CLASS IV.–METALLIC SUBSTANCES.
OF METALS IN GENERAL.
225. METALS, in a perfect state, are easily distinguished from other minerals, by a peculiar brilliancy which pervades their whole substance, and which has the name of metallic lustre; by their complete opacity, and their great weight in proportion to that of other mineral substances.
When taken from the earth they are found in one or other of the four following states: 1. In a native or metallic state, 2. Combined with sulphur, 3. In a state of oxide ([21]) 4. Combined with acid.
Metals, when found in a state of combination with other substances, have the name of ores. They are in general deposited in veins ([4]), of various thickness, and at various depths in the earth. The mode of obtaining them is to penetrate from the surface of the earth to the vein, and there to follow it, in whatever direction it may lie. The hollow places thus formed are called mines, and the men employed in them are denominated miners. When the veins are at a great depth, or extend to any considerable distance beneath the surface of the earth, it is necessary, at intervals, to make openings, or shafts, to the surface, for the admission and circulation of the air; and also to draw off the water which collects at the bottom, by drains, pumps, or steam-engines, as the situation or circumstances require.
After the metallic ores are drawn from the mine, they, in general, go through several processes before they are in a state fit for use. Some of them are first washed in running water, to clear them from earthy particles. They are then piled with combustible substances, and burnt or roasted, for the purpose of ridding them of the sulphur or arsenic with which they may happen to be combined, and which rises from them in a state of fume or smoke. Thus, having been freed from impurities, they undergo the operation of melting, in furnaces constructed according to the nature of the respective metals, or the uses to which they are to be subsequently applied.
The knowledge of metals is a subject of great importance to mankind. Their use in trade is so frequent, and in the arts so various and so interesting, that few objects can be more worthy of attention than these.
ORDER I.—MALLEABLE METALS;
OR, SUCH AS ARE CAPABLE OF BEING FLATTENED OR ELONGATED BY THE HAMMER, WITHOUT TEARING OR BREAKING.
226. PLATINA, the most ponderous of all the metals with which we are acquainted, is, when purified, about twenty times heavier than water. It is also one of the hardest and most difficult to be melted, is of white colour, but darker and not so bright as silver, and is found only in small blunted and angular grains or scales in the sands of some of the rivers in South America.
If platina could be obtained in sufficient quantity, it would perhaps be the most valuable of all metals. The important uses to which it is applicable may easily be imagined when we state that it is nearly as hard as iron, and that the most intense fire and most powerful acids have scarcely any effect upon it. Platina is not fusible by the heat of a forge, but requires either the concentrated rays of the sun in a burning mirror, the galvanic electricity, or a flame produced by the agency of oxygen gas.
It is admirably adapted for the uses of the philosophical chemist: although vessels made of it must always be found expensive, from its being necessary to solder them with gold; and although it has the disadvantage of being subject to corrosion by the application or use of caustic alkalies. Vessels made of it are not liable to be broken, and are as indestructible as those made of gold. When properly refined, its colour is somewhat betwixt that of silver and iron. Not being liable to tarnish like silver, platina is manufactured into several kinds of trinkets.
Its ductility is so great that it may be rolled into plates, or drawn into wire; and platina wire, for strength and tenacity, is considered much preferable to that either of gold or silver of equal thickness. Platina is also made into mirrors for reflecting telescopes, into mathematical instruments, pendulums, and clock-work; particularly where it is requisite that the construction of these should be more than usually correct, as platina is not only free from liability to rust, but is likewise subject to very little dilatation by heat. It is sometimes beaten into leaves and applied to porcelain, in the same manner as leaf gold; and its oxide ([21]) is used in enamel painting, and might be used, with great advantage, in the painting and ornamenting of porcelain. The platina employed for all these purposes is repeatedly melted with arsenic, as without the aid of this it could only be obtained in very small masses, owing to the intense heat that is required for its fusion.
This extraordinary metal was unknown in Europe until about the year 1735, when it was first brought from South America by Don Antonio Ulloa.
227. GOLD is a metal distinguished by its yellow colour; by its being next in weight to platina, softer than silver, but considerably more hard than tin; and being more easily melted than copper.
It is found in various states, massive, in grains, small scales, and capillary, or in small branches. It cannot be dissolved in any acid except that called aqua regia ([207]), and is more than nineteen times heavier than water.
The countries of hot climates are those chiefly in which gold is discovered. It abounds in the sands of many African rivers, and is very common in several districts both of South America and India. The gold mines of Lima and Peru have had great celebrity; but, since the late commotions in the Spanish colonies, the working of them has been much neglected. It is from Brazil that the greatest part of the gold which is seen in commerce is brought. The annual produce of the various gold mines in America has been estimated at nearly 9,500,000l. sterling.
The principal gold mines in Europe are those of Hungary, and next to them those of Saltzburg. Spain is probably very rich in gold. Considerable mines were worked there in former times, particularly in the province of Asturia; but, after the discovery of America, these were given up or lost. Gold has been found in Sweden and Norway, and also in several parts of Ireland, but particularly in the county of Wicklow.—Among the sands of a mountain stream in that county, and among the sand of the valley on each side, lumps of gold are occasionally found. Pieces have been discovered which weighed twenty-two ounces, but they are generally much smaller, from two or three ounces to a few grains. It is said that lumps of gold, of large size, have been used as weights in some of the common shops, and that others have been placed to keep open the doors of cottages and houses in some parts of Ireland, the owners not knowing what they were. Gold is also occasionally found in Cornwall, and some other counties of England. Wherever it occurs it is commonly observed in a state of alloy with copper or silver, and in the form of grains, plates, or small crystals.
Gold was formerly obtained in Scotland. It is asserted that, at the marriage of James V. there were covered dishes filled with coins made of Scottish gold, and that a portion of these was presented to each of the guests by way of dessert. Very extensive operations for the discovery of gold were carried on during the reign of Queen Elizabeth, at Leadhills, in Lanarkshire, under the direction of an Englishman whose name was Bulmer. The trenches, the heaps of soil that were turned up, and other marks of these operations, are yet visible near the road between Leadhills and Elvanfoot. It is said that 300 men were then employed; and that, in the course of a few years, a quantity of gold was collected, equal in value to 100,000l. sterling. Not many years ago similar operations were commenced under the superintendence of a celebrated manager of the Scottish lead mines. The gold was found immediately under the vegetable soil; and the method of obtaining it was to direct a small stream of water, so as to carry the soil along with it, to basins or hollow places, where the water might deposit the matters carried down by the force of its current. The matter thus deposited was repeatedly washed, till the whole of the earthy substances were carried off. The gold, being heaviest, sunk to the bottom, and remained behind. The soil still furnishes gold; but the produce would by no means be equal to the expense of collecting it. Searching for gold, therefore, is now regarded only as an amusement, and not as a source of profit. Grains of this metal are sometimes found, after great floods, among the sand of brooks in different parts of Scotland.
The mode of extracting gold from its ore is by reducing it into a fine powder, and mixing this powder with quicksilver ([228]). The latter having the quality of uniting with itself every particle of the precious metal, but being incapable of union with the other substances, extracts it even from the largest portions of earth. The quicksilver, which has absorbed the gold, is then separated by means of heat; it flies off in vapour, and leaves the other metal in the vessel used for the operation.
Gold has been known, and in request, from the very earliest ages of the world. By the assent of civilized nations, it has become the representative of wealth under the form of money; and it is now an universal circulating medium for the purchase of all kinds of commodities. It has been chosen to occupy this important place on account of its scarcity, its weight, and other valuable properties.
As gold is not liable to tarnish or rust, it is frequently employed for ornaments of dress. But, beyond its use in the coinage, its most important uses are for goldsmith’s work, in jewellery, and for gilding. In each of these its standard or purity is different. That denominated coinage, or sterling gold, consists of an alloy of about twenty-two parts of gold with two parts of copper; whilst gold of the new standard, of which gold plate, watch-cases, and many other articles are made, consists of only eighteen parts of gold, and six parts of copper. Each of these is stamped at Goldsmiths’ Hall; the former with a lion, a leopard’s head (the mark of the goldsmith’s company), a letter denoting the year, the king’s head, and the manufacturer’s initials; the latter is stamped with the king’s head, letter for the year, a crown, the number 18 to designate its quality, and the manufacturers initials. The coinage gold of Portugal and America is of the same standard as our own; that of France is somewhat inferior; and Spanish gold is inferior to the French. The Dutch ducats and some of the Moorish coins are of gold unalloyed. Trinket gold, which is unstamped, is in general much less pure than any of the above; and the pale gold which is used by jewellers is an alloy of gold with silver.
The ductility and tenacity of this metal, particularly when alloyed with copper, are extremely remarkable, and are fully proved by the great extent to which a very small quantity of it may be beaten into leaves, or drawn into wire. Leaves of gold may be beaten so thin, that a single grain may be made into fifty-six leaves, each an inch square. These leaves are only 1/282000 of an inch thick; and the gold leaf which is used to cover silver wire is but the twelfth part of that thickness. An ounce of gold upon silver wire is capable of being extended more than 1,300 miles in length: and sixteen ounces of gold, which, in the form of a cube, would not measure more than an inch and a quarter on each side, will completely gild a silver wire in length sufficient to compass the whole earth like a hoop.
Gold is beaten into leaves upon a smooth block of marble, fitted into the middle of a wooden frame about two feet square, in such manner that the surfaces of the marble and of the frame are exactly level. On three of the sides there is a high ledge; and the front, which is open, has a flap of leather attached to it, which the man who beats the gold uses as an apron for preserving the fragments that fall off. In this process there are three kinds of animal membranes used, some of which are laid between the leaves to prevent their uniting together, and others over them to defend them from being injured by the hammer. The exterior cover is of parchment. For interlaying with the gold, the smoothest and closest vellum that can be procured is first used; and, when the gold becomes thinner, this is exchanged for much finer skin, made of the entrails of oxen, prepared for this express purpose, and hence called gold beater’s skin. After the leaf has been beaten to a sufficient degree of thinness, it is taken up by a cane instrument, and thrown flat upon a leathern cushion, where it is cut to a proper size with a square frame of cane, or wood edged with cane. These pieces are then fitted into books of twenty-five leaves each, the paper of which has been well smoothed, and rubbed with red bole ([127]), to prevent them from sticking. The leaves are about three inches square, and the gold of each book weighs somewhat more than four grains and a half.
It was anciently the custom to beat gold into thin plates, and to gild the walls of apartments, the surfaces of dishes, drinking utensils, and other articles, by covering them with such. But this was not only an expensive, but it must have been a most clumsy mode of ornament. The present modes of gilding are very different. When wood is to be gilded, the surface is first smeared with an adhesive kind of oil, or with a kind of glue called size; and the gold leaf, above mentioned, is then spread upon it by a tuft of cotton or other soft substance.
The gilding of iron or copper is performed by cleaning and polishing its surface, and then heating it till it has a blue colour. When this has been done, a layer of gold leaf is put on, slightly burnished down, and exposed to a gentle fire. It is usual, in common work, to place three such layers, or four at the most, each consisting of a single leaf. The heating is repeated at each layer, and last of all the work is burnished. For gilding in or moulu, as it is denominated by the French, an amalgam consisting of ten parts of mercury and one part of gold is used. This is spread upon the metal, and is afterwards exposed to the action of a fire sufficiently strong to evaporate the mercury and leave the gold behind. The gilding in or moulu is much more solid and permanent than that by the former method.
When gilding is pale and dirty, it may be revived by means of what is called gilding wax, a composition of yellow wax, bole ([127]), verdigris ([230]), and alum.
A very beautiful gilding upon metals, and particularly upon silver, is effected by soaking clean linen rags in a solution of gold made by aqua regia ([207]). The rags are dried and burnt; and the ashes are carefully preserved. These ashes are used by taking a sound cork, moistening it with a little water, dipping it into the ashes, and then rubbing strongly a portion of them on the surface of the silver, which should be perfectly clean and bright. By this simple and economical process, it will be covered with an extremely thin coating of gold, the colour and brilliancy of which may be heightened by burnishing. The ornaments upon snuff-boxes, fans, and various kinds of trinkets, are merely thin plates of silver, gilded in this manner.
The edges of tea-cups, and other similar articles, may be gilded, though not in a very durable manner, by applying a thin coat of amber varnish ([224]), and then placing leaf-gold upon it. When the varnish is dry, the gold is to be burnished.
Gold, in a state of solution, is sometimes used for staining marble, ivory, ornamental feathers, and other articles, a purple-red colour, which cannot be effaced. By chemical processes an oxide ([21]) is obtained from this metal, which is employed for giving those beautiful shades of lilac, rose colour, red and purple, which we observe in glass and porcelain.
A gold powder for painting may be made by uniting one part of gold with eight parts of mercury ([228]), and afterwards evaporating the latter by heat.
The article denominated gold wire is generally silver wire gilded, very little wire being made entirely of gold. Its uses are chiefly for embroidery and filagree work. Gold thread consists of flatted silver gilt wire, laid over a thread of yellow silk, by twisting it in a machine with iron bobbins. It is of this, and not of gold, that the article called gold lace is made. The Chinese, instead of flatted wire, use slips of gilt paper, which they interweave in their stuffs, and twist upon silk threads.
228. MERCURY, in its native state, is called quicksilver, and is found in small globules of shining, silvery appearance, scattered through different kinds of stones, clay, and ores. It is nearly fourteen times heavier than water.
The principal ore of mercury, and that from which the metal is chiefly obtained, is cinnabar. This is of red colour, and consists of mercury mineralized with sulphur. It is sometimes found in a massive state, sometimes in grains, and sometimes crystallized; and chiefly among rocks of the coal formation.
The most productive mines of cinnabar are in the palatinate of Germany, at Idria in Carniola, and at Almaden in Spain. Those of Idria are supposed to be more valuable than any of the others. Their first discovery, which was somewhat more than three hundred years ago, was made in a very extraordinary manner. This part of the country was then much inhabited by coopers; and one of the men, on retiring from work in the evening, placed a new tub under a dropping spring, to try if it would hold water; and, when he came in the morning, he found it so heavy that he could scarcely move it. Examining into the cause of this extraordinary circumstance, the man observed that it was owing to a shining and ponderous fluid which was at the bottom. The affair was noised abroad, and a society of persons was formed to search further, and discover the mine from which this quicksilver had flowed. Such was their success that the reigning Duke of Austria paid them a compensation for the discovery, and took the mine into his own possession. The greatest perpendicular depth of this mine is now more than 830 feet. It is descended by buckets, or by ladders placed obliquely in a zigzag direction. In some parts of the mine the pure metal flows in small streams, so that in six hours a man has been known to collect more than thirty-six pounds weight of it. In other parts it is found in a multitude of little drops, either in ores or in clay. The whole produce of the mine is said to exceed a hundred tons weight of mercury per annum.
It has been asserted that, several years ago, in digging out clay for the foundation of a house opposite to the King’s Arms inn, in the street called Hyde-hill, in Berwick-upon-Tweed, a quantity of native mercury was discovered. The clay, when dug out, lay for some time in the place to which it was conveyed; and the mercury was observed to exude from the small fissures or cracks that were formed as it dried. It is said that, several years afterwards, in making some alteration in the yard of the same house, the workmen penetrated into the same bed of clay; and that it then appeared to be impregnated with native mercury, which ran out in small globules.
Mercury is sometimes imported into Europe from Peru, and from the East Indies.
The mode of extracting it from cinnabar is said to be by mixing this ore either with pounded chalk, or with half its weight of iron filings, and distilling it in a stoneware retort. By this process the sulphur combines with the iron, and the mercury, in a state of purity, passes into the receiver.
When pure or native mercury occurs in mixture with other substances, these are stamped or ground into a coarse powder. Water is poured upon them; they are briskly stirred until the water becomes thick and turbid, and then are left to settle. This operation is repeated till the water runs off perfectly clear. The substance at the bottom, which is principally mercury, is then put into large iron retorts and the metal is obtained, free from all extraneous matters, by distillation.
It is the singular property of this metal, which has no other alliance whatever with silver than its appearance, to be capable of division, by the least effort, into an indefinite number of particles, each of which assumes a spherical form; and to be always in a fluid state in the common temperature of our atmosphere. Even during the most intense frost, it still retains its fluidity. By the effect, however, of extreme cold artificially produced, mercury becomes a solid metal, and in this state may be beaten with a hammer and extended without breaking; but care must be taken that it does not touch the fingers, as it would blister them and cause unpleasant sores, in the same manner as any burning substance.
Mercury has been known from the remotest ages; and it was employed by the ancients in gilding, and in the operations of separating gold and silver from their ores, in the same manner as at present. Being the heaviest of all fluids of which we have any knowledge, and not congealing in the temperature of our climate, it has been preferred, before all others, for barometers, as a measure of the weight of the atmosphere. And, as heat dilates mercury similarly to other fluids, it is likewise made into thermometers. Mercury is sometimes used in medicine in its pure metallic state.
The combinations of mercury with other metals are termed amalgams. That of mercury and gold is formed so readily, that if gold be dipped into mercury, its surface immediately becomes as white as silver. An amalgam of mercury and gold is employed for the gilding, and of mercury and silver for the silvering of metals.
Mercury and tin combined together form the substance that is used for the silvering of looking-glasses. The process is as follows: A quantity of tin-foil, equal in size to the glass, is evenly placed on a flat stone or table; and mercury, in which some tin has been dissolved, is poured upon it, and spread with a feather, or bunch of cloth, until its union has covered every part. A plate of glass is then cautiously slided upon it, from one end to the other, in such manner that part of the redundant mercury is driven off, or swept away before its edge. The remainder is now united to the tin. The glass is then loaded with weights all over, so as to press out still more of the mercury. By inclining the table, this remaining mercury becomes discharged; and, in a few hours, the rest of the tin-foil and mercury adhere so firmly to the glass, that the weight may be removed without any danger of its falling. About two ounces of mercury are requisite for covering, in this manner, three square feet of glass.
By means of mercury a fulminating powder is made, which, when struck with a hammer on an anvil or flat iron, such as is used by laundresses, explodes with a stunning and disagreeable report, and with such force as to indent both the anvil and the hammer. Four or five grains are as much of this powder as ought to be used for such experiments. Its force is much greater than that of gunpowder, but does not extend so far. Hence it is a substance which might be rendered of great use in the blasting of rocks.
Corrosive sublimate is an extremely poisonous preparation from mercury. Among other uses, it is employed by dyers as a mordant to fix their colours. From certain proportions of corrosive sublimate rubbed together, until they are perfectly incorporated, is formed calomel; a salt which, of late years, has been extensively and most usefully employed in medicine.
A valuable red colour or pigment called vermilion, or artificial cinnabar, which was as well known to the ancients as it is to the moderns, is usually formed of three parts of mercury and one of sulphur, melted together, heated to redness, and then sublimated out of contact of the air. The manufacture of vermilion was long kept a secret by the Dutch; and it is stated that, before the late war, nearly 50,000 pounds weight of it were annually made, in three furnaces, by four workmen, near Amsterdam. Native cinnabar is sometimes used for the same purpose; but the artificial kind is preferred on account of the purity and brightness of its colour.
229. SILVER is a white, brilliant, sonorous, and ductile metal, somewhat more than ten times heavier than water.
It is found in different states. Of these the principal is denominated native silver, from its being nearly in a state of purity. Native silver sometimes occurs in small lumps, sometimes in a crystallized form, and sometimes in leaves, threads, or wire. In many instances the latter are so connected with each other as to resemble the branches of trees, in which case the ore is called dendritic. There are also several ores of silver, in which this metal is combined with lead, antimony, arsenic, sulphur, and other substances.
The silver that is produced from the mines of Potosi, in South America, is of the dendritic kind; and is considered by the Spaniards as the purest that is known. A range of mountains near Potosi, about twenty miles in circumference, is said to be perforated by more than 300 shafts, or openings of mines, and to produce, in the whole, from 30,000 to 40,000 dollars’ worth of ore per week. The annual produce of the silver mines in America has been estimated at near 2,400,000l. sterling.
Silver is also found in several parts of Europe; and, some years ago, there were mines of this metal, worked to a great extent, at Konigsberg in Norway. These were discovered in 1623, and they were found so profitable, that in 1751 forty-one shafts and twelve veins were wrought there; and 3,500 officers, artificers, and labourers, were employed. The perpendicular depth of the principal shaft was more than 750 feet. Specimens of native silver are not uncommon from some of the copper-mines of Cornwall; and, many years ago, a vein of silver ore was, for a short time, wrought with considerable advantage in the parish of Alva, Stirlingshire, Scotland. It is said that from 40,000l. to 50,000l. worth of silver was obtained from it before the repository was exhausted. We are informed that a mass of capillary native silver was found, in veins traversing the blue-coloured limestone of Isla, one of the Western Islands of Scotland. Great quantities of silver are extracted from lead. There was lately melted in one refining house in London 50,000l. worth of this metal, from lead of the Beralston mines in Devonshire.
Different methods are employed, in different countries, to extract silver from its ore. In Mexico and Peru the mineral is pounded, roasted, washed, and then mixed with mercury in vessels filled with water; a mill being employed for the more perfectly agitating and mingling them. By this process the silver combines with the mercury. The alloy thus obtained, after undergoing some further processes, is submitted to the action of heat, by which the mercury passes off in a state of vapour, leaving the silver behind. The silver is then melted and cast into bars or ingots. In other countries, after the earthy matters are cleared from the silver ore by pounding and washing, the remainder is melted with lead: which, by a subsequent process, is separated, and leaves the silver alone and pure.
This metal ranks next in value to gold. Like gold, it is coined into money, and is manufactured into various kinds of utensils, such as goblets, vases, spoons, and dishes, which have the general appellation of silver plate. For all these purposes it is alloyed with copper, which does not affect its whiteness, and is not easily detected, unless it be in too great proportion: the intention of this is to render it harder than it would otherwise be, and thereby the better to adapt it to receive fine and sharp impressions on being cast. Our standard silver is composed of somewhat more than 12¼ parts of pure metal and one part of copper; and the metal of this standard is used, both for silver plate, and in the coinage. The mark or stamp which is given to it at Goldsmiths’ Hall is similar to that which has been explained for sterling gold.
After platina ([226]) and gold ([227]), silver is considered the most unchangeable of all metals. The air does not easily act upon its surface in such manner as to injure it; but, when long exposed to the atmosphere, especially in frequented or smoky places, it acquires a covering or rust of dark brown colour, which, on examination, is found to be what chemists denominate sulphuret of silver. The fumes of sulphur and other inflammable substances blacken silver. Various powders have been contrived with a view to restore to plate its original lustre; but these should be used with caution, as some of them are very injurious.
Silver is nearly as ductile as gold. It may be beaten into leaves so thin that a single grain in weight will cover a space of more than fifty-one inches; and it may be drawn into wire much finer than a human hair, indeed so fine that a single grain of silver has, in this form, been extended nearly to the length of 400 feet. It is this wire gilded that has the name of gold wire; and what is denominated gold lace ([227]) is but flatted silver thread gilt, twisted round silk, and woven.
The plating of copper with silver is a very useful operation, and is thus performed. Plates of silver are bound with iron wire, upon small ingots of copper. The quantity generally allowed is one ounce of silver to twelve ounces of copper. The surface of the plate of silver is made not quite so large as that of the copper; and upon the edges of the copper, which are not covered by the silver, a little borax ([204]) is put. By exposing the whole to a strong heat, the borax melts; and, in melting, contributes to fuse that part of the silver to which it is contiguous, and to attach it, in that state, to the copper. The ingot, with its silver plate, is then rolled between steel rollers moved by machinery, till it is of proper thickness. It is afterwards cut into such sizes and to such shapes as may be required for use. An ounce of silver is thus often rolled out into a surface of three square feet, having its thickness, upon the copper, not more than the three-thousandth part of an inch. Hence we ought not to be surprised at the silver being soon worn from the sharp edges of plated goods. To prevent this, it is customary, with the best articles, to have all the edges, and the parts liable to be worn, formed, to a considerable thickness, of silver.
What is called French plate is made by heating copper, or more frequently, brass, to a certain degree, then applying leaf-silver to the surface, and strongly rubbing it with a burnisher. The durability of this plating depends of course on the number of leaves which are applied on a given surface. For ornaments that are not much used ten leaves may be sufficient; but a hundred will not last long, if the metal be exposed to frequent handling or washing.
Besides the above, there are various modes of silvering metal articles, or, as it is called, washing them with silver. All these are performed by different chemical preparations of this metal.
The article denominated shell-silver, used by painters, is prepared, by carefully grinding silver-leaf, with a little honey or gum water upon a slab, or in a mortar, and separating the honey or gum by means of water. When this is washed away, the silver may be put on paper, or kept in shells, for use. When it is to be used, it must again be diluted with gum water.
The application of silver-leaf for the silvering of paper or wood is similar to that of gold-leaf ([227]).
Silver, dissolved in aqua fortis (nitric acid, 30), yields crystals, which, afterwards melted in crucibles, form that grey mass usually called lunar caustic, and by chemists nitrat of silver. This preparation is of considerable use in surgical cases, being employed to keep down fungous or proud flesh, in wounds and ulcers, and also for the consuming of warts, small wens, and other excrescences upon the skin. It is likewise, though a most violent medicine, sometimes given internally, but in very small doses, to persons subject to epileptic fits. The liquid in which the silver is dissolved becomes excessively caustic. It gives to the skin, the hair, and almost all animal substances, an indelible black colour. Hence it is often used as a specific for dyeing the human hair. No person, however, would employ it for this purpose, who was acquainted with its injurious qualities, not only to the hair itself, but also to the skin, if permitted to come in contact with it.
The article called indelible, or permanent marking ink, for marking linen, and other wearing apparel, is formed by dissolving, in a glass mortar, two drachms of nitrat of silver, in six drachms of pure water, and then adding to them two drachms, by measure, of thick gum water. This is the ink for writing on the linen.—In another vessel dissolve half an ounce of salt of tartar, or of the subcarbonat of soda, of commerce, in four ounces of water; and add to the solution half an ounce, by measure, of thick gum water. This forms the preparatory liquor. With this the linen is to be thoroughly wetted at the part intended to be marked. The linen is to be dried, and then to be written upon by a clean pen dipped in the marking ink. The letters will at first be pale, but by exposure to light and heat, they will soon become black; and be so permanently fixed, that no washing nor bleaching can efface them.
The attention of the curious has of late been turned to a very extraordinary compound called fulminating silver, which explodes without heat, and with even the slightest degree of friction. Of this compound little fulminating balls have been made. These are globules of thin glass, each somewhat larger than a pea, and containing a grain or two of fulminating silver. After the silver is put in, it is secured by a piece of soft paper, pasted over the ball, so as completely to cover it. These balls explode by merely crushing them under the heel of the shoe. What are called fulminating bombs are similar balls, but of the size of hazel nuts. No one should attempt to explode these by crushing them with the shoe, as their explosive effect is so violent as sometimes to prove injurious.
Fulminating silver requires the utmost care. It should never be put into phials, nor should it be in any way handled so as to produce much friction. It is the most dangerous preparation that is known. The mere touch of a hard substance will sometimes explode it; and its very preparation is so hazardous that this ought never to be attempted without a mask upon the face with strong glass eyes.
The following are three pleasing experiments with preparations of silver:
1. Mix or amalgamate together four parts of silver leaf with two parts of mercury ([228]) and dissolve this in diluted aqua fortis. To the solution add as much water as will be equal to thirty times the weight of the metals employed. Pour a portion of the above mixture into a phial, and place at the bottom a small piece of silver. After it has stood awhile, little filaments of silver will be seen to shoot up from it somewhat in the form of a shrub. This apparent vegetation is popularly called the tree of Diana.
2. A production nearly similar may be obtained by adding a little quicksilver to a solution of nitrat of silver in water.
3. Drop upon a clean plate of copper a small quantity of solution of lunar caustic, or nitrat of silver. In a short time a metallic vegetation will be perceptible, branching out in pleasing forms, and in various directions.
230. COPPER is a red or orange-coloured metal, about nine times heavier than water. It is the most sonorous of all metals, and, except iron, the most elastic.
It is found under a great variety of forms, sometimes in masses of pure metal, but, more frequently, in combination with other substances, particularly sulphur.
There are valuable copper mines in every quarter of the world; and the use of copper is probably of greater antiquity than that of any other metal. It is mentioned in the Old Testament; and, at a very early period, domestic utensils and instruments of war were made of bronze, or a compound of copper and tin. Even during the Trojan war, as we learn from Homer, the combatants had no other armour than what was made of bronze. The Greek and Roman sculptors are said to have executed fine works of art in porphyry, granite, and other hard minerals, by means of copper instruments; whence historians have been induced to believe that the ancients possessed the secret of rendering this metal as hard as steel: some of them even imagined that they had the means of converting it into steel.
Copper is very abundant in several parts of Great Britain, particularly in the island of Anglesea. The copper mines of Anglesea are situated on the top of a mountain, and form an enormous cavity more than five hundred yards long, a hundred yards broad, and a hundred yards deep. The ore is got from the mine by pickaxes, and blasting with gunpowder. It is then broken with hammers into small pieces, an operation which is chiefly performed by women and children. After this, it is piled into kilns of great length, and each about six feet high; from the upper parts of which flues are attached that communicate with what are called sulphur chambers. The kilns are closely covered; and fires are lighted in different parts, that the ore may undergo the process of roasting. The whole mass gradually kindles, and the sulphur, which is combined with the ore, is expelled in fumes, by the heat, and is conveyed, through the flues, to the sulphur chamber. This process occupies from three to ten months, according to the size of the kilns; and, during that period, the sulphur chamber is cleared four or five times. When the operation is complete, or the ore is freed from the sulphur, it is taken to places denominated slacking pits. It is subsequently conveyed to the smelting houses, where, by intense heat, the pure metal is drawn off in a fluid state.
As the water, which passes through several parts of the Paris mine, is strongly impregnated with sulphat of copper ([209]), or copper held in solution by sulphuric acid ([24]), the proprietors turn the course of this water through certain large and shallow pits, which they have formed for the purpose, and in each of which they place a quantity of iron. A decomposition here takes place: the iron is corroded, and, at length, entirely dissolved, and the copper, in the form of a brown mud, falls to the bottom. One ton weight of iron, thus immersed, will produce nearly two tons of copper mud, each of which, when melted, will yield sixteen hundred weight of metal. This mode of obtaining copper is said to have been an accidental discovery from one of the workmen, several years ago, having left a shovel in the water, which, when afterwards taken out, appeared changed into copper.
The magnitude of the above mentioned copper works may readily be conceived, when it is stated that the beds of ore are, in some places, more than sixty feet in depth: that the proprietors employ more than 1000 workmen; and that they ship, from the adjacent port of Amlwch, upwards of 20,000 tons of copper, annually.
There is at Ecton, in Staffordshire, a copper mine which is now worked at the depth of 1416 feet below the surface of the ground. This is the deepest mine in England.
The uses of copper are numerous and important. When rolled into sheets, betwixt large iron cylinders, it is employed for the covering of houses, sheathing the bottoms of ships, and other purposes. As a covering for houses, copper is lighter than slate, but whether it be more durable has not been yet ascertained. The coppering of ships tends to facilitate their progress through the water, by presenting a smoother surface than that of wood, and not permitting shell animals to fasten to it as they do to wood. It likewise preserves the bottoms of the ships from being punctured by marine worms; and consequently secures to them a longer duration than they would otherwise have. Plates, or flat pieces of copper, are used by artists for engraving pictures upon, either by cutting them with a sharp steel instrument, or corroding them with aqua fortis ([206]), in lines drawn by a needle through a thin coat of wax spread upon their surface.
Copper is manufactured into various kinds of cooking utensils. Great care, however, ought to be taken that acid liquors, or even water intended for drinking, or to be mixed with food, be not suffered to stand long in such vessels, otherwise they will dissolve so much of the metal as to give them disagreeable and even poisonous qualities. Yet, it is remarkable that, while acid liquors are kept boiling, they do not seem to dissolve any of the metal. Hence it is that confectioners, by skilful management, prepare the most acid syrups in copper vessels, without their receiving any unpleasant taste or injurious quality from the metal. All vessels formed of this metal which are employed in cookery, ought to have their inner surface covered with a coat of tin ([238]).
As copper does not, like iron, strike fire by collision, it has on this, as well as on some other accounts, been substituted for iron in the machinery which is employed in gunpowder mills. It is also made into water pipes, and sometimes into sash frames. Under the hammer it is capable of being beaten into thin leaves like gold. Copper wire is much employed by bell-hangers and other artisans. The filings of this metal are used for giving a green colour to some kinds of artificial fire-works.
Several preparations of copper are employed in medicine, some of them internally, and others externally; but most of the former are violently emetic.
Verdigris is a rust or oxide ([21]) of copper, usually prepared from that metal by corroding it with vinegar. There is a large manufactory of verdigris at Montpelier in France. The workmen place alternate strata of copper plates and husks of grapes, the latter of which speedily become acid and corrode the metal. The verdigris, thus formed, is scraped off as it collects on the surface; it is afterwards dried, and put in bags or casks for sale. A manufactory of verdigris has lately been established at Deptford, near London.
A solution of this substance in distilled vinegar affords permanent crystals, which are improperly called distilled verdigris, and are made into a green paint. Verdigris is principally consumed by dyers in combination with logwood, for striking a black colour. It is a virulent poison.
Oxide of copper is employed for giving a beautiful green colour to porcelain. It also imparts the same colour to glass, and hence is frequently employed for the formation of artificial emeralds.
Alloys of Copper.
Of all metals that are known, copper is the most susceptible of alloy. The most frequent and useful of these alloys are made with copper and zinc, in different proportions.
Brass is an alloy composed of three parts of copper, and about a fourth part of zinc ([241]). It is a beautiful, useful, and well-known yellow metal. Not being so apt to tarnish and rust as copper, and being, in other respects, better adapted for the purpose than that metal, it is much used for clock-work, and for mathematical and astronomical instruments. It is more ductile than either copper or iron, and hence is peculiarly fitted to be made into wire, for the strings of musical instruments, and other purposes. Sieves are woven with brass wire, after the manner of cambric weaving, and of such extreme fineness that similar ones could not possibly be made with copper wire. Brass wire, flatted and gilded, is sometimes made into lace. The finest brass is manufactured at Geneva. It unites great beauty of colour to a high degree of ductility; and is used chiefly for escapement wheels, and other nicer parts of watch-making. For work in which there is no friction it is necessary to cover brass with a kind of varnish or laquer, to improve its colour, and prevent it from being tarnished by exposure to the atmosphere.
Prince’s Metal, or Pinchbeck, is an alloy containing three parts of zinc ([241]), and four of copper. This metal has nearly the same colour as gold, and was formerly much in use for the manufacture of ornamental articles of different kinds.
Dutch Gold is formed by the cementation of copper-plates with calamine ([241]), hammered out into leaves. This article is chiefly manufactured in Holland and Germany, and has about five times the thickness of gold leaf.
Bronze, and the metal of which cannons are made, consist of from six to twelve parts of tin ([238]) combined with 100 parts of copper. This alloy is brittle, heavier than copper, and of a yellow colour. Before the method of working iron was brought to perfection, it was used by the ancients for the manufacture of sharp-pointed instruments; and it is supposed to have been the æs or brass of the Romans.
Bell Metal, or the metal of which bells are formed, is usually composed of three parts of copper and one of tin. Its colour is greyish white; and it is very hard, sonorous, and elastic.
Bronze and bell metal are not, however, always made of copper and tin only. They frequently have other admixtures, consisting of lead, zinc, or arsenic. Bell-makers sometimes abuse the vulgar credulity by pretending that they add a certain quantity of silver to the alloy, for the purpose of rendering the bells more melodious: but they are better acquainted with their business than to employ so valuable a metal in the operation.
White Copper is an alloy composed of equal parts of copper and arsenic ([242]). The metal produced by this mixture is of a whitish colour, but with a coppery tinge. It is freed from the latter by being melted several times; and, by this process, is at last rendered as white as silver. White copper is very brittle; but, if the arsenic be evaporated by heat, it resumes its ductility, and still preserves its white colour. When the operation is well performed, it is easy, at the first glance, to mistake white copper for silver; but the difference may immediately be ascertained from the properties inherent to the two metals.
White copper is employed in the manufacture of many kinds of trinkets: and of a great number of domestic utensils; such as tea-pots, coffee-pots, and candle-sticks.
231. MALACHITE is a solid green copper ore, the surface of which has frequently a bubbled appearance, and the interior is marked with numerous irregular zones, and layers of different shades of green. It is somewhat more than three times as heavy as water, and is so soft as to be easily scratched by a knife.
In its appearance, malachite somewhat resembles green jasper; but it is by no means so hard. It is, however, capable of being cut and polished as a gem, and is manufactured into various kinds of trinkets, which of late years have been much in request for necklaces, brooches, and bracelets. It is also cut into slabs, and mounted into snuff-boxes. Such is the size of which it is sometimes found, that M. Patrin saw, at Petersburgh, a plate of malachite thirty-two inches long and seventeen inches broad, which was valued at 20,000 livres; but the finest specimens in Europe are some slabs that are adapted as the tops of tables, sideboards, &c. at Trianon, in the Park of Versailles: the largest of these are nearly four feet in length and two feet wide. They may indeed have been formed by various pieces joined together; but, if so, the joints are so completely concealed as not to be discoverable even by the closest examination. Malachite is sometimes employed for the engraving of cameos, but is seldom cut in intaglio. Smaller pieces of this substance, that are used for trinkets, are about the same value as carnelian. Independently of its use, in the above respects, and also as an ore of copper, malachite, when pure, is ground into powder, and employed as a green pigment.
The Vosges Mountains in Lorraine, and certain copper mines of Saxony, are celebrated for producing very fine specimens of malachite. This beautiful mineral is also found in our own country, in the copper mines of Cornwall and Wales.
232. TURQUOISE. The beautiful light blue substances that are called turquoises have usually been considered as the bones or teeth of animals, impregnated with blue oxide ([21]) of copper; but they are sometimes found in nodules which are certainly not of an osseous nature.
Turquoises are frequently set in rings, necklaces, brooches, and other female ornaments. In Persia they are very common; and, amongst the Turks, are held in such estimation that persons of rank almost constantly wear them in some part of their dress, as ring-stones, and to adorn the handles of stilettoes. They are imported into England from Russia, stuck with pitch upon the ends of straws; because if mixed together in parcels, the purchaser would not easily be able, in turning them over, to observe their colour, and ascertain their value.
In the turquoise there is nothing that can recommend it to notice except the agreeable softness of its colour, which is particularly distinguishable by candle-light; this alone has rendered it so fashionable as an ornament in female dress, for rings, ear-drops, and brooches, that the demand for it is at present greater than the supply. Imitations of turquoise are easily made in paste, and not unfrequently imposed upon the ignorant purchaser; but in these, though the colour is correctly given, there is a glassy lustre much higher than that of the real stone.
Of late years a spurious kind of turquoise has also found its way into Europe, which is much softer than the genuine kind; has more of a green than a blue cast, and is by no means capable of so good a polish.
233. IRON is a well-known metal, of livid greyish colour, hard and elastic, and capable of receiving a high polish. Its weight is nearly eight times as great as that of water.
It is seldom found in a truly native state, but occurs, abundantly, in almost every country of the world, in a state of oxide ([21]), and mineralized with sulphuric ([24]), carbonic ([26]), and other acids.
Iron is found in plants, in several kinds of coloured stones, and even in the blood of animals.
Of all the metals there are none which, in the whole, are so useful, or are so copiously and variously dispersed as iron. Its uses were ascertained at a very early period of the world. Moses speaks of furnaces for iron, and of the ores from which it was extracted, and tells us that swords, knives, axes, and instruments for cutting stones, were, in his time, all made of this metal.
The most considerable iron mines at present existing are those in Great Britain and France. After iron ore is dug out of the earth, it is crushed or broken into small pieces, by machinery. It is next washed, to detach the grosser particles of earth which adhere to it. This operation ended, it is roasted in kilns, formed for the purpose, by which the sulphur, and some other substances that are capable of being separated by heat, are detached. It is then thrown into a furnace, mixed with a certain portion of limestone and charcoal, to be melted. Near the bottom of the furnace there is a tap-hole, through which the liquid metal is discharged into furrows made in a bed of sand. The larger masses, or those which flow into the main furrow, are called sows; the smaller ones are denominated pigs of iron; and the general name of the metal in this state is cast iron.
With us iron is employed in three states, of cast iron, wrought iron, and steel.
Cast iron is distinguishable, by its properties of being, in general, so hard as to resist both the hammer and the file; being extremely brittle, and for the most part, of a dark grey or blackish colour.
A great number of useful and important articles are formed of cast iron, such as grates, chimney backs, pots, boilers, pipes, and cannon shot. These are made by casting ladles full of the liquid metal into moulds that are shaped, for the purpose, in sifted sand.
Wrought iron. The process of converting cast iron into wrought or malleable iron, is called blooming. The cast iron is thrown into the furnace, and kept melted by the flame of combustibles which is made to play upon its surface. Here it is suffered to continue for about two hours, a workman constantly stirring it, until, notwithstanding the continuance of the heat, it gradually acquires consistency, and congeals. It is then taken out, while hot, and violently beaten with a large hammer worked by machinery. In this state it is formed into bars for sale.
The value of iron is beyond all estimate, and infinitely greater than even that of gold. By means of this metal the earth has been cultivated and subdued. Without it houses, cities, and ships, could not have been built; and few arts could have been practised. It forms also the machinery by which the most useful and important mechanical powers are generated and applied.
Steel is usually made by a process called cementation. This consists in keeping bars of iron in contact with powdered charcoal, during a state of ignition, for several hours, in earthen troughs, or crucibles, the mouths of which are stopped up with clay. Steel, if heated to redness, and suffered to cool slowly, becomes soft; but if plunged, whilst hot, into cold water, it acquires extreme hardness. It may be rendered so hard as even to scratch glass; and at the same time, it becomes more brittle and elastic than it was before. Although thus hardened, it may have its softness and ductility restored, by being again heated, and suffered to cool slowly. A piece of polished steel, in heating, assumes first a straw-yellow colour, then a lighter yellow, next becomes purple, then violet, then red, next deep blue, and at last of all bright blue. At this period it becomes red hot, the colours disappear, and metallic scales are formed upon, and encrust its surface. All these different shades of colour indicate the different tempers that the steel acquires by the increase of heat, from that which renders it proper for files, to that which fits it for the manufacture of watch springs. Mr. Stoddart has availed himself of this property to give to surgical, and other cutting instruments, those degrees of temper which their various uses require.
The kind of steel which has been most celebrated in this country is that imported from Syria under the name of Damascus steel. Germany is also noted for its steel. The best steel manufactured in Britain is known by the name of cast steel; and the making of it, although it was long kept a profound secret, is now discovered to be a simple process. It consists merely in fusing it with carbonat of lime ([140]), or in what is called cementation, with charcoal powder, in a peculiar kind of furnace. The iron produced in Sweden is considered superior to that of any other country in Europe for the manufacture of steel.
All kinds of edge tools, where excellence is required, are made of steel; and a steel instrument may be immediately known from an iron one, by letting fall upon it a drop of nitric acid or aqua fortis ([206]), somewhat diluted with water. If it be steel, this will occasion a black spot; but if it be iron, it will not have this effect. Steel is attracted by the magnet, and is capable of receiving a permanent magnetic property, which has led to the discovery of the mariner’s compass. Had iron been productive of no other advantages to mankind than this, it would on this account alone have been entitled to their greatest attention.
Iron, when exposed to the moisture of the atmosphere, becomes gradually covered with a brown, or yellowish substance, known by the name of rust, which, if suffered to continue without interruption, will corrode the entire substance of the iron. The rust or oxide of iron ([21]) is a substance in considerable request by calico printers for a dye. Iron-moulds are spots on linen occasioned by its exposure to iron in damp situations; these are removeable only by the application of an acid.
There are various modes of preserving iron and steel from rust. The following is recommended by an eminent French chemist as one of the best. Mix copal varnish, made greasy with oil, with about four-fifths of the best spirit of turpentine. Apply this by means of a sponge, over the whole surface, and allow it to dry. This varnish may be successfully used for all the metals; and particularly for the preservation of such philosophical instruments as, by being brought into contact with water, are liable to lose their splendour, and become tarnished.
234. METEORIC STONES are a species of iron ore, which have at different times been known to fall from the atmosphere.
They have been seen only in shapeless masses, of from a few ounces to several hundred pounds in weight. Their texture is granular. They are covered externally with a thin blackish crust, and are, internally, of an ashy grey colour, mixed with shining minute particles.
There is sufficient evidence to show that solid masses of stone have been observed to fall from the air at a period considerably anterior to the Christian era. Notwithstanding this, so very extraordinary was the phenomenon, that, until the year 1802, it was generally regarded by philosophers as a vulgar error. Mr. Howard, in that year, submitted to the Royal Society a paper which contained an accurate examination of the testimonies connected with events of this kind; and described a minute analysis of several of the substances which had been said to have fallen in different parts of the globe. The result of his examination was that all these stony bodies differ completely from every other known stone; that they all resemble each other, and are all composed of the same ingredients.
The greatest number of the stones which have fallen from the air have been preceded by the appearance of luminous bodies or meteors. These meteors have burst with an explosion, and then the shower of stones has fallen to the earth. Sometimes the stones have continued luminous until they sunk into the earth, but most commonly their luminousness disappeared at the time of the explosion. Their motion through the air is surprisingly rapid, in a direction nearly horizontal; but they seem to approach the earth before they explode. In their flight they have frequently been heard to yield a loud whizzing sound. They are hot when they first reach the earth; and exhibit, on their surface, visible marks of fusion.
A general tradition has prevailed in almost all ages, and amongst all people, of the fall of solid bodies from the atmosphere, under various denominations, but, with us, more particularly, under that of thunderbolts. In barbarous and uncivilized countries, these have usually been ascribed to the miraculous judgment of the deity; and they may be considered as the true origin of the worship of stones. The image of Diana, mentioned in the Acts of the Apostles, as believed by the Ephesians to have fallen down from Jupiter, and the Palladium or sacred statue of Minerva, which also is said to have fallen from Heaven, and to have been preserved in Troy, as a treasure, on the safety of which that of the city depended, had each, no doubt, this origin. The Psalmist evidently alludes to the falling of meteoric stones, when, speaking of the Almighty, he says, “He made darkness his secret place; his pavilion round about him with dark water, and thick clouds to cover him. At the brightness of his presence his clouds removed; hailstones and coals of fire. The Lord also thundered out of Heaven, and the Highest gave his thunder; hailstones and coals of fire.”
Among numerous other instances of these stones, it is recorded that, on the seventh of November, 1492, betwixt eleven and twelve o’clock at noon, a dreadful clap of thunder was heard at Ensisheim, a considerable town in Alsace, and that a huge stone was seen to fall on a field lately sown with wheat. On several of the neighbours going to the place, the hole it had formed was found to be about three feet in depth, and the stone when dug out, weighed two hundred and sixty pounds. It was preserved in the cathedral of Ensisheim until the beginning of the French Revolution, when it was conveyed to the public library at Colmar. There are in the British Museum two small pieces of this stone, and fragments of several other meteoric stones which have fallen in different parts of the world.
Two stones fell near Verona in Italy, in the year 1672, one of which weighed three hundred, and the other two hundred pounds.
Mr. Sowerby, the publisher of English Botany, and of several other highly estimable works, possessed a meteoric stone which fell near Wold Newton in Yorkshire, in the afternoon of the thirteenth of December, 1795, and weighed fifty-six pounds. Whilst this stone was in motion through the air, several persons perceived a body passing along the clouds, although they were unable to ascertain what it was. It passed over several different villages, and was also accurately and distinctly heard. The day was foggy; and, though there was some thunder and lightning at a distance, it was not until the stone fell that an explosion took place which alarmed all the adjacent country; and created, distinctly, a sensation that something very extraordinary had happened. A shepherd belonging to Captain Topham was within a hundred and fifty yards of the place where it fell; George Sawden, a carpenter, within sixty yards; and John Shepley, one of Captain Topham’s farming servants, was so near that he was forcibly struck by some of the mud and earth that were raised by the stone dashing into the ground. In its fall the stone excavated a place nineteen inches in depth (seven inches of which were in a solid rock of chalk), and somewhat more than three feet in diameter, fixing itself so firmly that some labour was required to dig it out.
Another stone of considerable size fell in Scotland on the fifth of April, 1704. A misty commotion was observed in the atmosphere, and, nearly at the time of the stone falling, a report was heard as loud as if three or four cannon had been fired at a little distance. The report was succeeded by a violent rushing or whizzing noise; and, almost immediately afterwards, the stone fell into a drain, in the presence of two men and two boys, splashing the water to a distance of twenty feet around. The stone, when dug out, was found to have sunk about eighteen inches into the earth.
On the fifth of November, 1814, about half past four o’clock in the afternoon, a dreadful peal of thunder was heard in the Doab in Persia, and was immediately succeeded by a shower of large stones, many of them from twenty-six to thirty pounds weight each. Several inhabitants of the adjacent country were present at the time; and not fewer than nineteen of the stones were collected.
Professor Pallas, many years ago, discovered lying on the surface of a hill in Siberia, a mass of native iron, which weighed 1680 pounds. It was considered by the natives as a holy relic, and was believed by them to have fallen from heaven. M. de Bougainville, the French circumnavigator, discovered, on the banks of the river La Plata, in South America, an enormous mass of native iron, which he calculated to have weighed about 100,000 pounds. And a mass of native iron, appearing in every respect to have been of meteoric origin, was, some years ago, discovered in the district of St. Jago del Estro, in South America. It was in the middle of a great plain, and had no rock nor mountain near it, and was calculated to have weighed about thirty tons.
The origin of meteoric stones is involved in great obscurity. Some writers have imagined that they might be projected from distant volcanoes; others, that they may have been detached from rocks, and had their substance considerably changed by a concurrence of natural causes; others, that they may have been generated in the air by a combination of mineral substances; and others, that they may have been projected from the moon. The latter was the opinion of La Place the astronomer, who says that a mass, if thrown by a volcano from the moon, with a velocity of about a mile and half per second, it will thence be projected beyond the sphere of the moon’s attraction, and into the confines of that of the earth; the consequence of which will be, that the mass must presently fall to the earth, and become a part of it.
235. LOADSTONE, or MAGNETIC IRONSTONE, is a compact blackish kind of iron ore, which is possessed of the power of attracting iron, as well as every substance which contains ferruginous particles. It is betwixt four and five times as heavy as water.
This mineral is found in masses of different form and size in most of the iron mines of Europe and America, and, when submitted to the furnace, it yields a considerable proportion of metal. It makes excellent bar iron, but very indifferent cast iron. In Sweden, and particularly at Roslager, magnetic iron stone is found quite pure, and the iron that is wrought from it is imported in considerable quantities into Great Britain, for the purpose of being manufactured into steel.
The appellation of load, or leading stone, has been given to this kind of iron from its magnetic virtues; for it is not only endowed with the property of attracting iron, but also of pointing itself, and even enabling a needle touched with it to point, towards the poles of the world. We are, however, entirely ignorant what is the cause of this very extraordinary property.
Artificial magnets, constructed of steel, not only possess all the essential virtues of the genuine loadstone, but even in a much higher degree. The natural magnet is consequently now little esteemed except as an object of curiosity.
236. PYRITES, or MARCASITE, is a mineral substance, formed by a combination of iron with sulphur.
It is usually of a bronze, yellow, or brownish colour, very various in form, being massive, globular, club-shaped, oval, or crystallized; and so hard as to strike fire with flint.
Few minerals are more common than this, as it occurs, in some state or other, in almost every rock and vein. It is often found among coals; and, when heated, decrepitates with a loud unpleasant noise and sulphureous smell. To the decomposition of this mineral it is that the hot temperature of almost all the mineral waters may be ascribed.
The name of pyrites, which in the Greek language signifies firestone, has been obtained by this mineral from its property of striking sparks from steel. It was formerly used for fire-arms, as we now use flints. In commerce it is known by the name of marcasite. Some years ago it was much used, particularly in France, for the making of buttons and buckles; and was cut and polished, by lapidaries, for trinkets, particularly for the rims and hands of watches, and various kinds of female ornaments. If skilfully cut in the form of small rose diamonds, although an opaque substance, it has somewhat the appearance of a diamond. In the tombs of the Peruvian princes, with whom a considerable portion of their valuables was always interred, there have been found polished plates of marcasite, which appear to have served them as mirrors.
This mineral is never worked as an ore of iron; and it is principally valued on account of the sulphur which can be obtained from it by means of heat; and the green vitriol, or copperas ([208]), which it affords by exposure to the air.
Ignorant persons frequently mistake iron pyrites for gold; but it is easily distinguished from that precious metal by its brittleness. It breaks when hammered, whereas gold is malleable, or may be extended by hammering: it also strikes fire with steel, which gold will not.
237. RED OCHRE, REDDLE, or RED CHALK, is an iron ore of blood-red colour, which is sometimes found in powder, and sometimes in a hardened state. It has an earthy texture, and stains the fingers when handled.
The principal use of red chalk is for drawing: the coarser kinds are employed by carpenters and other mechanics, and the finer kinds by painters. For the latter purpose it should be free from grit, and not too hard. In order to free it from imperfections, and render it better for use, it is sometimes pounded, washed, mixed with gum, and cast into moulds of convenient shape and size.
Under the name of reddle, this substance is much used for the marking of sheep; and (when mixed with oil) for the painting of pales, gates, and the wood-work of out-buildings.
Another kind of iron ore, or rather a compound of the ores of iron and manganese, is called umber. This mineral, which is of a brown colour, is found in beds in the island of Cyprus, and is used as a kind of paint both in a raw state and burnt.
238. TIN is a white metal, somewhat like silver in appearance, but is considerably lighter, and makes a squeaking or crackling noise when bent. It is very soft and ductile, and has but little elasticity.
This metal is always found either in a state of oxide ([21]), or in combination with sulphur and copper; and is about seven times as heavy as water.
The principal tin mines which are known to us are those of Cornwall, Devonshire, Germany; the island of Banca, and peninsula of Malacca, in India; and Chili and Mexico in America. Of these the most celebrated are the mines of Cornwall, which are known to have been worked before the commencement of the Christian era. Diodorus Siculus, who wrote forty years before the birth of Christ, gives an account of these mines, and says that their produce was conveyed to Gaul, and thence to different parts of Italy. This species of metal was used in the time of Moses, and is mentioned in the writings of Homer.
Tin is found in veins, or beds, but chiefly in veins, running through granite and other rocks. In some of the valleys and low grounds of Cornwall, the tin ore is found in rounded grains and masses. In these situations, small grains of gold are sometimes found with it. To separate the tin from earthy and other matters with which it is intermixed, streams of water are passed over them; and these deposits have the name of stream-works.
When the tin ore has been dug from the earth, or has been collected at these stream-works, it is thrown into heaps, and broken to pieces. After this it is washed, and subsequently roasted in an intense heat, for the purpose of dissipating some of the substances with which it is combined. It is lastly melted in a furnace, and thereby reduced to a metallic state. The metal is then poured into quadrangular moulds of stone, each containing about 320 pounds weight. These have the denomination of block-tin, and are stamped by officers of the Duke of Cornwall, with the impression of a lion, the arms of that duchy. This is rendered a necessary operation before the tin can be offered for sale; and on stamping, it pays a duty of four shillings per hundred weight to the Prince of Wales, as Duke of Cornwall, who thence derives a very considerable income.
The article usually called tin, or tin-plate, and, in Scotland, white iron, of which saucepans, boilers, drinking vessels, and other utensils of domestic economy are made, consists only of thin iron plate coated with tin. It is thus formed. The iron plates are immersed in water rendered slightly acid by spirit of salt (muriatic acid, 202) or spirit of vitriol (sulphuric acid, 211): after which, to clean them completely, they are scoured quite bright. These plates are then each dipped into a vessel filled with melted tin, the surface of which is covered with suet, pitch, or resin, to prevent the formation of dross upon it. The tin not only covers the surface of the iron, but completely penetrates it, giving to its whole substance a white colour.
In a manner similar to this, stirrups, buckles, bridle-bits, and other articles, are tinned.
Iron is usually tinned before, but copper always after it has been formed into utensils. The object to be attained by the tinning of copper is to prevent the vessels made of that metal from being corroded, and to preserve the food prepared in them from being mixed with any particles of that poisonous substance called verdigris, which is formed by such corrosion. In the tinning of copper vessels, their interior surface is first scraped very clean with an iron instrument, and then rubbed over with sal-ammoniac ([207]), for the purpose of more completely cleansing them, and also of preventing the formation of verdigris from the copper during the operation. The vessel is then heated, and a little pitch is thrown into it. While quite hot, a piece of tin is applied to the copper, and this, instantly uniting with it, soon clothes the whole surface with tin.
This metal, when amalgamated with mercury, is used for the silvering of looking-glasses ([228]). When tin is melted in an open vessel, its surface is soon found to be covered with a grey powder, which is an oxide ([21]) of the metal, and is generally called dross. If the heat be continued, the colour of this powder becomes yellow. In this state it is known by the name of tin-putty, and is employed in polishing glass, steel, and other hard substances. When the heat is very violent, the metal takes fire, and is converted into a fine white oxide, which is used to render glass opaque, for the forming of enamel. Oxide of tin is also an important article to dyers. It is employed by them, in large quantities, to give brightness to such colours as are used in forming scarlets and other reds: and to precipitate the colouring matter of other dyes.
Tin is an essential ingredient in bell-metal, bronze, pewter, and various other compounds. It may be combined with lead, in any proportion, by fusion; and this alloy is harder, and possesses much more tenacity than tin. The hardest alloy is a composition of three parts of tin and one of lead. The presence of the tin destroys, in a great measure, the noxious qualities of the lead. It is sometimes customary to tin copper vessels with this mixture, and it has been ascertained that such vessels are in no respects injurious.
There are three kinds of pewter in common use. These are called plate, trifle, and ley pewter. The first, which is made into plates and dishes, is formed of tin, with a small proportion of lead and antimony ([245]). The second, or trifle pewter, which is made in somewhat different proportions, is used for the quart and pint pots of the publicans: and the ley pewter, which is formed of three parts of tin and one of lead, is manufactured into wine and spirit measures.
Tin may be beaten into leaves or plates that are much thinner than paper. But, when it is thus worked, several leaves must be joined together. They then support each other, and yield to the hammer without tearing. These leaves are used for the silvering of glass globes, and the plating of other metals. Those that are used for the silvering of looking-glasses are much thicker. The article called tin-foil is an alloy, consisting generally of two parts of tin and one of lead; and capable of being beaten to less than the thousandth part of an inch in thickness.
239. LEAD is a heavy metal, of pale and livid grey colour when broken, not sonorous when pure, very flexible, and so soft that it may be marked with the nail. It stains paper or the fingers of a bluish colour, and is about eleven times heavier than water.
The most common state in which lead is found is in combination with sulphur and a small portion of silver. This ore is known by the name of galena, and is frequently in the form of blackish cubical crystals. Lead is also found in union with arsenic ([242]) and many acids.
Great Britain possesses the most important lead-mines in the world; and those that are best known are in the counties of Flint and Derby. The latter are supposed to have been worked even in the time of the Romans.
Lead mines are entered sometimes by perpendicular shafts, and sometimes (when in the sides of hills) by levels. In some of the Derbyshire mines, where the depth of the veins will admit of it, the men work, at different heights, of from four to six feet above each other, along what are called stoops; the uppermost men being two or three yards before those next in succession, and thus forming a kind of steps. The implements used are picks, hammers, and strong iron wedges; and the rocks are also frequently loosened by means of gunpowder.
When the ore is brought out of the mine, it is sorted and washed, to free it from dirt and rubbish. After this it is spread on a board; the best pieces are picked out and separated; and those containing ore mixed with spar ([194]) or other substances, are placed separate, to be broken, and again picked. After the ore, by pickings and washing, has been sufficiently cleansed from extraneous matters, it is roasted in a kind of kiln to free it from the sulphur that is combined with it. The next process is to mix it with a certain quantity of coke, charcoal, or peat, and submit it to the smelting furnace. In this furnace there are tap-holes, which, when the lead is melted, are opened, and the metal, in a fluid state, runs into a large iron pan. The dross which floats on its surface is now skimmed off; and the metal is taken out by ladles, and poured into cast iron moulds, with round ends. The lead thus formed, is ready for use, and has the name of pig lead. According to their size, the pieces that are thus cast have the appellation of pigs, and half-pigs.
Lead is mentioned in the Sacred Writings; and is described by Homer as in common use at the period of the Trojan war. The ancients seem to have considered it as nearly allied to tin. The Romans employed it to sheathe the bottoms of their ships, fastening it to the planks and timbers by nails made of bronze.
When first melted, lead is bright, but it soon tarnishes by exposure to the air. It melts at a temperature very low in comparison with most other metals; and when a strong heat is applied, it boils and evaporates.
Lead is much employed in the useful arts. When rolled between iron cylinders to a requisite state of thinness and uniformity, it is used for the covering of houses and churches, notwithstanding the danger, in case of fire, to persons within, who are exposed to a shower of burning metal. It is cast into pipes, cisterns, and reservoirs for water, as well as into large boilers for chemical purposes. But all culinary or domestic vessels made of lead, particularly if intended for the keeping of acid liquors, should carefully be avoided, as the surface of the lead is thereby corroded, and the liquid contained in them is rendered poisonous. Hence arises that dreadful complaint, too well known where cyder is kept in leaden cisterns, called the Devonshire colic; hence also the injury which sometimes follows from the use of lead in the glazing of coarse earthenware.
Great quantities of lead are consumed for the making of shot. For this purpose the metal is alloyed with arsenic ([242]), to render it more brittle; and to render the grains more round and perfect than they otherwise would be. Shot is formed by dropping the melted alloy into water, through an iron or copper frame, perforated with round holes, according to the size required. For the smallest shot the elevation is about ten feet above the water; and for the largest about a hundred and fifty feet.
An alloy of lead and tin, in the proportion of two parts of lead and one of tin, forms the solder which is used by plumbers. The types that are used by printers for very large characters are sometimes composed of an alloy of lead and copper. Lead is also used, with tin, in the manufacture of pewter.
Oxides of Lead.
The different oxides ([21]) of lead are easily soluble in oil, and consequently are of great use to painters. Of these the following are the most important:
White Lead, or Ceruse.—This is made by suspending thin plates of lead over heated vinegar, in such manner that the vapour which rises from the acid may circulate about the plates. By this process the plates become at length entirely corroded, and converted into a heavy white powder. The manufacture of white lead is a most unhealthy trade, and is confined to a few persons, who have large conveniences for the purpose. This substance, when mixed with oil, is used as a paint for wood-work both of the outsides and insides of buildings. The fumes that are emitted from white paint are extremely noxious. Persons who breathe them are frequently seized with pains, and experience symptoms not much unlike those that precede palsy; and the danger which attends the inhabiting of apartments recently painted is well known. The odour of vinegar will correct the pernicious effect of these exhalations, by acting as a solvent, and combining with, and precipitating them. We are informed that white lead, dangerous as it is, was in great request among the Roman ladies as a cosmetic. It is sometimes used as an external application for ulcers and other kinds of sores.
Massicot is a mineral substance of yellow colour, used for painting, and prepared from the dross or pellicle that is formed by the melting of lead.
Red Lead, or Minium, is a mineral substance of red colour, used for painting, and made, by a tedious and troublesome process, from massicot. For this purpose the massicot is ground to a fine powder, put into a furnace, and constantly stirred, whilst the flame of the burning coals plays against its surface for about forty-eight hours, when it is converted into a red powder, which is the article under consideration. It is subsequently passed through very fine iron sieves. The use of red lead as a pigment is well known; but as it is liable to turn black, vermilion is generally preferred to it. It is sometimes employed in medicine as an external application for abating inflammations, for cleansing and healing ulcers, and the like; and is used in the manufacture of glass.
Litharge is another kind of oxide of lead. This is prepared by exposing calcined lead to a brisk fire for a certain length of time. The substance, on cooling, concretes into a flaky matter. Litharge is used by potters for the glazing of earthenware, but vessels that are glazed with it are thereby rendered unwholesome. It is also employed, in the composition of the finer kinds of glass, for the purpose, not only of giving them greater transparency, but also of rendering them capable of sustaining sudden changes from heat to cold, and of giving to them a susceptibility of being cut without breaking. It, however, adds considerably to the weight of the glass.
Litharge Plaster, or Diachylon Plaster, as it is more frequently called, is prepared by boiling two pints of olive oil with one pint of litharge, adding water, and constantly stirring the mixture till they are duly incorporated. This plaster is applied in excoriations of the skin, slight wounds, and other sores.
Sugar of Lead is a preparation either from the metal itself, or from white lead and distilled vinegar. It is usually observed in the form of small slender crystals, which have a glossy appearance like satin. This substance is employed, in considerable quantity, by dyers and calico printers; and is the basis of a liquid frequently used in medicine, called Goulard, or Goulard’s Extract. Although in itself a most virulent poison, it is often used by unprincipled dealers for correcting the rancidity of oil of almonds and olive oil; and a similar pernicious fraud is practised by dissolving a portion of it in wines which are becoming acid, in order to correct their acidity. These frauds, however, are easily detected by preparations or tests, which are sold by chemists for that purpose. Perhaps the best and simplest test is Harrowgate water: a little of this poured into the suspected compound will discover the presence of lead by giving to the fluid a dark brown or blackish tinge.
The following is a pleasing experiment. Dissolve an ounce of sugar of lead in about a quart of water; filter the solution through a piece of blotting paper, and put it into a glass decanter, suspending in it a piece of zinc by a brass wire. A decomposition will take place; the lead will be set at liberty, and will attach itself to the zinc, forming there a sort of metallic tree.
It has been stated that silver is usually a component part of lead ore. To disengage this, where the quantity is sufficient to repay the expense, the lead, after it has been smelted, is subjected to the action of what is called a refining furnace. A continued blast of fresh air is thrown upon its surface by means of large bellows, while the lead is kept in a state as intensely hot as possible. This by degrees converts the lead into a yellow scaly oxide or dross. The oxide, thus formed, is driven off from the melted metal as it rises, and the silver is left alone at the bottom, in a metallic state. After the operation is complete, the oxide is fused with charcoal, and again reduced to metallic lead.
We must not omit to mention that, in some of the mines of Derbyshire, there is a singular variety of lead ore called slickenside. This is a kind of galena, which presents, to the eye, a smooth and bright surface, appearing as if it were plated. Sometimes it forms the sides of cavities; and it has the extraordinary property, when merely pierced with the miner’s tool, of rending with great violence, and exploding with a crackling noise. Some miners, fearless of danger, venture to scratch it with their tools; and, on coming again to the spot, they often find that, during their absence, the slickenside has exploded, and fallen off in considerable quantity. Sometimes, however, they suffer for their imprudence. Mr. Mawe, in his account of the Mineralogy of Derbyshire, says, that he has seen a man come out of a mine cut violently, as if he had been stabbed about the neck and in other parts of the body, in consequence of the explosion of slickenside which he had pierced. The cause of this extraordinary phenomenon has not been explained.
240. NICKEL, when pure, is a fine white metal, somewhat resembling silver in appearance, but it is attracted by the magnet, and has itself the property of attracting iron.
It is ductile and malleable, difficult of fusion, and about nine times heavier than water. This metal is always mixed with arsenic ([242]) and iron.
Nickel is found in Cornwall, and in some other counties of England; in Germany, Sweden, France, Spain, and several parts of Asia. The Chinese employ it in making white copper; and, in conjunction with copper and zinc, they manufacture it into various kinds of children’s toys. Nickel gives a certain degree of whiteness to iron. It is used, with advantage, by some of the Birmingham manufacturers, in combination with that metal, and by others in combination with brass. If it were possible to discover an easy method of working nickel, there can be little doubt but it would be found a very valuable metal for surgical instruments, for compass needles, and other articles, as it is not, like iron, liable to rust. When nickel is freely suspended, it points to the north and south, in precisely the same manner as the common magnetic needle.
Oxide of nickel is used for giving colours to enamels and porcelain. In different mixtures it produces brown, red, and grass-green tints.
241. ZINC, or SPELTER, as it is sometimes called, is a bluish white metal formed in thin plates adhering together. It has a very perceptible taste, is about seven times heavier than water, rather harder than silver; and possesses but a small degree of malleability and ductility, except under certain circumstances.
This metal is never found in a pure state; and the principal ores from which it is procured are known by the names of Calamine and Blende. Of these the former is an oxide ([21]) of zinc combined with carbonic acid ([26]), and the latter is a combination of zinc with sulphuric acid ([24]).
The ores of zinc are very abundant in many countries. We are informed that nearly the whole of Flintshire in North Wales abounds with calamine; and that, so entirely ignorant were the inhabitants of its use, as, till after the middle of the eighteenth century, to have even mended their roads with it. These roads, however, have since been turned up in many places, and the materials have been converted to more valuable purposes. Derbyshire affords a great quantity of the ores of zinc, particularly calamine. This is found at various depths, generally in beds of yellow, or reddish brown clay, and usually near some vein of lead ore.
The mode of extracting zinc from its ore is by distillation. The process adopted, in some parts of Saxony, is equally simple and ingenious. An inclined stone is placed near the anterior part of a furnace, in which the ore of lead containing zinc is fused. A great part of the zinc condenses upon this stone, and flows, in drops or globules, into a quantity of charcoal placed at the bottom to receive it. These globules are afterwards again melted, to run the metal into a mass.
When exposed to the air, the surface of zinc is soon tarnished, but it scarcely undergoes any other change. It has a certain degree of ductility. When heated a little above 218° of Fahrenheit, it is malleable; and, when annealed, may be passed through rollers, and formed into thin sheets or leaves. Although, previously to being thus heated, it is brittle; on now cooling, it continues soft, flexible, and ductile. The inconvenience arising from the brittleness of the zinc being removed, this metal is applicable to many useful purposes. It may even be drawn into wire, but the tenacity of this is not great: a piece of zinc wire, one tenth of an inch in diameter, will sustain only a weight of twenty-six pounds without breaking. It has been proposed to substitute zinc in the place of tin for the lining of copper vessels; but it has not hitherto been ascertained whether this can be done with effect, and without injury. Prizes have of late been offered, to a considerable extent, in France, for the ascertainment of this fact. In China, zinc is employed as a current coin of the country; and for this purpose it is used in the utmost purity. The Chinese also, as well as the artists of our own country, employ it to a great extent in various alloys. It is used in the manufacture of brass, pinchbeck or prince’s metal, and bronze, all of which consist of this metal in combination with different proportions of copper ([230]). Tutenag is a well known white metal, made principally of zinc, and used for forming candlesticks and other articles. When tutenag is well manufactured, it is of good colour, and not more disposed to tarnish than silver. Zinc is one of the metals employed to form the galvanic or voltaic apparatus; and its filings are mixed with gunpowder, to produce those brilliant stars and spangles which are seen in the best kinds of artificial fire-works. Preparations of zinc are occasionally used in medicine. If a thin plate of zinc be applied to the upper surface of the tongue, and a shilling to the lower surface, and both metals, after a little while, be brought into contact, a very peculiar taste will, at that instant, be perceived. The same sensation will be perceived, though in a weaker degree, if the silver be placed at the top and the zinc at the bottom.
If a silver probe be introduced high up one of the nostrils, and be brought into contact with a piece of zinc placed on the tongue, a sensation not unlike that of a strong flash of light will be produced in the corresponding eye. A similar perception will result, both at the moment of contact and that of separation, if one of the metals be applied as high as possible between the gums and upper lip, and the other in a similar situation with the under lip, or even under the tongue.
A white oxide ([21]) prepared from zinc, was, some years ago, proposed as a substitute for white lead in house painting. This oxide is not dangerous in its application; and does not become yellow when mixed with oil. But these advantages are counterbalanced by some defects, which have hitherto caused it to be rejected. It is lighter than white lead: does not cover the surface so equally, nor so well; and is of considerably higher price.
Calamine.—The principal use of calamine is in the manufacture of brass ([230]); and the mines of Derbyshire, and of Limbourg in the Netherlands, supply with this mineral nearly all the brass works in Europe. After the calamine is dug out of ground, it is reduced to pieces not in general larger than a nut. It is then roasted for five or six hours, in what is called a reverberating furnace. The large pieces are separated, and the small ones are passed through a sieve. It is washed; and, when dry, is ground in a mill. In this state it is sold. The principal demand for it is at Birmingham, for the different brass founderies in that town.
The use of calamine in the composition of brass was known at a very early period. It is mentioned by Aristotle, who also makes a distinction between the compound resulting from the mixture of copper and calamine or brass, and that resulting from the mixture of copper and tin or bronze.
ORDER II.—BRITTLE METALS,
OR SUCH AS ARE NOT CAPABLE OF BEING FLATTENED OR ELONGATED BY THE HAMMER WITHOUT TEARING OR BREAKING.
242. ARSENIC, in a metallic state, has a bluish white colour, and considerable brilliancy; it is remarkably brittle, is the softest of all known metals, and is somewhat more than eight times heavier than water.
It is found nearly pure, and in considerable abundance, in different parts of Germany; usually occurring in masses of various shapes, and in combination with a small portion of iron, gold, or silver.
The arsenic sold in the shops, and too well known for its poisonous qualities, is an oxide ([21]) of this metal artificially prepared.
In some mines on the Continent arsenic is very abundant, and is found extremely injurious to the workmen. Being very volatile, its fumes affect and destroy the lungs, and occasion death in a short time to many of them. One of its ores, arsenical pyrites, is found abundantly in Cornwall and Devonshire, accompanying ores of copper and tin; and, in combination with other metals, it occurs, in a greater or less proportion, in almost all mines.
Arsenic is occasionally used in the arts. It is employed in various metallic combinations where a white colour is required, and, particularly, for the whitening or bleaching of copper, which is thereby also rendered capable of taking a fine polish; hence its use in many of the compositions for the mirrors of reflecting telescopes, and for other optical instruments. The manufacturers of glass frequently employ the oxides of arsenic in the fabrication of that article. Arsenic is used in the processes of dyeing and calico printing; and for the imparting of different artificial shades and colours to furs. It is also used in the manufacture of small shot, from its rendering the lead more brittle, and better capable of being formed into grains, than it would be without such admixture.
The arsenic of commerce is prepared to a great extent in Bohemia and Saxony, by roasting cobalt ores for the manufacture of zaffre ([247]). White arsenic is made, by mixing the common oxide with potash, and submitting it to a certain degree of heat, in vessels adapted to the purpose; the arsenic, rising in fumes, is separated, leaving the sulphur behind, united to the potash. This process is called sublimation.
Of all substances with which we are acquainted this is perhaps the most deadly. If only a few grains of it be taken into the stomach, it proves fatal; and it has frequently proved the more injurious from its deceitful appearance, in which it somewhat resembles salt or white sugar. Carelessly left in places open to the access of children, arsenic has not unfrequently been mistaken by them for sugar, and has been attended with the most dreadful consequences. If thrown on heated coals, however, it is immediately known, by the smell of garlic, and the white fumes which it gives out. The best remedy for this poison is said to be a few scruples of liver of sulphur (sulphuret of potash), dissolved in half a pint or a pint of water, and administered a little at a time, as the patient can bear it.
Notwithstanding its deleterious qualities, arsenic is occasionally used in medicine, though in extremely small doses; and it has, in particular, been found efficacious in many cases of intermittent fever.
It is employed as a poison for rats and mice; and, diluted with water, it attracts and poisons flies, whence it is sometimes called by the French, poudre a mouches. There cannot, however, be too great caution used either in the preparation, or in the application, of this fatal poison.
243. YELLOW ORPIMENT is a mineral substance of lemon colour, which consists of arsenic in combination with sulphur; and in the proportion of about fifty-seven parts of the former and forty-three of the latter.
It is about thrice as heavy as water; and is found both in a massive and crystallized state; but the crystals are so confused that their figures cannot easily be determined.
The orpiment of commerce is an artificial production, and is chiefly imported from different parts of the Levant. The Turks, and other Orientals, use it in the depilatories which serve to render bald the top of the head. A very beautiful, but fugitive pigment, called King’s yellow, is prepared from this mineral; and other preparations of orpiment are occasionally used by painters, and also by dyers and calico printers. The whole of these, however, are extremely poisonous.
Orpiment is found in a natural state, along with copper and other ores, in Natolia, Servia, Hungary, Turkey, and some other countries.
244. REALGAR, or RED ORPIMENT, is a mineral substance of red or orange colour, which consists of arsenic in combination with sulphur; and in the proportion of seventy-five parts of the former, and twenty-five of the latter.
It is somewhat more than three times as heavy as water; and occurs sometimes in a crystallized, and sometimes in a massive or disseminated state.
This production, which, by ignorant persons, is not unfrequently mistaken for red lead, is in considerable request by painters, dyers, and calico printers. In China it is manufactured into small pagodas and other ornaments. And the Chinese form it into medical cups, and use lemon juice which has stood for some hours in them, as a cathartic. Realgar is poisonous, but by no means so much so as arsenic ([242]).
It is found in Sicily, Hungary, and various parts of Germany: and is very common in several districts of China.
245. ANTIMONY is a compact metallic substance of brilliant and slightly bluish white colour, destitute of ductility, and about seven times heavier than water.
Its texture is laminated, the plates crossing each other in almost every different direction. It is as hard as silver, and so brittle that it may easily be reduced to powder, in a mortar.
In the state of the Connecticut, North America, it is said that antimony, in a pure metallic form, is found in such abundance that, in some places, large masses of it may be seen lying on the surface of the ground. The principal supply of antimony in Europe is from an ore which is found in Hungary and Norway, called sulphuret of antimony. The process of bringing it into a state for use is very simple. The mineral is put into pots, each of which has a hole in the bottom, and which is placed on another pot bedded in the earth. The upper pots, which are filled with the mineral, are heated. As soon as the antimony is fused it flows into the lower pots, while the substances with which it was combined remain in the upper ones. The antimony fixes, and forms cakes of the shape of the pots which receive it. In this state the metal presents, in its fracture, a surface thick-set, with long needle-shaped crystals, which, lying by the side of each other, compose, as it were, the whole of the mass. It is afterwards re-melted and cast into cakes for sale.
This metal, in a pure state, or alloyed only with a very small portion of silver and iron, is found in veins of mountains in some parts of France and Sweden, occurring in massive and kidney-shaped lumps of white colour.
The only mine of antimony in Britain, which is of any importance, is at Glendinning in Dumfries-shire. It was discovered in 1760, in searching for lead ore, but was not regularly worked till 1763. In the first five years about a hundred tons’ weight of antimony were obtained from it. This at 84l. per ton, produced the sum of 8400l. The undertaking was afterwards relinquished, but, as the price of antimony is now at least thrice what it then was, it is supposed that this work, if resumed, might prove an advantageous speculation. The vein of ore is only from eight inches to a foot and a half in thickness.
Antimony was known to the ancients. The earliest account we have of it is in the Sacred Writings. The passage in the Second Book of Kings,[[4]] which states that, on the approach of Jehu to the city of Jezreel, “Jezebel painted her face,” implies, in the original, that she stained her eyes and eyebrows with antimony, for the purpose of making them look black and large, a custom which, at that period, was prevalent in several of the Eastern countries. Antimony was likewise considered by the ancients a remedy against inflammations of the eyes.
This metal is the basis of many of the officinal preparations which are now in use; and it was the basis of many others which were formerly used, but are now discontinued. No mineral substance has so much attracted the attention, or so much divided the opinion of physicians, as antimony. One party extolled it as an infallible specific for almost every disease; whilst another described it as a virulent poison, which ought to be expunged from the list of medicines. It was on this metal that the alchemists of the middle ages principally founded their hope of discovering the philosopher’s stone; and, by a kind of good fortune, of which we can cite but few examples, it has happened that, in pursuing a chimera, they hit upon a succession of important realities. To the unremitted perseverance with which they tormented this metal, if we may so express it, the art of healing has been most essentially indebted.
[4]. Ch. ix. v. 30. See also Ezek. Ch. xxiii. v. 40.
The first rational account of the properties of antimony was given, about the end of the seventeenth century, by a French chemist, whose name was Lemeri. Its great importance in medicine will be seen by an enumeration of some of the most valuable preparations of it which are still in use.
Antimonial Wine is prepared from antimony, in conjunction with white Lisbon wine. It is employed as an emetic; but, if mixed with milk, this quality is said to be completely destroyed, and it becomes narcotic.
Emetic Tartar, which is much more employed in this country than all the other antimonial preparations put together, is formed from antimony mixed with its own weight of tartar, and a certain proportion of water, and afterwards boiled, filtered, and suffered to crystallize.
Butter of Antimony is obtained from a combination of antimony with corrosive sublimate. It is denominated by chemists muriat of antimony, and is usually a thick fatty mass of greyish white colour.
Glass of Antimony is a vitreous substance of reddish brown colour, which is occasionally used in medicine, but more frequently in colouring the imitations of yellow diamond, Oriental, Brazil, and Saxon topaz, hyacinth, emerald, and beryl.
James’s Powder, or Antimonial Powder, is a well-known medicine, composed of phosphat of lime and antimony.
An alloy consisting of sixteen parts of lead and one part of antimony constitutes the metal of which printers’ types are formed. This alloy does not differ from lead except in being considerably harder and more tenacious. The plates on which music is engraved are formed of a mixture of tin and antimony; and the oxides of antimony are used for the colouring of glass.
246. BISMUTH is a reddish white semi-metal, harder than silver, and composed of broad brilliant plates adhering together.
It is nearly ten times heavier than water, and is so brittle as readily to break under the hammer. None of the semi-metals are so easy to be fused as this; it melts even in the flame of a wax candle, and long before it becomes red hot, and has the singular property of expanding as it cools.
The ores of bismuth chiefly occur in Sweden, Norway, Germany, France, and England. This metal appears to have been known to the ancients. It was confounded by them with tin; and, even in our own manufactories, it is known to the workmen by the name of tin-glass.
It is not of much use in the arts; but its fusibility renders the working of it very simple and easy. It is employed in the composition of some of the soft kinds of solder; and is also used for giving hardness to tin and other metals. Amalgamated with mercury it renders that metal less fluid; and the addition of it to mercury and tin is found useful in the foliating or silvering of looking-glasses. Some manufacturers use it in the composition of pewter; but it is said that this ought not to be done, particularly for the formation of vessels intended to contain food, as bismuth partakes of the noxious properties of lead, and sometimes contains even arsenic. It is also occasionally employed in the fabrication of printers’ types.
A very singular metal is formed by melting together eight parts of bismuth, five of lead, and three of tin. Tea-spoons formed of this metal surprise all who are unacquainted with their nature: they have somewhat the appearance of common spoons, but they melt as soon as they are put into boiling water.
Bismuth reduced to powder, mixed with the white of eggs and applied to wood, gives it, when gradually dried and rubbed with a polisher, the appearance of being silvered. If this metal be dissolved in aquafortis ([30]), and water be poured into the solution, a white powder precipitates, which is an oxide of bismuth, and which, after being well washed, is used as a pigment, under the name of pearl-white. From its beautiful appearance, this powder is sometimes employed by ladies for painting their skin; a practice which cannot be too much condemned, both on account of the danger with which it is attended, and from its soon injuring both the texture and natural colour of the skin. It has the further disadvantage of turning black when touched by the fumes of fetid and other substances; and ladies, who have used this cosmetic, and have afterwards bathed in the Harrowgate waters, have come from the bath a perfectly tawny colour. It was probably the oxide of bismuth which the Roman ladies used for whitening their skin; for Martial, in speaking of a lady, who made too free an use of cosmetics, describes her as afraid even of the sun. The oxide of bismuth is used in the composition of most of the pomades employed in France for painting the face.
A preparation of bismuth has lately been employed in medicine, as a remedy against spasmodic affections of the stomach.
The following is a pleasing experiment, illustrative of metallic crystallization. Melt a ladleful of bismuth, and allow it to cool slowly and quietly till a thin crust is formed on the surface: then, with a pointed iron, make two small opposite apertures through the crust: and, through one of these, quickly pour out the fluid portion, as carefully and with as little motion of the mass as possible. The air having entered by the other aperture, there will appear, on removing the upper crust by means of a chisel, when the vessel has become cold, a cup-shaped concavity, studded with very brilliant crystals, and more or less regular according to the quantity of metal employed, the tranquillity and slowness with which it has cooled, and the dexterity with which the fluid portion of the mass was poured off before it became solid. The same effect may be produced by melting bismuth in a crucible which has a hole in the bottom, lightly closed by an iron rod or stopper; this is to be drawn out when the mass begins to congeal. By so doing, the upper portion, which is fluid, is made to run off, and a cake studded with crystals will be left.
247. COBALT is a semi-metal of grey colour with a shade of red, brittle, somewhat harder than silver, nearly eight times as heavy as water, is attracted by the magnet, and is itself capable of being rendered permanently magnetical.
The ores of cobalt are not numerous, and are, for the most part, combinations of this substance with other metals, or of its oxides ([24]) with arsenic, or with sulphuric acid ([21]).
The name of this metal implies an evil being, (Kobold, German, goblin) and is said to have been given on account of the vapour of arsenic, which issues from it, tormenting the miners, and making them believe that they are afflicted by wicked spirits. Hence it was once customary in Germany to introduce into the church service a prayer that God would preserve miners and their works from cobalts and spirits.
Cobalt is found in several parts of Europe, but most plentifully in the southern borders of France, and in Saxony; and the cobalt ores of Hesse, although they were formerly used for no other purpose than the mending of roads, are said now to yield a clear profit of nearly 15,000l. a year. Some parts of our own country yield this substance in considerable abundance, particularly the Mendip Hills in Somersetshire, and a mine near Penzance in Cornwall.
After the ore is taken from the earth, it is broken into pieces about the size of a hen’s egg, and the stony parts are picked out. The sorted mineral is then pounded in mills, and sifted through brass-wire sieves. The lighter particles are next carried off by water. After undergoing some other preparations, to rid it of the impurities and foreign matters with which it is connected, it appears in the form of a dark grey oxide. The working of the cobalt ores in Germany is considered so injurious, on account of the arsenic with which they are combined, that much of the labour is performed by criminals who are condemned to it for the commission of crimes which, by the laws of the country, have deserved the punishment of death.
As a metal, cobalt was unknown till the year 1733, when it was discovered by a celebrated Swedish chemist whose name was Brant. In its metallic state it is not employed in the useful arts; but in a state of oxide it is found extremely valuable in the colouring of porcelain, in painting, enamelling, and for other purposes. Cobalt and ultramarine form the most permanent blue colours with which we are acquainted. The old painters generally used them for the representation of the sky and of blue drapery, and this is the reason why these parts in some old pictures have been found so much more durable than any others.
Zaffre is an oxide of cobalt mixed with about three times its own weight of calcined and pounded flint. It has been chiefly imported into this country from Saxony and Bohemia, but it is now also manufactured from cobalt dug from mines in the Mendip Hills and in Cornwall. In Staffordshire there are several persons who carry on a considerable trade in preparing this colour for the earthenware manufacturers of that county.
This substance is extremely valuable for the colouring of porcelain and glass; as it resists without change, the effects of the most intense heat. Hence also it is advantageously used for giving various shades of blue to enamels, and to glass manufactured in imitation of lapis lazuli, turquoise, sapphire, and various precious stones. So intense is the colour imparted by it that a single grain of zaffre will give a full blue tint to 240 grains of glass.
Smalt is a kind of glass, of dark blue colour, formed by melting zaffre with three parts of sand and one of potash; when this substance is ground to a coarse powder, it has the name of strewing-smalt, and is much used by sign painters, as an ornamental filling up of the vacant space betwixt the letters of signs. In Germany it is frequently employed instead of sand for the purpose of drying ink after writing. The same substance reduced to a perfectly fine or impalpable powder, is the article which is sold under the name of powder-blue, and which is not only used by laundresses and others in the getting up of linen, but also as the basis of several kinds of paint; and by the manufacturers of writing and printing papers, to give a blue tinge to those articles.
A solution of the oxide of cobalt in spirit of salt (muriatic acid, 29) and afterwards diluted till nearly the whole of its colour disappears, forms one of the most beautiful sympathetic inks with which we are acquainted. If a landscape be drawn with Indian ink, and, afterwards, the foliage be washed over with this solution, it will have no peculiar appearance; but, on holding the paper near the fire, the part representing the vegetation will gradually assume a green tint, which will subside on removing the paper into a cool situation.
248. MANGANESE, in the state that we usually see it, is a black oxide of a metal which is of a silvery grey colour, of leafy or foliated texture, and somewhat more than six times as heavy as water.
Mines of manganese have long been worked in several parts of Great Britain, but particularly in the counties of Devon and Somerset. Near Exeter and in the Mendip Hills this mineral is found in great abundance.
It is employed for various useful purposes. In the manufacture of the finer kinds of glass it is used in a double capacity, both as a colouring material and as a destroyer of colour. As a colouring ingredient, the imitators of several precious stones are indebted to it for the red and purple tints which they give to the oriental ruby, the balais ruby, and the amethyst.
The violet colour given to porcelain is obtained from manganese. This substance is also used for the glazing of black earthen ware, as a paint, and an ingredient in printers’ ink. As a discharger of colour it is applied in small quantities, and, by the oxygen which it gives out, it is said completely to destroy any tinge left in the glass, by the presence of iron, and some other colouring matters. This property has obtained for it the appellation of the soap of glass.
It is from manganese that all the oxygen gas ([21]) used by chemists is obtained. By the application of a red heat this is yielded in such abundance that an ounce of the oxide of this metal will yield about two quarts of gas. The consumption of manganese has, of late years, become very considerable by the discovery of the oxygenated muriatic acid, which is now extensively used in the bleaching of linen and cotton; that liquor being made by the distillation of the oxide of manganese with spirit of salt (muriatic acid, 29).