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in water. By means of a gas blowpipe it as tolerably easy to expel

74.] BASES OF G&OUF II. 177

the whole of the sulphuric acid from small quantities of magne-
sium sulphate (Expt. No. 30). Ignited with ammonium chloride
magnesium sulphate is not decomposed.


ffO 40-30

120-37 100-00

b. Ammonium magnesium phosphate is a white crystalline
powder. It dissolves, at the common temperature, in 15293 parts
of cold water (Expt. No. 31). In water containing ammonia, it is
much more insoluble. 1000 grm. of a mixture of 3 parts water
and 1 part ammonia solution, dissolved only a quantity correspond-
ing to 0-004 grm. pyrophosphate (KISSEL *) ; the salt was consid-
erably more soluble when ammonium chloride was also present ;
thus, in one of KISSEL'S experiments a quantity corresponding to
O'Oll grm. pyrophosphate was dissolved by 1000 grm. fluid con-
taining 18 grm. ammonium chloride. Presence of excess of mag-
nesium sulphate diminishes the solubility in dilute ammonia, even
in the presence of ammonium chloride, to such an extent that the
quantity dissolved by 1000 grm. fluid cannot be estimated (KISSEL);
the precipitate, under these circumstances, is liable, especially in
the absence of much ammonium chloride, and when a large excess
of magnesium sulphate is present, to contain some magnesium
hydroxide or basic magnesium sulphate (KuBEL,f. KISSEL).' Sodium
phosphate also diminishes (to about the same extent as magnesium
sulphate) the solubility of the salt in water containing ammonium
chloride and ammonia (W. HEINTZ j). It dissolves readily in acids,
even in acetic acid. Its composition is expressed by the formula
NH 4 MgPO 4 + 6H 2 O. 5 mol. of water escape at 100, the remain-
ing water together" with ammonia are expelled, at a red heat, leav-
ing Mg 2 P 2 O 7 . On the application of a stronger heat the mass
passes through a state of incandescence, if the salt were pure ; the
weight of the residue is not affected. The incandescence may not
take place at all jh the presence of small quantities of calcium salts,

* Ztitschr. j . analyt. CJiem., vnr, 173. f lb. t vui, 125. \ lb., ix, 16.

178 FORMS. [ 74.

of other magnesium salts, or of silicic acid. It is occasioned not
by the passage of the orthophosphate into the pyrophosphate, but
by the passage from the crystalline to the amorphous condi-
tion (O. POPP *). If ammonium magnesium phosphate is dissolved
in dilute hydrochloric or nitric acid and ammonia be then added
to the solution, the salt is reprecipitated completely, or more cor-
rectly, only so much remains in solution as corresponds to its
ordinary solubility in water containing ammonia and ammonium

c. Magnesium pyrophosphate presents the appearance of a
white mass, often slightly inclining to gray. It is barely soluble in
water, but readily so in hydrochloric acid, and in nitric acid. It
remains unaltered in the air, and at a red heat ; at a very intense
heat it fuses unaltered. Exposed at a white heat to the action of
hydrogen, Mg 3 (PO 4 ) 3 is formed, while PH 3 , P and P 2 O 3 escape.
3Mg,P 9 O 7 = 2Mg s (PO 4 ), + P,O 6 (STRuvEf). It leaves the color
of moist turmeric-, and of reddened litmus-paper unchanged. If
we dissolve it in hydrochloric or nitric acid, add water to the solu-
tion, boil for some time, and then precipitate with ammonia in
excess, we obtain a precipitate of ammonium magnesium phosphate
which, after ignition, affords less Mg a P a O 7 , than was originally
employed. WEBER J gives the loss as from 1*3 to 2*3 per cent.
My experiments (Expt. ISTo. 32) confirm this, and show under
what conditions the loss is smallest. By long-continued
fusion with mixed potassium and sodium carbonates, magnesium
pyrophosphate is completely decomposed, the pyrophosphoric
acid being re-converted into orthophosphoric. If, therefore,
we treat the fused mass with hydrochloric acid, and then
add water and ammonia, we re-obtain on igniting the precipitate
the whole quantity of the salt used. If the solution of magnesium
pyrophosphate in nitric acid is evaporated to dryness a white resi-
due is left ; if this is heated more strongly hyponitric acid is liber-
ated, and the residue turns the color of cinnamon ; on cooling it is
yellowish-white. By heating still more strongly to incipient red-
ness, rapid decomposition sets in, more hyponitric acid is evolved,
and pure-white magnesium pyrophosphate is left. Unless the heat
is applied with care the evolution of gas may be so rapid as to
carry away particles of the substance (E. LUCK).

* ZeiUchr. f. analyt. Chem. , xiu, 305. f Jour. f. prakl. Chen,., IAXIX, 349^

* Ann., LXXIIJ, 146.




O ^

222-6 100-00

d. Magnesium oxide is a white, light, loose powder. It dis-
solves in 55,368 parts of cold, and in the same proportion of boil-
ing water (Expt. No. 33). Its aqueous solution has a very slightly
alkaline reaction. It dissolves in hydrochloric and in other acids,
without evolution of gas. Magnesium oxide dissolves readily and
in quantity, in solutions of normal ammonium salts, and also in
solutions of potassium chloride and sodium chloride (Expt. No.
34) and potassium sulphate and sodium sulphate (R. WARINGTON,
Jr.) it is more soluble than in water. Exposed to the air, it slowly
absorbs carbonic acid and water. Magnesium oxide is highly infusi-
ble, remaining unaltered at a strong red heat, and fusing super-
ficially only at the very highest temperature.


Mg 24-3 60-30

O 16-0 39-70

40-3 . 100 00


Aluminium is usually precipitated as HYDROXIDE, occasionally as


a. Aluminium hydroxide, recently precipitated from a solu-
tion of an aluminium salt by an alkali is translucent, and when
dried at 100 has the formula, A1 2 (OH) 6 . The precipitate inva-
riably retains a minute proportion of the acid with which the
aluminium was previously combined, as well as of the alkali which
has served as the precipitant ; it is freed with difficulty from these
admixtures by repeated washing. It is insoluble in pure water ;

180 FOKMS. [ 75.

but it readily dissolves in soda, potassa, and ethylamine (SONM.N-
SCHEIN) ; it is sparingly soluble in ammonia, and insoluble in am-
monium carbonate; presence of ammonium salts greatly diminishes
its solubility in ammonia (Expt. No. 35). The correctness of this
statement of mine in the first edition of the present work, has
been amply confirmed since by MALAGUTI and DUROCHER;* and
also by experiments made by my former assistant, Mr. J. FUCIIS.
The former chemists state also that, when a solution of aluminium
is precipitated with ammonium sulphide, the fluid may be filtered
off five minutes after, without a trace of aluminium in it. Fr< -us
did not find this to be the case (Expt. No. 36). Aluminium
hydroxide, recently precipitated, dissolves readily in hydrochloric
or nitric acid; but after filtration, or after having remained for
some time in the fluid from which it has been precipitated, it
does not dissolve in these acids without considerable difficulty,
and long digestion. Aluminium hydroxide shrinks considerably
on drying, and then presents the appearance of a hard, translucent,
yellowish, or of a white, earthy mass. "When ignited, it loses
water, and this loss is frequently attended with slight decrepitation,
arid invariably with considerable diminution of bulk. Aluminium
hydroxide precipitated from a solution of aluminium in potassa or
soda by ammonium chloride is milk-white, denser, easier to wash,
and much less soluble in ammonia than the variety above de-
scribed. When dried at 100, it has the formula A1 2 O S + (II a O) a
(J. LowEf).

b. Aluminium oxide or alumina, prepared by heating the
hydroxide to a moderate degree of redness, is a loose and soft mass ;
but upon the application of a very intense degree of heat, it con-
cretes into small, hard lumps. At the most intense white heat, it
fuses to a clear glass. Ignited alumina is dissolved by dilute acids
with very great difficulty ; in fuming hydrochloric acid, it dis-
solves upon long-continued digestion in a warm place, slowly, but
completely. It dissolves tolerably easily and quickly by first heat-
ing with a mixture of 8 parts of concentrated sulphuric acid nnd
3 parts of water, and then adding water (A. MITSCHERLICH:}:).
Ignition in a current of hydrogen gas leaves it unaltered. By
fusion with potassium disulphate, it is rendered soluble in water.
Upon igniting alumina with ammonium chloride, aluminium

*Ann. de Chim. et de Phys., 8 Ser. 17, 421.

f Zeittchr. /. analyt, Chem., iv, 350. \ Jour. f. prakt. CJiem., LXXXI, 110.


chloride escapes ; but the process fails to effect complete volatili-
zation "of the alumina (II. ROSE). When alumina is fused at a
very high temperature, with ten times its quantity of sodium car-
bonate, sodium alnminate is formed, which is soluble in water
(R. RICIITER). Placed upon moist red litmus-paper, pure alumina
does not change the color to blue.


A1 2 54-2 53-03

O 3 48-0 46-97

102-2 100-00

c. If to the solution of a salt of aluminium, sodium carbonate
or ammonium carbonate be added, till the resulting precipitate only
just redissolves on stirring, and then sodium acetate or ammonium
acetate poured in in abundance and the mixture boiled some time,
the aluminium is precipitated almost completely as basic acetate in
the form of translucent flocks, so that if the filtrate be boiled with
ammonium chjoride and ammonia only unweighable traces of
aluminium hydroxide separate. If the quantity of sodium acetate
employed be too small, the precipitate appears more granular, the
filtrate would then contain a larger amount of aluminium. The
precipitate cannot be very conveniently filtered and washed. In
washing it is best to use boiling water, containing a little sodium
acetate or ammonium acetate. The precipitate is readily soluble
in hydrochloric acid.

d. If, instead of the acetates mentioned in <?, the corresponding
formates be used, a flocculent voluminous precipitate of basic
aluminium formate is obtained, which may be very readily washed



Chromium is usually precipitated as CHROMIC HYDROXIDE, and
always weighed as chromic oxide.

a. Chromic hydroxide recently precipitated from a green solu-
tion, is greenish-gray, gelatinous, insoluble in water : it dissolves
readily, in the cold, in solutions of potassa or soda, to a dark green
fluid ; it dissolves also in the cold, but rather sparingly, in solution

* Chem. CentralU. 1861, 3.

182 FORMS. [ 77.

of ammonia, to a light violet red fluid. In acids it dissolves
readily, with a dark green color. Presence of ammonium chloride
exercises no influence upon the solubility of the hydroxide in
ammonia. Boiling effects the complete separation of the hydroxide
from its solutions in potassa, or ammonia (Expt. No. 37). The
dried hydroxide is a greenish-blue powder ; it is converted into
oxide with loss of water at a gentle red heat.

b. Chromic oxide, produced by heating the hydroxide to dull
redness, is a dark green powder ; upon the application of a higher
degree of heat, it assumes a lighter tint, but suffers no diminution
of weight ; the transition from the darker to the lighter tint is
marked by a vivid incandescence of the powder. The feebly
ignited oxide is difficultly soluble in hydrochloric acid, and the
strongly ignited oxide is altogether insoluble in that acid. It
remains unaltered when ignited with ammonium chloride, or in
a current of hydrogen. By fusion with sodium carbonate and
potassium nitrate, potassium chromate is formed.


Cr a . . . . 104-2 68-4:6

O, .... 48-0 31-54:

152-2 100-00


1. ZINC.

Zinc is weighed in the form of OXIDE or SULPHIDE ; it is precipi-

a. Basic zinc carbonate, recently precipitated, is white, floccu-
lent, nearly insoluble in water (one part requiring 44600 parts,
Expt. No. 38 but readily soluble in potassa, soda, ammonia, am-
UK 'ilium carbonate, and acids. The solutions in sod;t or potassa, if
concentrated, are not altered by boiling ; but if dilute, nearly all
the zinc present is thrown down as a white precipitate. From the
solutions in iimmonia ;md ammonium carbonate, especially if they
are dilute, /inc is likewise separated upon boiling. When a neutral
solution of zinc is precipitated with sodium carbonate or potassium
carbonate, carbonic acid is set free, since the precipitate formed is not


ZnCO 3 , but consists of a compound of zinc hydroxide, with normal
carbonate in proportions varying according to the concentration of
the solution, and to the mode of precipitation. Owing to the
presence and action of this carbonic acid, part of the zinc remains
in solution ; if filtered cold, therefore, the filtrate gives a precipi-
tate with ammonium sulphide. Bat if the solution is precipitated
boiling, and kept at that temperature for some time, the precipi-
tation of the zinc is complete to the extent that the filtrate is not
rendered turbid by ammonium sulphide ; still, if the filtrate, mixed
with ammonium sulphide, be allowed to stand at rest for many
hours, minute and almost unweighable flakes of zinc sulphide will
separate from the fluid. The precipitate of zinc carbonate,
obtained in the manner just described, may be completely freed
from all admixture of alkali by washing with hot water. If
ammonium salts be present, the precipitation is not complete till
every trace of ammonia is expelled. If the solution of a zinc salt
is mixed with potassium or sodium carbonate in excess, the mix-
ture evaporated to dry ness, at a gentle heat, and the residue
treated with cold water, a perceptible proportion of the zinc is
obtained in solution as double carbonate of zinc and potassium or
sodium ; but if the mixture is evaporated to dryness, at a boiling
heat, and the residue treated with hot water, the whole of the
zinc, with the exception of an extremely minute proportion, as we
have already had occasion to observe, is obtained as zinc carbonate.
The dried basic zinc carbonate is a brilliant, white, loose powder ;
exposure to a red heat converts it into oxide.

~b. Zinc oxide, produced from the carbonate by ignition, is a
white light powder, with a slightly yellow tint. When heated, it
acquires a yellow color, which disappears again on cooling. Upon
ignition with charcoal, carbon monoxide and zinc fumes escape.
By igniting in a rapid current of hydrogen, metallic zinc is pro-
duced; whilst by igniting in a feeble current of hydrogen,
crystallized zinc oxide is obtained (S r r. CLAIRE DEVILLE). In the
latter case, too, a portion of the metal is reduced and volatilized.
Zinc oxide is insoluble in water. Placed on moist turmeric paper,
it does not change the color to brown. In acids, zinc oxide dis-
solves readily and without evolution of gas. Ignited with ammo-
nium chloride, fused zinc chloride is produced which volatilizes
with very great difficulty if the air is excluded : but readily and
completely, with free access of air, and with ammonium chloride

184 FOII.MS. [77.

fumes. Mixed with a sufficiency of powdered sulphur and ignited
in a stream of hydrogen, the corresponding amount of sulphide is
obtained (II. EOSE).


Zn 65-4 80-344

O 16-0 19-656

81-4 100-000

c. Zinc sulphide, recently precipitated, is a white, loose hydrate.
The following facts should here be mentioned with regard to its
precipitation.* Colorless ammonium sulphide precipitates dilute
solutions of zinc, but only slowly ; yellow ammonium sulphide
does not precipitate dilute solutions of zinc (1 : 5000) at all. Am-
monium chloride favors the precipitation considerably. Free
ammonia acts so as to keep the precipitate somewhat longer in
suspension, otherwise it exerts no injurious influence. If the con-
ditions which I shall lay down are strictly observed, zinc may be
precipitated by ammonium sulphide from a solution containing
only ^nnnnr* Hydrated zinc sulphide on account of its slimy
nature easily stops up the pores of the filter, and cannot therefore
bo washed without difficulty on a filter. The washing is best
performed by using water containing ammonium sulphide, and
continually diminished quantities of ammonium chloride (at last
none) (see Expt. Ko. 39). The hydrate is insoluble in water, in
caustic alkalies, alkali carbonates, and the monosulphides of the
alkali metals. It dissolves readily and completely in hydrochloric
and in nitric, but only very sparingly in acetic acid. When dried,
the precipitated zinc sulphide is a white powder ; when air-dried
its composition is 3ZnS + 2II,O ; dried at 100, 2ZnS + H a O ;
at 150, 4ZnS + H,O (A. SouciiAYf). On ignition it loses the
wliole of its water. During the latter process some hydrogen
sulphide escapes, and the residue contains some oxide. By roast-
ing in the air, and intense ignition, small quantities of zinc
sulphide may be readily converted into the oxide. On igniting
the dried xinc sulphide, mixed with powdered sulphur, in a stream
of hydrogen, the pure anhydrous sulphide is obtained (II. EOSE).
The latter suffers no loss of weight worth mentioning by ignition
for five minutes over the gas blowpipe ; but if such ignition is

* Jour.f. prakt. Chem , LXXXII, 263. f ZeitscJir.f. analyt. Chem., vu, 78.


very protracted the loss of weight becomes considerable (AL.



Zn 65-40 67-10

S 32-07 32-90

97-47 100-00


Manganese is weighed either as PROTOSESQUIOXIDE (MANGANOSO-


PYROPHOSPHATE. With the view of converting it into these forms,

a. Manganese carbonate, recently precipitated, is white, floccu-
lent, nearly insoluble in pure water, but somewhat more soluble in
water impregnated with carbonic acid. Presence of sodium car-
bonate or potassium carbonate does not increase its solubility
Recently precipitated manganese carbonate dissolves pretty readily
in ammonium chloride : it is owing to this property that a solution
of manganese cannot be completely precipitated by potassium or
sodium carbonate, in presence of ammonium chloride (or any other
ammonium salt), until the latter is completely decomposed. If
the precipitate, while still moist, is exposed to the air, or washed
with water impregnated with air, especially if it is in contact with
alkali carbonate, it slowly assumes a dirty brownish- white color, part
of it becoming converted into hydrated protosesquioxide. Even
long-continued washing will not remove the last traces of alkali
salt from the precipitate. The wash-water often comes through
turbid. If the filtrate and wash-water are evaporated to dryness
and the residue is treated with boiling water, the email traces of
manganous carbonate which were partly dissolved and partly sus-
pended will remain behind in the form of hydrated protosesqui-
oxide. Dried by pressure the precipitate is white, and consists of
MnCO 3 + II 2 O ; dried in a vacuum it consists of 2(MnCO 3 ) + II 2
(E. PRIOR!) ; when dried with free access of air, the powder is of
a dirty-white color. When strongly heated with access of air,

* Zeitschr.f. analyt. Chem., iv, 421. f lb vm 428 '

186 FOKMS. |_ 78.

this powder first turns black, and changes subsequently to brown
protosesquioxide of manganese. However, this conversion takes
some time, and must never be held to be completed until two
weighings, between which the precipitate lias been ignited again
with free access of air, give perfectly corresponding results. On
igniting the 'manganous carbonate, mixed with powdered sulphur,
in a stream of hydrogen,, manganese sulphide is obtained (II. ROSE).
i b. Manganous hydroxide recently thrown down forms a
white, flocculent precipitate, barely soluble in water and alkalies,
but soluble in ammonium chloride ; it immediately absorbs oxygen
from the air, and turns brown, owing to the formation of hydrated
protosesquioxide. On drying it in the air, a brown powder is
obtained which, when heated to intense redness, with free access
of air, is converted into protosesquioxide, and on ignition with
sulphur, in a stream of hydrogen, is converted into sulphide.

c. Protosesquioxide of manganese, artificially produced, is a
brown powder. All the oxides of manganese are finally converted
into this by strong ignition in the air. Each time it is heated it
assumes a darker color, but its weight remains unaltered. It is
insoluble in water, and does not alter vegetable colors. If ignited
with ammonium chloride, it is converted into the manganous
chloride. When heated with concentrated hydrochloric acid, it
dissolves to chloride with evolution of chlorine (Mn 3 O 4 -J- 8IIC1 =
3Mn01 2 -j" 2C1 + 4H 2 O). On ignition with sulphur in a stream
of hydrogen it is converted into sulphide (II. ROSE). On ignition
in oxygen it is converted into manganic oxide (SCHNEIDER). On
ignition in hydrogen it is converted into manganous oxide.


Mn 3 .... 165 72-05

O 4 . . . . . 64 27*95

229 100-00

d. Manganese dioxide is occasionally produce* 1 in analysis b}
exposing a concentrated solution of mungannus nitrate to ?
gradually increased temperature. At 140 brown flakes separate,
at 155 much nitrous acid is disengaged, and the whole of the
manganese separates as anhydrous dioxide. It .is brownish-black,
and is deposited on the sides of the vessel, with metallic lustre. It
is insoluble in weak nitric acid, but dissolves to a small amount in


hot and concentrated nitric acid (DEVILLE). In hydrochloric acid
it dissolves with evolution of chlorine, in concentrated sulphuric
acid with liberation of oxygen. The dioxide is also sometimes
obtained in the hydrated condition in analytical separations, thus
when we precipitate a solution of a manganous salt with sodium
hypochlorite, or, after addition of sodium acetate, with bromine or
chlorine in the heat. The brownish-black flocculent precipitate
thus obtained, contains alkali, from which it cannot be well freed
by washing.

e. Manganese sulphide, prepared in the wet way, generally
forms a flesh-colored precipitate. I must make a few remarks
with reference to its precipitation.* This is effected but incom-
pletely if we add to a pure manganous solution only ammonium
sulphide, no matter whether it be colorless or yellow, while it is
perfectly effected if ammonium chloride be used in addition. A
large quantity even of ammonium chloride does not impede the
precipitation. Ammonia in small quantity is not injurious, but in
large quantity it interferes with complete precipitation, especially
in the presence of ammonium polysulphide (A. CLASSEN*)-). In all
cases we must allow to stand at least 24 hours, and with very
dilute solutions 48 hours, before filtering. Colorless or slightly
yellow ammonium sulphide is the most appropriate precipitant.
In the presence of ammonium chloride even a large excess of
ammonium sulphide is uninjurious. If the precipitation is con-
ducted as directed, the manganese can be precipitated from solu-
tions which contain an amount equivalent to only ^roVmr ^ tne
manganous oxide. If the flesh-colored hydrated sulphide remains
some time under the fluid, from which it was precipitated, it
sometimes becomes converted into the green anhydrous sulphide.^
This conversion is more likely to take place when a large excess of
ammonium sulphide has been used ; heating favors it, ammonium
chloride hinders it. Tl^e conversion is occasionally rapid. The
green sulphide thus obtained consists of eight-sided tables dis-
tinctly visible under the microscope (F. MUCK). In acids (hydro-
chloric, sulphuric, acetic, &c.) the hydrated sulphide dissolves with
evolution of hydrogen sulphide. If the precipitate, while still
moist, is exposed to the air, or washed with water impregnated with
air, it changes to brown, hydrated protosesquioxide of manganese

*' Journ. f. prakt. Chem., LXXXII, 265. \ Zeitechr.f. analyt. Chem., vm, 370.
%Journ.f. prakt, Chem., LXXXII, 268. Zeitechr.f. Chem., N. F. vi, 6,

188 FORMS. [ 78.

being formed, together with a small portion of manganous sulphate.
Hence in washing the hydrate we always add some ammonium sul-

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