the most valuable of all the metals, is of a bright yellow colour when pure, but becomes more or less white in proportion as it is alloyed with other metals. It is the heaviest of all known bodies, platinum only excepted, its specific gravity being to that of distilled water as 19,640 to 1000. It melts, in a low white heat; requiring, according to Mr Wedgwood's calculation, 5237 degrees of Fahrenheit's, or 32 of his own, thermometer for its fusion; a heat greatly superior to that which melts silver or copper; the former requiring only 4717, and the latter 4587 of Fahrenheit. Other metallurgists, however, have differed, and assert that copper requires for its fusion a greater degree of heat than either gold or silver.
Gold is by far the most tough and ductile, as well as the most malleable, of all metals. According to Cronstedt, one grain of it may be stretched out so as to cover 98 Swedish ells, equal to 63.66 English yards of silver wire; but Wallerius affirms, that a grain of gold may be stretched in such a manner as to cover 500 ells of wire. At any rate, the extension is prodigious; for, according to the least of these calculations, the millionth part of a grain of gold may be made visible to the naked eye. Nor is its malleability inferior to its ductility. Boyle, quoted by Apligny in his Treatise of Colours, says, that one grain and an half of gold may be beaten into 50 leaves of one inch square, which, if interlaced by parallel lines drawn at right angles to each other, and distant only the 1000th part of an inch from each other, will produce 25 millions of little squares, each very easily discernible by the naked eye.
Mr Magellan tells us, that its surface may be extended by the hammer 15992 times. "I am informed (says he) by an intelligent gold-beater in England, that the finest gold leaf is that made in new skins, and must have an alloy of three grains of copper to the ounce troy of pure gold, or else it would be too soft to pass over the irregularities of the skins. He affirms, that 80 books, or 2000 leaves of gold, each measuring 3.3 square inches, viz. each leaf containing 12.89 square inches, weigh less than 384 grains. Each book, therefore, or 25 leaves = 272.23 inches, weighs less than 4.8 grains; so that each grain of the metal will produce 56.718 square inches." From further calculations it may be made to appear, that the thickness of these leaves is less than 1/1000000th of an inch; and that 16 ounces of gold would be sufficient to gild a silver wire equal in length to the whole circumference of the globe.
Gold is more elastic than lead or tin, but less so than iron, or even copper. It grows hard and brittle by hammering, but resumes its ductility on being slowly heated. Gold leaf exhibits a fine green colour on being interposed between the eye and the beams of the sun or any other luminous body. When exposed for some time to a strong heat, it becomes ignited, and at last melts, assuming at the same time a fine bluish-green colour; and, when cold, crystallizes into quadrilateral pyramids. This bluish-green colour, according to Mr Magellan, as well as the former, when a thin film of the metal is interposed betwixt the eye and the luminous body, is owing to transmitted light. "The green light (says he) is transmitted in both cases, since all reflected colours are produced by the transmission of light, as the ingenious philosopher Mr Delaval has lately discovered and demonstrated in his very elaborate treatise on this subject, inserted in the second volume of the memoirs published in 1785 by the Philosophical Society of Manchester." Sir Isaac Newton, in his Optics (page 162, edition of 1730), accounts for that phenomenon, saying, that "gold foliated, and held between the eyes and the light, looks of a greenish blue; and therefore (says he) mussy gold lets into its body the blue rays to be reflected to and fro within it, till they be stopped and stifled; while it reflects the yellow outwards, and therefore looks yellow." It is therefore, in the two above cases, that some of the blue rays are transmitted along with the yellow ones; and both together appear of a bluish-green. If gold be exposed to the joined rays of light, excepting only the yellow ones, which we suppose stopped after they were separated by a prism, it only looks white like silver; "which shows (says Sir Isaac Newton) that its yellowness arises from the excess of intercepted rays tingling that whitens them with their colour when they are let to pass. It is a pleasing observation to look with a deep magnifier on various pieces of gold, silver, and Dutch (copper) leaves between the eye and the sunshine. The particles of silver are seen in the form of oblong dark lumps, with some interfaces, like net-work, between them: those of the copper-leaf are more numerous and more regularly distributed; but the particles of the gold-leaf appear like little green semitransparent and similar particles, uniting themselves by nearly diaphanous joints, as if they were forced to flatten in their edges, rather than they would break their mutual cohesion with one another."
Gold is more generally found native than any other metal; though Bergman informs us, that he does not know an instance of its ever being found perfectly free of alloy. Kirwan says it is seldom found so; being generally alloyed with silver, copper, or iron, and sometimes with all the three. According to Wallerius, native gold is found, 1. In solid masses, in Hungary, Transylvania, and Peru. 2. In grains in the Spanish West Indies. 3. In a vegetable form, like the branches or twigs of plants. 4. In a drusy figure, as if composed of groups or clutters of small particles united together, found in Hungary. 5. Composed of thin plates, or thin pellicles, covering other bodies, found in Siberia. 6. In a crystalline form in Hungary.
The same author informs us, that gold, in its regular state, is formed either into angular crystals composed of yellow octahedrons, or into yellow irregular masses, which show a grain-like texture. Brunnich says, that the native gold found in leaves is always crystallized on the surface; and with a magnifier they may be seen of a triangular pyramidal form. He informs us also, that in Transylvania he procured a specimen of cubic native gold, but never saw it anywhere else.
Gold is also found in the form of thick solid pieces; it is in general more frequently imbedded in quartz, and mixed with it, than with any other stone; and the quartz in which the gold is found in the Hungarian garian mines, Mr Magellan tells us, is of a peculiar mild appearance. Sometimes, however, it is found in limestone, or in hornblende, &c.
Europe is principally supplied with gold from Chili and Peru in South America. A small quantity is likewise imported from China and the coast of Africa. The principal gold mines of Europe are those of Hungary, and next to them the mines of Salzburg. The mines of Adelfors in Smoland are likewise worked to advantage; and the veins of metal appear to be diffused over a great tract of land. Some gold from four to seven grains in the mark is also said to be extracted from the silver of the mines of Osterfjordberg in the province of Dalarne. Native gold has also been found in Lapland above Torne, and in Westmanland. In Peru it is found mixed with a stony matter not well known, from which it is extracted by amalgamation. Mr Pallas mentions three gold mines that are worked there, near the river Pychma, in which 500 men are employed. The metal is found in a powdery form, and also in thin plates or leaves. Sometimes kernels or lumps of a spongy texture, and very light, are met with which contain a good quantity of gold-dust. This gold-dust or wash-gold is usually washed out of sands wherein it lies in the form of loose grains or lumps. It is distinguished by the variously coloured substances wherewith it is mixed. The metal is also found separate from any matrix in lumps or visible grains mixed with sands. Thus it is met with in many rivers of Europe as well as the other quarters of the world. It is also visibly dispersed through masses of sand, particularly such as is of a yellowish-red or violet colour; and in this state it is so universally diffused through every kind of earth, that Mr Bergman thinks it the most common of all the metals, iron alone excepted. If 100 pounds of sand contain 24 grains of gold, the separation is said to be worth attending to. In Africa 5 pounds of sand often yield 63 grains of gold, or even more; and the heaviest sand, which is often black or red, contains the most. In Hungary, however, only 10 or 12 grains of gold are contained in 10,000 pounds of sand; and even this trifling quantity has been extracted, though with loss.
Gold is brought down with most of the large rivers; even those which do not take their rise in mountains where gold is found. In Transylvania the river of Avanos affords subsistence to upwards of 700 Cipley families, who collect the gold from it. In Brazil it is found in such abundance, that their torrents are often turned with great labour and expense into new beds, in order to gather the gold there deposited by the running waters.—It is also found there mingled with the earth in various shapes and forms.—It is likewise said to be sometimes found in veins running through beds of coals.
Gold is said to be mineralized, when it is mixed with some other substance in such a manner as not to be acted upon by aqua regia. In this manner gold is mineralized.
1. By Sulphur. Many have insisted, that as gold and sulphur are not found to have any chemical attraction for one another, it is impossible that marcasite can contain any of the metal, or indeed that it can be found in any ore containing sulphur; but since we know by experience, that gold can be melted out of these ores, even after they have been digested in aqua regia, and that gold likewise enters into their sulphurated regulus, there is the greatest reason to believe, that some third substance, probably a metal, has by its admixture enabled the sulphur to unite with a certain quantity of gold. Marcasites, however, contain, at any rate, only a small quantity of the precious metal; and none is to be expected from them in places where no gold is in the neighbourhood. “I am not perfectly clear (says Cronstedt) whether the gold is really dissolved and indurated, or, if I may so express myself, vitrified in the schists; provided, by this mineral body, we mean a garnet substance. But I have seen a piece of what is called flint, whose texture was exactly like the Schemnitz blend; and in this case it might perhaps hold the same contents.”
2. With Sulphur by means of Iron: Golden pyrites, or marcasitical gold-ore. This is a close and compact substance of a bright yellow colour. Here the gold is said to be mineralized by sulphur by means of iron, because it cannot be extracted by aqua regia or by amalgamation. A kind of gold pyrites is found at Adelfors in the province of Smoland, which contains an ounce or less of gold in an hundred weight of the ore. The Transylvania gold pyrites, according to Brunnich, in which no gold can be perceived by the naked eye, contain from 50 to 100 and 110 ounces and upwards in an hundred weight. Those where the gold appears in the pyrites like strewed Spanish fruits, hold 250 ounces, but they are very scarce. The mountain of Facezbaya, near Zalatina, is remarkable for its gold pyrites; and here they seem also to contain ferrimetallic parts.
The following is M. Magellan’s method of accounting for the union of gold with this kind of pyrites. “It is well known, that gold may be dissolved by liver of sulphur. The process given for this purpose by M. Apicius, p. 156 of his Treatise on Colours, is as follows. Reduce to powder four pounds of vegetable alkali (salt of tartar), and as many of sulphur, with one of leaves of gold. Melt the mixture in a crucible with its cover; pour the fused matter out on a marble stone; pound it again when cold, and put the whole in a matress with hot water; which being filtrated is of a greenish-yellow colour, containing the gold dissolved. Now, as we know that hepatic sulphur has been found in several pyrites, and Mattei says that he found it in those lagoons near Sienna in Italy; is it not very natural to conclude, that this noble metal may be really mineralized in the auriferous pyrites?”
3. Auriferous Cinnabar, in which the metal is mineralized by means of quicksilver, said to be found in Hungary. Mr Sage speaks of a specimen of gold from Hungary, now in the French king’s cabinet at Paris, which is crystallized into quadrangular prisms of a grey-yellowish colour and a brittle consistency, which he supposes to be the result of a mercurial amalgam of native gold.
4. The Schemnitz Blend, in which the gold is mineralized by means of zinc and iron. Cronstedt informs us, that the ores of zinc at Schemnitz in Hungary contain a great deal of silver, and that this silver is very rich in gold. Professor Brunnich enumerates the following varieties of this ore. Gold is mineralized by means of a cubic lead-ore, containing silver found in the mines of Michaeli and some places in Transylvania. 2. By a copper pyrites with silver. This kind of ore is called gilly in Hungary; it has a compact surface of a pale yellow colour; but must not for that reason be confused with the auriferous pyrites. 3. The Creminitz-ores in which the metal is mineralized by means of red gilder ore. 4. By means of antimony, in which it sometimes appears. This kind is found at the foot of the Carpathian mountains. 5. By cubic lead-ore, iron, and some unknown volatile parts. This ore, as described by Scopoli, is of a black colour; the richest pieces are lamellated almost like an iron-glimmer, with a degree of flexibility. The vein is quartz, which is sometimes loose, and the metal scattered very minutely in it. It is found in Transylvania. 6. Native gold, with black-lead (or molybdena), has been found near Rimezembat in Upper Hungary; but our author (Professor Brunnic) has not had any opportunity of examining whether it is mineralized by it or not. In all the above species, the gold is either entirely native, but so minutely divided, and so loosely scattered, that it can only be seen through microscopes, and often cannot be seen at all before it is separated by various processes; or it may not be in the form of native gold, but the metal as it were in embryo; in which case fire is necessary to bring the constituent parts together, and to add those that are wanting; in that case likewise it is never without silver.
"To these (says Mr Magellan) may be added the following ores. 1. Gold, with arsenical pyrites, is found also at Saltzberg in Tyrol, in mountains of quartz and schistus. It contains only 25 grains in the quintal; nevertheless it affords a profit of £500 per annum. 2. With a white, red, or vitreous silver-ore, near Creminitz and Schemnitz in Hungary. 3. With a sulphurated ore of silver, iron, lead, and manganese, at Nagaya in Transylvania. Its specific gravity is 4.043, and it is said to afford 10 ounces per quintal. 4. With sulphurated iron, copper, and manganese, at Nagaya."
The strongest heat of any furnace does not change the metallic properties of gold. Kunckel and Boyle made the experiment by exposing gold for several months to the fire of a glass-house. It appears, however, that, by the violent heat of the sun-beams collected in the focus of a burning-glass, some alteration may be produced in it. Homberg observed that gold, when exposed to the lens of Tichirnhausen, formed, was volatilized, and even vitrified; and Macquer found, that the metal, when exposed to the lens of Mr Trudaine, exhaled a fume which gilded silver, and was therefore gold in a volatile state: the globule of melted gold was agitated with a rapid circular motion, and became covered with a dull and as it were calcareous pellicle; and lately, that a violet vitrification was formed on the middle of the globule. This vitrification gradually extended, and produced a kind of button, flatter, or of a larger curvature, than that of the globule, and which stuck upon it as the transparent cornea appears on the sclerotic of the eye. This glass increased in size, while the gold itself continually diminished: the support always appeared tinged with a purple colour, seemingly produced by the absorption of part of the glass. Time did not permit him to vitrify a quantity of gold entirely. He observes, that it is a necessary condition that the violet glass should be reduced with combustible matters, in order to justify the assertion that it is the calx of that perfect metal, which would evidently appear to be the case if it became revived into gold. But however this may be, Mr Fourcroy is of opinion that this ought to be considered as a true vitrified calx of gold; and this with the greater probability, as in many operations with this metal the purple colour is constantly produced, and many preparations of gold are employed to give that colour to enamel and porcelain. "Gold (says he) is therefore calcinable like the other metals; and only requires, as likewise does silver, a stronger heat, and a longer time to unite with the base of air than other metallic substances." Mr Kirwan, on the other hand, tells us, that "gold exposed to the utmost heat of Mr Parker's lens for some hours, lost no sensible part of its weight; yet, when in contact with earthy matters, it communicated a blue or purplish tinge to them; so that he believes an exceeding small portion of it might be deplogiticated."
This experiment with the lens of Mr Parker does not invalidate that of Macquer: for either Trudaine's lens may be more powerful than Mr Parker's; or the air in France being more clear than in England, the action of the sun must be stronger. We are assured, however, that by means of the electric fire gold may be instantaneously calcined and even vitrified: whence we must conclude, not only that gold is really calcinable, but that the electric fire is almost infinitely more powerful than any other; as by its means we may in a moment accomplish what either cannot be done otherwise at all, or very imperfectly, even by the fiercest fire we can raise. The flame of a lamp blown by deplogiticated air is also found sufficient to volatilize gold.
Gold being thus indestructible by the common operations of fire, equally resists its slow action in the atmosphere. It is altogether exempted from rusting; and though its surface becomes tarnished by exposure to the air, it is merely in consequence of the deposition of foreign bodies upon it. Water produces no change, says Mr Fourcroy; though, according to the experiments of Lagaraye, it seems capable of dividing it nearly in the same manner as it does iron.
Gold combines with various metals; and is commonly alloyed in a certain proportion with copper, which gives it a red colour and greater firmness than it possesses when very pure, at the same time that it is thus rendered more fusible. In this state it is used for money, plate, and toys of different kinds. It is sometimes also alloyed with silver, which deprives it of its colour, and renders it very pale: this alloy, however, is not made without some difficulty, on account of the very different specific gravities of the two metals, as Homberg observed, who saw them separate during their fusion. The alloy of gold with silver forms the green gold of the jewellers and gold-beaters.
As gold has been rendered, by the universal consent of mankind, the most valuable substance in the world, it is of great consequence to be able to discover its degree of purity, in order to prevent the adulterations which would naturally be practised, and to produce an equality of value in the different pieces divided in commerce. The chemical methods by which this is accomplished, are related under the ar- ticles Chemistry, and Essaying of Metals. To ascertain with precision the quantity of imperfect me- tal it may contain, a given mass of gold is supposed to contain 24 parts called carats; each carat being sup- posed divided into 32 parts called thirty-seconds of a carat. If the gold after the operation has lost one grain in 24, it is gold of 23 carats; if it has lost a grain and a half, it is gold of 22 carats 16 thirty-se- conds, and so on. The weight used in the assay of gold is called the assay weight, and usually consists of 24 grains; it is divided into 24 carats, which are likewise subdivided into 32 parts. An assay weight is likewise used which weighs 12 grains; and is likewise divided in- to 24 carats, subdivided again into thirty-seconds.
The scarcity and great price of gold prevent its be- ing made into vessels or utensils; but as its brilliancy and colour are agreeable, methods have been found of applying it to the surface of a great number of bodies, which it thus not only beautifies, but by its indestruc- tibility preserves from the injuries of the atmosphere. The art of applying it in this manner is called gilding; and the immense ductility of gold already mentioned, renders it capable of being applied in this manner at much less expense than could be imagined. It is used besides in gilding, either in a state of solution by acids, or amalgamated with mercury, which are called water- gilding. It was formerly used in medicine, and great virtues were ascribed to it; whence the great number of golden tinctures, elixirs, &c. of quacks; but all these are now deservedly exploded, and the best practi- tioners allow that gold, in whatsoever manner it be prepared, is either inactive or dangerous.
Gold in its metallic state cannot be combined with the vitrifiable earths, but its calces may; for which reason they are often used in enamel-painting and in porcelain, where they produce a beautiful violet-colour. Glass is tinged by them of a beautiful red; of which we have an account in Neri's art of glass-making; though Dr Lewis says he never could succeed in ma- king the colour diffuse itself equally throughout the substance of the glass. See Colouring of Glass.
The preparation of gold called aurum fulminans is taken notice of under the article Chemistry, p. 1103. M. Magellan takes notice of its extraordinary fulminating property, and says that its fragor is 64 times greater than that of an equal quantity of gun-powder. Ac- cording to Bergman, the strength of the explosion is 176 times greater than that of gun-powder (20 grains of aurum fulminans being equivalent to half a pound of gun-powder). Bergman accounts for the amazing strength of this explosion, by supposing it owing to the quantity of air extricated at the time; but this, ac- cording to his own account, cannot be at all sufficient for such a purpose; and Magellan is of opinion that "this wonderful phenomenon seems not yet comple- tely accounted for by any hypothesis yet known." See the articles Chemistry, and Explosion.
"It is on account of the singular and excellent na- tural qualities of this metal (says our author), which are considerably heightened by its scarcity, that gold is so much valued among all the civilized nations of the world." Mr Pauclon, in his Metrologie, p. 94, says,
that one cubic foot (French measure) of gold is worth 2,153,000 livres tournois, or 89,708 guineas and seven shillings, supposing the Louis d'Or to be equal to the guinea; and that the respective value of the same cu- bic foot of gold is equal to 25.6 cubic feet of silver; each of this last metal being reckoned worth about 84,000 French livres, or 3503 guineas and eight shil- lings: so that if we suppose the monied specie in France to be but two milliards of French livres, ac- cording to the estimation of Mr Neckar in his Treat- ise upon the Commerce of Corn, the whole amount should make but a solid cube of gold less than 10 feet on each side. So trifling is the physical object that excites the activity of 22 millions of the human spe- cies, the number that is said to be that of the inhabi- tants of France.
We shall close this article with some observations by M. Magellan on the state in which gold is found in the bowels of the earth, and consequently of the origin of gold ores. "As to the natural existence of gold in the bowels of the earth (says he), there have been two opinions among mineralogists; some pretending that it is only found in its metallic or native form; and others, that it is sometimes found mineralized in an intimate union with other substances. Mr Kirwan holds the former; and the celebrated Bergman the latter. But, says Mr Kirwan, 'though Mr Bergman inclines to the opinion of the mineralization, yet he is candid enough to own, that the gold, when extracted from this ore, is of a granular or angular form. It is there- fore very doubtful, whether it was not rather mixed, than truly combined with the sulphur and iron: and its proportion being exceedingly small, so that 100 pounds of the pyrites scarcely contain an ounce of gold, it is not a wonder that it should escape the action of aqua regia; more especially as the nitrous acid becomes so phlogisticated by acting on the pyrites, as not to be able to dephtlogiticate the marine. Likewise mercury, by reason of the gold particles being enveloped in the sulphureous iron, can have no access to it.'"
"These arguments (says M. Magellan) against the true mineralization of gold, are fully answered by the facts already mentioned. Besides, it is well known, that gold can be combined and calcined, via fissa, by the liver of sulphur and semimetals. This being acknowledged on both sides of the question, why should we insist on denying this mineralization, when it is out of doubt, among mineralogists of rank, that vol- canic fires have had a great share in the convulsions and revolutions of this globe, of which every one has the most convincing proofs almost everywhere. The ac- count given by Mr Hacquet of the gold mines at Nagy ag in Transylvania, the ancient Dacia, which lies about 45° latitude, offers the most convincing proofs of this assertion. The country all round these mines bears an incontestable appearance of being a vol- canic one; and among various other metals, there are at least 13 kinds of gold ores, most of them mineralized. These are, 1. Gold mineralized by sulphur, zinc, and arsenic, in a grey-yellowish volcanic ore, which is called cottoners, or cotton-ore, on account of its lightness and texture. 2. By iron and arsenic, formed by tra- cia; one containing black silver ore, then spatium, gal- ena, quartz, and grey gold ore: it yields about half an ounce in the 100 pounds. 3. By sulphur, antimo- ny, ny, zinc, some arsenic, and sometimes iron: this is a grey gold ore mixed with some quartz. 4. In the form of crooked threads mixed with quartz and gypseous spath; a poor mine. 5. Dendritiform, like the mocho stone, or the agate from Aberstein in the Palatinate; but these black dendrites are in a reddish stone. 6. Amorphous, very compact, in small grains, with spath and quartz. A quintal of it yields two ounces of gold, and more of silver. 7. By sulphur, great part of zinc, and a little antimony and arsenic; not rich. 8. Of a black or dark-reddish colour, containing an auriferous pyrites; not rich. 9. Of a bluish colour, mineralized by sulphur, antimony, iron, and a little arsenic mixed with silver; very rich in gold. 10. Partly laminated with needles of a blackish yellow colour: this gives 66 ounces of gold per 25 of gold, according to Scopoli. 11. Foliated with gypseous spath and yellow pyrites. 12. In irregular laminae, on a greyish argillie. The gold looks like silver, and is surrounded by spars of a pale rosy colour. 13. In crystallized laminae from two to four lines diameter, of an hexangular form, and very much resembling molybdena. The vein was lost for some time, but lately found again on mining for letting out water from the main. This ore is very rare, and has given 372 ounces per 25 of a mixed metal; five of which were gold, and one silver.
Method of Recovering Gold from Gilt Works. The solubility of gold, and the indissolubility of silver, in aqua regia, affords a principle on which gold may be separated from the surface of silver; and, on this foundation, different processes have been contrived, of which the two following appear to be the best.—Some powdered sal ammoniac, moistened with aquafortis into the consistence of a paste, is spread upon the gilt silver, and the piece heated till the matter smokes and becomes nearly dry: being then thrown into water, it is rubbed with a scratch brush composed of fine brass-wire bound together, by which the gold easily comes off. The other way is, by putting the gilt silver into common aqua regia, kept so hot as nearly to boil, and turning the metal frequently till it becomes all over black: it is then to be washed with a little water, and rubbed with the scratch brush, to get off what gold the aqua regia may have left. This last method appears preferable to the other; as the same aqua regia may be made to serve repeatedly till it becomes saturated with the gold, after which the gold may be recovered pure by precipitation with solution of vitriol, as directed under the article Metallurgy.
For separating gold from gilt copper, some direct a solution of borax to be applied on the gilt parts, but nowhere else, with a pencil, and a little powdered sulphur to be sprinkled on the places thus moistened; the principal use of the solution of borax seems to be to make the sulphur adhere; the piece being then made red hot, and quenched in water, the gold is said to be so far loosened, as to be wiped off with a brush. Others mix the sulphur with nitre and tartar, and form the mixture with vinegar into a paste, which is spread upon the gilt parts.
Schluter recommends mechanical means, as being generally the least expensive, for separating gold from the surface both of silver and copper. If the gilt vessel is round, the gold is conveniently got off by turning it in a lathe, and applying a proper tool, a skin being placed underneath for receiving the shavings: he says it is easy to collect into two ounces of shavings all the gold of a gilt vessel weighing three as many pounds. Where the figure of the piece does not admit of this method, it is to be properly fixed, and scrapers applied of different kinds according to its size, and figure; some large, and furnished with two handles, one at each end; others small and narrow, for penetrating into depressed parts. If the gold cannot be got off by either of these ways, the file must be had recourse to, which takes off more of the metal underneath than the turning tool or the scraper, particularly than the former. The gold scrapings or filings may be purified from the silver or copper they contain, by the methods described under the article Metallurgy.
The editors of the Encyclopédie give a method of recovering the gold from wood that has been gilt on a water-size: this account is extracted from a memoir on the same subject, presented to the Academy of Sciences by M. de Montamy. The gilt wood is steeped for a quarter of an hour in a quantity of water sufficient to cover it, made very hot: the size being thus softened, the wood is taken out, and scrubbed, piece by piece, in a little warm water, with short stiff bristle brushes of different sizes, some small for penetrating into the carvings, and others large for the greater dispatch in flat pieces. The whole mixture of water, size, gold, &c., is to be boiled to dryness, the dry matter made red hot in a crucible to burn off the size, and the remainder ground with mercury, either in a mortar, or, where the quantity is large, in a mill.
Gold-Coast. See Guinea.
Gold-Wire, a cylindrical ingot of silver, superficially gilt or covered with gold at the fire, and afterwards drawn successively through a great number of little round holes, of a wire-drawing iron, each less than the other, till it be sometimes no bigger than a hair of the head. See Wire-Drawing.
It may be observed that, before the wire be reduced to this excessive fineness, it is drawn through above 140 different holes; and that each time they draw it, it is rubbed afresh over with new wax, both to facilitate its passage, and to prevent the silver's appearing through it.
Gold-Wire flattened, is the former wire flattened between two rollers of polished steel, to fit it to be spun on a stick, or to be used flat, as it is, without spinning, in certain stuffs, laces, embroideries, &c. See Stuff, &c.
Gold-Thread, or Spun-gold, is flattened gold, wrapped or laid over a thread of silk, by twisting it with wheel and iron-bobbins.
To dispose the wire to be spun on silk, they pass it between two rollers of a little mill: these rollers are of nicely polished steel, and about three inches in diameter. They are set very close to each other, and turned by means of a handle fastened to one of them, which gives motion to the other. The gold wire in passing between the two is rendered quite flat, but without losing any thing of its gilding; and is rendered so exceedingly thin and flexible, that it is easily spun on silk-thread, by means of a hand-wheel, and so wound on a spool or bobbin. See Wire-Drawing. Gold-Leaf, or Beaten Gold, is gold beaten with a hammer into exceeding thin leaves, so that it is computed, that an ounce may be beaten into 1600 leaves, each three inches square, in which state it takes up more than 159,052 times its former surface. See Gold-Leaf.
It must be observed, however, that gold is beaten more or less, according to the kind or quality of the work it is intended for; that for the gold-wire drawers to gild their ingots within, is left much thicker than that for gilding the frames of pictures, &c. See Gilding.
Gold-Brocade. See Brocade.
Fulminating Gold. See Chemistry, no 1103.
Mosaic Gold, is gold applied in panels on a proper ground, distributed into squares, lozenges, and other compartments; part of which is shadowed to raise or heighten the rest. See Mosaic.
Gold Plates for Enamelling are generally made of ducat gold, whose fineness is from $2\frac{3}{4}$ to $3\frac{3}{4}$ carats; and the finest gold is the best for this purpose, unless where some parts of the gold are left bare and unpollished, as in watch-cases, snuff-boxes, &c., for which purpose a mixture of alloy is necessary, and silver is preferred to copper, because the latter disposes the plates to tarnish and turn green. See Enamelling.
Shell-Gold, is used by the gilders and illuminers, and with which gold letters are written. It is made by grinding gold leaves, or gold-beaters fragments, with a little honey, and afterwards separating the honey from the powdered gold by means of water. When the honey is washed away, the gold may be put on paper or kept in shells; whence its name. When it is used, it is diluted with gum-water or soap-suds. The German gold-powder, prepared from the Dutch gold-leaf in the same manner, is generally used; and when it is well scoured with varnish, answers the end in japanners gilding as well as the genuine.
Gold-Size for burnished gilding is prepared of one pound and an half of tobacco-pipe clay, half an ounce of red chalk, a quarter of an ounce of black lead, forty drops of sweet oil, and three drams of pure tallow: grind the clay, chalk, and black lead, separately, very fine in water; then mix them together, add the oil and tallow, and grind the mixture to a due consistence.
Gold-size of japanners may be made by pulverizing gum animi and asphaltum, of each one ounce; red-lead, litharge of gold, and umbre, of each one ounce and a half, mixing them with a pound of linseed-oil, and boiling them, observing to stir them till the whole be incorporated, and appears on growing cold of the consistence of tar: strain the mixture through a flannel, and keep it stopped up in a bottle for use. When it is used, it must be ground with as much vermilion as will give it an opake body, and diluted with oil of turpentine, so that it may be worked freely with the pencil. A simple preparation consists of one pound of linseed oil and four ounces of gum animi; powder the gum, and mix it gradually with the boiling oil; let it continue to boil till it becomes of the consistence of tar; strain it through a coarse cloth; keep and use it as the other.
Gold-Finches, in ornithology. See Fringilla.
There are feed-birds of very curious colours, and which, were they not so common in this country, would probably be very much esteemed.
They are usually taken about Michaelmas, and soon become tame; but they differ very much in their song.—They frequently breed in the upper part of plum-trees, making their nests of the moss that grows upon apple-trees, and of wool; quitting the inside with all sorts of hairs they find upon the ground. They breed three times a-year; and the young are to be taken with the nest at about ten days old, and fed as follows:—Pound some hemp-feed very fine in a mortar; then sift it through a sieve, and add to it as much wheat-bread as hemp-feed; and likewise a little flour of canary-seeds: then with a small stick or quill take up as much as the bigness of a white-pea, and give them several times a-day. This ought to be made fresh every day: for if it is suffered to sour, it will spoil their stomachs, causing them to cast up their meat; which if they do, it is very probable that they will die.—These young birds must be carefully kept warm till they can feed themselves, for they are very tender. In feeding, be sure to make your bird clean his bill and mouth. If any of the meat falls upon his feathers, take it off, or else he will not thrive. Such as eat hemp-feed, to purge them, should have the seeds of melons, succory, and mercury; or else let them have lettuce and plantane for that purpose. When there is no need of purging, give them two or three times a-week a little sugar or loam in their meat, or at the bottom of the cage; for all seeds have an oiliness, so that if they have not something to absorb it, in length of time it fouls their stomachs, and brings on them a flux, which is very dangerous.