C. Remigius Fresenius.

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slowly absorbs water (Expt. No. 10). At a gentle heat it is un-
altered, at a strong red heat it fuses without decomposition or loss
of weight. At a white heat it loses \\vight by volatilization of
sodium sulphate and also of sulphuric acid (AL. Mns< IIKRI.K n,



BASKS OF GROUP I. 165

BOUSSINGAULT). When ignited with ammonium chloride, it be-
haves like potassium sulphate.



COMPOSITION.



ONa Na a O .... 62 10 43 '68

QNa ~ S0 3 .... 80-07 56-32

142-17 .100-00



The acid sodium sulphate (sodium hydrogen sulphate,
which is always produced upon the evaporation of a solution of the
normal salt with sulphuric acid in excess, fuses even at a gentle
heat ; it may'be readily converted into the normal salt in the same
manner as the acid potassium sulphate (see 68, a).

5. Sodium nitrate crystallizes as obtuse rhombohedra. In
analysis it is usually obtained as an amorphous saline mass. It is
readily soluble in water, is practically insoluble in absolute alcohol,
and is but very slightly soluble in alcohol. It is indifferent
towards vegetable colors. Under ordinary circumstances it is
unalterable in the air, but attracts moisture from very moist air.
It fuses far below a red heat, and without decomposition (comp.
Expt. No. 11); at a higher temperature it is decomposed like
potassium nitrate ( 68). Ignited with ammonium chloride, or
in hydrochloric- acid gas, and evaporated with oxalic acid or
aqueous hydrochloric acid, it behaves like the corresponding
potassium salt. The decomposition with aqueous hydrochloric
acid is more readily effected, i.e., with fewer evaporations, than
is the case with potassium nitrate (BAIJMHAUEK *).

COMPOSITION.

Ka o ff/_ Na ' ' 39 ' 05 45 ' 89
~ 1N XO~~]SrO a . . . 46-04 54-11

85-09 100-00
c. /Sodium chloride crystallizes in cubes, octahedra, and hollow

* Jour. f. prakt. Chem., LXXVIII, 213.



160 HMLMS. [ 69.

four-sided pyramids. In analysis it is frequently obtained as an
amorphous mass. It dissolves readily in water, but is much less
soluble in hydrochloric acid ; it is nearly insoluble in absolute
alcohol, and but sparingly soluble in common alcohol ; 100 parts
of alcohol of 75 per cent, dissolve, at a temperature of 15, 0' 7 part
(WAGNER). It is neutral to vegetable colors. Exposed to a
somewhat moist atmosphere, it slowly absorbs water (Expt. No. 12).
Crystals of this salt that have not been kept drying a considerable
time decrepitate when heated, yielding a little water, which they
hold mechanically confined. The salt fuses at a red heat without
decomposition ; at a white heat, and in open vessels even at a
bright red heat, it volatilizes in white fumes (Expt. JTo. 13). If a
carburetted hydrogen flame acts on fusing sodium chloride, hydro-
chloric acid escapes, and some sodium carbonate is formed. On
evaporation with oxalic or nitric acid as well as by ignition with
ammonium oxalate, it behaves like the corresponding potassium
salt.

COMPOSITION.

Na . . . . 23-05 39-40

01 35-4:5 60 60



58-50 100-00

d. Anhydrous sodium carbonate is a white powder or a white
very friable mass. It dissolves readily in water, but much less so
in solution of ammonia (MAKGUERITTE) ; it is insoluble in alcohol.
Its reaction is strongly alkaline. Exposed to the air, it absorbs
water slowly. On moderate ignition to incipient fusion it scarcely
loses weight ; on long fusion, however, it volatilizes to a consider-
able extent (Comp. Expt. 14).

COMPOSITION.

r , n ONa _ Na a O . . . . 62-10 58-53

< ONa - z CO 44-00 41 -47

106-10 100-00

e. Sodium platinic chloride crystallizes with 6 mol. water,
(NaCl),.PtCl 4 -f 6II,O, in light yellow, transparent, prismatic
crystals which dissolve readily both in water and in common
alcohol.



70.] BASES OF GROUP I. 167

f. Sodium silicqfluoride is similar in properties to the corre-
sponding potassium salt. It has an analogous composition, and is
decomposed in the same way by alkalies. It is, however, con-
siderably more soluble in water and in diluted alcohol.



70.
3. AMMONIUM.

Ammonium is most appropriately weighed as AMMONIUM
CHLORIDE, or as AMMONIUM pLATiNic CHLORIDE, or it may be esti-
mated from the weight of the PLATINUM in the latter compound.

Under certain circumstances ammonium may also be estimated
from the volume of the NITROGEN GAS eliminated from it ; and it
is frequently estimated by alkalimetry.

a. Ammonium chloride crystallizes in cubes and octahedra, but
more frequently in feathery crystals. In analysis we obtain it
uniformly as a white mass. It dissolves readily in water, but is
difficultly soluble in common alcohol. It does not alter vegetable
colors, and remains unaltered in the air. Solution of ammonium
chloride, when evaporated on the water-bath, loses a small quantity
of ammonia, and becomes slightly acid. The diminution of weight
occasioned by this loss of ammonia is very trifling (Expt. No. 15).
At 100 ammonium chloride loses nothing, or very little of its
weight (comp. same Expt.). At a higher temperature it volatilizes
readily, and without undergoing decomposition.

COMPOSITION.

KH 4 . . 18-072 33-77 ISTH, . . 17-064 31-88

Cl. . . 35-450 66-23 HC1 . . 36-458 68-12

53-522 100-00 53-522 100-00

100 parts of ammonium chloride correspond to 48*72 parts of
ammonium oxide.

b. Ammonium platinic Moride occurs either as a heavy,
lemon-colored powder, or in small, hard octahedral crystals of a
bright yellow color. It is difficultly soluble in cold, but more

/readily in hot water. It is very sparingly soluble in absolute
alcohol, but more readily in common alcohol 1 part requiring of
absolute alcohol, 26535 parts; of alcohol of 76 per cent., 1406



168 FORMS. [ 71.

parts; of alcohol of 55 per cent., 665 parts. The presence of
free acid sensibly increases its solubility (Expt. No. 16). It
remains unaltered in the air, and at 100. It loses a little water
between 100 and 125. Upon ignition chlorine and ammonium
chloride escape, leaving the metallic platinum as a porous mass
(spongy platinum). However, if due care be not taken in this
process to apply the heat gradually, the escaping fumes will carry
off particles of platinum, which will coat the lid of the crucible.
For properties of metallic platinum, see 89, a.

COMPOSITION.

(X 11,01),. .107-044 24-12 (NH 4 ) t . . 36-144 8-15
HC1 4 . . . 336-700 75-88 Pt . . . 194-900 43-92

01. . . . 212-700 47-93
443-744 100-00

443-744 100 00

N t . . . . 28-080 6-33 (NH 8 ), . . 34-128 7-691

H 8 ... 8-064 1-82

Pt ... 194-900 43-92 (HC1), . . 72-916 16-432

01. ... 212-700 47.93 PtCl 4 . . 336-700 76-010



443-744 100-00 443-744 100-000

100 parts of ammonium platinic chloride correspond to 11*76
parts of ammonium oxide.

c. Nitrogen gas is colorless, tasteless, and inodorous ; it mixes
with air, without producing the slightest coloration ; it does not
affect vegetable colors. Its specific gravity is 0-996971.* One
litre weighs at 0, and 0-76 metre bar., 1-254035 grm. It
is difficultly soluble in water, 1 volume of water absorbing, at 0,
and 0-76 pressure, 0-02035 vol. ; at 10, 0-01607 vol. ; at 15,
0*01478 vol. of nitrogen gas (BUNSEN).

BASIC RADICALS OF THE SECOND GROUP.

71.

1. BARIUM.
Barium is weighed sis UAIMUM SULPHATE, BARIUM CARBONATE,

and BARIUM SILICOKI.IOUIDK.

a. Artificially pivpuivd Imrhnn, sulphate presents the appear-
ance of a fine white powder. "When recently precipitated, it is

* According to REGNAULT, 0-97137.



71.] BASES OF GROUP II. 169

difficult to obtain a clear filtrate, especially if the precipitation was
effected in the cold, and tlie solution contains neither hydrochloric
ac d nor ammonium chloride. It is as good as insoluble in cold
and in hot water. (1 part of the salt requires more than 400,000
parts of water for solution.) It has a great tendency, upon pre-
cipitation, to carry down with it other substances contained in the
solution from which it separates, more particularly barium nitrate,
nitrates and chlorates of the alkali metals, ferric oxide, &c. - Several
of the impurities, such, for instance, as potassium or sodium chlo-
rates, may be removed by igniting the barium sulphate, moistening
with hydrochloric acid, evaporating the latter off and exhausting
the residue with water ; other impurities again, such as potassium
or sodium nitrates, cannot be removed by this treatment. Even
the precipitate obtained from a solution of barium chloride by
means of sulphuric acid in excess contains traces of barium chloride,
which it is impossible to remove, even by washing with boiling
water, but which are dissolved by nitric acid (SIEGLE). Cold dilute
acids dissolve trifling, yet appreciable traces of barium sulphate ;
for instance, 1000 parts of nitric acid of 1 "032 sp. gr. dissolve 0*062
parts (CALVERT), 1000 parts of hydrochloric acid containing 3 per
cent, dissolve 0*06 parts.* Cold concentrated acids dissolve con-
siderably more ; thus, 1000 parts of nitric acid of 1*167 sp. gr. dis-
solve 2 parts (CALVERT). Boiling hydrochloric acid also dissolves
appreciable traces; thus 230 c. c. hydrochloric acid of 1*02 sp. gr.
were found, after a quarter of an hour's boiling with 0*679 grm.
barium sulphate, to have dissolved of it 0*048 grm. Acetic acid
dissolves less barium sulphate than the other acids ; thus, 80 c. c.
acetic acid of 1 *02 sp. gr. were found, after a quarter of an hour's
boiling with *4 grm., to have dissolved only 0*002 grm. (SIEGLE).
Free chlorine considerably increases its solubility (O. L. ERDMANN).
Several salts more particularly interfere with the precipitation of
barium by sulphuric acid. I observed this some time ago with
magnesium chloride, but ammonium nitrate (MITTENTZWEY), alkali
nitrates generally,* and more particularly alkali citrates (SPILLER),
possess this property in a high degree. In the last case the pre-
cipitate appears on the addition of hydrochloric acid. If a fluid
contains metaphosphoric acid, barium cannot be completely pre-
cipitated out of it by means of sulphuric acid ; the resulting pre-
cipitate too contains phosphoric acid (SCHEERER, RUBE). Barium
* Zeitschr. f. anal. C7wm. t ix, 62.



170 FORMS. [71.

sulphate dissolves in considerable quantity in concentrated sulphuric
acid, but separates again on dilution. It is as good as insoluble
in a boiling solution of ammonium sulphate (1 in 4). Barium
sulphate remains quite unaltered in the air, at 100, and even at
a red heat. At a strong white heat it loses sulphuric acid (Bous-
SINGAULT).* On ignition with charcoal, or under the influence of
reducing gases, it is converted comparatively .easily, but as a rule
only partially, into barium sulphide. On ignition with ammonium
chloride, barium sulphate undergoes partial decomposition. It is
not affected, or affected but very slightly, by cold solutions of the
hydrogen carbonates of the alkali metals or of ammonium carbo-
nate ; solutions of normal sodium and potassium carbonates when
cold have only a slight decomposing action upon it ; but when
boiling, and upon repeated .application, they effect at last the
complete decomposition of the salt (H. ROSE). By fusion with
sodium or potassium carbonate, barium sulphate is readily decom-

posed.

COMPOSITION.

^O^ BaO . . . . 153-40 65-70
' Ua< O^ ~SO, .... 80-07 34-30

233-47 100 00

b. Artificially prepared barium carbonate presents the appear-
ance of a white powder. It dissolves in 14137 parts of cold, and in,
15421 parts of boiling water (Expt. No. 17). It dissolves far more
readily in solutions of ammonium chloride or ammonium nitrate;
from these solutions it is, however, precipitated again, though not
completely, by caustic ammonia. In water containing free carbonic
acid, barium carbonate dissolves to an acid carbonate. In water con-
taining ammonia and ammonium carbonate, it is nearly insoluble,
one part requiring about 141000 parts (Expt. No. 18). Its solution
in water has a very faint alkaline reaction. Alkali citrates and
tnotaphosphatea impede the precipitation of barium by ammonium
carbonate. It is unalterable in the air, and at a ivd heat. When
exposed to the strongest heat of a blast-furnace, it slowly yields up
the whole of its carbonic acid ; this expulsion of the carbonic acid
is promoted by the simultaneous action of aqueous vapor. Upon
heating it to redness with charcoal, caustic baryta is formed, with
evolution of carbon monoxide.



* Zeitschr.f. analyt. Chm., v, 344.



72.] BASES OF GROUP II. 171

COMPOSITION.

B _ BaO .... 153-4 77-71
0> -C0 3 .... 44 22-29

197-4 10000

c. Barium silicofluoride forms small, hard, and colorless crys-
tals, or (more generally) a crystalline powder. It dissolves in 3800
parts of cold water ; in hot water it is more readily soluble (Expt.
No. 19). The presence of free hydrochloric acid increases its solu-
bility considerably (Expt. No. 20). Ammonium chloride acts also
in the same way (1 part silicofluoride of barium dissolves in 428
parts of saturated, and 589 parts of dilute solution of ammonium
chloride. J. "W". MALLET). In common alcohol it is almost insoluble.
It is unalterable in the air, and at 100 ; when ignited, it is decom-
posed into silicon fluoride, which escapes, and barium fluoride,
which remains.

COMPOSITION.

BaF 2 . . . 175-5 62-66 Ba . . . 137-4 49-05
SiF 4 . . . 104-6 37-34 Si ... 28-4 10-14

F 6 . . . 114.3 40-81

280-1 100-00 .

280-1 100-00

72.

2. STRONTIUM.
Strontium is weighed either as STRONTIUM SULPHATE, or as

STRONTIUM CARBONATE.

a. Strontium sulphate, artificially prepared, is a white powder,
sometimes dense and crystalline, sometimes loose and bulky. It
dissolves in 6895 parts of cold, and 9638 parts of boiling water
(Expt. No. 21). In water containing sulphuric acid, it is still more
difficultly soluble, requiring from 11000 to 12000 parts (Expt. No.
22). Of cold hydrochloric acid of 8*5 per cent., it requires 474 parts ;
of cold nitric acid of 4-8 per cent., 432 parts ; of cold acetic acid of
15-6 t/er cent, of HC 2 H 3 O 2 , as much as 7843 parts (Expt. No. 23).
It dissolves in solutions of potassium chloride and magnesium chlo-
ricte, in quantity which increases with the concentration, also in solu-
tions of sodium chloride and calcium chloride in greatest quantity



172 * OEMS. L 72-

when the solutions are of medium concentration (A. YIRCK*) ; it
it is precipitated from these solutions by sulphuric acid. Meta-
phosphoric acid (SCHEERER, RUBE), and also alkali citrates, but not
free citric acid (SPILLER), impede the precipitation of strontium by
sulphuric acid. It is as good as insoluble in absolute alcohol, in
common alcohol, and in a boiling solution of ammonium sulphate
(1 in 4). . If does not alter vegetable colors ; and remains unaltered
in the air, and at a red heat. When exposed to a most intense red
heat, it fuses with loss of a small quantity of sulphuric acid (M.
DARMSTADT f); all the sulphuric acid will escape on very strong
ignition continued for a length of time (BOUSSINGAULT J). When
ignited with charcoal, or under the influence of reducing gases, it
is converted into strontium sulphide. Solutions of acid and nor-
mal carbonates of potassium, sodium, and ammonium decompose
strontium sulphate completely at the common temperature, even
when considerable quantities of alkali sulphates are present (II.
ROSE). Boiling promotes the decomposition.

COMPOSITION.
SrO . . . 103-00 50-41



183-67 100-00

b. Strontium carbonate, artificially prepared, is a white, soft,
loose powder. It dissolves, at the common temperature, in 18045
parts of water (Expt. No. 24) : presence of ammonia diminishes
its solubility (Expt. No. 25). It dissolves pretty readily in solu-
tions of ammonium chloride and ammonium nitrate, but is precipi-
tated again from these solutions by ammonia and ammonium car-
bonate, and more completely than barium carbonate under similar
circumstances. Water impregnated with carbonic acid dissolves it
as an acid carbonate. Its reaction is very feebly alkaline. Alkali
citrates and metaphosphates impede the precipitation of strontium
by alkali carbonates. Ignited with access of air it is infusible,
but when exposed to a most intense heat, it fuses and gradually
loses its carbonic acid. On ignition with charcoal, strontium oxide
is formed, with evolution of carbon monoxide gas.

* Zeitschr.f. analyt. Chem., i, 473. ^ lb. t \i, 370. \lb., vir, 244.



73.] BASES OF GROUP II. 173

COMPOSITION.

> O-< _ SrO

-o- -co, . . ,





3. CALCIUM,

Calcium is weighed either as CALCIUM SULPHATE, CALCIUM CAR-
BONATE, or CALCIUM OXIDE ; to convert it into the latter forms, it
is first usually precipitated as calcium oxalate.

a. Artificially prepared anhydrous calcium sulphate is a loose,
white powder. It dissolves, at the common temperature, in 430
parts, at 100, in 460 parts of water (POGGIALE). Presence of
hydrochloric acid, nitric acid, ammonium chloride, sodium sulphate,
or sodium chloride, increases its solubility. It dissolves with com-
parative ease, especially on gently warming, in aqueous solution of
sodium thiosulphate (DIEHL), and also in a boiling solution of
ammonium sulphate (1 in 4). The aqueous solution of calcium
sulphate does not alter vegetable colors. In alcohol of 90 per cent
or stronger it is almost absolutely insoluble. Exposed to the air,
it slowly absorbs water. It remains unaltered at a dull-red heat.
Heated to intense bright redness, it fuses, losing weight consider-
ably from loss of sulphuric acid (AL. MITSCHERLICH *). On long
ignition at a white hsat all the sulphuric acid escapes (BoussiN-
GAULTf). On igniti-.m with charcoal, or under the influence of

I / O

reducing gases, it is converted into calcium sulphide. Solutions
of normal and acid carbonates of the alkali metals decompose cal-
cium sulphate more readily still than strontium sulphate.

COMPOSITION.

so .0^ pa _ CaO . . . 56-10 41-20
1 < O^ "SO, ... 80-07 58-80

136-17 100-00

b. Caldum carbonate artificially produced by the precipitation
of a calciuln salt with ammonium carbonate is at first loose and

*7w./. prakt. Chem., LXXXIII, 480. t Zeitschr.f. analyt. Chem., vn, 324.



174 FORMS. [ 73.

amorphous, but after some time becomes a white, fine, crystalline
powder, which under the microscope has sometimes the form of
calcite, sometimes that of aragonite. It is very slightly soluble
in water. By protracted boiling 1 litre of water dissolves 0*034
grm. according to A. "W. HOFMANN, or 0*036 grm. according to
C. WELTZIEN; so one part requires 28500 parts of water for solu-
tion. The solution has a barely-perceptible alkaline reaction. In
water containing ammonia and ammonium carbonate the crystal-
lized salt dissolves much more sparingly (Expt. No. 56), one
part requiring about 65000 parts ; this solution is not precipitated
by ammonium oxalate. Amorphous calcium carbonate is also
much more insoluble in water containing ammonia than in pure
water (DIVERS*). Presence of ammonium chloride and of ammo-
nium nitrate increases the solubility of calcium carbonate ; but the
salt is precipitated again from these solutions by ammonia and
ammonium carbonate, and more completely than barium carbonate
under similar circumstances. Normal salts of potassium and sodium,
and also normal calcium and magnesium salts (!!UNT), likewise
increase its solubility, the precipitation of calcium by the alkali
carbonates is completely prevented or considerably interfered with
by the presence of alkali citrates (SPILLER) or metaphosphates
(RUBE). Water impregnated with carbonic acid dissolves calcium
carbonate as acid carbonate. Calcium carbonate remains unaltered
in the air at 100, and even at a low red heat ; but upon the appli-
cation of a stronger heat, more particularly with free access of air,
it gradually loses its carbonic acid. By means of a gas blowpipe-
lamp, calcium carbonate (about 0*5 grm.), in an open platinum
crucible, is without difficulty reduced to calcium oxide ; attempts
to effect complete reduction over a spirit lamp with double draught
have, however, failed (Expt. No. 27). It is decomposed far more
readily when ignited with charcoal, giving off its carbonic acid in
the form of carbon monoxide.

COMPOSITION.

.O r CaO . . . . 56-1 56-04
-O- = CO a . . . . 44-0 43-96

100-1 100-00
* Jour. Cfom. Soc. 1870, 362.



78.] BASES OF GROUP II. 175

c. Calcium oxalate, precipitated from hot or concentrated solu-
tions, is a fine white powder consisting of infinitely minute indis-
tinct crystals, and almost absolutely insoluble in water. The salt
has the formula, CaC 2 O 4 -f- H a O. When precipitated from cold,
extremely -dilute solutions, the salt presents a more distinctly crys-
talline appearance, and consists of a mixture of CaC 2 O 4 + H 2 O and
CaC 2 O 4 + 3H a O (SOUCHAY and LENSSEN). Presence of free oxalic
acid and acetic acid slightly increases the solubility of calcium
oxalate. The stronger acids (hydrochloric acid, nitric acid) dissolve
it readily ; from these solutions it is precipitated again unaltered,
by alkalies, and also (provided the excess of acid be not too great)
by alkali oxalates or acetates added in excess. Calcium oxalate
does not dissolve in solutions of potassium chloride, sodium chlo-
ride, ammonium chloride, barium chloride, calcium chloride, and
strontium chloride, even though these solutions be hot and concen
trated ; but, on the other hand, it dissolves readily and in appreci-
able quantities, in hot solutions of the salts belonging to the mag-
nesium group. From these solutions it is reprecipitated by an
excess of alkali oxalate (SOUCHAY and LENSSEN). Alkali citrates
(SPILLER) and metaphosphates (RUBE) impede the precipitation of
lime by alkali oxalates. When treated with solutions of many of
the heavy metals, e.g., with solution of cupric chloride, silver
nitrate, &c., calcium oxalate suffers decomposition, a soluble cal-
cium salt being formed, and an oxalate of the heavy metal, which
separates immediately,- or after some' time (REYNOSO). Calcium
oxalate is unalterable in the air, and at 100. Dried at the latter
temperature, it has invariably the following composition (Expt. No.
28, also SOUCHAY and LENSSEN *).

CO O\ CaO . . . 56-100 38*39

| > Ca 4- H,0 = C 2 3 . . . 72-000 49-28

CO-0/ H a O . . . 18-016 12-33

146-116 100-00

At 205 calcium oxalate loses its water, without undergoing
decomposition; at a somewhat higher temperature, still scarcely'
reaching dull redness, the anhydrous salt is decomposed, without
actual separation of carbon, into carbon monoxide and calcium
carbonate. T'he powder, which was previously of snowy whiteness,

* Annal. d. Chem. und Pharm., c, 322.



176 FORMS. [ 74.

transiently assumes a gray color in the course of this process, even
though the oxalate be perfectly pure. Upon continued applica-
tion of heat this gray color disappears again. If the calcium
oxalate is heated in small, coherent fragments, such as are obtained
upon drying the precipitated salt on a filter, the commencement
and progress of the decomposition can be readily traced by this
transient appearance of gray. If the process of heating be con-
ducted properly, the residue will not contain a trace of calcium
oxide. Hydrated calcium oxalate exposed suddenly to a dull-red
heat, is decomposed with considerable separation of carbon. By
ignition over the gas blowpipe calcium oxalate is converted into
calcium oxide.

d. Calcium oxide obtained by continued strong ignition of the
oxalate or carbonate appears as a white, infusible powder, unalter-
able by ignition. By standing in the air it attracts water and car-
bonic acid, but not rapidly enough to interfere with accurate
weighing (Expt. No. 20). By treatment with a little water
calcium hydroxide is formed with evolution of much heat; on
igniting again the w^ater of hydration is readily and completely
removed. Pure calcium oxide dissolves in dilute hydrochloric
acid with evolution of heat, but without effervescence.

74.
4. MAGNESIUM.

Magnesium is weighed as MAGNESIUM SULPHATE, MAGNESIUM
PYROPIIOSPHATE, or MAGNESIUM OXIDE. To convert it into the pyro-
phosphate, it is precipitated as NORMAL AMMONIUM MAGNESIUM PHOS-
PHATE.

a. Anhydrous magnesium sulphate presents the appearance of
a white, opaque mass. It dissolves readily in water. It is nearly
altogether insoluble in absolute alcohol, but it is somewhat soluble
in common alcohol.

It does not alter vegetable colors. Exposed to the air it absorbs
water rapidly. At a moderate red heat, it remains unaltered ; but
when heated to intense redness, it undergoes partial decomposition,
losing part of its acid, after which it is no longer perfectly soluble



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