cotton has been greatest. There is not only a much greater quantity of work done by the machinery than could possibly be done by hand; but the size of the yarn has been more varied, and it has been made finer and more regular than the unassisted hand could possibly have made it. A single pound of fine cotton has been spun by a mule into 350 hanks, each hank measuring 840 yards, and forming, when united, a thread 167 miles in length. Weaving is also now extensively carried on by means of what is called power-looms, or looms set in motion by machinery, so that every step of the process is now done by means of machines. It is however remarkable, although these machines have in a great variety of cases supplied the place of the hand, and have produced a much greater quantity of cotton cloth than could have been produced by mere manual labour, yet the demand for cotton cloth and the consumption have gone on so rapidly increasing, that double the number of hands are now required to attend these machines and make

them, than were employed altogether in the cotton trade fifty years ago. So that it is quite evident, though the introduction of machines may change the nature of employment, it does not diminish its quantity.

The following account of the labour vested in one pound of cotton, which is taken from the Monthly Magazine, will serve to give our readers some idea of the quantity of persons employed in preparing cotton for the market, and the increased value their labour gives it. Some cotton wool was brought from the East Indies to London, and went from there to Manchester, where it was cleaned and spun. From Manchester it was sent to Paisley, where it was woven, and thence it was sent to the town of Ayr, where it was tamboured. It went back to Paisley, and was veined; and was then sent to Dumbarton, where it was hand sewed, and was afterwards returned to Paisley. It was sent to Renfrew to be bleached, returned again to Paisley,whence it went to Glasgow and was finished, and from Glasgow was sent by the coach to London. The time occupied in bringing this article to market, from the time of its being packed in India, was three years; and it must have been conveyed 5000 miles by sea, and 900 by land; it contributed to the support of not less than 150 people, and its value was enhanced, probably,more than a hundred fold.

We have already, in some of our preceding Numbers, described bleaching at length, which, together with printing and dyeing, are the only parts of the cotton manufacture which can be called chemical arts, or which can be explained on chemical principles. The cleaning, spinning, and weaving of cotton, are all mechanical arts; and for this reason we have thought it right to pass them cursorily by, that we may treat more at length of that part of the subject which belongs to chemistry, we mean dyeing and calico printing. Dyeing is a very ancient art, as we learn from the

sacred writings; for there were scarlet threads in the days of Judah, and the midwife used one to mark Tamar's child. There can be no doubt that, at the same period, or more than three thousand years ago, the Egyptians,--who perhaps taught the art to the Jews, and learnt it themselves from the inhabitants of India, who preceded them in the acquisition of knowledge,-practised it with singular success. Thus, at the present day, there are two principal modes of dyeing; one of which consists in the direct application to the cloth of the colouring matter, in the other, the colouring matter can only be applied through the medium of another substance, called techinally a mordant; and this last, which is the more difficult of discovery, and more extensively applied, was known to the Egyptians. Pliny says of them, that they began by painting or drawing on white cloth with drugs, which in themselves possessed no colour, but had the property of attracting or absorbing colouring matters. After which, these cloths were immersed in a heated dyeing liquor; and though they were colourless before, and though this dyeing liquor was of one uniform colour, yet, when taken out of it, soon afterwards they were found to be wonderfully tinged of different colours, according to the peculiar nature of the several drugs which had been applied to their respective parts, and these colours could not be afterwards discharged by washing.

The Jews were not the only nation which borrowed its arts from the Egyptians. The Tyrians and the Greeks both adopted numerous arts from them, and the former, improving on what they borrowed, became the inventors of that dye known in all antiquity by the name of the Tyrian purple. So beautiful was this colour, that the Roman Emperors, when they became masters of the world, confined the use of purple to themselves, and forbad, on pain of death, any other person to wear it, even though it should be covered with vestments

of another colour. It thus became associated with all the monstrous vices by which those persons made themselves infamous, and the sacred purple must have been the abhorrence of mankind. The practice of allowing nobody to wear this cloth, limited the number of manufacturers, and by the time the Roman empire was extinct, the art of dyeing purple was lost to the world. It was even supposed, for a long period, that such an art had never really existed, and that the accounts handed down on the subject were wholly fabulous; but the art has been recovered in modern times, and though not used, because better processes and better colours have been found out, it has been clearly shown that the shell fish, a species of whilks, from which the ancients obtained this dye, yet exist in abundance in several parts of the world, and still furnish a white liquor, which, when exposed to the light, becomes first green, then blue, then red, and in a few minutes a beautiful purple. Our ancestors, the Germans and ancient Britons, were not ignorant of the art of dyeing, and perhaps the discovery of the valuable properties of woad for this purpose was owing to them.

At present, dyers distinguish the colours they employ into two species, and call those which of themselves produce permanent dyes, such as indigo, woad, and different metallic solutions of iron, gold, cobalt, platinum, and silver, substantive colours; while those which only give dyes by the instrumentality of mordants, are called adjective colours. In dyeing cloths with the former, little more is necessary than, after they are well cleaned, to immerse them in a solution of the colouring matter. In using the latter, the mordants must first be applied. The principal mordants in use in Great Britain are acetate of iron, acetate of alumina, and various solutions of tin. When piece goods are to be dyed of one uniform adjective colour, they are immersed in a solution of one of these mordants, and are then exposed to dry. During the drying, the sub

stance used having an affinity for the oxygen of the atmosphere, generally absorbs a considerable quantity. That part of the mordant which has not chemically combined with the cloth, is afterwards removed by washing, or by steeping the cloth in water mixed with cowdung, which is extensively employed for this purpose. It is afterwards passed through a solution of the colouring matter which it is to receive. When a piece is to be dyed of different colours, the mordant for each colour is only applied to the particular place, so that the colour is fixed only in that spot. The cloth is, indeed, wholly coloured, but the colouring is easily removed from the parts to which the mordant was not applied, by exposure to the atmosphere. Al though it is plain that the mordants, both in combining with the cloth in the first instance, in afterwards combining with the oxygen of the atmosphere, and with the colouring matter, act by chemical laws, yet the combinations of the mordants with the colours are different, as the substance dyed is wool, silk, linen, or cotton. In many cases this difference of action has been referred to its right source; and, perhaps, no modern art has been more than dyeing indebted to chemistry. Almost all the metallic colours, and which are at present the chief colouring matters, have been discovered by the chemist, and by him applied to the art of dyeing. Numerous researches, too, have been made on the nature and effects of the colouring matters; but still the whole is much better practically known than theoretically explained. We shall, therefore, only observe on this part of the subject, that the great object is to find out colouring substances, the brighter the better, which have little or no affinity with any other substance but the chemical mordant; and although it cannot be expected that this should ever be fully realized, yet the nearer we approach to it, the greater will be our improvement in the art of calico printing.