GOLD. 
same ivory fixed Sn the tubes ; through the 
centre of the plates is a small circular hole, 
about the size of the pupil of the eye, for 
the transmission of the rays of light. These 
goggles must be worn regularly and con- 
stantly, till the muscles of the eye are 
brought to act properly and uniformly, so 
as to direct the pupil straight forward. 
GOLD is a yellow metal, of much greater 
specific gravity than any other body in 
nature, except platina. It is soft, very 
tough, ductile, and malleable ; unalterable 
and fixed, whether exposed to the atmo- 
sphere, or to the strongest heat of furnaces. 
Tire most powerful burning mirrors are said 
to have volatilized it ; and it has been driven 
up in fumes, in the metallic state, by flame 
urged upon it by a stream of oxygen gas. 
The electric shock converts it into a purple 
oxide, as may be seen by transmitting that 
commotion through gold leaf between two 
plates of glass ; or by causing the explosive 
spark of three or more square feet of coated 
glass to fall upon a gilded surface. A strong 
heat is required to melt it, which does not 
happen till after ignition. Its colour, when 
melted, is of a blueish green; and the same 
colour is exhibited by light transmitted 
through gold-leaf. 
Ihe limits of the ductility and malleabi- 
lity of gold are npt known, and its tenacity 
exceeds that of any other metal. A gold wire 
of one tenth of an inch diameter, requires 
500 lb. weight to break it. 
The method of extending gold used by 
the gold-beaters, consists in hammering a 
number of thin-rolled plates between skins 
or animal membranes. By the weight and 
measure of the best wrought gold-leaf, it is 
found, that one grain is made to covet 56| 
square inches ; and from the specific gravity 
of the metal, together with this admeasure- 
ment, it follows, that the leaf itself is 
parts of an inch thick. This, however, is 
not the limit of the malleability of gold ; for 
the gold-beaters find it necessary to add 
three grains of copper in the ounce to 
harden the gold, which otherwise would 
pass round the irregularities of the newest 
skins, and not over them ; and in using the 
old skins, which are not so perfect and 
smooth, they proceed so far as to add twelve 
grains. The wire which is used by the 
lace-makers is drawn from an ingot of silver, 
previously gilded. In this way, from the 
known diameter of the wire, or breadth 
when flattened, and its length, together with 
the quantity of gold used, it is found, by 
computation, that the covering of gold is 
VOL. III. 
only one-twelfth part of the thickness of 
gold-leaf, though it still is so perfect as to 
exhibit no cracks when viewed by a mi- 
croscope. 
No acid acts readily upon gold but the 
nitro-muriatic acid, called aqua-regia, and 
the oxygenized- muriatic acid. The sulphu- 
ric acid, distilled from manganese, has some 
action upon it ; as have likewise the pale ni- 
tric acid, and the phosphoric acid when 
boiling. Chromic acid added to the muriatic 
enables it to dissolve gold. 
The small degree of concentration of 
whicii tire oxygenized-muriatic acid is sus- 
ceptible, and the imperfect action of the* 
latter acids, render aqua-regia the most con- 
venient solvent for this metal. 
When gold is immersed in aqua-regia, an 
effervescence takes place with the escape of 
gas ; the solution tinges animal matters of a 
deep purple, and corrodes them. By care- 
ful evaporation, fine crystals of a topaz co- 
lour are obtained. The gold is precipitated 
fr om its solvent by a great number of sub- 
stances. Lime and magnesia precipitate it 
in the form of a yellowish powder. Alkalies 
exhibit the same appearance; but an excess 
of alkali redissolves the precipitate. The 
precipitate of gold obtained from aqua-regia 
by the addition of a fixed alkali appears to 
be a true oxide, and is soluble in the sul- 
phuric, nitric, and muriatic acids; from 
which, liowever, it separates by standing, or 
by evaporation of the acids. Gallic "acid 
precipitates gold of a reddish colour, very 
soluble in the nitric acid, to which it com- 
municates a fine blue colour. 
Ammonia precipitates the solution of gold 
much'more readily than fixed alkalies. This, 
precipitate, which is of a brown, yellow, or 
orange colour, possesses the properly of de- 
tonating with a very considerable noise, 
when gently heated. It is known by the 
name of fulminating gold. The presenefe of 
ammonia is necessary to give the fulmina- 
ting property to the precipitate of gold ; and 
it will be produced by precipitating it with 
fixed alkali from an aqua-regia previously 
made by adding sal ammoniac to nitric 
acid ; or by precipitating the gold from 
pure aqua-regia, by means of sal ammonia, 
instead of the ammonia alone. The fulmi- 
nating gold weighs one-fourth more than 
the gold made use of. A considerable de- 
gree of precaution is necessary in preparing 
this substance. It ought not to be dried 
but in the open air, at a distance from a 
fire, because a very gentle heat may cause 
it to explode. Several fatal accidents have 
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