COPPER

COPPER, the finest of the imperfect metals, called by the alchemists Venus, on account of its facility of uniting with a great number of different metallic substances. Its colour, when pure, is pale red, and its specific gravity from 8.7 to 9.3, which depends not only on its degree of purity, but also on its condensation by hammering. The specific gravity of Japan copper is to water as 9000 to 1000; but that of the Swedish kinds only as 8784 or 8843. — The colour, when

Copper. when clean, is very brilliant, but it is extremely liable to tarnish. It has a disagreeable smell, very perceptible on friction or on being heated: its taste is typtic and nauseous, but less perceptible than that of iron. Its tenacity, ductility, and hardness, are very considerable, and its elasticity superior to that of any other metal except steel. From this last quality masses of the metal emit a loud and lasting sound when struck; and this more especially when cast into a proper form, viz. such an one as may make the metal vibrate in the most simple manner possible. Thus, if cast into the hollow form of a bell, without any cracks or imperfections, an uniform tone will be produced by it; or at least the tones produced by the stroke will consist of a single predominant one, and of others that have an agreement with it. When broken by often bending backward and forward, it appears internally of a dull red colour, without any brightness, and of a fine granulated texture; not ill resembling, as Cramer observes, some kinds of earthen ware. It continues malleable in a red heat, and in this state extends much more easily than when cold; but has not that valuable quality of iron, by which two pieces cohere together when heated to a great degree. In a heat far below ignition, the surface of a piece of polished copper becomes covered with various ranges of prismatic colours; the red of each order being nearest to the end which has been most heated. Reduced to a fine powder, or even to filings, and thrown across a flame, it produces blue or green colours, whence its use in fireworks. It requires a fierce heat to melt it; less, according to Mr Wedgwood, than gold or silver*, but more according to some other metallurgists.—It is remarkably impatient of moisture when in a state of fusion; and the contact even of a very small quantity of water will cause a vast mass of melted metal to be thrown about with incredible violence, to the imminent danger not only of the bystanders but even of the strongest furnaces and buildings. Effects of this kind are said to have been produced by so slight a cause as the workmen spitting in a furnace full of melted copper.

Copper is found in the bowels of the earth in the following states.

I. Native copper, having the red colour, the malleability, and all the other properties of the metal. It is distinguished, says Mr Fourcroy, into two kinds: copper of the first formation and copper of the second formation or cementation. The copper of the first formation is dispersed in laminae or fibres, in gangue almost always quartzose; some of its crystals resemble a kind of vegetation, but other specimens are in masses or grains. Copper of cementation is commonly in grains or superficial laminae, on stones or on iron: this last appears to have been deposited in waters containing vitriol of copper which has been precipitated by iron. Native copper is found in many places of Europe; particularly in various parts of Scotland, England, and Wales; at St Bell in Lyons; at Norberg in Sweden, and Newfol in Hungary. It is also to be met with in several parts of America.—Mr Kirwan says, it is met with either of its own peculiar colour or blackish or grey; and that either in grains or in large shapeless solid lumps; in a foliated, capillary, or arborecent form, or crystallized in quadrangular pyramids, in or on clay, chissus, quartz, fluors,

zeolites, &c. He accounts for its origin by supposing it to have been originally precipitated by iron from waters which held it in solution, which is the purest sort; but in many cases it could not have been produced in that manner; and then this sort is never very pure, but mixed with gold, silver, or iron, or with sulphur; which last combination is called black copper.

Native copper is found in very considerable quantities at Cape Lizard in Cornwall: it is formed into threads or branches, and lies in veins of some thickness, contained in blackish serpentine mixed with brownish red, and covered externally with a greenish nephrite, partly adherent to it and partly loose. Native copper, in large lumps, has also been found in the same rocks: but a more considerable quantity is found at Huel Virgin in the same county. Here it shoots into various branches and in various directions: the pieces seem to be formed of small rhomboidal crystals interspersed with quartz, the impressions of which are to be seen in the copper itself; from whence we might conclude that the quartz existed before the metal. Some of these lumps of native copper have been found in this spot that weighed from 20 to 30 pounds; and in the month of March 1785 there were no less than 28 millions of pounds of rich copper ore extracted from this mine. At a place called Caturash, contiguous to Huel Virgin, some crystallized native copper has been found, with the transparent vitreous copper ore, to be afterwards mentioned, crystallized in octahedrons of a ruby colour; though the latter now begins to be very scarce. Near this place also a compact native copper is found in lumps of a spherical form; the copper either still in its metallic form, or beginning to be transformed into red copper-glass, imbedded in decayed granite. Native copper of a tender and moss-like form, united to vitreous ruby copper-ore, crystallized in rhombs, is found in the cliffs of the mountains composed of killas, near Poldry.—An indurated iron-clay has lately been found under the surface of the sea in the Faro isles, in which there is scattered a zeolite with native copper.

II. Mineralized by fixed air; of which there are several varieties. 1. Red copper, or hepatic ore of copper. This is known by its red dusky colour, similar to that of the scales beat off from copper by hammering. It is seldom met with, and then is generally mixed with native copper and mountain green. Sometimes it is crystallized in octahedrons or silky fibres, and is called flowers of copper. Mr Kirwan says, that it is sometimes met with in a loose form, and generally called copper ochre; but is usually of a moderate hardness, though brittle; sometimes crystallized and transparent, either in a capillary form, or in cubes, prisms, or pyramids: it effervesces with acids, and is found in Scotland, England, and Germany. According to Mr Fontana, 100 parts of it contain 73 of copper, 26 of fixed air, and one of water. Mr Kirwan distinguishes the hepatic ore as being of a brown colour. It contains a variable proportion of iron or pyrites, and sometimes sulphurated copper; and hence affords from 20 to 50 per cent. of copper. It is often iridescent (we suppose showing the colours of the rainbow). 2. Earthy copper, mountain-green, green chrysocolla or malachite. The last, according to Mr Kirwan, looks like green

green jasper, but less hard, and does not strike fire with steel, is of a radiated or equable texture, generally of an oval form, and the size of an egg, but sometimes forming capillary filaments. Mûschenbrook fixes its specific gravity from 3.5 to 3.994. It is sometimes mixed with calcareous earth and gypsum. According to Mr Fontana, 100 parts of the purest sort contain 75 of copper and 25 of aerial acid and water. Mountain green is generally found in a loose and friable state, rarely crystallized and indurated, often mixed with calcareous earth, iron, and some arsenic. An hundred parts of the purest kind contain 72 of copper, 22 of aerial acid, and 6 of water.

A compact green copper ore, like malachite, mixed with grey copper ore, and likewise green velvet-like copper in the form of bunches, are found at Huell Virgin in Cornwall. At Carrarach, in the same county, is found also an amorphous green copper ore, on a decayed granite; and at St Menan, the same is found stratified betwixt quartz, and covered with a brownish iron. Cronstedt informs us, that both the green and blue colours of copper ores depend on a menstruum, and therefore may be often edulcorated or washed away. In Saalfeld they find also a sort of green, somewhat indurated, calcareous substance, containing copper: this, when broken, looks fat, and somewhat shining; but, upon the whole, it resembles a jasper. It is there very improperly called a green copper glis-ore. Good copper is made of it; and, with a phlogistic substance, without being ultulated, it forms a kind of bell-metal fit for being employed for that purpose.

The malachite, according to Mr Fourcroy, is frequently found in Siberia, composing beds, some of which represent nipples of various magnitudes. Some specimens are composed of needles, converging towards a common centre. The grain of malachite is sufficiently hard to take a fine polish, and is therefore formed into toys of different kinds; but as it is frequently porous and full of unequal cavities, the solid pieces of a certain size are reckoned valuable. The strata in which it is found are often of different shades of green. The mountain green is a true ochre of copper, of a more or less deep green, not heavy, and unequally distributed on its gangue: it appears to be combined with the cretaceous acid. There are two varieties besides the malachite, viz. the simple mountain green, and that which is crystallized, or the silky copper ore of China. It is common in the Hartz, and likewise in China. It is very pure, and crystallized in long silky bundles of considerable solidity. To these three states, says Mr Fourcroy, we may add a beautiful green sand, brought by M. Dombey from Peru, which appears to be a calx of this metal mixed with sand, and containing a small quantity of muriatic acid.

3. The third variety of this species is the mountain blue, or blue chrysocolla. This, according to M. Fourcroy, is a calx of copper of a deep blue colour, sometimes regularly formed in rhomboidal prismatic crystals of a fine blue, in which case it is called azure of copper. "All these calces of copper (says he) appear to have been precipitated from vitriolic solutions of copper, by the intermedium of calcareous earths through which the waters have transfused. M. Sage considers these blue copper ores as combinations

of copper with the volatile alkali; from which he affirms that they differ only in their degree of solubility; he likewise thinks that the malachites is produced from this blue, which he calls transparent azure copper ore; but most mineralogists are of a different opinion." Mr Kirwan tells us, that 100 parts of this ore contain about 69 of copper, 29 of aerial acid, and 2 of water. Mr Morveau, in the Memoirs of the Academy of Dijon for 1782, has shown, that the calces of copper ore determined to a blue rather than a green colour, by a greater proportion of phlogiston.

III. Cupreous stones. These are the turquoise and lapis armenus. The former of these is improperly called a stone, being the tooth of an animal penetrated by the blue calx of copper. It loses its colour when heated; is opaque, of a lamellar texture, and susceptible of a fine polish; its specific gravity from 2.5 to 2.908; some are of a deep blue, some more white, and become deeper when heated. They are found in Persia and in Languedoc in France; the copper may be extracted from them by distilled vinegar. Reaumur informs us, Mem. Par. 1715, that nitrous acid will not dissolve the Persian turquoise, though it will that of France. The lapis armenus has calcareous earth or gypsum for its base; whence it sometimes effervesces with acids and sometimes not. It is used in painting, when ground to a fine powder, under the name of Bice. To these Mr Fourcroy adds "copper mineralized by the muriatic acid and united to clay." This ore has been confounded with tale; and it was exposed to sale at Paris, in the year 1784, under the name of green mica. It consists of small beautifully green crystals, or small brilliant scales. It was discovered by Mr Forster in the mines of John Georgenstadt; the green cupreous sand of Peru already mentioned, perhaps belongs to the same class.

IV. Copper mineralized by sulphur, with scarce any iron, improperly called vitreous copper ore. This is of a deep violet grey, greenish brown, or liver colour; melting with a very gentle heat, ponderous, sometimes flexible, and always yielding to the knife. When broken it appears of a bright golden colour. It is sometimes found in shapeless masses, sometimes regularly crystallized; is much more fusible than pure copper, and has a specific gravity from 4.81 to 5.338. It is found in mines of other copper ores, in limestone, spar, quartz, mica, and clay: it is the richest of all the copper ores; affording from 80 to 90 per cent. of copper, 10 or 12 of sulphur, and a small proportion of iron.

V. Copper mineralized by sulphur with a large proportion of iron, azure copper ore; does not differ from the preceding but in the quantity of iron it contains, which sometimes amounts to 50 per cent. It yields 50 or 60 pounds of copper per hundred, the rest being sulphur. The less iron this ore contains, the richer it is in copper; and it has by many been confounded with indurated mountain blue.

VI. Copper mineralized by sulphur, with much iron, the yellow copper ore, or yellow pyrites. The colour of this is yellow, or yellow mixed with red or green, or variegated like a pigeon's neck; it is inferior in hardness to the other pyrites, not readily giving fire with steel as they do. It is sometimes found crystallized, and sometimes in shapeless masses; its specific gravity

Copper. gravity is about 4.16. It occurs both in separate masses and embodied in stones, being the most common of all the copper ores. The crystallized kind affords least metal, containing only from 4 to 8 per cent. the remainder being chiefly iron. It is generally reddish, and is in fact only a martial pyrites with a small portion of copper; the greenish yellow contains most sulphur, and from 15 to 20 per cent. of copper; the pure yellow contains most copper, viz. from 20 to 30 per cent. The cupreous pyrites (says M. Fourcroy) often present very brilliant blue or violet colours at their surface, which are produced by the decomposition of their principles: they are then called chatoyant ores of copper, or ores resembling the peacock's tail: they commonly contain a large quantity of sulphur, a small quantity of iron, and are not rich in copper; such are the ores of Derbyshire in England, some of those of St Bell in Lyons, and many ores of Alsazia, such as those of Caulenbach and Feldens.¹¹

¹¹ Arsenical or grey copper ore. VII. Copper united to sulphur, arsenic, iron, and a small quantity of silver. This is called arsenical or grey copper ore, and is of a white, grey, or brown colour; of moderate hardness, very brittle, sometimes crystallized, and often of an indeterminate figure. It is very difficult of fusion, and more ponderous than the former. It contains from 35 to 60 per cent. of copper; the brown is the richest in copper; the white or grey contains most arsenic; and if the silver it contains exceed 1 or 2 per cent. it is called grey silver ore. It is found embodied in all sorts of stones, and mixed with other copper ores, as well as with the ores of other metals.

A great variety of sulphurated copper ores is to be met with in the mines of Cornwall, viz. a whitish-grey ore crystallized in small triangular and quadrangular pyramids, with truncated points, is found along with the solid copper ore at Poldice and Dolcoth: but the richest are the solid grey ones found in various places; some of which may be cut with a knife like the soft vitreous silver ore. The most remarkable of the yellow ores is the stalactitical ore, of an hemispherical form, called run-yellow-copper, often variegated with different colours. A compact red glassy copper ore, covered with mountain green, or green copper, and with calciferous copper of a vermilion red colour, is found in crystallized quartz, mixed with tender green mica. We also meet with an olive-green-coloured copper ore which is arsenical, and crystallized into tender spiculæ of about three lines long, standing up straight, either single or fasciculated, or radiated, found on the granitic mountain at Carrarach. These crystals melt before the blow-pipe with an arsenical smoke, and afterwards melt, forming a button of a grey colour, which, on being melted again with borax, soon produces a very pure copper. Another kind of arsenical cupreous crystals are likewise met with in the form of green cubes run together, with smooth and shining surfaces, upon grey copper-ore, in a mass of crystallized compact quartz, with various crystals in itself; and greatly resembling small cubes of fluor.

¹² Brown or blende copper ore. VIII. Copper mineralized by sulphur and arsenic with zinc and iron; brown or blende copper ore. Mr Monnet found this ore only at Catherineberg in Bohemia; it is brown, granulated, and very hard, and contains from 18 to 30 per cent. of copper.

This kind of ore may be analysed in the liquid way by solution in nitrous acid, and precipitation of the copper by iron. The iron and zinc are precipitated by the Prussian alkali; the precipitate is then calcined and redissolved in nitrous acid, and the solution evaporated to dryness. The iron being thus dephlogisticated, becomes insoluble in the nitrous acid, but the calx of zinc is redissolved, and again precipitated by the Prussian alkali. An hundred grains of this precipitate are equivalent to 20 of zinc in its metallic state; and 100 grains of dephlogisticated iron are equivalent to 73$\backslash frac\{1\}\{2\}$ of iron in its metallic state.

¹³ IX. Argillaceous schistose, or slaty copper ore, seems to consist of the vitreous copper ore intimately combined with schistus, and not barely dispersed through it in visible particles: it is of a brown or black colour, lamellar texture, and very heavy; affording from 6 to 10 per cent. of copper, and is of difficult fusion, unless limestone be added. It contains a little bitumen, calcareous earth, and iron.

¹⁴ X. Bituminous copper ore is a kind of pitecoal found in Sweden. It burns with little or no flame, but leaves ashes from which copper is extracted.

¹⁵ XI. Black copper ore, of the colour of pitch. Mr Black Gellert denominates it copper ore in scoriae: it is a residuum of the decomposition of the yellow and grey copper ores which contain neither sulphur nor arsenic, and approaches to the state of malachite; it has a black shining appearance like pitch.

¹⁶ XII. Copper united to sulphur and arsenic containing antimony, or antimonial copper ore, is mentioned by Mr Sage in his Elements of Mineralogy. It is grey, and bright in its fracture like antimony, and contains from 14 to 20 per cent. of metal.

XIII. Copper dissolved by the vitriolic acid. In the year 1673, our countryman Dr Brown visited a famous copper-mine at Hern-grundt, about seven English miles from Newfol in the Upper Hungary; and he informs us, that there he saw two springs, called the Old and New Ziment, which turned iron to copper, as it is vulgarly said. But the case is, that the iron is dissolved by the vitriolic acid of this spring-water, and the copper is precipitated in its metallic form in the place of the iron. It has been the custom in Germany for some centuries to collect the copper contained in these waters, by filling with them some pits made purposely for this operation. Old iron is thrown in, and being dissolved by the acid, is suspended in the water, whilst the copper is precipitated: the mud being raked out, is melted afterwards in a furnace, and a very fine copper is produced: from 100 tons of iron, 84 and sometimes 90 tons of fine copper is thus produced.

But although this method of obtaining copper has been long practised in Germany, yet it is but of late years, says Bishop Watson (p. 238. of the first volume of his Essays), that any successful attempts of this kind have been made either in England or Ireland. In this last, at least, it was quite owing to an accident. There are the very celebrated copper-mines at Arklow, in the county of Wicklow in Ireland; and from these mines issues a great quantity of water, strongly impregnated with vitriol of copper. One of the workmen having accidentally left an iron shovel in this water, he found it some weeks after so incrustated with a coat

Copper. of copper, that it was thought to be changed into copper.

The proprietors of the mines, in pursuance of this hint, made proper pits and receptacles for the water; and have obtained, by means of soft iron bars put into them, such quantities of copper, that these streams are now of as much consequence as the mines themselves. One ton of iron produces near two tons of copper mud; and each ton of mud produces, when melted, 16 hundred weight of copper, which sells for L. 10 Sterling a ton more than the copper which is fluxed from the ore.

There is in the isle of Anglesey, on the coast of North Wales, a mountain called Paris, which abounds in copper-ore, the bed of ore being above 40 feet in thickness. The lessees of this mine annually raise from six to seven thousand tons of merchantable ore, and daily employ above 40 furnaces in smelting it. This ore contains a great quantity of sulphur, which must be separated by roasting before it can be fluxed into copper. The phlogiston, with part of the vitriolic acid, is dispersed into the air by the force of the fire; another part of the acid attacks and dissolves such a quantity of the copper, that the water in which the roasted ore is washed (by means of old iron immersed in it according to the German method) produces great quantities of fine copper, so that the proprietors have there obtained in one year near 100 tons of the copper precipitated from this water.

If this water was afterwards evaporated, it would yield green vitriol or vitriolated iron, at nearly the rate of 200 tons of vitriol for each hundred ton of iron at least; which, at the rate of L. 3 Sterling per ton, might perhaps produce very good profit to the undertakers, if any should settle such a manufacture there.

Besides the celebrated copper-mines at Arklow in the county of Wicklow in Ireland, there are no less than seventeen different places in Britain in which copper-mines are found, as mentioned by Dr Campbell in the 2d vol. p. 44. of his Political Survey of Britain. These are Cardiganshire, Cheshire, Cornwall, Cumberland, Derbyshire, Devonshire, Lancashire, Isle of Man, Northumberland, Shropshire, Somersetshire, Staffordshire, Yorkshire, Wales, Warwickshire, Westmoreland, and North Britain: some that are worked at this time give such large products of this metal, that the opening more copper-mines in this island would probably affect the copper-trade of Europe in a very considerable manner. The Eton mine, in the estate of the Duke of Devonshire, on the frontiers of Derbyshire, but properly situated in the county of Staffordshire, produces at least 300 tons of copper per annum. That of the mountain called Paris, in the island of Anglesey, whose bed of ore is about 40 feet in thickness, produces about 1500 tons of copper in the year; and the copper-mines of Cornwall produce no less than 4000 tons in the same period. Mr Jars, who visited these mines in the year 1770, found, upon calculation, that the annual produce of these mines amounted to L. 140,000 Sterling; and M. H. Klaproth, in his Observations on the Fossils of Cornwall, just published (in 1787), asserts that this account is not an exaggerated one.

Copper is purified with less difficulty than iron; and

its goodness is judged of by the bright redness of its colour.

The impurity of copper proceeds from the mixture of heterogeneous substances that are alloyed with it, on account of being naturally contained in the copper when cool. Iron and arsenic are the chief of these natural mixtures. The copper-ores of variegated colours, the white copper-ores, and generally those mineralized by sulphur, contain a greater proportion of iron; whilst the blue and green copper-ores commonly produce a purer metal, being free, for the most part, of any considerable ferruginous mixture. The great aim, therefore, of the metallurgist must be directed to separate these mixtures from the copper, beginning by the proper examination of the ore, and by ascertaining the proportion of sulphur that may be required to scorify the quantity of iron there contained. The ore should always be roasted by a slow fire, in a close furnace, which contributes the best towards scorifying the ferruginous and heterogeneous mixtures; and the same operation must be repeated after the second and third fusion of the metal, till its grain becomes of an homogeneous fine texture. The mixture of sulphureous pyrites in the fusion of the metal contributes towards obtaining this object; if their quality be chosen according to the quantity of sulphur wanting. But in the second, third, and following operations, only pure sulphur should be added, to scorify the remainder of the iron that is still intermixed with the copper. This should be done when the metal is already well fused; covering it immediately with a proper quantity of charcoal, and separating the scoria or dross formed on the surface of the fused metal.

The copper extracted from those mines near Newfol, in Upper Hungary, is said to be usually melted 14 times before it is fit for use. These are the greatest copper-mines in all Hungary. There are, however, other mines, whose copper requires far less fusions to be well purified. The above was the process of Mr Delius, director of the mines of Bannat near Temesware in Hungary, proposed by him to the imperial board of the Austrian mines.

Pure copper allowed to cool slowly will form itself into regular crystallizations, which the Abbe Mongaz describes as quadrangular pyramids, sometimes solid, and sometimes composed of other similar small pyramids laterally adhering. When heated it becomes coloured on its surface, nearly in the same manner as steel; the colours are blue, yellow, and lastly violet; it does not melt but by a violent white heat, though much inferior to that which melts iron. When in a state of fusion it appears covered with a green flame, which the filings of the metal likewise produce when projected through flame; and hence are used in fireworks, as has been already remarked. The crystallization of the metal above mentioned is best perceived by suffering the metal to cool slowly; and after the surface is become congealed, the fluid portion being poured off, the remaining solid part is found to be crystallized in pyramids, which are more regular and large in proportion as the fusion has been more complete and cooling more gradual. The pyramids, according to Fourcroy, are quadrangular, and appear to be formed of a great number of octahedrons inserted into one another.

Copper. another. When heated with excess of air, this metal burns at its surface, and is converted into a calx of a dark red colour, in proportion as it absorbs the base of the dephlogisticated part of the atmosphere. The calx may be easily obtained by heating a ball of copper red-hot, the form of which causes the calx to scale off; and the same effect takes place when red-hot copper is quenched in cold water; the separation of the calx being promoted by the sudden contraction of the metal. This calx is called the scale of copper, and may be further calcined till it becomes of a deep brown; after which, by violent heat, it may be melted into a blackish or deep reddish brown mass. The scoria may partly be reduced without any additional phlogiston; for the founders, who buy them of the coppersmiths, take no other trouble with them than that of throwing them into large crucibles on the melted copper, with which they incorporate by fusion; and the same method is made use of to melt the filings. The calx of copper appears to possess some saline properties, but its nature has not yet been ascertained.

20 How the calx is obtained.

21 The scoria partly reduced without addition.

22 Copper rusts by exposure to the air, but without any corrosion of its internal parts.

23 Patina, a name for the rust of copper on medals.

24 Qualities of this metal when taken into the human body.

25 Of the tinning of copper.

Copper calcines when exposed to the air, and is converted into a green rust or calx, which is in some degree soluble in water, and communicates a taste as well as pernicious qualities to it. It is remarkable, however, that this rust does not corrode the internal parts like that of iron, but is confined to the surface; and thus, instead of destroying, contributes, for a long time at least, to the preservation of the metal. This is particularly observable in the antique medals and statues, which are very well preserved under a covering of rust. The antiquarians call this crust patina, and put a high value upon the pieces of antiquity covered with it; but the Italians and others have got a method of imitating this crust, and thus there is great danger of being deceived.

Copper, when taken into the human body, acts as a violent emetic, and has been generally accounted poisonous, though lately received with some applause into the materia medica as a tonic. The pernicious qualities, however, and very disagreeable taste which it certainly communicates on some occasions, render it highly necessary to observe some cautions in the use of this metal, of which so many kitchen utensils are made. Besides an exact attention to cleanliness, it is altogether improper to let any fluid remain in a copper vessel till it be cold; for copper is much more calcinable in the cold than when heated. Mr Fourcroy explains this by supposing the calcination to be produced by water in a state of extreme division: as long, therefore, as the fluid is boiling and the vessel hot, the aqueous vapour does not adhere to its surface; but when the vessel is cold, the drops of water which adhere to its sides calcine it, and reduce it to a green calx. The air and the eretaceous acid (fixed air), he says, also contribute greatly to this calcination; for by distilling the rust of copper fixed air has been obtained.

In order to prevent the pernicious effects of copper, the vessels made of it are usually covered with tin in the inside. To tin copper-vessels, they are first scraped clean and bright; after which they are rubbed with sal ammoniac to clean them more perfectly. They are then heated and sprinkled with powdered resin, which prevents the surface of the copper from being calcined; after which the melted tin is poured on and spread a-

bout. It is, however, justly complained, that the tinning of copper-vessels is not sufficient to defend them from the action of the air, moisture, and saline substances; because these vessels, even when well tinned, are observed to be subject to rust. This might possibly be remedied by a thicker covering of tin; and a manufacture of this kind was some time ago established at Edinburgh, though it does not appear to have much attracted the notice of the public; which, however, is no objection to the usefulness of the invention. The method employed was to make the surface of the copper very rough, with a machine contrived for that purpose, and the tin put upon it in this situation; after which the copper was hammered smooth as before. Mr Fourcroy objects to this thicker covering of tin, that there "is reason to fear that a degree of heat superior to that of boiling water, to which these vessels are often exposed, would melt the tin and leave the surface of the copper uncovered." This objection is surely void of foundation: for as long as there remains any liquid in the vessel, the tin will not melt though the heat were applied to it directly without any intervention of copper; and if a dry heat were applied, a thin covering of tin would be still less able to resist it than a thick one. Our author, however, observes, that to prevent this accident the tin may be alloyed with iron, silver, or platina, to diminish its fusibility, and render it capable of being applied in thicker strata on the copper. Alloys of this kind, he tells us, are already used in several manufactures.

The very small quantity of tin required to cover the surface of the copper is surprising; a vessel of 9 inches in diameter and 3$\backslash frac\{1\}\{4\}$ inches in depth, being found to gain no more than 21 grains by this operation. This small quantity is nevertheless sufficient to prevent the dangers which might arise from the use of copper-vessels, provided care be taken not to allow substances capable of dissolving the tin to remain too long in them; but more especially that the tin be frequently renewed, as the friction, heat, and action of spoons, with which the included substances are stirred, very soon destroy it. There is likewise another cause of apprehension, according to our author, viz. that the tin is often alloyed with lead, even to the quantity of one-fourth of its weight; in which case the latter may exert its mischievous influence, especially as it is known that lead is easily soluble in fatty substances. To prevent this sophillation, he is of opinion that government should take sufficient care that the braziers be not deceived in the tin they purchase, and that they may not employ any but the Malacca or Banca tin, in the state it is received from the East Indies, without having been alloyed or melted by the pewterers. A better method, however, seems to be that proposed by M. Folie of Rouen, to use vessels of forged iron covered over on the inside with zinc, which, he says, have already been used with advantage by certain persons; and it were to be wished that its use might become more general.

Copper is also used in mixture with other metals, particularly tin and zinc, in enamel-painting, dyeing, &c. Mixed with tin in considerable quantity, it produces BELL-METAL; with a smaller proportion BRONZE; with zinc it forms BRASS, PINCHBECK, or SIMILOR, MANHEIM GOLD, &c. according to the proportion; it being

being always observable, that the compounds most nearly resembling gold in colour have the least ductility and are most brittle. See these articles, and CHEMISTRY-Index.

With regard to the poisonous qualities of copper when taken into the body, much less danger seems to arise than from those of arsenic, on account of its easy solubility; nor indeed have we met with any well authenticated instance of a person who has died in consequence of swallowing even verdigrease itself. In one case, where an unlucky boy had swallowed some bits of this substance thrown out of a chemist's laboratory, the symptoms were only violent sickness and vomiting, from which he recovered by drinking warm water largely; and probably nothing else would be requisite in any case, though Mr Fourcroy advises emetics, abundance of water, liver of sulphur, alkalies, &c. The use of emetics in such a case, however, seems altogether superfluous; since verdigrease, in the quantity of a grain or a grain and a half, has been ordered by some medical writers in the case of poison swallowed otherwise, as the emetic most quick in its operation that could be thought of.