GOLD.— Jewellers’ Gold. 103

legal weight are each sounded on an iron block, inorder to prevent such as are “ dumb ” or crackedfrom passing into circulation. Finally the finishedcoins are tied in bags, and, provided that suchsamples as are selected for assay are found to boof the legal composition, are issued to the public.

Jewellers’ Gold. —The jeweller receives his goldin the form of ingots, which approach absolutepurity, or 24 carats fine. lie begins his operationsby alloying it with copper or silver, or both, incertain calculated proportions, either to reduce it tothe legal standard or to give it the particular colourrequired. The following are the three standardsfixed by the statutes enacted in France on thesubject:—1. High standard gold , consisting of 920parts of pure gold in 1000 of alloy, which is equiva-lent to 22 cts. one-fourth ct. gr. and 4 ex. gr. Thisis the alloy usually employed by the French jewellers,and is nearly identical with the standard gold of theEnglish coinage. 2. French standard gold, consistingof 840 parts of gold in 1000 of alloy, or 20 cts. five-eighth ct. gr. Sometimes it is reduced to only 20carats. 3. Common gold is 750 parts in 1000, or 18carats. The licence or tolerance allowed is 3 parts in1000 .

In England a greater number of standards isemployed for jewellery, namely, 9, 12, 15, 18, and22 carats; but the amount made of the secondand fifth of these is extremely limited, and prac-tically only the remaining three are in use.

In order that the gold may be easily worked, thealloy must be perfectly homogeneous, and the jewel-ler accordingly brings it to this state by repeatedfusions. If the alloy has been badly made, and stillexhibits a grainy appearance, with a liability to crackunder the action of the hammer or between thelaminating rollers, it must be again introduced intothe crucible, and thoroughly fused with a mixtureof borax and saltpetre.

In the “ Dictionnaire des Arts et Manufactures,”the colours most commonly required in articles ofjewellery are stated to be composed as follows:—

Colours. Composition.

Yellow gold,. Pure or fine gold, 1000.

Red gold,. Fine gold, 750; rose copper, 250.

Green gold,. Fine gold, 750; silver, 250.

Dead-leaf gold,... Fine gold, 700; silver, 300.

Water-green gold, Fine gold, 600; silver, 400.

,, J An alloy of gold and silver in which

° ’ '.J the latter predominates.

Blue gold,. Fine gold, 750; iron, 250.

The last-mentioned alloy is somewhat difficult toprepare. It is obtained by introducing thick ironwire among the melted gold, and withdrawing thecrucible from the fire as soon as the alloy is formed.When poured out and cooled, it should have noappearance of porosity. It is then forged, andformed into sheets or wires of different thicknesses.

Various shades of colour are likewise given bythe jeweller to articles or ornaments of gold by thefinishing process, which consists in exposing themto certain chemical reagents, to dissolve out a portionof the copper or silver from the surface, withoutattacking the gold. By this means the surface of

the article is made to appear like pure gold, whichit really is, while below the surface the quantity ofcopper or silver may be considerable. The liquorusually employed by goldsmiths and jewellers forthis purpose is a mixture of 2 parts of nitrate ofsoda, 1 part of chloride of sodium, and 1 of Romanalum, in 3 or 4 parts of water. The trinkets orother articles are kept in this solution, at the boil-ing point, from fifteen to twenty-five minutes,according to the shade required. They are thentaken out, washed in water, and after burnishing withbloodstone, the operation is finished. The pickle, orsauce as the liquor is termed, dissolves not only thecopper or silver on the surface, but likewise a certainquantity of the gold itself. To recover the gold, theliquor is diluted with at least twice its bulk of boil-ing water, and a solution of very pure protosulphateof iron is poured into it. The precipitated gold iswashed upon a filter, dried, and purified by fusingin a crucible, along with a mixture of equal partsof nitrate and biborate of soda. The other metalscan likewise be recovered by very simple methods.

Gold-Beating. —The art of beating gold intothin leaves seems to have been known from a veryremote period. The fact that the Hebrews wereacquainted with it has been already stated; andfrom the circumstance that, on the coffins of theTheban mummies, specimens of leaf-gilding are metwith, in which the gold is so thin as to resemblemodern gilding, it may be inferred that the Egyptianshad carried the art to a high degree of perfection.This art is distinctly referred to by Homer, and waspractised extensively by the later Greeks, even todecorate the external sculpture of their temples andstatues. Pliny states that after the destruction ofCarthage the Romans began to gild the ceilingsof their temples and palaces, and that luxury ad-vanced on them so rapidly that in a little time evenprivate and comparatively poor persons gilded thewalls, vaults, and other parts of their dwellings.Horace’s remark, that neither ivory nor gilded archfigured in his house, is familiar to the classical stu-dent. Pliny further states, that 1 oz. of goldwas extended to 750 leaves, each 4 fingers square.Locretids compared the Roman gold-leaf to aspider’s web, and Martial described it as littleother than a vapour; yet, according to Pliny ’saccount, it must have been three times the thicknessof the ordinary leaf-gold of the present time.

Experiments have been made to ascertain towhat degree of thinness gold and silver could bereduced: it was found that 1 grain of gold wasspread to the extent of 75 square inches, and the sameweight of silver to the still more extraordinary dimen-sions of 98 square inches. Taking 1 cubic inch ofgold to weigh 4900 grains, it will be found .that thegold was the 367,500th part of an inch in thickness,or about 1200 times thinner than ordinary writingpaper. Thus, if 367,500 leaves of gold were placedon one another they would constitute a pile onlyan inch high, while the same number of leaves ofpaper would form a pile half the height of theMonument of London. The same weight of silver,