342 
Schcelo, who obtained it by treating sugar of 
milk with nitric acid. It is also obtained by 
treating gupi-arabic with nitric acid. 
Of prussic acid. — 1 he prussic acid is 
formed by exposing the horns, hoofs, or 
dried blood of animals, with an equal quan- 
tity ol fixed alkali, to a red heat. The al- 
kali is found to be neutralised by the acid 
thus formed, and, on evaporation, will yield 
a salt in crystals, which is then called prussi- 
ate of potash or of soda, according to the 
alkali which has been employed. The prus- 
siates of alkali precipitate all metals from 
their solution; the alkali uniting with the acid 
which holds the metal in solution, whilst the 
prussic acid unites with the metallic oxyd, 
and communicates to it a peculiar colour. 
r l hus gold is precipitated of a yellow colour, 
lead ot a white, copper of a brownish-red, 
and iron of a dark blue, forming a prussiate 
of iron, or the substance called Prussian 
blue. From this substance the prussic acid 
may be again separated, by digestion with 
pure alkali, the prussiate of alkali being again 
formed, and the iron left in the state of a 
brown oxyd. This acid has a sour taste and 
suffocating smell, but, except its capacity of 
combining with alkalis and metals, it mani- 
fests no conspicuous acid properties. It 
does not redden the most delicate vegetable 
blues. 
For 'the remainder of the compounds 
formed by the acids with the salifiable bases, 
see tiie Tables. 
Of metals . — Among the most useful sub- 
stances in nature, are the metals. Many 
of the mechanic arts depend upon them"; 
and without a knowledge of them, perhaps 
mankind would never have attained their 
present degree of civilization. Their use is 
still unknown to many nations inhabiting 
the numerous islands of the South Sea. They 
are seldom met with in the earth in a native 
or pure state, but generally in combination 
with oxygen, sulphur, arsenic, and the acids. 
In their different states of combination, they 
are said to lie mineralized, and they are then 
.called ores. 
The ores of metals are generally found ip 
mountainous countries, chiefly in crevices of 
rocks, forming veins of ore ; which are distin- 
guished' into level, inclined, direct, or ob- 
lique, according to the angle they make with 
the horizon. The part of the rock resting 
on the vein, is called the roof, and that on 
which the vein rests, the bed of tiie vein. 
Tlie cavities made in the earth, in order to 
extract these ores, are called mines. The 
metallic matter of ores is generally incrusted, 
and intermingled with some earthy sub- 
stance, different from the rock in which the 
vein is situated, which is termed its matrix. 
This, however, ought not to be confounded 
with the mineralizing substance with which 
the metal is combined, such as sulphur, ike. 
The art or distinguishing ores from each 
other, and the method of describing them 
with accuracy and precision, are called Mine- 
ralogy. 
The art of assaying or analysing them, in 
order to ascertain the component parts, 
forms a branch of chemistry, called the Doci- 
mastic art. See Assa ying. 
To procure the pure metal from the ore, 
it is first cleared as much as possible from the 
foreign or stony substances with which it is 
Wended, and which are called the gangue, by 
. CHEMISTRY. 
first reducing the ore to powder, in which 
state it is called slich, and then by washing. 
R is then ton ified, or roasted, to dissipate the 
sulphur and arsenic; and lastly fused by the 
addition ot some flux containing the coaly 
principle, to disengage the oxygen with 
which the metal lias been Impregnated dur- 
ing the previous calcination or torrefactiou. 
Metals are distinguished from all other 
bodies by a peculiar brilliancy, which is term- 
ed metallic lustre, and by their weight, or 
specific gravity; the heaviest fossil, not me- 
tallic, being lighter than the lightest metal. 
I hev any also distinguished by their mal- 
leability, or their property of being extended 
under the hammer, and’ their ductility, or 
the property of being drawn into wire : 
though these two qualities are not possessed 
by all the metals. They are fusible by a suf- 
ficient degree ot heat, and when suffered to 
cool gradually, they crystallize into regular fi- 
gures. (See Crystallization.) If continued 
in fusion, they lose their brilliancy, and be- 
come an opaque powder, or metallic oxyd, 
acquiring weight, and absorbing a certain por- 
tion of oxygen during the transition. This 
process was formerly called calcination ; it 
is now called oxydation. The pure metal it- 
self was formerly known by the name of re- 
gains; as the regains of tin, of gold, &c. 
1 bat metals are calcined or oxydated in 
consequence of their absorbing oxygen, is 
proved by this process taking place only 
when oxygen is present, and by their giving 
it out in exactly the same quantity and pro 
portion on their reduction to. their metallic 
state. They undergo this process also from 
the action of humidity. The water is de- 
composed, its hydrogen being dissipated, 
whilst its oxygen unites with the metal. 
They are soluble in acids, and are precipi- 
tated from them by alkalis. Some of the 
acids are decomposed during their combi- 
nation with metals ; their oxygen combining 
with the metal, forming a metallic oxyd, 
which is then dissolved by the remainder of 
the acid, and forms a metallic salt. 
When perfectly fused, they are for the 
most part miscible, or combinable with each 
other, or with unmetallic substances, as sul- 
phur, phosphorus, and charcoal If urged by 
a stronger heat, they are converted into a 
vi triform substance, or metallic glass. These 
metallic glasses, as well as the oxyds, pos- 
sess other properties than their reguli. They 
are of different colours: and the metallic 
oxyds tinge the earthy and saline glasses 
with which they vitrify, with various colours 
conformably to the difference of their own 
nature. They do this frequently, even when 
added in but smaLl quantity. Such metallic 
oxyds as do not themselves yield a trans- 
parent glass, may deprive another of its 
transparency if fused with it. On the com- 
bination of other glasses with the metallic 
ones, and on the colouring of the first by 
means of the latter, depends the preparation 
of artificial gems and glass pastes, the pig- 
-ments for enamel and porcelain-painting, 
the enamel itself, and the glazings for earth- 
enware. 
'Fhe operation by which metallic glasses 
and oxyds are restored to the reguline form, 
is called the reduction or reviving of metals. 
In their reduction from the oxyds and 
glasses, the addition of a combustible sub- 
stance is always necessary ; charcoal, for 
instance, or such matters as contain carbon ; 
as soap, pitch, resin, fat, and oil. In the 
smelting-works, the fuel itself is employed as 
a means of reduction, by fusing the metal 
interspersed among the coals. Some metals, 
as iron and platinum, grow soft before they 
fuse, and on this depends their very useful 
property of being welded. 
Metals are the best conductors of elec- 
tricity and galvanism. 
Oj platinum . — Platinum is found only in a 
metallic form in small grains. It was un- 
known in Europe before tiie year 1748. ' It 
is brought from South America. It is the 
heaviest, hardest, and most infusible, of all 
the metals. It is ductile, and may be ham- 
mered into plates, or drawn into’ wire. It 
may r be welded together in a white heat, 
is unalterable in the air, and is on this account 
found a very valuable material for making 
specula, or reflecting mirrors for telescopes. 
No acid acts upon it, except the nitro-muri- 
atic. It is ot a white colour, between that 
of silver and tin. 
1 he process which is generally used for 
obtaining malleable platinum, is as follows : 
1 riturate common platinum (which is gene- 
raiiy in grains) with water, to wash off every 
contaminating matter that water can carry 
away. Mix the platinum with about one-filth 
pait white arsenic, and one fifteenth jiart pot- 
ash, putting the whole into a proper crucible 
in the following manner: having well healed 
the crucible, put in one-third of the mixture; 
apply to this a strong heat, and add one-third 
more; after a renewed application of heat, 
throw in the last portion. After a thorough fu- 
sion of the whole, cool and break the mass, 
ruse it a second time, and if necessary, even 
a third time, till it comes to be magnetic. 
Break itinto small pieces, and melt those pieces 
in separate crucibles; and in portions of a pound 
and a half of the platinum to each crucible, 
with an equal quantity of arsenious acid, and 
halt a pound of potash. After cooling the 
contents of the different crucibles in an hori- 
zontal position, in order to have them 
throughout of equal thickness, heat them under 
a m uflle, to volatilize the arsenious acid ; 
and keep them in this state without increase 
of heat, for the space of six hours. Heat 
them next in common oil, til! the oil shall 
have evaporated to dryness, d hen immerse 
them in nitric acid, boil them in water, heat 
them to redness in a crucible, and hammer 
them into a dense mass. They are now fit 
to be heated in a naked fire, and hammered 
into bars for use. Platinum is generally mixed 
with iron, and therefore it is magnetic. It 
forms alloys with most of the metals. That 
with copper is the most useful ; it takes a fine 
polish, and does not tarnish. See Platinum. 
OJ gold. Gold is always found in na 
ture in a metallic state. It is generally 
met with in grains, called gold-dust, mixed 
with the sand of rivers ; being carried away 
by them, from the rocks and mountains, 
wlieie itis found in leaves or ramifications, 
adhering to quartz, and other stones. Itis 
found chiefly in Africa and Hungary; and 
some has been discovered lately in the 
county ot \\ ickiow, in Ireland, where the 
largest piece of native gold hitherto seen 
was found. Its weight was 22 ounces, and 
it was almost pure. Small quantities of gold 
have been found in a vast variety of sub- 
stances. Indeed, in very minute quanti- 
