Encyclopaedia Britannica, or, a Dictionary of arts, sciences, and miscellaneous literature : enlarged and improved. Illustrated with nearly six hundred engravings > Volume 19, Scripture-SUG

Zircon
Genus.
ANALYSIS OF STONES,
beiirr precipitated, have been thrown down. The fo-
lution being filtered, the earths and metallic oxides re¬
main on the filter. Add nitric acid to the liquid till it
acquire a flrong four tafie, and evaporate till the bora-
cic acid appear free.
The fluid is then to be filtered, and evaporated to
drynefs, and the dry mafs being expofed to a heat of
about 450° Fahrenheit, the nitrate of ammonia is de*
compofed, and the nitrate of potalli or foda remains be-
hind.
To dcteft fluoric acid, which has been fometimes met
with as a component part of ftones, Klaproth heats the
mineral with fulphuric acid in a glafs retort, the corro-
fion of which, and the depofition of filica in the water
of the receiver, are certain tells of fluoric acid.
After the general obfervations which have now been
offered, we proceed to give examples of the analyfis of
minerals belonging to the different genera of earths and
Hones j and we fhall follow the fame order in which
thofe genera are defcribed in the article Minera¬
logy.
By this management, the filiceous earth feparated in
flimy, intumefced grains, and weighed, after ignition,
23^ grains*
F. The faint ion, thus freed from its filica, was now
faturated with a boiling ley of mild alkali •, and the pre¬
cipitate was waflied and dried in the air. This lafl
weighed 114 grains, proving, upon every trial, to be
jargonic earth. A fourth part of it, heated to rednefs,
w-eighed 161, grains ; which make the whole amount to
66 grains.
G. The above fix grains D, with the 234- grains- E,
in the whole 294 grains of filiceous earth, were ignited
with a quadruple weight of vegetable alkali. When
this mafs had been again foftened with water, it left a
refidue, which was extracted by muriatic acid. From
this muriatic folution, alfo, when faturated with potafh,
jargonic earth fell dorvn, weighing four grains after ig¬
nition. Hence, fubtrafting thefe, the quantity of filice¬
ous earth is reduced to 254 grains.
One hundred parts of hyacinth, therefore, have
given
71?
Siliceous
Genus.
^ *
i. Zircon Genus.
The mineral affording the earth which chara&erifes
this genus, was analyfed by7 Klaproth in the following
st r/r manner We feledt that fpecies which is called hya-
tPiys> . ,
i 15)5. cinth. _ # .
A. IOO grains of hyacinth being levigated in the
flint mortar, received an increafe of weight of half a
grain.
B. This pulverized hyacinth, digefted w'ith two
ounces of nitro-muriatic acid, yielded, upon faturating
the folution with potarti, a light-brown precipitate, of
three grains and a half, when dried. Ammonia, aad-
ed to it, diffolved nothing*, and it remained colourlefs.
After the precipitate had been again feparated from the
volatile alkali, muriatic acid was added, which diffolved
its ferruginous contents, leaving a white earth behind,
which, when ignited, weighed i| grain. The portion
of iron, precipitated by cauftic ammonia from the mu¬
riatic folution, weighed half a grain, when ignited, and
became black and refplendent. It was fufed with a
neutral phofphate, upon charcoal, to find whether it
contained manganefe ; no trace was perceptible.
C. The above grain of earth B u^ere now added
again to the hyacinth, after treatment with acids. The
Hone was then fubje&ed to red heat, with fix times its
quantity of cauftic alkali, in the manner explained in
the effay on the jargon of Ceylon ; the ignited mafs was
again liquefied with water y and the earth remaining af¬
ter this procefs weighed 123 grains, when collefted,
edulcorated, and dried.
D. The alkaline lixivium was then faturated w-ith
muriatic acid, and evaporated. At firft it continued
clear*, but towards the end filiceous earth feparated,
the quantity of which, alter ignition, amounted to fix
grains.
E. To the 1 23 grains, previoufly well waftied with
Water, a fufficient quantity of muriatic acid was added }
which, with the afliftance of heat, diffolved nearly the
whole, a trifling refidue excepted. I his muriatic lolu-
tion, evaporated in a moderate heat to a fixth or eighth
part, loft its fluidity, and formed a limpid gelatinous
coagulum. It was then covered with water,^ and ex-
pofedj with repeated agitation, to a digelting heat.
I
70
i
25
0.50
95*5°
Lofs, 4.50
100
2. Of the Siliceous Genus.
A great proportion of the ftones belonging to this-
genus are tranfparent, and have a vitreous appearance.
They are fo hard as to fcratch glafs, and, excepting the
fluoric acid, they are not a&ed upon by acids. By fu-
fion with alkalies they form glafs ; they alfo enter into
fufion wfith boracic acid, and the acid of phofphorusi
Stones compofed chiefly of pure filica, are tranfparent
and colourlefs. When a mineral is prefented for exa¬
mination, even if it poffefs moft of the properties which
charadlerize Hones belonging to this genus, fome pre¬
liminary proceffes may be purfued to afeertain farther its
nature and component parts.
A. It is fometimes difficult to reduce ffliceous Hones
to a fine powder. To facilitate this operation, a portion
of the Hone may be heated to rednefs, and in this Hate
fuddenly plunged into cold water. If by the firfi heat¬
ing it is not fufficiently brittle, the operation may be re¬
peated until the mineral can be reduced to a fine powder,
as already direfted.
B. One part of the Hone in fine powder is now to be
mixed with four or five parts of potalh, diffolved in the
fame quantity of water. The mixture is introduced in¬
to a filver crucible, and evaporated to drynefs, fiirring
it conflantly with a filver rod, according to the direc¬
tions given above. The mafs being evaporated to dry.
nefs, the heat is to be gradually inereafed, till the cru¬
cible appears of a dull red heat, or till the mafs enter
into quiet fufion. In this Hate it is kept for an hour.
C. Remove the crucible from the fire before it is
completely cold j foften the mafs with water, by adding
fVeffi
Jargoma,
Silica,
Subtra£l
Oxide of iron,
F
G
G
A
B
66
4
252-