« AnteriorContinuar »
doubt that a complete examination of the process would indicate others worthy of notice. Ether, naphtha, and the essential oils, take gold from its solvent, and form liquors which have been called potable gold. The gold which is precipitated by evaporation of these fluids, or by the addition of sulphate of iron to the solution of gold, is of the utmost purity. In the dry way, gold resists the action of neutral salts, more especially nitre, which deflagrates with the imperfect metals. Nitre, however, does not afford an expeditious way of purifying gold, because this metal in some measure protects and covers the alloys from its action. It is remarked that borax, used as a flux with gold, renders it paler; and that this alteration of colour disappears by the addition of nitre or commou salt. As the acid of borax forms a compound with gold, which falls to the bottom when this acid is added to the metal in solution, it is probable that the paleness produced by borax may arise from the combination of a small portion of its acid with the gold, which might be driven off by a continuance of the heat, and united by stronger affinity with the alkali of the nitre, or of the common salt, in proportion as their acids are dissipated by heat. Earth and alkalies do not act on gold in the dry way. Sulphur, which combines with most metals, has no effect on this. A process, called dry-parting, is grounded on this property; and is more especially used in separating silver from gold, when the quantity of the latter metal is too small to answer the expense of dissolving the larger mass of silver in nitric acid. For this purpose the mixed metal is fused, and flowers of sulphur thrown on its surface. These combine with the silver in the form of a black scoria, while the gold remains at the bottom in its metallic state. The operation of dry-parting does not leave the gold in a state of purity; because the last portions of silver are defended from the action of the sulphur. But when the quantity of silver is thus diminished, the operation of parting with aqua-fortis, or nitric acid, may be advantageously used. Sulphuret of potash dissolves gold in the dry way. Equal parts of sulphur and potash are hastily fused with one-fourth of a part of gold leaf. This combination is soluble in water, with which it forms a yellowish green solution. By the addition of an acid, the gold is thrown down in
combination with the sulphur, of which it may be deprived by heat. Most metals unite with gold by fusion. With silver it forms a compound, which is paler, in proportion to the quantity of silver added. It is remarkable that a cer. tain proportion, for example, a fifth part, renders it greenish. From this circumstance, as well as from that of a considerable proportion of these metals separating from each other by fusion, in consequence
of their different specific gravities, when
their proportions do not greatly differ, it should seem that their union is little more than a mere mixture without combination; for, as gold-leaf transmits the green rays of light, it will easily follow that particles of silver, enveloped in particles of gold, will reflect a green instead of a white light. A strong heat is necessary to combine platina with gold : it greatly alters the colour of the gold if its weight exceed the forty-seventh part of the mass. Mr. Francillon, however, informs us, that six parts of gold and one of malleable platina produce a metal of a beautiful colour, great malleability, susceptible of a fine polish, and more unalterable than gold itself. It does not much affect the ductility. The Spanish ministry has prohibited the exportation of platina from America, lest it should be used in adulterating gold; but this does not appear to be a danger which need be feared, as chemistry has long been in possession of several simple and expeditious methods of detecting this fraud, which besides is evident to the sight when the quantity of debasement is considerable. It may be questioned, likewise, whether the value of platina would not soon equal that of gold, if its properties and uses were bet. ter known in society. Gold made standard by platina, and hammered, is tolerably elastic. Mercury is strongly disposed to unite with gold, in all proportions with which it forms an amalgam: this, like other amalgams, is softer, the larger the proportion of mercury. It softens and liquifies by heat, and crystallizes by cooling. Lead unites with gold, and considerably impairs its ductility, one-fourth of a grain to an ounce rendering it completeIy brittle. Copper renders gold less ductile, harder, more fusible, and of a deeper colour. This is the usual addition in coin, and other articles used in society.— Tin renders it brittle in proportion to its quantity; but it is a common error of chemical writers, to say that the slightest addition is sufficient for this purpose.— When alloyed with tin, however, it will not bear a red heat. With iron it forms a grey mixture, which obeys the magnet. This metal is very hard, and is said to be much superior to steel for the fabrication of cutting instruments. Bismuth renders gold white and brittle; as do likewise nickel, manganese, arsenic, and antimomy. Zinc produces the same effect; and, when equal in weight to the gold, a metal of a fine grain is produced, which is said to be ...i adapted to form the mirrors of reflecting telescopes, on account of the fine polish it is susceptible of, and its not o subject to tarnish. The alloys of gold with molybdena are not known. It could not be mixed with tungsten on account of the infusibility of this last substance. Mr. Hatchett gives the following order of different metals, arranged as they diminish the ductility of gold: bismuth, lead, antimony, arsenic, zinc, cobalt, manganese, nickel, tin, iron platina, copper, silver. The first three were nearly equal in effect; and the platina was not quite pure. For the purpose of coin, Mr. Hatchett considers an alloy of equal parts of silver and copper as to be preferred, and copper alone is preferable to silver alone. Gold is found mostly in the metallic state, Rhough generally alloyed with silver, copper, iron, or all three. It is found either in separate lumps, or visible grains, among the sands of rivers, in many parts of Europe and elsewhere. The quantity is, for the most part, insufficient to pay the cost of separating it; but it is thought to be more universally diffused in sands and earths than any other metal, except iron. The greatest quantity of gold is imported into Europe from South Ame. rica. Some is brought from the East Indian islands and China, and some from the coast of Africa. The principal gold mines in Europe are those of Hungary.— Some sands afford gold by simple washing; the heavy metallic particles subsiding soonest: but when it is bedded in earths, or stones, these substances are pounded, and boiled with one-tenth of their weight of mercury together with water. The mercury, after a certain time, absorbs the gold, and may be separated by pressure through leathern bags, and subsequent distillation. Or, other. wise, if the sand be heated red hot, and quenched in water several times, for the
purpose of cracking and dividing it, and the whole be then melted into glass, with twice its weight of the oxide of lead, call. ed litharge, and charcoal powder be then added, the lead will be revived in the me. tallic state, and will carry the gold along with it. By exposure to a proper degree of heat, with access of air, the lead may again be converted into litharge, and the gold will be left pure. . This last opera. tion is, in fact, a method of assaying sands which contain gold, rather than of obtaining it from them in the large way. Gold is also found in certain martial pyrites in Sweden and elsewhere; from which it may be extracted by torrefaction, or burning of the sulphur, and subsequent digestion in aqua-regia. To obtain gold in a state of purity, or to ascertain the quantity of alloy it may contain, it is exposed to a strong heat, together with lead, in a porous crucible. This operation is called cupellation. After gold has passed the cupel, it may still contain either of the other perfect metals, platina or silver. The former is seldom suspected; the latter is separated by the operations called quartation and parting. For all these operations, see AsSAYING. The quantity of alloy is never considered as part of the value of metals which contain either gold or silver. In estimating or expressing the fineness of gold, the whole mass spoken of is supposed to weigh 24 carats of 12 grains each, either real or merely proportional, like the assayer's weights; and the pure gold is called fine. Thus, if gold be said to be 23 carats fine, it is to be understood that, in a mass weighing 24 carats, the quantity of pure gold amounts to 23 Carats. In such small works as cannot be as-2 sayed by scraping off a part, and cupelling it, the assayers endeavour to ascertain its quality or fineness by the touch. This is a method of comparing the colour and other properties of a minute portion of the metal with those of certain small bars whose composition is known. These bars are called touch-needles; and they are rubbed upon the black basaltes, which, for that reason, is called the touch-stone. Black flint, or pottery, will serve the same purpose. Sets of golden needles may consist of pure gold; pure gold twenty-three and a half carats with half a carat silver; twenty-three carats gold with one carat silver; twenty-two and a half carats gold with one and a half carat silver, and so forth, till the silver amounts
to four carats, after which the additions may proceed by whole carats. Other needles may be made in the same manner, with copper instead of silver; and other sets may have the addition, consisting either of equal parts of silver and copper, or such proportions as the occasions of business require. In foreign countries, where trinkets and small works are required to be submitted to the assay of the touch, a variety of needles are necessary; but they are not much used in England. They afford, however, a degree of information, which is more considerable than might at first be expected. The attentive assayer not only compares the colour of the stroke made upon the touchstone by the metal under examination with that produced by his needle, but will likewise attend to the sensation of roughness, dryness, smoothness, or greasiness, which the texture of the rubbed metal excites when abraded by the stone. When two strokes, perfectly alike in colour, are made upon the stone, he may then wet them with aquafortis, which will affect them very differently if they be not similar compositions; or the stone itself may be made red hot by the fire, or by the blowpipe, if thin black pottery be used, in which case the phenomena of oxydation will differ according to the nature and quantity of the alloy. Gold ores may be assayed in the moist way by pounding them very fine, weighing a determinate portion, and attempting their solution in nitric acid, which will dis. solve the matrix if it consist of calcareous earth; or if it be sulphate of lime, the E. may be i. in aqua-regia as ong as any metallic substance is taken up ; after which the gold may be precipitated by an addition of sulphate of iron, which will cause it to fall down in the Inetallic state. The principal use of gold is as the medium *::::::: in coin, for which it has been chosen to occupy the first place, on account of its scarcity, its great weight, and its not being subject to tarnish. The gold coins of Great Britain contain eleven parts of gold and one of copper. See Corn. Gold is likewise used in gilding. See CoI LnINg. The other uses of gold, in laces, &c. are sufficiently known. Goln beating. See Gold. 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. It may be observed, that before the wire be reduced to this excessive fineness, it is drawn through above an hundred and forty 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 flatted, is the former wire flatted 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. Gold thread, or †. gold, is a flatted gold, wrapped or laid over a thread of silk, by twisting it with a wheel and iron bobbins. Manner of forming gold wire and gold thread, both round and flat. First, an ingot of silver, of 24 pounds, is forged into a cylinder of about an inch in diameter: then it is drawn through eight or ten holes, of a large, coarse, wire-drawing iron, both to finish the roundness, and to re. duce it to about three-fourths of its for. mer diameter. This done, they file it very carefully all over, to take off any filth remaining on the forge ; then they cut it in the middle ; and thus make two equal ingots thereof, each about 26 inches long, which they draw through several new holes, to take off any inequalities the file may have left, and to render it as smooth and equable as possible. The ingot thus far prepared, they heat it in a charcoal fire; then taking some gold leaves, each about four inches square, and weighing twelve grains, they join four, eight, twelve, or sixteen of these, as the wire is intended to be more or less gilt, and when they are so joined as only to form a single leaf, they rub the ingots reeking hot with a burnisher. These leaves, . thus prepared, they apply over the whole surface of the ingor, to the number of six, over each other, burnishing or rubbing them well down. When gilt, the ingots are laid anew in a coal fire; and when raised to a certain degree of heat, they go over them a second time, both to solder the gold more perfectly, and to finish the polishing. The gilding finished, it remains to draw the ingot into wire. in order to this, they pass it through 20 holes of a moderate drawing-iron, by which it is o to the thickness of the tag of a lace : from this time the ingot loses its name, and commences gold wire. Twenty holes more of a lesser iron leaves it small enough for the least iron; the finest holes of which last scarcely exceeding the hair of the head, finish the work. 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 bobin. GOLD FINCH. See FRING ILLA. Goln size. See S1ze. GOLDSMITH, or as some choose to express it, silver-smith, an artist who makes vessels, utensils, and ornaments in gold and silver. The goldsmith's work is either performed in the mould, or beat out with the hammer, or other engine. All works that have raised figures are cast in a mould, and afterwards polished and finished : plates, or dishes, of silver or gold are beat out from thin flat plates; and tankards, and other vessels of that kind, are formed of lates soldered together, and their mouldings are beat, not cast. The business of the goldsmiths formerly required much more labour than it does at present; for they were obliged to hammer the metal from the ingot to the thinness they wanted: but there are now invented flattingmills, which reduce metals to the thinness that is required, at a very small expence. The goldsmith is to make his own moulds, and for that reason ought to be a good designer, and have a taste in sculpture: he also ought to know enough of metallurgy, to be able to assay mixed metals, and to mix the alloy. The goldsmiths in London employ several hands under them, for the various articles of their trade: such are, the jeweller, the snuff-box and toy-maker, the silver turner, the gilder, the burnisher, the chaser, the refiner, and the gold-beater. Goln, mosaic, that applied in pannels, on properground, distributed into squares, lozenges, and other compartments, part whereof is shadowed, to heighten or raise the rest.
Gold, shell, that used by the illuminers to write gold letters. It is made with the parings of leaf-gold, and even of the ieaves themselves, reduced into an impalpable powder, by grinding on a marble
with honey. After leaving it to infuse some time in aqua-fortis, they put it in shells, where it sticks. To use it they dilute it with gum-water, or soap-water. ... Gold, pure, that purged by fire of all its impurities, and all alloy. The moderns frequently call it gold of 24 carats, but in reality there is no such thing as gold so very pure, and there is always wanting at least a quarter of a carat. Gold of 22 carats has one part of silver, and another of copper; that of 23 carats has haif a part, i.e. half a twenty-fourth of each. See CARAT. GOLDEN number, in ehronology, a number shewing what year of the moon’s cycle any given year is. See Chnoxology. The rule for finding the golden number is this; add one to the given year, and divide by 19, the quotient is the number of cycles which have revolved since the commencement of the Christian aera, and the remainder will be the golden number for the given year: the golden number
of cycles, and 5 the remainder will be the golden number: when there is no remainder the golden number is 19. Gold EN rod. See Solin Ago. Gold EN rule, in arithmetic, is also called the rule of three, and the rule of proportion. See Propontiox, and RULE or Th R.E.E. GOM.PHIA, in botany, a genus of the Decandria Monogynia class and order. Essential character: calyx five-leaved; corolla five petalled; berries two, on a large receptacle ; seed solitary. There are three species. GOMPHRENA, in botany, globe amaranth, a genus of the Pentandria Digynia class and order. Natural order of Amaranthi, Jussieu. Essential character: calyx coloured, outer three-leaved; leaflets two, converging, keeled ; petals rude, villose; nectary cylindric, five-toothed; style cloven half way; capsule one-seeded. There are nine species. GONATOCARPUS, in botany, a genus of the Tetrandria Monogynia class and otder. Essential character; corolla fourcleft ; drupe eight cornered, one-seeded. There is only one species; viz. G. micranthus. GONDOLA, in naval architecture, a flat kind of boat, very long and narrow, chiefly used on the canals at Venice. GONG, in music, an instrument used in China, is made of a metal composed of silver, lead, and copper, and its shape is a sort of circular concave. The tone is
= 95 for the number
loud, harsh, and clanging. It is never introduced, except on occasion of giving a national cast to the music in which it is employed, or to awaken surprise, and rouse the attention of the company.
GENIOMETRY, a method of measuring angles with a pair of compasses, and that without any scale whatever, except an undivided semicircle. Thus, having any angle drawn upon paper to be measured, produce one of the sides of the angle backwards behind the angular point; then with a pair of fine compasses describe a pretty large semicircle from the angular point as a centre, cutting the sides of the proposed angle, which will intercept a part of the semicircle. Take then this intercepted part very exactly between the points of the compasses, and turn them successively over upon the arc of the semicircle, to find how of. ten it is contained in it, after which there is commonly some remainder: then take this remainder in the compasses, and in like manner find how often it is contained in the last of the integral parts of the first arc, with again some remainder : find in like manner how often this last remainder is contained in the former; and so on continually, till the remainder become too small to be taken and applied as a measure. By this means is obtained a series of quotients, or fractional parts, one of another, which, being properly reduced into one fraction, give the ratio of the first arc to the semicircle, or of the proposed angle to two right angles, or 180 degrees, and consequently that angle itself in degrees and minutes. Thus, suppose the angle B A C (plate VI. Miscellany, fig. 4.) be proposed to be measured. Produce BA out towards f, and from the centre, A, describe the semicircle a bef, in which a b is the measure of the proposed angle. Take a b in the compasses, and apply it four times on the semicircle, as at b, c, d, and e, then take the remainder fe, and apply it back upon e d, which is but once, viz. at g : again, take the remainder g d. and apply it five times on ge, as at h, i, k, l, and in lastly, take the remainder me, and it is contained just two times in m /. Hence the series of quotients is 4, 1, 5, 2; consequently, the fourth, or last arc, em, is , the third, m l of g d, and therefore
GOOD behaviour, in law. Surety for good behaviour, is the bail for any person's good conduct for a certain time; as surety for the peace is a recognizance taken by a competent judge of record for keeping the King's peace.
Justices of the peace may also bind persons of evil fame to their good behaviour, &c. 34 Edward III. c. 1. This statute being penned in such general words, seems to empower justices, not only to bind over those who seem to be notoriously troublesome, and likely to break the peace, as eves-droppers, &c. but also those who are publicly scandalous, or contumers of justice, &c. as haunters of bawdy houses, or keepers of lewd women in their own houses, common drunkards, or those who sleep in the day, and go abroad in the night, or such aw keep suspicious company, or such are generally suspected as robbers, such as speak contemptuous words of inferior magistrates, as justices of the pos. mayors, &c. not being in the ac