GOLD. 
Nitre, however, docs not afford an ex- 
peditious way of purifying gold, because 
this metal in some measure protects and 
covers the alloys from its action. It is 
remarked that borax, used a? a flux with 
gold, renders it paler ; and that this altera- 
tion of colour disappears by the addition of 
nitre or common salt. As the acid of bo- 
rax 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 
beat. 
Earths 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 pur- 
pose 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 ad- 
vantageously used. 
Sulphuret of potash dissolves gold in the 
dry way. Equal parts of sulphur and pot- 
ash are hastily fused with one-fourth of a 
part of gold leaf. This combination is solu- 
ble 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 de- 
prived 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 certain 
proportion, for example, a fifth part ren- 
ders it greenish. From this circumstance, 
as well as from that of a considerable pro- 
portion 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. Fran- 
cillon, however, informs us, that six parts of 
gold and one of malleable platina produce 
a metal of a beautiful colour, great mal- 
leability, 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 ap- 
pear 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 debase- 
ment is considerable. It may be questioned 
likewise whether the value of platina would 
not soon equal that of gold, if its proper- 
ties and uses were batter known in society. 
Gold made standard by platina, and ham- 
mered, is tolerably elastic. 
Mercury is strongly disposed to unite 
with gold, in all proportions with which it 
forms an amalgam: this, like other amal- 
gams, is softer, the larger the proportion of 
mercury. It softens and liquefies by heat, 
and crystallizes by cooling. 
Lead unites with gold, and considerably 
impairs its ductility, one-fourth of a gram 
to an ounce rendering it completely 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. Bis- 
muth renders gold white and brittle ; as do 
likewise nickel, manganese, arsenic, and 
antimony. 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 well adapted to form the mirrors 
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