CHEMISTRY. 
343 
ties it is frequently met with ; and from this 
circumstance, and from its being found after 
chemical processes where none was ever ex*- 
pected, many of the supposed formations of 
gold by the alchymists have taken their ori- 
gin. It has been obtained from rotten ma- 
nure, garden-mould, uncultivated earth, and 
from vegetables. 
It is of a rich yellow colour; and is the 
heaviest ot the metals, except platinum. It is 
not very hard when pure. It is the most 
| ductile of all the metals. Gold-leaf transmits 
light of a lively green colour ; but silver, 
{copper, and all the rest of the metals which 
[can be formed into leaves, are perfectly 
; opaque, being much thicker. Gold melts at 
• 32 degrees of Wedgewood’s pyrometer, and 
is volatilized by an intense heat, such as that 
I of a mirror or 'lens. It cannot be oxy dated 
• by any heat of a furnace, but may by elec- 
I tricity and galvanism. 
| Gold is not acted upon by any acid, except 
j the oxygenated muriatic, or mtro-muriatic 
acids, which latter was called from this aqua 
| rcgia, because gold was named by the alehy- 
j mists the king ot the metals. This solution 
of gold, called nitro-muriate of gold, yields 
by evaporation crystals of a beautiful yellow 
; colour, which, when dissolved in water, tinge 
j the skin indelibly of a deep purple. When 
precipitated from this solution by tin, it forms 
\ the purple precipitate of Cassius, so much 
used in enamelling. This consisls of an oxyd 
j of gold, mixed with an oxyd of tin. if, into 
j a solution ot gold, a piece of charcoal is 
| put, and exposed to the sun’s rays, the gold 
I "dll be revived, and appear in" a metallic 
I state on the charcoal, forming a .kind of gild- 
ing. 
Gold maybe taken from its solution by 
i; aether, which then retains it in solution, form- 
j ing an tuthereal solution of gold. If any sub- 
stance is dipped in the nitro-muriate of gold, 
|;and then exposed to a stream of hydrogen 
l the gold will be reduced, and the snb- 
stance covered with it. When ammonia is 
J added to a solution of gold, a yellow precipi- 
tate is formed, called fulminating gold, be- 
! cause it has the property of exploding when 
j exposed to heat. 
Gold is precipitated from its solution in a 
metallic state by green sulphate of iron. Gold 
easily alloys with mercury, which is therefore 
: employed for the purpose of extracting it 
from the substances with which it is mixed. 
The mercury, being more volatile, is driven 
off by heat, and the gold remains free. With 
silver it forms an alloy' of considerable ducti- 
lity. Copper heightens its colour, and ren- 
ders it harder without much impairing its 
ductility. Tin and lead considerably impair 
its tenacity. With platinum it forms an alloy 
i which is vety ductile. With zinc it affords a 
brittle and hard mixture, susceptible of po- 
lish. It unites well with iron, and hardens it 
remarkably. 
On account of its peculiar property of not 
tarnishing in the air, it is much used for de- 
fending other metals ; and on account of its 
beautiful lustre, it is much employed in or- 
naments. See Gold. 
Of silver . — Silver is often found native, 
and also combined with lead, copper, mer- 
cury, cobalt, sulphur, arsenic, &c. When 
found in the metallic state, it appears in 
grains or leaves, adhering to various sub- 
stances. It is found in the greatest quantities 
in Peru and Mexico ; but there are silver- 
mines in many other countries. When pure 
it is of a very brilliant white. It is malle- 
able, ductile, and laminable, in a greatdegree, 
though inferior to gold in these qualities. It 
may be beaten out into leaves, which are 
only T ~f—~ part of an inch in thickness. 
It melts at 28 degrees of Wedgewood’s py- 
rometer, and is volatilized in very high tem- 
peratures. It does not tarnish in the air, ex- 
cept when sulphureous vapours are present. 
It forms alloys with most of the metals. With 
gold it forms a metal of a greenish colour, 
called green gold. Copper makes it much 
harder, without lessening its ductility. It 
to rips an amalgam with mercury. The alloy 
of British coinage is fifteen parts of fine sil- 
ver and one of copper. It unites to phos- 
phorus and sulphur, forming phosphuret and 
sulphuret of silver. 
Silver is acted upon by the sulphuric and 
nitric, but not by the muriatic acid. With 
the nitric acid it forms a colourless solution, 
which stains animal and vegetable sub- 
stances with an indelible black colour: hence 
it is used as a permanent ink, and is employed 
for dying human hair black; though, ’for 
this purpose, it should be used with great 
caution, and much diluted, as it is extremely 
caustic or corrosive. It is also employed for 
marking linen. Nitric acid dissolves more 
than half its weight of silver, the solution de- 
positing crystals. When these are fused by 
a gentle heat, they lose some of the acid, and 
being poured into moulds, form the substance 
called lunar caustic (nitrate of silver), used 
in surgery. 
Nitrate of silver, prepared with common 
silver, is greenish, butthis is on account of the 
copper usually mixed with the silver. Silver 
i-< precipitated from its solution. in nitric acid, 
by muriatic acid, in the form of a white curd ; 
which, when fused, forms a semi-transparent 
mass of the consistence of horn, called horn 
silver, but more properly muriate of silver. 
It soon blackens in the air, and is very little 
soluble in water. Since the muriatic acid 
has a strong affinity for the oxyd of silver, 
and since the muriate of silver is not very so- 
luble in water, the ni irate of silver is em- 
ployed as a re-agent, to discover the presence 
of muriatic acid in any liquid; for if it con- 
tains that acid, muriate of silver will fall down 
in a white cloud, on dropping nitrate of sil- 
ver into it. 
I he nitric acid sold in the shops is usually 
adulterated with muriatic or sulphuric acid, 
or with both : lienee the nitrate of silver is 
used to free the nitric from the two latter 
acids. For this purpose nitrate of silver is 
poured into it by degrees, until no more pre- 
cipitate is produced ; after which it is ren- 
dered clear by liltring. Nitric acid thus 
purified is called by artists precipitated aqua- 
fortis ; but it still contains some silver, from 
which it cannot be freed, except by distillation. 
When precipitated from nitrate of silver by 
ammonia, it forms fulminating silver ; a very 
dangerous preparation, for it explodes by the 
mere contact of any body. More than a 
grain cannot be exploded at a time with anv 
safety. When mercury is added to the ni- 
tric solution of silver, a precipitation of the 
silver is formed, resembling vegetation in ap- 
pearance, called arbor Diana?, or the tree of 
Diana. See Argentum Arborescen s. 
If a few drops of the nitrate of silver are p ut 
upon a piece of glass, and a copper wire 
placed in it, a beautiful precipitation of the 
silver will take place, in the form ofi a plant. 
The affinity of silver for other metals, and its 
solution in acids, are the properties on which 
Plating, Silvering depend. See Silver. 
Of mercury . — Mercury, called also quick- 
silver, always appears in a liquid state, in the 
common temperature of the atmosphere ; 
but in intense cold, as at 40 below zero, it 
becomes solid, and is then malleable, resem- 
bling silver. It is found in nature, sometimes 
in a pure state, but chiefly united to sulphur, 
when it forms cinnabar ; and sometimes to 
silver. It is also united to the acids, and to 
oxygen. It is mostly found in Spain and 
South America. Like other fluids, it boils, 
and is converted into vapour. This process 
is employed to separate it from other sub- 
stances. It is acted upon by most of the 
acids. It combines with sulphur and phos- 
phorus; and forms alloys with most of the 
metals, which are then called amalgams. On 
this property depend some of the methods of 
gilding and of silvering mirrors. When acted 
upon by heat and air for a long time, it ab- 
sorbs oxygen, and is converted into a real 
oxyde, called precipitate per se, or red oxyd 
of mercury. When the heat is increased, 
this oxyd gives out its oxygen, the mercury 
reassuming its metallic appearance. When 
agitated long in air, mercury is converted into 
a black oxyd. 
The sulphuric acid acts on mercury, if as- 
sisted by heat ; sulphureous acid gas is then 
disengaged, and a white oxyd is formed. 
'Hot water being poured on this, it becomes a 
yellow oxyd, called turbith mineral, the wa- 
ter holding in solution sulphate of mercury. 
The nitric acid dissolves mercury, even with- 
out heat, nitrous gas being disengaged ; one 
part of the acid oxydates the metal, whilst 
the other dissolves the oxyd. 
The nitrate of mercury is corrosive. When 
dry, it detonates upon coals. By a moderate 
heat it yields oxygen, or nitrogen gas ; the 
remaining oxyd becoming yellow', and at 
length a lively red, being the red precipitate 
of mercury ; and if fresh nitric acid is dis- 
tilled from it three or foufi times, it appears 
in small crystals, of a very superb red colour. 
The muriatic acid does not sensibly act on 
mercury, except by long digestion ; when it 
oxydates a part, which oxyd it dissolves." It 
completely dissolves the mercurial oxyds ; 
and when these have a small quantity of oxy- 
gen, and are nearly in a metallic state, the 
muriate of mercury is formed. When, on 
the contrary, it is saturated with oxygen, the 
oxy-muriate of mercury, or corrosive subli- 
mate of mercury, is formed. 
To obtain the mild muriate of mercury, 
mercurius duleis, or calomel, equal parts of 
quicksilver and of oxygenated muriate are 
completely blended by trituration, and ex- 
posed to sublimation. A beautiful artificial 
cinnabar may be prepared, by triturating 
mercury and flowers of sulphur with a solu- 
tion of caustic vegetable alkali, keeping it at 
a proper temperature, and afterwards wash- 
ing it repeatedly with boiling water. See 
Mercury. 
Of copper . — Copper is found native, but 
in very small quantities. It is generally met 
with in the state of an oxyd, or united to acids 
and sulphur. There are manv copper-mines 
in Britain, Germany, Ike. The largest cop- 
