C. Remigius Fresenius.

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other basic radicals ; 2, $, generally only to effect the separation
of calcium together with the other alkali-earth metals from the
alkalies. As many bodies (alkali citrates, and metaphosphates)
interfere with the precipitation of calcium by the precipitants
given, these, if present, must be first removed.

3. The volumetric methods of estimation, which are
particularly to be recommended when a large number of deter-
minations are to be made, will be described after the gravimetric

1. Determination of Calcium Sulphate,
a. By Precipitation.

Mix the solution of the calcium salt in a beaker, with dilute sul-
phuric acid in excess, and add three or four times the volume of
alcohol ; let the mixture stand twelve hours, filter, and thoroughly
wash the precipitate with alcohol, dry, and ignite moderately
( 53). For the properties of the precipitate, see 73. The re-
sults are very accurate. A direct experiment, No. 61, gave
99-64: instead of 100.

"b. By Evaporation.

The same method as described under barium, 101, 1, 5.

2. Determination as Calcium Carbonate or Calcium

a. By Precipitation with Ammonium Carbonate.

The same method as described 101, 2, a. The " precipitate
can be most conveniently weighed as calcium carbonate. It must
be exposed only to a very gentle red heat, but this must be con-
tinued for some time. For the properties of the precipitate, see


This method gives very accurate results, the loss of substance
incurred being hardly worth mentioning.

If the solution contains ammonium chloride or similar ammo-
nium salts in considerable proportion, the loss of substance in-
curred is far greater. The same is the case if the precipitate is
washed with pure instead of ammoniacal water. A direct experi-


ment, No. 62, in which pure water was used, gave 99 'IT instead
of 100 parts of lime.

If it is feared that some calcium oxide has formed, from the
heat being too high, the residue is moistened with a little water,
a small piece of ammonium carbonate added, the whole slowly
evaporated, and heated again to gentle redness, i.e. , till the bot-
tom of the crucible is just dull-red. If a gas blowpipe is at
hand, the calcium carbonate may be converted into oxide by pro-
longed, strong ignition, and then weighed as such. Comp. I*.

b. By Precipitation with Ammonium Oxalate.
a. The Calcium Salt is soluble in Water.

To the hot solution in a beaker add ammonium oxalate in
moderate excess, and then ammonia sufficient to impart an ammo-
niacal smell to the fluid ; cover the glass, and let it stand in a
warm place until the precipitate has completely subsided, which
will require twelve hours, at least. Pour the clear fluid gently
and cautiously, so as to leave the precipitate undisturbed, on a
filter ; wash the precipitate two or three times by decantation with
hot water; lastly, transfer the precipitate also to the filter, by
rinsing with hot water, taking care, before the addition of a fresh
portion, to wait until the fluid has completely passed through the
filter, f Small particles of the precipitate, adhering firmly to the
glass, are removed with a feather. If this fails to effect their
complete removal, they should be dissolved in a few drops of
highly dilute hydrochloric acid, ammonia added to the solution,
and the oxalate obtained added to. the first precipitate. Devia-
tions from the rules laid down here will generally give rise to the
passing of a turbid fluid through the filter. After having washed
the precipitate, dry it on the filter in the funnel, and transfer the
dry precipitate to a platinum crucible, taking care to remove it as

* In converting precipitated calcium carbonate into calcium oxido, FRITZ-
SCHE (Zeitschr.f. analyl. Chem., in, 179), and A. COBSA (ib., vnr, 141) obtained
somewhat too little (99 - 7 instead of 100). This, I think, may be because the
calcium carbonate employed by FUITZSCIIE (which he dried at 160), was not
anhydrous, and which he himself hints.

f In order to make the calcium oxalate settle more rapidly and filter it off
clearly, MUCK recommends adding 1 c. c. of ammonia-alum solution containing
O'OOl grm. alumina. An excess of ammonia is to be avoided, and O'OOl grm.
must be deducted from the weight of the calcium oxide. (Zeit&chr. f. analyt.
Chem., ix, 451.)

103.] CALCIUM. 271

completely as possible from the filter ; burn the filter on a piece
of platinum wire, letting the ash drop into the hollow of the lid
( 53) ; put the latter, now inverted, on the crucible, so that the
filter ash may not mix with the precipitate ; heat at first very
gently, then more strongly, until the bottom of the crucible is
heated to very faint redness. Keep it at that temperature from
ten to fifteen minutes, removing the lid from time to time. I
am accustomed during this operation to move the lamp back-
wards and forwards under the crucible with the hand, since, if
you allow it to stand, the heat may very easily get too high.
Finally allow to cool in the desiccator and weigh. After weigh-
ing, moisten the contents of the crucible, which must be perfectly
white, or barely show the least tinge of gray, with a little water,
and test this after a time with a minute slip of turmeric paper.
Should the paper turn brown a sign that the heat applied was
too strong rinse off the fluid adhering to the paper with a little
water into the crucible, throw in a small lump of pure ammo-
nium carbonate, evaporate to dryness (best in the water-bath),
heat to very faint redness, and weigh the residue. If the weight
has increased, repeat the same operation until the weight remains
constant. I wish to particularly point out that by closely adher-
ing to the rules laid down above regarding the method of ignition,
the tedious evaporation with ammonium carbonate may be al-
ways avoided. For the properties of the precipitate and residue
see 73. This method gives nearly absolutely accurate results.
A direct experiment, No. 63, gave 99 -99 instead of 100.
Equally accurate results were recently obtained also by A. Sou-
CHAY in my laboratory.*

If a gas blowpipe is at hand, or any other arrangement by
means of which a platinum crucible may be raised to a white
heat, the calcium oxalate may be converted into CAUSTIC LIME
with results almost equally accurate; and I believe that this
method, which requires less patience than the other, is more certain
to yield good results in the hands of many persons. The calcium
oxalate and the filter ash are transferred to a moderate-sized
platinum crucible, which is ignited first over the BUNSEN flame,
and then over the blowpipe. The crucible is then weighed, and

*Zeitschr.f. analyt. Chem., x, 323.


ignited again over the blowpipe. The second igmtkm over the
blowpipe should not reduce the weight. The duration of the
ignition necessary varies from 5 to 15 or more minutes, accord-
ing to intensity of heat and quantity of the precipitate. It is well
to weigh the empty crucible again at the end of the operation, as
platinum sometimes loses weight after violent and prolonged igni-
tion. The results obtained by FRITZSCHE, COSSA,* and SOUCHAY
scarcely differ from the calculated numbers. For properties of
calcium oxide, see 73.

The calcium oxalate may also be converted into sulphate.
SCHROTTER ignites in a covered platinum crucible with pure
ammonium sulphate. Or you may ignite in a covered platinum
dish till the precipitate is for the most part converted into oxide,
add a little water, then hydrochloric acid to effect solution, then
pure sulphuric acid in excess, evaporate and ignite moderately.
This process is also quite accurate,

Some chemists collect the calcium oxalate on a weighed filter,
dry at 100, and weigh. The composition of the precipitate so
obtained is CaC a O 4 -f- II 3 O. This method, however, is more
troublesome, as well as less accurate, than the first.
ft. The Salt is insoluble in Water.

Dissolve the salt in dilute hydrochloric acid. If the acid of
the calcium salt is of a nature to escape in this operation (e.g.,
carbonic acid), or to admit of its separation by evaporation (e.g.,
silicic acid), proceed, after the removal of the acid, as -directed
in <x. But if the acid cannot thus be readily got rid of (e.g.,
phosphoric acid), proceed as follows : Add ammonia until a pre-
cipitate begins to form, re- dissolve this with a drop of hydro-
chloric acid, add ammonium oxalate in excess, and finally sodium
acetate ; allow the precipitate to subside, and proceed for the re-
mainder of the operation as directed in of. In this process the
free hydrochloric acid present reacts on the sodium acetate and
ammonium oxalate, forming sodium and ammonium chlorides,
with liberation of a corresponding amount of oxalic and acetic
acids in which calcium oxalate is nearly insoluble. In this
method the loss is very slight. The method yields accurate re-
sults. A direct experiment, No. 64, gave 99 -78 instead of 100.

* FRITZSCHE (Zeitochr.f. analyt. Chem., in, 179) and A. COSSA (lb. t viu, 141).

103.] CALCIUM. 273

c. By Ignition.

The Same method as described 101, 2, I (barium). The
residue remaining upon evaporation with ammonium carbonate
(which operation it is advisable to perform twice) must be ignited
very gently. The remarks made in 101, 2, &, in reference to
the accuracy of the results, apply equally here. By way of con-
trol, the calcium carbonate may be converted into oxide or into
calcium sulphate (see 5, or), or it may be determined alkalimetri-
cally ( 223).

3. Volumetric Methods.

a. Regarding the alkalimetric determination of calcium
oxide or carbonate, see 223. 13y properly carrying out the
process, a mixture of calcium oxide and carbonate, obtained by
moderately igniting calcium oxalate in the air, affords very good
results (Expt. No. 65).

J. Precipitation as calcium oxalate, and direct estimation of
the oxalic acid in the precipitate. The oxalic acid in the well-
washed, but not dried, calcium oxalate, is determined by means
of potassium permanganate ( 137). Results are very good
(Expt. No. 65).

c. Precipitation of calcium oxalate and indirect estimation
of the oxalic acid in the precipitate. In this method (KRAUT*)
the calcium salt must be soluble in water. Add to the solution
of the calcium salt, contained in a measuring-flask, an exactly
measured quantity of decinormal oxalic-acid solution ( 215),
more than sufficient to precipitate the calcium, add ammonia
until the liquid is alkaline, heat to boiling, cool, fill the flask up
to the mark, and shake. Then- filter through a dry filter, meas-
ure off an aliquot part of the filtrate (at least one-half), determine
in it the oxalic acid by potassium permanganate, as in 137, and
calculate the quantity for the whole of the filtrate ; the quantity
of oxalic acid which has been used up to combine with the cal-
cium, gives the quantity of the latter present. 1 c. c. of deci-
normal oxalic-acid solution 0*0028 grm. lime. The method
is rapid, and gives accurate results. If the quantity of calcium
is small in comparison with the volume of the liquid, no correc-
tion will be necessary for the space the calcium oxalate occupies
in the measuring flask.

*Chem Centralbl. 1856, 316. ~




a. Solution.

Many magnesium salts are soluble in water ; those which are
insoluble in that menstruum dissolve in hydrochloric acid, with the
exception of some silicates and aluminates (see 105 and 140).

b. Determination.

Magnesium is weighed ( 74) either as sulphate or as pyro-
phosphate, or as magnesium oxide. In the form of oxide or car-
bonate, it may be determined also by the alkalimetric method
described in 223.

We may convert into


a. Directly. 1). Indirectly.

All magnesium salts of vola- All magnesium salts soluble

tile acids, provided no other in water, and also those which,

non-volatile substance be pres- insoluble in that menstruum,

eiit. dissolve in hydrochloric acid,

with separation of their acid
(provided no ammonium salts
be present).


AJ1 magnesium compounds without exception.


a. Magnesium salts of organic acids, or of readily volatile inor-
ganic oxygen acids.

I. Magnesium chloride, and magnesium compounds convertible
into that salt.

The direct determination as magnesium sulphate is highly
recommended in all cases where it is applicable. The indirect con-
version into the sulphate serves only in the case of certain separa-
tions, and is hardly ever had recourse to where it can possibly be
avoided. The determination as pyrophosphate is most generally
resorted to ; especially also in the separation of magnesium from
other bases. The method based on the conversion of magnesium
chloride into oxide is usually resorted to only to effect the separa-

104.] MAGNESIUM. 275

tion of magnesium from the alkali metals. Magnesium phosphates
are analyzed as 135 directs.

1. Determination as Magnesium Sulphate.

Add to the solution excess of pure dilute sulphuric acid, evapo-
rate to dryness, in a weighed platinum dish, on the water-bath;
then heat at first cautiously, afterwards, with the cover on more
strongly here it is advisable to place the lamp so that the flame
may play obliquely on the cover from above- until the excess of
sulphuric acid is completely expelled ; lastly, ignite gently over
the lamp for some time; allow to cool, and weigh. Should no
fumes of hydrated sulphuric acid escape upon the application of a
strongish heat, this may be looked upon as a sure sign that the
sulphuric acid has not been added in sufficient quantity, in which
case, after allowing to cool, a fresh portion of sulphuric acid is
added. The method yields very accurate results. Care must be
taken not to use a very large excess of sulphuric acid. The resi-
due must be exposed to a moderate red heat only, and weighed
rapidly. For the properties of the residue, see 74.

2. Determination as Magnesium Pyropliospliate.

The solution of the magnesium salt is mixed, in a beaker, with
ammonium chloride, and ammonia added in slight excess. Should
a precipitate form upon the addition of ammonia, this may be con-
sidered a sign that a sufficient amount of ammonium chloride has
not been used ; a fresh amount of that salt must consequently be
added, sufficient to effect the re-solution of the precipitate formed.
The clear fluid is then mixed with a solution of sodium phosphate
or sodium ammonium phosphate* in excess, and the mixture stirred,
taking care to avoid touching the sides of the beaker with the stir-
ring-rod ; otherwise particles of the precipitate are apt to adhere
so firmly to the rubbed parts of the beaker, that it will be found
difficult to remove them ; the beaker is then covered, and allowed
to stand at rest for twelve hours, without warming ; after that time
the fluid is filtered, and the precipitate collected on the filter, the
last particles of it being rinsed out of the glass with a portion of
the filtrate, with the aid of a feather ; when the fluid has completely
passed through, the precipitate is washed w T ith a mixture of 3 parts
of water, and 1 part of solution of ammonia of 0*90 sp. gr., the

* According to MOHR (NaNH 4 H)PO 4 is preferable to (Na 2 H)PO 4 as a pre-
cipitant. (See Zeitschr.f. analyt. Chem., xu, 36.)


operation being continued until a few drops of the fluid passing
through the Ulter mixed with nitric acid and a drop of silver nitrate
show only a very slight opalescence.

The precipitate is now thoroughly dried, and then transferred
to a platinum crucible ( 53) ; the latter, with the lid on, is exposed
for some time to a very gentle heat, which is finally increased to
intense redness. The filter, as clean as practicable, is incinerated
in a spiral of platinum wire, and the ash transferred to the cru-
cible, which is then once more exposed to a red heat, allowed to
cool, and weighed. If the magnesium pyrophosphate is not per-
fectly white, moisten with a few drops of nitric acid, and ignite
again, applying the heat at first carefully.

For the properties of the precipitate and residue, see T4.

This method, if properly executed, yields most accurate results.
The precipitate must be washed completely, but not over-washed,
and the washing water must always contain the requisite quantity
of ammonia.

3. Determination as Magnesium Oxide.

a. In Magnesium Salts of Organic or Volatile Inorganic

The magnesium salt is gently heated in a covered platinum
crucible, increasing the temperature gradually, until no more fumes
escape; the lid is then removed, and the crucible placed in an
oblique position, with the lid leaning against it. A red heat is
now applied, until the residue is perfectly white. For the prop-
erties of the residue, see 74. The method gives the more accu-
rate results the more slowly the salt is heated from the beginning.
Some loss of substance is usually sustained, owing to traces of the
salt being carried off with the empyreumatic products. Mag-
nesium salts of readily volatile oxygen acids (carbonic acid, nitric
acid), may be transformed into magnesium oxide in a similar way, by
simple ignition. Even magnesium sulphate loses the whole of its
sulphuric acid when exposed, in a platinum crucible, to the heat
of the gas blowpipe-flame (SONNENSCHKIN). As regards small quan-
tities of inairnrsiuiu sulphate, I can fully confirm this statement.

b. Conversion of Magnesium Ch'r<>/' into M<><!i<>. ium Oxide.
To the concentrated solution, in a porcelain crucible, add a

mixture of water and pure mercuric oxide in more than sufficient
quantity to enable the oxygen of the oxide to convert all the
magnesium chloride present into magnesium oxide, evaporate the

105.] ALUMINIUM. 27?

mixture on a water-bath, dry thoroughly, cover the crucible, and
heat to redness until all the mercuric chloride formed and also
the excess of mercuric oxide have been expelled. (The operator
should carefully guard against inhaling any of the vapors
evolved.) The residue, magnesium oxide, may be weighed in the
crucible, or, if its separation from alkalies is intended, it is col-
lected on a filter, washed with hot water, dried and ignited ( 53).
Regarding other methods whereby the object intended may be
attained, and which are frequently more convenient for effecting
separations, see 153, B, 4 (17 to 21).




a. Solution.

Aluminium compounds which are insoluble in water dissolve,
for the most part, in hydrochloric acid. Native crystallized alu-
minium oxide (sapphire, ruby, corundum, &c.), and many native
aluminium compounds, and also artificially produced aluminium
oxide after intense ignition, require fusing with sodium carbon-
ate, caustic potassa, or barium hydroxide, as a preliminary step
to their solution in hydrochloric acid. Many aluminium com-
pounds (e.g., common clay) which resist the action of concen-
trated hydrochloric acid, may be decomposed by protracted heat-
ing with moderately concentrated sulphuric acid, or by fusion
with sodium disulphate ; potassium disulphate also effects the de-
composition, but it gives rise to the formation of a double salt of
potassium and aluminium difficultly soluble in water or acids, and
which renders further analysis more difficult (L. SMITH *).

1). Determination.

Aluminium is almost invariably weighed as aluminium oxide'
occasionally also as phosphate (compare, for instance, 209, 7, n).
In the former case the several aluminium salts are converted into
aluminium oxide, either by precipitation as aluminium hydroxide,
and subsequent ignition, or by simple ignition. Precipitation as
basic acetate or basic formate is resorted to only in cases of sepa-

* Amer. Jour, of Sc. and Arts, XL, 248; Zeitschr.f. analyt. Chem., iv, 412.


ration. For the indirect (acidimetric) estimation of aluminium
in alum, etc., see 215.
"We may convert into


a. By Precipitation. b. By Heating or Ignition.

All aluminium salts soluble a. All aluminium salts of

in water, and those which, in- readily volatile oxygen acids

soluble in that menstruum, dis- (e.g., aluminium nitrate),
solve in hydrochloric acid, with /?. All aluminium salts of

separation of their acid. organic acids.

With regard to the method a, it must be remembered that
the solution must contain no organic substances which would
interfere with the precipitation e.g., tartaric acid, sugar, &c.
Should such be present, the solution must be mixed with sodium
carbonate and potassium nitrate, evaporated to dryness in a
platinum dish, the residue fused, then softened with water, trans-
ferred to a beaker, digested with hydrochloric acid, and the solu-
tion filtered, and then, but not before, precipitated.

The methods J, a and /? are applicable only in cases where
no other fixed substances or ammonium chloride are present (on
igniting the latter with aluminium oxide, aluminium chloride
volatilizes). The methods of determining aluminium in its com-
binations with phosphoric, boric, silicic, and chromic acids
will be found in Part II. of this Section, under the heads of
these several acids.

Determination as Aluminium Oxide.

a. By Precipitation.

Mix the moderately dilute hot solution of the aluminium salt,
In a beaker or dish, with a tolerable quantity of ammonium chlo-
ride, if that salt is not already present ; add ammonia slightly in
excess, boil gently till the fluid gives a neutral or barely alkaline
reaction (the fluid adhering to the test paper must be washed
back). The fluid must not be heated too long, or it may become
acid through decomposition of ammonium chloride, and some of
the precipitate may redissolve; and this must, of course, be
avoided. Precipitation is best effected in a large platinum dish ;
in default of this a porcelain one will answer, but glass is not to

105.] ALUMINIUM. 279

be recommended because it is markedly attacked by hot ainmo-
niacal liquids (see p. 88). Allow the precipitate to settle ; then
decant the clear supernatant fluid on to a filter, taking care not
to disturb the precipitate ; pour boiling water on the latter in the
beaker, stir, let the precipitate subside, decant again, and repeat
this operation of washing by decantation a second and a third time ;
transfer the precipitate now to the filter, and finish the washing
with boiling water, Suction is particularly useful in filtering off
aluminium hydroxide ( 47), as the precipitate may , without further
treatment, be at once ignited as detailed on p. 117. If suction
is not employed, the ignition of the moist precipitate is a rather
critical operation. If the precipitate is to be dried before igni-
tion, however, the drying must first be very thorough, after which
ignite ( 52), and weigh. The heat applied should be very gentle
at first, and the crucible kept well covered, to guard against
the risk of loss of substance from spirting, which is always to
be apprehended if the precipitate is not thoroughly dry. In
whichever way the precipitate is ignited, it is always advisable
to expose it for some time to an incipient white heat by means of
the gas blowpipe, before weighing, in order to be sure that every
trace of moisture has been expelled. A. MITSCHEELICH.* In the
case of aluminium sulphate the foregoing process is apt to leave
some sulphuric acid in the precipitate, which, of course, vitiates
the result. To insure the removal of this sulphuric acid, the
precipitate should be exposed for 5-10 min. to the heat of the gas
blowpipe flame. If there are difficulties in the way, preventing
this proceeding, the precipitate, either simply washed or mod-
erately ignited, must be re-dissolved in hydrochloric acid (which
requires protracted warming with strong acid), and then precipi-
tated again with ammonia ; or the sulphate must first be con-
verted into nitrate by decomposing it with lead nitrate, added in
very slight excess, the excess of lead removed by means of hydro-
gen sulphide, and the further process conducted according to
the directions of a or 1). The precipitation may also be effected
by means of ammonium carbonate or ammonium sulphate, in-
stead of ammonia ; the accuracy of the results is not, however,
thereby increased.

* Zeitschr. /. analyt. Chem., i, 67,


For the properties of aluminium hydroxide and ignited alu-
minium oxide, see 75. The operator should never neglect to

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