C. Remigius Fresenius.

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viously a little blackened by light, is easily diffused in the fluid,
and is but tardily deposited. This depends upon the mercuric salt
being taken up ; if the silver salt is washed the mercuric salt will
be removed. Mercuric nitrate acts in a similar way, but a certain
quantity of silver passes at the same time into solution. Silver
chloride is much more difficultly dissolved by mercuric acetate than
by mercuric nitrate ; therefore, if you have a solution of mercuric
nitrate containing silver chloride, if the mercuric salt is not present
in enormous quantity, the silver may be almost absolutely thrown
down by addition of an alkali acetate (H. DEBRAY*). Solutions
of potash and soda decompose silver chloride, even at the ordinary
temperature, more readily on boiling ; silver oxide separates, and
chloride of the alkali metal is formed. Solution of sodium or
potassium carbonate decomposes silver chloride only very imper-
fectly even on boiling ; after long boiling decided traces of chlorine
are found in the filtrate. Silver chloride dissolves readily in aque-
ous ammonia, and also in the solution of potassium cyanide and
that of sodium thiosulphate. According to WALLACE and LAMONif
1 part of silver chloride dissolves in/1 2' 88 parts of strong aqueous
ammonia of 0*89 sp. gr. Under the influence of light silver chlo-
ride soon changes to violet, finally black, losing chlorine, and pass-
ing partly into Ag a Cl. The change is quite superficial, but the
loss of weight resulting is very appreciable (MULDER, op. cit., p.
21). If silver chloride that has become violet or black from the
influence of light be treated with aqueous ammonia, it dissolves
with separation of a very small quantity of metallic silver, Ag 2 Cl
gives AgCl and Ag (WITTSTELN). On long contact (say for 24

* ZeitscJir.f. Chem., xni, 348. f Chem. Gaz. 1859, 137. .



200 FORMS. [ 82.

hours) with water, especially at 75, silver chloride, although
removed from the influence of light, becomes gray, and, it appears,
decomposed ; the precipitate is found to contain silver oxide, and
the water hydrochloric acid (MULDER). On digestion with excess
of solution of potassium bromide or iodide, silver chloride is com-
pletely transformed into silver bromide or iodide, as the case may
be (FIELD*). On drying, silver chloride becomes pulverulent ; on
heating it turns yellow ; at 260 it fuses to a transparent yellow
fluid ; at a very high heat it volatilizes without decomposition.
On cooling after fusion it presents a colorless or pale yellowish
mass. Fused in chlorine gas, it absorbs some chlorine ; on cooling,
this escapes, but not completely. If it is to be completely expelled,
and, in very delicate experiments this must be done, we pass car-
bon dioxide before allowing to cool (&TAS f). Ignition with char-
coal fails to effect its reduction to the metallic state ; but it may
be readily so reduced in a current of hydrogen, carburetted hydro-
gen, or carbon monoxide.

COMPOSITION.

Ag'. 107-92 75-27

Cl 35-45 24-73



143-37 100-00

c. Silver sulphide, prepared in the wet way, is a black precipi-
tate, insoluble in water, dilute acids, alkalies, and alkali sulphides.
It is unalterable in the air ; after being allowed to subside, it is
filtered and washed with ease, and may be dried at 100 without
deco.m posit ion. It dissolves in concentrated nitric acid, with
separation of sulphur. Solution of potassium cyanide dissolves
it with difficulty, if it has been precipitated from a very dilute
solution with less difficulty; the quantity of potassium cyanide,
too, has great influence on the effect. For instance, if silver cya-
nide, is dissolved in a bare sufficiency of potassium cyan i< le and
hydrogen sulphide, or ammonium sulphide is added, silver sulphide
is thrown down ; if, on the other hand, a large excess of potassium

* Quart. Journ. Chem. 8oc., x, 234; Journ. f. prakt. Chem., LXXIII, 404.

f Recherches sur les rapports reciproques des poids atomiques, p. 37. Brux-
elles, 1860. The loss of weight which about 100 grra. silver chloride suffered,
by the expulsion of the absorbed chlorine, was from 7 to 13 ingrm.



83.] BASES OF GROUP V. 201

cyanide is present, no precipitate will be produced. If silver
sulphide is dissolved in a concentrated solution of potassium cya-
nide, it will generally separate at once on addition of much water
(BECHAMP*). Ignited in a current of hydrogen, it passes readily
and completely into the metallic state (H. ROSE).

COMPOSITION.

Ag a ..... 215-84 87-06

S 32-07 12-94:



24:7-91 100-00

d. Silver cyanide, recently thrown down, forms a white curdy
precipitate insoluble in water and dilute nitric acid, soluble in
potassium cyanide arid also in ammonia ; exposure to light fails
to impart the slightest tinge of black to it ; it may be dried at 100
without decomposition. Upon ignition, it is decomposed into
cyanogen, which escapes, and metallic silver, which remains, mixed
with a little paracyanide of silver. By boiling with a mixture of
equal parts of sulphuric acid and water, it is, according to GLASS-
FORD and NAPIER, dissolved to silver sulphate, with liberation of
hydrocyanic acid.

COMPOSITION.

AS 107-92 80.56

CN 26-04: 19-44



133-96 100-00

83.



2.

Lead is weighed as OXIDE, SULPHATE, CHROMATE, CHLORIDE, and
SULPHIDE. Besides these compounds, we have also to study the

CARBONATE and the OXALATE.

a. Normal lead carbonate forms a heavy, white, pulverulent
precipitate. It is but very slightly soluble in perfectly pure (boiled)
water, one part requiring 50550 parts (see Expt. No. 42, a) ; but
it dissolves somewhat more readily in water containing ammonia
and ammonium salts (comp. Expt. No. 42, <b and c), and also in

* Journ. f. prakt. Chem., LX, 64.



202 FORMS. f 3.

water impregnated with carbonic acid. It loses its carbonic acid
when ignited.

I. Lead oxalate is a white powder, very sparingly soluble in
water. The presence of ammonium salts slightly increases its solu-
bility (Expt. No. 43). When heated in close vessels, it leaves lead
suboxide ; but when heated with access of air, the yellow oxide.

c. Lead oxide, produced by igniting the carbonate or oxalate,
is a lemon-yellow powder, inclining sometimes to a reddish-yellow,
or to a pale yellow. When this yellow lead oxide is heated, it
assumes a brownish-red color, without the slightest variation of
weight. It fuses at an intense red heat. Ignition with charcoal
reduces it. When exposed to a white heat, it rises in vapor. Placed
upon moist red litmus paper, it changes the color to blue. When
exposed to the air, it slowly absorbs carbonic acid. Mixed with
ammonium chloride and ignited, it is converted into lead chloride.
Lead oxide in a state of fusion readily dissolves silicic acid and the
earthy bases with which the latter may be combined.



COMPOSITION.



Pb 206-92 92-82

O. 16-00 7-18



222-92 100-00

d. Lead sulphate is a heavy white powder. It dissolves, at
the common temperature, in 22800 parts of pure water (Expt. No.
44*) ; it is less soluble in water containing sulphuric acid (1 part
requiring 365.00 parts Expt. No. 45) ; it is far more readily solu-
ble in water containing ammonium salts ; from this solution it may
be precipitated again by adding sulphuric acid in excess (Expt. No.
46). It is almost entirely insoluble in common alcohol. Of the
ammonium salts, the nitrate, acetate, and tartrate are more espe-
cially suited to serve as solvents for lead sulphate : the two latter
salts are made strongly alkaline by addition of ammonia, previous
to use (WACKENRODER). Lead sulphate dissolves in concentrated
hydrochloric acid, upon heating. In nitric acid it dissolves the
more readily, the more concentrated and hotter the acid ; water
fails to precipitate it from its solution in nitric acid ; but the addi-
tion of a copious amount of dilute sulphuric acid causes its preoipi-

* According to G. F. RODWKLL 1 part dissolves in 31696 parts water at 15
(C/iem. New*, 1666, 00; Zeittcfir.f. anuyt. Chern., v, 403.)



83.] BASES OF GROUP v. 203

tation from this solution. The more nitric acid the solution con-
tains, the Inore sulphuric acid is required. It dissolves sparingly
in concentrated sulphuric acid, and the dissolved portion precipi-
tates again upon diluting with water (more completely upon addi-
tion of alcohol). A moderately concentrated solution of sodium
thiosulphate dissolves lead sulphate completely even if cold, more
readily if warmed. On boiling, the solution becomes black, from
separation of a small quantity of lead sulphide (J. LOWE*). The
solutions of alkali carbonates and alkali hydrogen carbonates con-
vert lead sulphate, even at the common temperature, completely
into lead carbonate. The solutions of the normal alkali carbonates,
but not those of the alkali hydrogen carbonates, dissolve some lead
oxide in this process (II. RosEf-). Lead sulphate dissolves readily
in hot solutions of potassa or soda. It is unalterable in the air, and
at a gentle red heat ; when exposed to a full red heat, it fuses with-
out decomposition (Expt. No. 47), provided always reducing gases
be completely excluded for, if this is not the case, the weight will
continually diminish, owing to reduction to sulphide (EKDMANN^:).
At a white heat the whole of the sulphuric acLl gradually escapes
(BoussiNGAULT ). When it is ignited with charcoal, lead sulphide
is formed at first ; if the heat be raised, this sulphide reacts on
undecomposed sulphate, metallic lead and sulphur dioxide being
produced. Fusion with potassium cyanide reduces the whole of
the lead to the metallic state. Lead sulphate mixed with sulphur
and exposed to intense ignition in a current of hydrogen yields
the sulphide, but loss can scarcely be avoided (compare f).

COMPOSITION.

n O pl _PbO . . . / 222-92 73-57
'* J *<O > "SO,. . . ./. 80-07 26-43

302-99 100-00

e. Lead chloride obtained by precipitation is a white crystalline
powder. It separates in needles from a hot solution containing a
certain quantity of hydrochloric acid; occasionally it presents
wedge-shaped crystals, or when separated from a strong hydro-
chloric solution, hexagonal tables. Atl7*7 water dissolves 0-946

* Journ.f. prakt. Chem., LXXIV, 348. \Pogg. Annal., xcv, 426.

\ Journ.f. prakt. Chem., LXII, 381. Zeitschr.f. anatyt. Chem., YII, 344..



204 FORMS. [ 83.

per cent. ; a fluid containing 15 per cent, of hydrochloric acid of
1-162 sp. gr. dissolves 0*09; a fluid containing 20 per cent, acid
dissolves 0*111 per cent. ; a fluid containing 80 per cent, acid dis-
solves 1 "498 per cent. Pure hydrochloric acid of the above strength
dissolves 2 -9 per cent. (J. CARTER BELL*). Lead chloride is
less soluble in water containing nitric acid than in water (1 part
requires 1636 parts, BISCHOF). It is extremely sparingly soluble
in alcohol of 70 to 80 per cent., and altogether insoluble in absolute
alcohol. It is unalterable in the air. It fuses at a temperature
below red heat, without loss of weight. When exposed to a higher
temperature, with access of air, it volatilizes slowly, being partially
decomposed : chlorine gas escapes, and a mixture of lead oxide and
chloride remains.

COMPOSITION.

Pb ...... 206 92 74-47

01, 70-90 25-53



277-82 100-00

f. Lead sulphide, prepared in the wet way, is a black precipi-
tate, insoluble in water, dilute acids, alkalies, and alkali sulphides.
In precipitating it from a solution containing free hydrochloric
acid, it is necessary to dilute plentifully, otherwise the precipitation
will be incomplete. Even if a fluid only contain 2*5 per cent. HC1,
the whole of the lead will not be precipitated (M. MARTIN f). It
is unalterable in the air; it cannot be dried at 100 without
decomposition. According to II. ROSE it increases perceptibly in
weight by oxidation ; in the case of long-protracted drying even
becoming a few per-cents heavier.^ I have confirmed his state-
ment (see Expt. No. 48). If lead sulphide mixed with sulphur is
heated gently in a current of hydrogen, so that the lower quarter
of the crucible is red hot, lead sulphide is left without loss of
weight. By continuing a gentle heat the weight gradually dimin-
ishes; by strong ignition the loss is rapid. This loss is partly
owing to volatilization of lead sulphide, but mainly to escape of
sulphur in the form of hydrogen sulphide and formation of Pb,S,
or even of lead (A. SOUCHAY ). It dissolves in concentrated hot

* Journ.f. prakt. Chem., cv, 188; Jour. Chem. Soc. (2), vi, 355.
\Journ.f. prakt. CJiem., i/xvu, 374. J Pogg. Annul., xci, 110, and ex, 134.
|2MfMAf. /. analyt. Chem., rv, 63.



84.] .BASES OF GROUP V. 205

hydrochloric acid, with evolution of hydrogen sulphide. In mod-
erately strong nitric acid lead sulphide dissolves, upon the applica-
tion of heat, with separation of sulphur; if the acid is rather con-
centrated, a small portion of lead sulphate is also formed. Fuming
nitric acid acts energetically upon lead sulphide, and converts it
into sulphate without separation of sulphur.

COMPOSITION.

Pb 206-92 86-38

S . 32-07 13-42



238-99 lOO'OO

g. For the composition and properties of lead chromate, see
Chromic acid, 93.

84.

3. MERCURY IN MERCUROUS COMPOUNDS ; and 4. MERCURY IN
MERCURIC COMPOUNDS.

Mercury is weighed either in the METALLIC STATE, as MERCUROUS
CHLORIDE, or as SULPHIDE, or occasionally as MERCURIC OXIDE.

a. Metallic mercury is liquid at the common temperature ; it
has a tin- white color. When pure, it presents a perfectly bright
surface. It is quite unalterable in the air at the common tempera-
ture. It boils at 360. It evaporates, but very slowly, at the
ordinary temperature of summer. Upon long-continued boiling
with water, a small portion of mercury volatilizes, and traces escape
along with the aqueous vapor, whilst a very minute proportion
remains suspended (not dissolved) /ill the water (comp. Expt. ~No.
49). This suspended portion of mercury subsides completely after
long standing. When mercury is precipitated from a fluid, in a
very minutely divided state, the small globules will readily unite
to a large one if the mercury be perfectly pure ; but even the
slightest trace of extraneous matter, such as fat, etc., adhering to
the mercury will prevent the union of the globules. Mercury
does not dissolve in hydrochloric acid, even in concentrated ; it is
barely soluble in dilute cold sulphuric acid, but dissolves readily in
nitric acid.

&. Mercurous chloride, prepared in the wet way, is a heavy



206 FORMS. [ 84.

white powder. It is almost absolutely insoluble in cold water ; in
boiling water it is gradually decomposed, the water taking up
chlorine and mercury ; upon continued boiling, the residue acquires
a gray color. Highly dilute hydrochloric acid fails to dissolve it
at the common temperature, but dissolves it slowly at a higher
temperature; upon ebullition, with access of air, the whole of the
mercurous chloride is gradually dissolved ; the solution contains mer-
curic chloride (Hg a Cl a + 2HC1 + O=2IIgCl a + H 2 O). When acted
upon by boiling concentrated hydrochloric acid, it is rather speedily
decomposed into mercury, which remains undissolved, and mer-
curic chloride, which dissolves. Boiling nitric acid dissolves it to
mercuric chloride and nitrate. Chlorine water and nitrohydrochlo-
ric acid dissolve it to mercuric chloride, even in the cold. Solutions
of ammonium chloride, sodium chloride, and potassium chloride,
decompose it into metallic mercury and mercuric chloride, which
latter dissolves ; in the cold, this decomposition is but slight ; heat
promotes the action. It is soluble in hot solution of mercurous
nitrate, and still more in that of mercuric nitrate; on cooling it
crystallizes out almost completely (DEBRAY*). It does not affect
vegetable colors ; it is unalterable in the air, arid may be dried at
100, without loss of weight ; when exposed to a higher degree of
heat, though still below redness, it volatilizes completely, without
previous fusion.

COMPOSITION.

Hg, 400-0 84-94

Cl a . TO- 9 15-06



470-9 100-00

c. Mercuric sulphide, prepared in the wet way, is a black pow-
der, insoluble in water. Dilute hydrochloric acid and dilute nitric
acid fail to dissolve it, hot concentrated nitric acid scarcely attacks
it, boiling hydrochloric acid has no action on it. By prolonged
heating with red fuming nitric acid it is finally converted into a
white compound, 2lIgS + IIg(NO 3 ) a , which is insuluMe, or barely
soluble, in nitric acid. It dissolves readily in nitrohydrochloric
acid. From a solution of mercuric chloride containing much free

hydrochloric acid, the whole of the metal cannot be precipitated as
^

* Compt. Rend., LXX, 995.



84.] BASES OF GROUP v. 207

sulphide by means of hydrogen sulphide, until the solution is prop-
erly diluted. Should such a solution be very concentrated, mer-
curous chloride and sulphur are precipitated (M. MAKTIN*). Solu-
tion of potassa, even boiling, fails to dissolve it. It dissolves in
potassium sulphide, but readily only in presence of free alkali. It
is insoluble in potassium hydrosulphide and in the corresponding
sodium compound, and is therefore precipitated from its solution
in potassium or sodium sulphide by hydrogen sulphide or by
ammonium hydrosulphide (C. BARFOEDf). Small but distinctly
perceptible traces dissolve on cold digestion with yellowish or yel-
low ammonium sulphide, but after hot digestion it is scarcely possi-
ble to detect any traces in solution. Potassium cyanide and sodium
sulphite do not dissolve it. On account of the solubility of mer-
curic sulphide in potassium sulphide, it is impossible to precipitate
mercury by means of ammonium sulphide completely from solutions
containing potassium or sodium hydroxides or carbonates. Such
solutions may occur, for instance, when a solution of mercuric
chloride contains much potassium chloride, or sodium chloride, for,
in this case, no mercuric oxide would be precipitated on the addi-
tion of potassa or soda (H. ROSE). In the air it is unalterable,
even in the moist state, and at 100. When exposed to a higher
temperature, it sublimes completely and unaltered.

COMPOSITION.

Hg 200-00 86 18

S 32-07 13-82



232-07 100-00

d. Mercuric oxide, prepared in the dry way, is a crystalline
brick-colored powder, which, when exposed to the action of heat,
changes to the color of cinnabar, corid subsequently to a violet-black
tint. It bears a tolerably strong heat without decomposition ; but
when heated to incipient redness, it is decomposed into mercury
and oxygen ; perfectly pure mercuric oxide leaves no residue upon
ignition. Its escaping fumes also should not redden litmus-paper.
Water takes up a trace of mercuric oxide, acquiring thereby a very
weak alkaline reaction. Hydrochloric or nitric acid dissolves it
readily.

*Joun. f. prakt. Chem., LXVII, 376. f Zeitschr. f. analyt. Chem., iv, 436.

} lb., in, 140. Poffff. AnnaL, ex, 141. '



FORMS. [ 85.



COMPOSITION.



Hg 200 92-59

O 16 7-41



216 100-00



5. COPPER.

Copper is usually weighed in the METALLIC STATE, or in the
form of CUPRIC OXIDE, or of CUPROUS SULPHIDE. Besides these
forms, we have to examine CUPRIC SULPHIDE, CUPROUS OXIDE, and

CUPROUS SULPHOCYANATE.

a. Copper, in the pure state, is a metal of a peculiar well-
known color. It fuses only at a white heat. Exposure to dry air,
or to moist air, free from carbon dioxide, leaves the fused metal
unaltered ; but upon exposure to moist air impregnated with
carbon dioxide, it becomes gradually tarnished and coated with a
film, first of a blackish-gray, finally of a bluish-green color. Pre-
cipitated finely divided copper, in contact with water and air,
oxidizes far more quickly, especially at .an elevated temperature.
On igniting copper in the air, it oxidizes superficially to a varying
mixture of cuprous and cupric oxide. In hydrochloric acid, in the
cold, it does not dissolve if air be excluded ; in the heat it dissolves
but slightly if the metal is in a compact state. Finely divided
copper on the contrary dissolves slowly when heated with strong
hydrochloric acid, hydrogen being evolved and cuprous chloride
being formed (WELTZIEN*). Copper dissolves readily in nitric
acid. In ammonia it dissolves slowly if free access is given to the
air ; but it remains insoluble if the air is excluded. Metallic
copper brought into contact in a closed vessel with solution of
cupric chloride in hydrochloric acid, reduces the cupric to cuprous
chloride, an atom of metal being dissolved for every molecule of
chloride.

b. Cupric oxide. If a dilute, cold, aqueous solution of a cupric
salt is mixed witli solution of potassa or soda in excess, a light blue
precipitate of cupric hydroxide, Cu(OII),, is formed, which it is
found difficult to wash. If the precipitate be left in the fluid

* Ann. d. Chem. u. Pharm., cxxxvi, 100.



85.] BASES OF GROUP V. 209

from which it has been precipitated, it will, even at a summer
heat, gradually change to brownish-black, passing, with separation
of water, into 6CuO + H 2 O (SOUCHAY). This transformation is
immediate upon heating the fluid nearly to boiling. The fluid
filtered off from the black precipitate is free from copper. It
follows from this that the black precipitate is insoluble in dilute
potassa. Concentrated potassa or soda on the "contrary dissolves the
hydroxide, and on long warming even the black oxide (O. Low*).
The resulting blue solutions remain clear on boiling, even if mixed
with some water ; but if boiled after being much diluted the whole
of the copper will separate as black oxide. If a solution of a
cupric salt contains non-volatile organic substances, the addition of
alkali in excess will, even upon boiling, fail to precipitate the
whole of the copper. The hydrated cupric oxide, 6CuO -|- H a O,
precipitated with potassa or soda from hot dilute solutions obsti -
nately retains a portion of the precipitant ; it may, however, be
completely freed from this by washing with boiling water. The
precipitated oxide after ignition, or the oxide prepared by decom-
posing cupric carbonate or nitrate by heat, is a brownish-black, or
black powder, the weight of which remains unaltered even upon
strong ignition over the gas- or spirit-lamp, provided all reducing
gases be excluded (Expt. No. 50). If cupric oxide is exposed to a
heat approaching the fusing point of metallic copper, it fuses,
yields oxygen, and becomes Cu 6 O, (FAVRE and MAUMENE). It is
very readily reduced by ignition with charcoal, or under the in-
fluence of reducing gases ; heated in the air for a long time, the
reduced metallic copper re-oxidizes. Mixed with sulphur and
ignited in a current of hydrogen, towards the end strongly, cupric
oxide passes into cuprous sulphide (Cn 2 S II. ROSE). Cupric oxide,
in contact with the atmosphere, absorbs water ; less rapidly after
being strongly ignited (Expt. No. 51). It is nearly insoluble in
water; but it dissolves readily in hydrochloric acid, nitric acid,
&c. ; less readily in ammonia. It does not affect vegetable colors.

COMPOSITION.

Cu . . . . 63-6 80-00

O . . . . 16-0 20-00

79-6 100-00

* Zeitsc7ir. f. analyt. Chem. , ix, 463.



210 FOKMS. [ 85.

c. Cupric sulphide, prepared in the wet way, is a brownish-
black, or black precipitate, almost absolutely insoluble in water.*
When exposed to the air in a moist state, it acquires a greenish
tint and the property of reddening litmus paper, cupric sulphate
being formed. Hence the sulphide must be washed with water
containing hydrogen sulphide. It dissolves readily in boiling
nitric acid, with separation of sulphur. Hydrochloric acid dis-
solves it with difficulty. This is the reason why hydrogen sulphide
precipitates copper entirely from solutions which contain even a
very large amount of free hydrochloric acid (GnuNDMANNf). Only
when we dissolve a copper salt directly in pure hydrochloric acid
of I'l sp. gr. does any copper remain unprecipitated (M. MARTINA).
It does not dissolve in solutions of potassa and of potassium
sulphide, particularly if these solutions be boiling; it dissolves
perceptibly in colorless, and much more readily in hot yellow
ammonium sulphide. Potassium cyanide dissolves the freshly pre-
cipitated sulphide readily and completely. Upon intense ignition
in a current of hydrogen it is converted into pure Cu a S.

d. If the blue solution which is obtained upon adding to solu-
tion of copper tartaric acid and then soda in excess, is mixed with
solution of grape sugar or sugar of milk, and heat applied, an
orange-yellow precipitate of cuprous hydroxide is formed, which



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