Part 16

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.