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

7i6 ANALYSIS OF
Preliminary diffolve, it may be thrown down by adding a fmall por-
Prceefles. tjon 0f Weak alcohol. After being made red hot in a
"n-"1 crucible, it is to be weighed, and the lime will amount to
of the weight. Thefolution containing the remain¬
ing fulphates being diluted with a large portion of wa¬
ter, a fmall excefs of acid is to be added, and then a
Saturated carbonate of potafh. The magnefia and oxide
of manganefe remain diffblved, and the oxides of chro¬
mium, iron, and nickel, are precipitated. This preci¬
pitate may be denominated C.
Add to the folution a folution of hydrofulphuret of
potalh, and the manganefe in the date of a hydroful¬
phuret will be precipitated. Calcine the precipitate in
contaft with air, and weigh it. The addition of pure
potalh to the folution will precipitate the magnelia,
which being walked, and fubjedled to a red heat, is alfo
tb be weighed.
The refiduum C is to be repeatedly boiled with nitric
acid, and then mixed with pure potalh ; and, being
heated, the liquid is to be decanted off. The precipi¬
tate thus obtained, confiding of the oxides of iron
and nickel, is to be walked with pure water, and this
water is to be added to the folution of the nitric acid
and potalh. The chromium, if any be prefent, is con¬
tained in that folution, and is in the form of an acid.
Add to the folution muriatic acid in excefs, and let the
evaporation be continued till the liquor become of a
green colour-, then add a pure alkali, by which the
chromium is precipitated in the date of oxide, which is
to be dried in the ufual way, and weighed.
The precipitate containing the oxides of iron and nic¬
kel is to be diffolved in muriatic acid ammonia is to
be added in excefs, when the oxide of iron precipitates;
and being collefted, wadied, and dried, is to be weigh¬
ed. By evaporating the folution, the oxide of nickel
will be alfo precipitated, or the whole may be precipi¬
tated by the addition of hydrofulphuret of ammonia.
This being treated in the fame manner as the other fub-
ftanees, is alfo to be weighed.
The weight of the whole fubdances thus obtained be¬
ing added together, and being compared with the
weight of the matter originally operated upon, if the
two be equal, or if the difference do not exceed three or
four parts in 100, it may be inferred that the analyfis is
nearly correft; but a confiderable lofs of weight indi¬
cates fome error, and requires the analyfis to be careful¬
ly repeated. If the fame lofs of weight appear, it may
be concluded that the done contained fome fubdance
which is foluble in water, or has been driven off by the
heat. To afcertain the lad point, a portion of the done
is to be broken into dual] pieces, and expofed to a drong
heat, in a porcelain retort. If it contain water, or any
volatile fubdance, it will come over into the receiver,
and by this means the nature and weight of the ingre¬
dients feparated may be afeertained. If nothing come
over into the receiver, or if what is obtained be not
equal to the deficient weight, it may be inferred that the
done contains fome matter which is foluble in water.
A fixed alkali has been not unfrequently found in
fimple ftones; and to afcertain whether the mineral fub-
jjefted to analyfis contains any alkaline matter, different
methods have been purfued. Thefe methods we (hall
now defcribe. The done being reduced to an impalpa¬
ble powder, is cautioufly heated repeatedly with fulphu-
acid, and th® mafs is to be digeded in water j and
STONES, &c.
this folution being properly concentrated, is fet afide Preliminary
for fome days. The appearance of crydals of alum is a Procefies.
certain indication that the mineral contained potalh; "■V"-*
and the quantity of potalh may be edimated at of
the weight of thofe crydals; but if no crydals be ob¬
tained, the folution is to be evaporated to drynels, and
the reliduum expofed to a moderate red heat. Diged;
it afterwards in water, and add carbonate of ammonia,
and filter; evaporate again to drynefs, expofe the refi-
due to a heat of 700°, and rediffolve it. The folution
being properly concentrated, will give crydals of iul-
phate of loda or of potath, as the one or the other al¬
kali is prefent. Potalh may be diicovered by adding to
the folution of the fait, a folution of nitro-muriate of
platina fomewhat concentrated. A yellow precipitate,
which is muriate of platina and potalh, is thus ob¬
tained.
Klaproth’s method for difcovering fixed alkalies in
minerals is the following. He takes four parts oi ni¬
trate of barytes to one of the mineral to be examined,
and fufes them together in a porcelain crucible. A
fpongy mafs of a light-blue colour was thus obtained,
and with the addition of diluted muriatic acid, was com ¬
pletely diffolvtd. The folution, which was of a yellow
colour, was then mixed with a fufficient quantity of ful-
phuric acid, by which the barytes is precipitated, and
the muriatic acid expelled. The liquid is next evapo¬
rated to drynefs, and the mafs being digefted in water,
is filtered, and the fulphate of barytes and lilica remain
on the filter. The clear folution is falurated with car¬
bonate of ammonia, and filtered a fecond time; and all
the earthy and metallic bodies being feparated, the ful¬
phates of fixed alkali and ammonia only remain in the
folution, which being evaporated to drynefs, the dry fa-
line mafs is introduced into a porcelain crucible, and
fubjedded to fuch a degree of heat as is fufficient to drive
off the fulphate of ammonia. The refiduum is then dif¬
folved in water, and cryfiallized; and thus a pure, fix¬
ed alkaline fulphate is obtained, which is again diflol-
ved in water, and decompofed, by adding acetate of
barytes. The folution is then filtered, and the liquid is
evaporated to drynefs. The faline mafs obtained is the
acetate of a fixed alkali, which being expofed to heat in
a crucible, became of a reddilh colour. The carbona¬
ceous refiduum is then to be diffolved in water, filtered,
and cryftallized, and the fait thus procured is a carbo¬
nate of a fixed alkali, the nature of which may be ea-
fily recognifed by the means Hated above.
Mr Davy’s method of detedling a fixed alkali in mi¬
nerals, is different *. One hundred grains of the Hone * Nick
in very fine powder are to be fufed for half an hour at a •
ftrongred heat, in a crucible of platina or filver, with*11*’
200 grains of boracic acid. An ounce and a half of ni¬
tric acid diluted with feven or eight times its quantity
of water, is then digefted upon the fufed mafs, till the
decompofition of the whole is completed. Evaporate
the fluid to about two ounces, or one ounce and a half;
by this means the filiceous earth is feparated, which be¬
ing colle£led on a filter, is to be walked with diftilled
water, till the boracic acid and the whole of the faline
matter are feparated. The fluid is then mixed with wa¬
ter that has paffed through the filter, and evaporated to
the quantity of half a pint, after which it is faturated
with carbonate of ammonia, and boiled with an excefs
of this fait, till the whole of the fubflances capable o£
being