Encyclopaedia Britannica, or, a Dictionary of arts, sciences, and miscellaneous literature : enlarged and improved. Illustrated with nearly six hundred engravings > Volume 5, BUR-CHI

Tin, Stc.
1781
1782
Sulphates.
I783
Nitrates.
1784
Muriates.
I78S
Phofphates,
&c-
1786
Ufes.
1787
Hiflory.
C H E M
2. Ammonia has a ftill more powerful a&ion on
zinc. Hydrogen gas is more copioufly evolved, and
the oxide which is formed is more abundantly diffolved
in the liquid, and at the end of feme time a confiderable
quantity of white oxide is depofited. 'Ihefe alkaline
folutions become turbid by expofure to the air 5 its oxy¬
gen and carbonic acid, a6ling at the fame time, preci¬
pitate the oxide.
3. The alkaline and earthy fulphates are readily de-
compofed by zinc, with the afliftance of heat. It at¬
tracts the oxygen of the fulphuric acid, and thus de-
compolxng it, feparates the fulphur, which combines
with the bafes of the fulphates. Alum boiled in fo-
lution with zinc, is decompofed, and there is formed
a triple fait, which is fulphate of zinc and alumina.
4. The nitrates produce a vivid inflammation with
zinc at a red heat. The acid is decompofed, its oxy¬
gen combines with the metal, and by this rapid com¬
bination, a violent detonation is produced. The azo¬
tic gas is difengaged, and the zinc is fully oxidated.
Three parts of nitre well dried, and one of zinc in fine
powder, well mixed together and projected into a red-
hot crucible, produce a very brilliant inflammation.
The burning matter is fometimes thrown out to a confi¬
derable diftance 5 fo that the experiment fliould be
made with caution. Ihis compound is fometimes em¬
ployed in fire-works.
5. Zinc has a confiderable aCtion on the muriates.
Triturated with the muriate of ammonia, the fait is
decompofed, and ammonia is difengaged. By diftill-
ing this fait with zinc, ammoniacal and hydrogen gafes
are obtained *, the latter is obvioufly owing to the de-
compofition of the water contained in the fait, by
means of the zinc, which combines with the oxygen,
and then forms a muriate of zinc with the muriatic
acid.
6. The phofphates and borates combine by fufion
with the oxide of zinc, which communicates to the
glafs thus formed a greeniftr-yellow colour.
7. Zinc decompofes the greateft number of the me¬
tallic falts from their folutions, by its ftrong affinity for
oxygen. They are precipitated in the metallic form, or
in the date of oxide, but deprived of a portion of oxy-
gen.
8. Zinc is employed in many of the arts. It forms
ufeful alloys with fome of the other metals, fome of
which will be mentioned afterwards. It is alfo em¬
ployed in medicine. The fulphate of zinc is fome¬
times exhibited as an emetic, and frequently ufed in
folution as an eye-wafli. The oxide of zinc, or the
flowers of zinc, have been preferibed as an antifpaf-
modic, and particularly in cafes of epilepfy.
Sect. XVI. Of Tin and its Combinations.
1. Tin has been known from the earlieft ages. It
W'as much employed by the Egyptians in the arts, and
by the Greeks as an alloy with other metals. Pliny
fpeaks of it under the name of white lead, as a metal
well known in the arts, and even applied in the. fa¬
brication of many ornaments of luxury. He afenbes
to the Gauls the invention of the art of tinning, or
covering other metals with a thin coat of tin. The
alchemilts were much employed in their refearches
concerning tin. They gave it the name of Jupiter,
1788
I S T R Y.
from which the falts or preparations of tin were called
jovial. Since their time, the nature and properties of
tin have been particularly inveftigated by many che-
mifts, and it has proved the fubjeft of fome important
difeoveries in chemical fcience. So early as the year
1630, John Key threw out a conjefture, that the air
was fixed in this metal during its calcination. Boyle,
towards the end of the fame century, attempted to ac¬
count for the increafe of weight which this metal ac¬
quired during this procefs; but this was only fully af-
certained by Lavoifier, who repeated the experiment
of Boyle, and calcined the metal in clofe veflels; but
the method of conducing this experiment and the re-
fult of it, have been already detailed.
2. Tin exifts in nature in three different ftates. It Ores,
is found native, in the ftate of oxide, and in that of
fulphurated oxide. Native tin is in brilliant plates,
or regularly cryftallized. The native oxide of tin,
which is the molt common ore of this metal, exifts
under a variety of forms. It is generally found cry¬
ftallized. The fulphuret of tin is of a pale or dark
gray colour, and when pure, has fome reiemblanee to
an ore of filver. 1789
3. To obtain the metal from its ores, they are firft Anaiytis.
roafted, and then treated with a flux, to reduce the
metal. It has been recommended by fome, to mix a
fmall quantity of pitch with the fufed mafs, to prevent
the oxidation of the tin. After the ore is roafted, it
fufes readily with three times its weight of black flux,
and a little decrepitated muriate of foda.
In the humid way, native tin may be diffolved in
nitric acid, which readily oxidates, and reduces it to
the ftate of white powder, which is an oxide of tin j
and if it contain iron and copper, thefe two metals re¬
main in the folution.
4. Tin is of a white colour, nearly as brilliant as pr0perties.
filver. The fpecific gravity of tin is 7.291. It is
one of the fofteft of the metals. It may be fcratched
with the nail, and eafily cut with a knife. It is ex¬
tremely flexible, and produces a peculiar noife when
it is bent or folded. It is fo malleable, that it can be
eafily beaten out to t^Vo Part an inch, which is
the thicknefs of tinfoil. It has little elafticity or te¬
nacity. A wire of this metal about of an inch
in diameter fupports a weight of about 30 lbs. without
breaking. 17QT
5. Tin is fufceptible of very confiderable expanfion Adtion of
by means of caloric, and on this account it has been *ieat*
propofed to employ it as a pyrometer. Tin is one of
the moft fufible of the metals, and melts at the tem¬
perature of 442°, but it requires a very high tempera¬
ture to raife it in vapour. If it be allowed to cool
flowly, and when the furface becomes folid, by pouring
out part of the liquid metal, cryftals- are formed, in
large rhomboids, compofed of a great number of fmall
needles. . . . 1-92
6. Tin is a good conductor of eleftricity. It Odour, See.
poffeffes a peculiar odour, which is communicated
to the hands by friction. It has alfo a perceptibie-
tafte.
7. When this metal is expofed to the air4 it is foon Oxidation,
tarnifhed, and affumes a grayiih white colour j but it
undergoes no farther change. When it is melted in
an open veffel, it is foon covered with a grayilh pel¬
licle, which is the commencement of the oxidation of
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