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bonate, to which -J- the amount of the carbonate, or more, of

* Journ. f. prakt. Chem., LXXIX, 430.



618 SEPARATION. [ 154

potassium sulphate has been added. By this process, also, the
strontium and calcium sulphates are decomposed, the barium
sulphate remaining unacted on. If the basic metals are in solu-
tion, the above solution of potassium carbonate and sulphate is
added in excess at once, and the whole boiled. The precipitate,
consisting of barium sulphate and strontium and calcium car-
bonates, is to be treated as above with cold hydrochloric acid
ill. ROSE*).

4. Methods based on the Insolubility of Calcium Sul-
phate in Alcohol.

CALCIUM FROM MAGNESIUM.

a. Remove water and free hydrochloric from a solution of 32
the chlorides by evaporation, dissolve the residue in strong (but
not absolute) alcohol, add a slight excess of pure strong sulphu-
ric acid, digest in the cold, allow to stand for some hours, trans-
fer the precipitate consisting of calcium sulphate and some
magnesium sulphate to a filter, wash away the acid thoroughly
with nearly absolute alcohol, and then, but only after the acid
has been completely removed, continue the washing with alcohol,
sp. gr. 0'96 0*95, till a few drops of the washings give no
residue on evaporation. Weigh the calcium sulphate accord-
ing to 103, 1. Evaporate the alcohol from the filtrate, and
determine the magnesium according to 104, 2. The method

is in itself not new, but A. CinzYNSKi,f adopting the precautions
here given, has obtained excellent results, even in the presence
of phosphoric acid.

b. SMALL QUANTITIES OF CALCIUM FROM MUCH MAGNESIUM. 33
Convert into neutral sulphates, dissolve the mass in water, and
add alcohol, with constant stirring, till a slight permanent tur-
bidity is produced, Wait a few hours and then filter, wash the
precipitated calcium sulphate . with alcohol which has been
diluted with an r<|iial volume of water, and determine it after

103, 1, a (in which case the wiM^-lu-d sulphate must be tested
for magnesium), or dissolve the precipitate in water containing
hydrochloric acid and >rparate the calcium from the small quan-
tity of magnesium possibly coprecipitated . according to 36

(ScnEERERlf).

* 1'ogg. Ann., x( v, 2H(i, VQQ, 427. f Zeilschr.f. analyt. Chem., iv, 348.
d Chem u. Phann,., ex, 237.



154.] BASES OF GROUP II. 619

5. Methods based on the Insolubility of Strontium, and
Barium Sulphates in solution of Ammonium Sulphate.

STRONTIUM FROM CALCIUM.

If the mixture is soluble, dissolve in the smallest quantity 34
of water, add about 50 times the quantity of the substance of
ammonium sulphate dissolved in four times its weight of water,
and either boil for some time with renewal of the water that
evaporates and addition of a very little ammonia (as the solu-
tion of ammonium sulphate becomes acid on boiling), or allow to
stand at the ordinary temperature for twelve hours. Filter and
wash the precipitate, which consists of strontium sulphate and
a little ammonium strontium sulphate, with a concentrated solu-
tion of ammonium sulphate, till the washings remain clear on
addition of ammonium oxalate. The precipitate is cautiously
ignited, moistened with a little dilute sulphuric acid (to convert
the small quantity of strontium sulphide into sulphate), reig-
nited and weighed. The highly dilute filtrate is precipitated
with ammonium oxalate, and the calcium determined according
to 103, 2, I), a. If you have the solid sulphates to analyze,
they are very finely powdered and boiled with concentrated solu-
tion of ammonium sulphate with renewal of the evaporated
water and addition of a little ammonia. Results very close, e.g.,
1 -048 Sr(NO 3 ), instead of 1-053, and 0-497 CaCO a , instead
of 0-504(11. KOBE*).

BARIUM may be separated FROM CALCIUM in the same way. 35

6. Methods based upon the Insolubility of Calcium
Oxalate in Ammonium Chloride and in Acetic Acid.

CALCIUM FROM MAGNESIUM.

a. Mix the properly diluted solution with sufficient ammo- 36
nium chloride to prevent the formation of a precipitate by
ammonia, which is added in slight excess ; add ammonium oxa-
late as long as a precipitate forms, then a further portion of the
same reagent, about sufficient to convert the magnesium also
into oxalate (which remains in solution). This excess is abso-
lutely indispensable to insure complete precipitation of the cal-
cium, as calcium oxalate is slightly soluble in magnesiv m chlo-
ride not mixed with ammonium oxalate (Expt. No. 8c ). Let

* Pogg. AnnaL, ex, 296



620 SEPARATION. [ 154

the mixture stand twelve hours, decant the supernatant clear
fluid, as far as practicable, from the precipitated calcium oxa-
late, mixed with a little magnesium oxalate, on to a filter, wash
the precipitate once in the same way by decantation, then dis-
solve in hydrochloric acid, add water, then ammonia in slight
excess, and a little ammonium oxalate. Let the fluid stand
until the precipitate has completely subsided, then pour on to
the previous filter, transfer the precipitate finally to the latter,
and proceed exactly as directed 103, 2, , a. The first filtrate
contains by far the larger portion of the magnesium, the second
the remainder. Evaporate the second filtrate, acidified with
hydrochloric acid, to a small volume, then mix the two fluids,
and precipitate the magnesium with sodium ammonium phos-
phate (HNaNH 4 )PO 4 ,*as directed 104, 2. If the quantity of
ammonium salts present is considerable, the estimation of the
magnesium is rendered more accurate by evaporating the fluids
in a large platinum or porcelain dish to dryness, and igniting
the residuary saline mass, in small portions at a time, in a smaller
platinum dish, until the ammonium salts are expelled. The
residue is then treated with hydrochloric acid and water,
warmed, allowed to cool, and rendered just alkaline with ammo-
nia. If enough ammonium chloride is present, no magnesium
hydroxide will fall down, but occasionally small flocks of silica
or alumina are to be seen. Filter them off and finally precipi-
tate with ammonia and (HNaNH 4 )PO 4 . If the precipitate pro-
duced by ammonia is at all considerable, dissolve it in hydro-
chloric acid, evaporate the solution on a water-bath to dryness,
treat the residue with hydrochloric acid and water, render alka-
line with ammonia, filter, and add the filtrate to the principal
solution.

Numerous experiments have convinced me that this method,
which is so frequently employed, gives accurate results only if
the foregoing instructions are strictly complied with. It is only
in eases where the quantity of magnesium present is relatively
small that a single precipitation with ammonium oxalate may
be t'niind sullicieiit (eomp. Kxpt, No. 84 f).

* This is prrfVriiblc to sodium phosphate as a precipitant. See MOIIR,
Zeitachr.f. aitnlyt. Chem., xn, 30

f Further experiments will be found in Zeitschr. f. analyt. CJiem., vn, 310.



154.] BASES OF GROUP II. 621

1. Ift the case of calcium and magnesium phosphates, dis- 37
solve in the least possible quantity of hydrochloric acid, add
ammonia until a copious precipitate forms ; redissolve this by
addition of acetic acid, and precipitate the calcium with an
excess of ammonium oxalate. To determine the magnesium,
precipitate the filtrate with ammonia and (IINaNH 4 )PO 4 . As
free acetic acid by no means prevents the precipitation of small
quantities of magnesium oxalate, the precipitate contains some
magnesium, and as calcium oxalate is not quite insoluble in
acetic acid, the filtrate contains some calcium ; these two sources
of error compensate each other in some measure. In accurate
analysis, however, these trifling admixtures of magnesium and
calcium are afterwards separated from the weighed precipi-
tates of calcium carbonate or oxide and magnesium pyrophos-
phate respectively.

T. Method based upon the Insolubility of Strontium
Nitrate in Alcohol and Ether.

STRONTIUM FROM CALCIUM (after STROMEYER).

Digest the perfectly dry nitrates in a closed flask with abso- 38
lute alcohol, to which an equal volume of ether should be added
(H. ROSE). Filter off the undissolved strontium nitrate in a
covered funnel, wash with the mixture of alcohol and ether, dis-
solve in water, and determine as strontium sulphate ( 102, 1).
Precipitate the calcium from the filtrate by sulphuric acid.
The results are satisfactory.

8. Indirect Method.

STRONTIUM FROM CALCIUM.

Determine both bases first as carbonates or oxides, precipi- 39
tating them either with ammonium carbonate or oxalate ( 102,
103) ; then estimate the amount of carbonic acid in them, and
calculate the amount of strontium and calcium as directed in
" Calculation of Analyses ".( 200). The determination of the
carbonic acid may be effected by fusion with vitrified borax
( 139, II., c), but the application of a moderate white heat,
such as is given by a good gas blowpipe without the use of a

Compare also WITTSTEIN, Zeitschr. f. analyt Chem , u, 338. and COSSA, ib. t
Vin, 141. According to HAGER, ib., ix, 254. the precipitate of calcium oxalate
will be free from magnesium if filtered off immediately, however, I fear that a
little calcium might in this case be left in solution.



022 SEPARATION. [ 154.

crucible jacket, is alone sufficient to drive out all the carbonic
acid from both the carbonates (F. G. SCHAFFGOTSCH *). I can
strongly recommend this method. It is well to precipitate the
carbonates hot, to press the precipitate cautiously down in the
platinum crucible and turn over the agglomerated cake every
now and then till, after repeated ignitions, the weight has become
constant. The results are good if neither of the bases is present
in too minute quantity.

The indirect separation may, of course, be effected by means 40
of other salts, and can be used also for the determination of CAL-
CIUM IN PRESENCE OF BARIUM Or of BARIUM IN . PRESENCE OF

STRONTIUM. In the expulsion of carbonic acid from barium car-
bonate vitrified borax must be used ( 139, II., c).

Third Group.

ALUMINIUM CHROMIUM.

I. SEPARATION OF ALUMINIUM AND CHROMIUM FROM THE

ALKALIES.

155.

1. FROM AMMONIUM.

a. Aluminium and chromium salts may oe separated from 41
ammonium salts by ignition. However, in the case of alu-
minium, this method is applicable only in the absence of chlo-
rine (volatilization of aluminium chloride). The safest way,
therefore, is to mix the compound with sodium carbonate
before igniting.

b. Determine the ammonium by one of the methods given 42
in 99, 3, using solution of potassa or soda to effect the expul-
sion of ammonia. The aluminium and chromium are then
determined in the residue in the same way as in 43.

2. FKMM POTASSIUM AND SODIUM.

a Precipitate and determine the chromium and aluminium 43
with ;iin UK mia as directed in 105, a, and 106, 1, a. The ni-
trate contains the alkalies, which are then freed from the ammo-
nium salt formed, by evaporation to dryness and ignition. In
the presence of large quantities of alkali salts it is well to dis-

* Pogg. Annal., cxin, 615.



156.] BASES OF GROUP III. 623

solve the moderately ignited precipitate in hydrochloric acid
and reprecipitate with ammonia.

J. Aluminium may be separated also from potassium and 44
sodium by heating the nitrate (see 46).

II. SEPARATION OF ALUMINIUM AND CHROMIUM FROM THE
ALKALI-EARTH METALS.

156.
INDEX. (The numbers refer to those in the margin.

a. Aluminium from barium, 45-50, and 51.

" " strontium, 45-50, and 51.

" calcium, 45-50, and 52, 53, 54.
" magnesium, 45-50, and 53, 54.

b. Chromium from the alkali-earth metals, 55-58.

a. SEPARATION OF ALUMINIUM FROM THE ALKALI-EARTH

METALS.

A. General Methods.

THE WHOLE OF THE ALKALI-EARTH METALS FROM ALU-
MINIUM.

1. Method based upon the Precipitation of Alu-
minium Hydroxide by Ammonia, and upon its solution
in Soda.

Put the solution in a platinum dish or, with less advantage, 45
a porcelain dish. Let it be dilute and warm. Add a tolerable
quantity of ammonium chloride, if such be not already present,
then very gradually, almost drop by drop (WRINKLE*), ammo-
nia as free as possible from carbonic acid, in moderate excess,
and boil till no more free ammonia is observable. Under these
circumstances, a little magnesium hydroxide, and also a small
quantity of calcium, barium, or strontium carbonates are at first
precipitated along with the aluminium hydroxide ; on the boil-
ing with ammonium chloride, the coprecipitated alkali-earth
metal compounds redissolve, so that the aluminium hydroxide
finally retains only an unweighable or scarcely weighable trace
of them. Allow to deposit, and proceed with the aluminium
determination according to 105, a. In very exact analysis it
is well, after moderately washing the aluminium precipitate, to

* Zeilschr.f. analyt. Chem., x, 96.



624 SEPARATION. [ 156.

redissolve it in hydrochloric acid, arid reprccipitate with ammo-
nia as above. In separations of aluminium f rom calcium or
magnesium this double precipitation is especially necessary in
the presence of sulphates. After the aluminium oxide has
been weighed, fuse it for a long time with potassium disul-
phate, dissolve the fused mass in water, and determine any sili-
cic acid* that may remain. The solution, when mixed with
potassa in excess, will often not appear perfectly clear, but will
contain a few flocks of magnesium hydroxide (perhaps also
traces of barium, strontium, or calcium carbonates). If there is
any amount of the latter, filter it off, dissolve in nitric acid, pre-
cipitate with ammonia, boil till the fluid censes to smell of
ammonia, filter, evaporate the small quantity of fluid in a pla-
tinum capsule, ignite, weigh the residual magnesium oxide
(which may contain traces of other alkali-earth metals), deduct
it from the aluminium oxide, dissolve it in hydrochloric acid,
and add to the original filtrate. In order to the further separa-
tion of the alkali-earth metals, acidify the fluid containing them
with hydrochloric acid, evaporate (preferably in a platinum dish)
to a small bulk, and while still warm add ammonia just in
excess. A small precipitate of aluminium hydroxide is some-
times formed at this stage ; filter off, wash, and weigh with the
principal precipitate. In the filtrate determine the alkali-earth
metals according to 154.

Instead of precipitating the aluminium hydroxide as di-
rected, the following process may be followed : Add a moderate
excess of ammonia to the boiling-hot solution, boil about two
minutes, add acetic acid until distinctly acid, heat again for a
few minutes, add ammonia once more until weakly alkaline,
and proceed as above, f

[The difficulty of washing aluminium hydroxide usually
increases with lapse of time between precipitation and filtra-
tion. This difficulty may be to some extent obviated by the
following slight modification of the above-described manipula-
tion. Add ammonia to the solution, which may occupy a volume
of 400 c.c. for 0*2 gr. Al.,0, , until free acid is partially neu-
tralized, but not until a permanent precipitate is formed ; add

* A small quantity will always be found if you have boiled in a glass or
porcelain v< -^ -1.

\Handb. for anal. Chem. von II. RO.SE, 6. Aufl. von FINKENER, IT, 647.



156.] BASES OF GROUP III. 625

also ammonium chloride if but little free acid was present. Heat
nearly to boiling, and add ammonia slowly until a permanent
precipitate begins to form, then drop by drop until a slip of red
litmus-paper dipped into the fluid changes to blue and the odor
of ammonia becomes perceptible on boiling. Carefully avoid
the use of more ammonia than is sufficient to produce these
indications of a slight excess. Boil rapidly 7 to 10 minutes,
allow the precipitate to settle 5 to 10 minutes, filter and wash
the precipitate moderately upon the filter. Remove the filter
with the moist precipitate from the funnel, and unfold it upon
the side of a beaker having a height exceeding the diameter of
the filter, so that the latter may not extend to the bottom
of the beaker. Rinse the precipitate from the filter down
to the bottom of the beaker with a strong jet of water
and dissolve (completely or nearly) by adding concentrated
hydrochloric acid. Moisten also the filter with acid somewhat
diluted, and rinse the small amount of aluminium chloride solu-
tion thus formed out of the paper with a jet of water. Push
up the filter now, if necessary with a rod, so that it may be
above the solution, and allow it to remain adhering to the side
of the beaker. The solution need not, for this second precipi-
tation, occupy a volume above 200 250 c.c. Precipitate the
aluminium precisely as before, moistening also the filter with
ammonia solution. Immediately after boiling pour the solution
with the precipitate upon a filter. Push the old filter down to
the bottom of the beaker, wash it by adding and decanting
small successive portions of hot water, stirring and pressing the
paper with a rod and pouring the water upon the precipitate,
until a few drops of the decanted water give no turbidity wii.li
silver nitrate. Next complete the washing of the precipitate
on the filter with hot water. After the washing is complete,
beat up the old filter in the beaker with a glass rod and rinse it
out upon the top of the washed precipitate the old filter must
on no account be thrown away, since it may retain a little alu-
minium hydroxide which treatment with hydrochloric acid
failed to dissolve. Add to the united filtrates ammonia to
decided alkaline reaction ; heat until the solution becomes neu-
tral. If moro aluminium hydroxide separates, collect it on a
small filter.]



626 SEPARATION. [ 156.

2. Method based upon tlie unequal Deeomposability
of the Nitrates at a Moderate Heat (DEVILLE*).

To make tin's simple ;in<l convenient method applicable, the 46
basic metals must be present as pure nitrates. Evaporate to dry-
ness in a platinum dish, and heat gradually, with the cover on,
in the sand- or air-bath or, better still, on a thick iron disk,
with two cavities, one for the platinum dish, the other, filled
with brass turnings, for inserting a thermometer (compare 31)
to from 200 to 250, until a glass rod moistened with am-
monia ceases to indicate further evolution of nitric-acid fumes.
You may also, without risk, continue to heat until nitrous-acid
vapors form. The residue consists of aluminium oxide, barium,
strontium and calcium nitrates, and normal and basic magne-
sium nitrates.

Moisten the mass with a concentrated solution of ammonium
nitrate, and heat gently, but do not evaporate to dryness.
Repeat this operation until no further evolution of ammo-
nia is perceptible. (The basic magnesium nitrate, insoluble in
water, dissolves in nitrate of ammonia, with evolution of ammo-
nia, as normal magnesium nitrate.) Add water, and digest at

a L-vntle heat.

[If the ammonium nitrate has evolved only imperceptible
traoee <>f ammonia, pour hot water into the dish, stir, and add a
drop of dilute ammonia ; this must cause no turbidity in the
fluid ; should the fluid become turbid, this proves that the heat-
ing of the nitrates lias not been continued long enough ; in
which case you must again evaporate the contents of the dish,
and heat once more.]

The aluminium uxide remains undissolved in the form of a
dense granular substance. Decant after digestion, and wash with
hnilin- water; i-nite stnm:ly in the same vessel in which the
M-p:ir;iti,,ii has l.een eiTeete.1, ;m,l weigh. Test the weighed alu-
minium oxide according to 45. Separate the alkali-earth metals
as directed in 154.

In the same way aluminium may be separated also from
potassium and sodium (44).

3. Method in which the processes of 1 and 2 are
combined.

Precipitate the aluminium as in 45, wash in the same way 47
*Journ.f. prakt. C/tcm., 1853, LX, 9.



156.] BASES OF GROUP III. 627

<t

as tliere directed, then treat, while still moist, with nitric acid,
and proceed according to 46, to remove the trifling amount of
magnesium, etc., coprecipitated ; add the solution obtained to
the principal solution of the alkaline earths and treat the fluid
as directed in 45. This method may be employed also in the
case of chlorides ; it will be sometimes found useful.

4. Method based upon the Precipitation of Alumin-
ium by Sodium Acetate or Formate upon boiling.

The same process as for the separation of ferric iron from 48
the alkali-earth metals. The method is employed more par-
ticularly when both aluminium and ferric iron have to be
separated from alkali-earth metals at the same time. The
precipitation of the aluminium is usually not quite complete,
so that it will be necessary to separate the aluminium which
remains in solution from the filtrate (45).

5 . Method based on the Precipitation of Aluminium
by Ammonium Succinate.

Proceed as for the precipitation of ferric iron by the same 49
reagent ( 159); especially to be employed when aluminium
and ferric iron are both to be separated from alkali-earth metals
at the same time. The filtrate must be tested according to 48.

6. Method based upon the Formation of a Solu-
ble Alkali Aluminate in the dry way. (See 161.) 50

B. Special Methods.
SOME OF THE ALKALI-EARTH METALS FROM ALUMINIUM.

1 . Methods based upon the Precipitation of some of
the Salts of the Alkali-earth Metals.

a. BARIUM AND STRONTIUM FROM ALUMINIUM.
Precipitate the barium and strontium with sulphuric acid 51

( 101 and 102), and the aluminium from the filtrate as
directed in 105, a. This method is especially suited for the
separation of barium from aluminium. In accurate analyses
the barium sulphate must be purified according to 12.

b. CALCIUM FROM ALUMINIUM.

Add ammonia to the solution until a permanent precipitate 52
forms, then acetic acid until this precipitate is redissolved, then



028 SEPARATION. [ 156.

ammonium acetate, and finally ammonium oxalate in slight
excess ( 103, 2, 5, /?); allow the precipitated calcium oxalate
to deposit in the cold, then filter, and precipitate the alumin-
ium from the filtrate as directed in 105, a. Compare also
161, 4, I.

c. Magnesium and small quantities of Calcium from
Aluminium.

Add a little tartaric acid, supersaturate with ammonia, 53
and precipitate from the clear liquid (if sufficient aluminium
is present no calcium tartrate is precipitated) first the calcium,
by ammonium oxalate, and then the magnesium, with sodium-
ammonium phosphate. If the aluminium is to be estimated
in the filtrate, add to the latter some sodium carbonate and
potassium nitrate, evaporate to dry ness, ignite the residue,
soften with water, dissolve in hydrochloric acid (not in a plat-
inum dish), and precipitate the aluminium with ammonia.
The ammonium-magnesium phosphate, which may contain
basic magnesium tartrate, dissolve in hydrochloric acid, and
again precipitate with ammonia and a little sodium-ammo-
nium phosphate, and then ignite and weigh.

2. Method based upon the Precipitation of Alumin-
ium by Barium Carbonate.

ALUMINIUM FROM MAGNESIUM AND SMALL QUANTITIES OF
CALCIUM.

Mix the slightly acid dilute fluid in a flask with a moder- 54
ate excess of barium carbonate shaken up with water, cork the
flask and let the mixture stand in the cold until the aluminium
liv'lroxide has subsided, wash by decantation three times,
filter, and then determine the aluminium in the precipitate as
directed in 51 ; in the filtrate, first precipitate the barium by
Hilphuric acid (30) and then separate the calcium and mag-
nesium according to 154.

5. SEPARATION OF CHROMIUM FROM THE ALKALI-EARTH
METALS.

1. The best way to separate THE WHOLE OF THE ALKALI-
EARTH METALS from chromium at the same time is to convert



156.] BASES OF GROUP III. 629

the latter into chromic acid. This may be done in the dry or
the wet way.

a. Dry way. Mix the powdered substance with about 8 55
times its weight of a mixture of 2 parts of sodium carbonate
and 1 part of nitre and fuse in a platinum crucible. On treat-
ing the fused mass with hot water, the chromium dissolves as
alkali chromate (to be determined according to 130), while
the alkali-earth metals remain in the residue as carbonates or
oxides (magnesium oxide). If the residue is not perfectly
white, extract the remainder of the chromic acid from it by
boiling with solution of sodium carbonate.

b. Wet way. Suitable for separating chromium from 56
barium, strontium, and calcium.

a. Nearly neutralize the acid fluid with sodium carbonate,
add excess of sodium acetate, warm, and pass chlorine, adding
sodium carbonate occasionally to keep the fluid nearly neutral.



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