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

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C H E M I
Ziftc, &t-c. line, of a cleep orange or brown colour. The com-
Ponent of this fait are, according to
ionapofi-
bite vi-
I7<53
Prepara-
1769
?roperties.
1770
.ambines
OTth ful-
hur.
1771
toperties.
Acid
Oxide
Water
Bergman,
40
20
40
100
Kir wan.
20.5
40.0
39*5
100.0
3. The fait, known in commerce by the name of
white vitriol, is a fulphate of zinc, and is fuppofed to
contain an excefs of acid. It is in the form of white
granular maffes, refembling fugar, and often marked
with yellow fpots. This fait is ufually prepared by
roafting the fulphuret of zinc or blende, by which
means the fulphuret is converted into fulphuric acid. It
is then dilTolved in water, which is purified and evapo¬
rated, and the fait is cryftallized by hidden cooling.
Part of its water of cryftallization is afterwards driven
off by heat, fo that it is obtained in a regular, folid,
and granulated mafs. It is generally contaminated
with iron and other metals ; but it may be purified
from thefe, by adding filings of zinc, which preci¬
pitate the other metals, and leave a pure fulphate of
zinc.
2. Sulphite of Zinc.
Concentrated fulphurous acid readily combines with
the white oxide of zinc, without any effervefeence,
but with the evolution of heat, and the acid being de¬
prived of its odour. When the faturation is complet¬
ed, white cryftals appear on the furface of the liquid.
This fait has a pungent, aftringent tafte. It cryftal-
lizes readily. It is decompofed by the acids, with
effervefcence. It is infoluble in alcohol. It forms
white precipitates with the alkalies, and when expofed
to the air, it is readily converted into fulphate ef
zinc.
Sulphurated fulphite of Zinc.—When fulphurous acid
is added to zinc in the ftate of powder or filings, a
great degree of heat is produced j fulphurated hydro¬
gen gas is difengaged 7 the liquid becomes at firft
brown, fometimes muddy, and afliimes a yellow co¬
lour, and towards the end of the procefs it becomes
tranfparent. The folution has ati acrid, aftringent,
and fulphureous tafte. Sulphuric and muriatic acids
difengage with eftervefcence, fulphurous acid gas, and
precipitate a yellowifti white powder. Nitric acid at
firft feparates fulphurous acid gas, and afterwards a
flaky precipitate, which is pure fulphur. When this
iolution is expofed to the air, it becomes thick like ho¬
ney, and affords cryftals in the form of needles or fine
four-fided prifms, terminated by four-fided pyramids.
Thefe are cryftals of fulphurated fulphite of zinc,
which become white by expofure to the air, and form
a white powder infoluble in water. When this fait
is heated by the blow-pipe, it fwells up, gives out a
bright light like burning zinc, and forms dendritical
ramifications. This fait is partly foluble in alcohol.
The part not diflolved, only gives out fulphurous acid
£as by means of fulphuric acid, whilft the part which
is diffolyed affords, befides fulphurous acid gas, a copi¬
ous precipitate of fulphur. When it is diftilled in a
s T R Y. 651
retort, it gives out water, fulphurous acid, fulphu3*!; acid, Zincy&c.
and fulphur fubiimed. There remains behind oxide of H"r" ^ —^
zinc, mixed with a little of the fulphate.
In the folution of zinc in liquid fulphurous acid, wa-Theory of
ter, and part of the fulphurous acid itfelf, are decom- the procefs.
pofed j for fulphurated hydrogen gas is difengaged,
which is compofed of the hydrogen of the water and
part of the fulphur of the fulphurous acid. There is no
precipitation of fulphur during the folution, for it com¬
bines with the fulphite of zinc, as it is formed j but
this is not completely faturated, fince alcohol dilTolves
only the portion of fulphurated fulphite which it con¬
tains, and feparates the fulphite *. * Fourcroy,
1 1 v. p. 380.
3. Nitrate of Zinc.
1773
1. Concentrated nitric acid produces a violent a&ion Prepara-
with zinc, and fometimes even inflames it. To effecttitm*
this folution, with a moderate aftion, the acid ftiould
be diluted with water. Great heat is produced, with
violent effervefcence and the evolution of nitrous gas.
The acid is decompoied ; its oxygen combining with
the metal, forms an oxide, which combines with the
acid as it is formed. X774
2. This folution is of a greeniih-yellow colour, and Properties,
extremely cauftic. By evaporation it affords cryftals,
in the form of four-fided, compreffed, and ftriated
prifms, terminated by four-fided pyramids. The fpeci-
fic gravity is 2.096. This fait is deliquefeent in the
air. When it is heated on burning coals, it melts, and
detonates with a fmall red flame. When heated in a
crucible, it gives out red vapour, and affumes a deep
colour and gelatinous confiftence. When cooled in this
ftate, it retains its foftnefs for fome time. By continu¬
ing the heat, it dries, gives out nitrous and oxygen
gaffes, and leaves behind a yellow oxide.
4. Muriate of Zmc.
Muriatic acid produces a rapid asftion on zinc. Itp repara-
xs diffolved with effervefcence, and with the evolution tion.
of pure hydrogen gas. The folution of zinc in muria¬
tic acid is colourlefs ; it does not cryftallize, but af¬
fumes the form of a tranfparent jelly. It affords by
diftillation a fmall quantity of fuming acid, and a folid
muriate of zinc, which is fufible with a moderate heat,
and was formerly known by the name of butter of ’zinc.
When this muriate of zinc is fubiimed by heat, it be¬
comes of a fine white colour, compofing a mafs of cry¬
ftals in the form of fmall prifms. It is decompofed by
fulphuric acid, and is precipitated by the alkalies. BproneJtle*
is foluble in water, attracts moifture from the atmo- P ‘ ‘
fphere, and is foon converted into a ti-anfparent jelly.
The fpecific gravity is 1.377.
5. Muriate of Ammonia and Zinc.
This triple fait is formed by boiling white oxide of
zinc in a folution of muriate of ammonia. The oxide
of zinc is diffolved 7 part of which is afterwards depo-
fited, when the folution cools, but what remains in the
folution is not precipitated by the alkalies or the alka¬
line carbonates. 1
6. Fluate of Zinc.
Fluoric acid produces a violent action with zinc $
there is confiderable effervefcence, with the evolution
4 N 2 of