GOLD is of a deep and peculiar yellow colour. It melts at a bright red heat equivalent, according to Daniell, to 2016o of Fahrenheit's scale, and when in fusion appears of a brilliant greenish colour. Its specific gravity is 19.3. It is so malleable that it may be extended into leaves which do not exceed the one two-hundred and eighty-two thousandth of an inch in thickness, or a single grain may be extended over 56 square inches of surface. This extensibility of the metal is well illustrated by gilt buttons, 144 of which ore gilt by 5 grains of gold, and less than even half that quantity is adequate to give them a very thin coating. It is also so ductile that a grain may be drawn out into 500 feet of wire. The pure acids have no action upon gold. (Brande, 972.)

Gold in the pure or fine state is not employed in bulk for many purposes in the arts, as it is then too soft to be durable. The gold foil used by dentists for stopping decayed teeth is perhaps as nearly pure as the metal can be obtained: it contains about 6 grains of alloy in the pound troy, or the one-thousandth part. Every superficial inch of this gold foil or leaf weighs 3/4 of a grain, and is 42 times as thick as the leaf used for gilding.

The wire for gold lace prepared by the refiners for gold lace manufacturers, requires equally fine gold, as when alloyed it does not so well retain its brilliancy. The gold in the proportion of about 100 grains to the pound troy of silver, or of 140 grains for double-gilt wire, is beaten into sheets as thin as paper; it is then burnished upon a stout red-hot silver bar, the surface of which has been scraped perfectly clean. When extended by drawing, the gold still bearing the same relation as to quantity, namely, the 57th part of the weight, becomes of only one-third the thickness of ordinary gold-leaf used for gilding. In water-gilding, fine gold is amalgamated with mercury, and washed over the gilding metal, (copper and tin,) the mercury attaches itself to the metal, and when evaporated by heat, it leaves the gold behind in the dead or frosted state: it is brightened with the burnisher. (See Technological Repository, vol. ii., p. 361 - 1828.) By the electrotype process a still thinner covering of pure gold may be deposited on silver, steel, and other metals. Mr. Dent has introduced this method of protecting the steel pendulum springs of marine chronometers and other time-pieces from rust. - See Note, p. 252.

Fine gold is also used for soldering chemical vessels made of platinum.

Gold Alloys

Gold-leaf for gilding contains from 3 to 12 grains of alloy to the oz., but generally 6 grains. The gold used by respectable dentists, for plates, is nearly pure, but necessarily contains about 6 grains of copper in the oz. troy, or one 80th part; others use gold containing upwards of one-third of alloy, the copper is then very injurious.

With copper, gold forms a ductile alloy of a deeper colour, harder and more fusible than pure gold: this alloy, in the proportion of 11 of gold to 1 of copper, constitutes standard gold; its density is 17.157, being a little below the mean, so that the metals slightly expand on combining. One troy pound of this alloy is coined into 46 22/40 sovereigns, or 20 troy pounds into 934 sovereigns and a half. The pound was formerly coined into 44 guineas and a half. The standard gold of Franco consists of 9 parts of gold and 1 of copper. (Brand*., 979.)

For (hid Plate the French have three different standards: 92 parte gold 8 copper; also 84 gold, 16 copper; and 75 gold, 26 copper.

In England, the purity of gold is expressed by the terms 22, 18, 16, carats, etc. The pound troy is supposed to be divided into 24 parts, and the gold, if it could be obtained perfectly pure, might be called 24 carats fine.

The " Old Standard Gold." or that of our present currency, is called fine, there being 22 parte of pure gold to 2 of copper.

The " Now Standard," for watch-cases, etc. is 18 carats of fine gold, and 8 of alloy. No gold of inferior quality to 18 carats, or the " New Standard," can receive the Hall mark; and gold of lower quality is generally described by its commercial value, as 60 or 40 shilling gold, etc.

The alloy may be entirely silver, which will give a green colour, or entirely copper for a red colour, but the copper and silver are more usually mixed in the one alloy according to the taste and judgment of the jeweller

The following alloys of gold ore transcribed from the momoranda of the proportions employed by a practical jeweller of considerable experience.*

First Group. Different kinds of gold that are finished by polishing, burnishing, etc. without necessarily requiring to be coloured: - The gold of 22 carats fine, or the " Old Standard," is so little used on account of its expense and greater softness that it has been purposely omitted.

18 cants, or New Standard gold, of yellow tint: *

15

dwt.

0

grs.

gold.

2

dwt

18

grs.

silver.

2

dwt

6

grs.

copper.

20

dwt

0

grs.

18 carats, or New Standard gold, of red tint: •

15

dwt.

0

grs.

gold.

1

dwt.

18

grs.

silver.

3

dwt

6

grs.

copper.

20

dwt.

0

grs.

16 carats, or Spring gold: this, when drawn or rolled very hard, makes springs little inferior to those ofsteel.

1

oz.

16

dwt

gold.

or

112

6

dwt.

silver.

-

4

dwt.

copper.

-

.12

2

oz

14

dwt.

2.8

60s gold of yellow tint or the fine gold of the jewellers; 16 carats nearly.

1

oz..

0

dwt.

gold.

7

dwt.

silver.

5

dwt.

copper.

1

oz

12

dwt.

60s. gold of red tint, or 16 carats:

1

oz.

0

dwt.

gold.

2

dwt.

silver.

8

dwt.

copper.

1

oz.

10

dwt.

40s. gold, or the old-fashioned jewellers gold, about 11 carats fine: no longer used:

1

oz.

0

dwt.

gold.

12

dwt.

silver

12

dwt.

copper.

2

oz

4

dwt.

When it is not otherwise exprssed, it will be undsratood all these alloys are made with free gold,, fine silver,and fine copper, obtained direct from the refiners. And to ensure the standard gold passing the test of the Hall, three or four grains additional of gold are usually added to every ounce.

Second Group. Coloured golds; these all require to be submitted to the process of wet-colouring, which will be explained: they are used in much smaller quantities, and require to be very exactly proportioned.

Full red gold:

5

dwt.

gold.

5

dwt.

copper.

10

dwt.

Red gold:

10

dwt.

gold.

1

dwt.

silver.

4

dwt.

copper.

15

dwt.

Green gold:

5

dwt.

0

grs.

gold.

21

grs.

silver.

5

dwt.

21

grs.

Grey gold: (Platinum is also called grey gold by jewellers.)

3

dwt.

15

grs.

gold

1

dwt.

9

grs.

silver.

5

dwt.

0

grs.

Blue gold: scarcely used.

5

dwt.

gold.

5

dwt.

steel filings.

10

dwt.

Antique gold, of a fine greenish-yellow colour:

18

dwt.

9

grs.

gold,

or

18.9

21

grs.

silver,

-

1.3

18

grs.

copper,

-

.12

20

dwt.

0 grs.

200

Third Group. Gold solders; these are generally made from gold of the same quality and value as they are intended for, with a small addition of silver and copper, thus: -