C. Remigius Fresenius.

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cause of loss of ammonium carbonate by too active an ebullition.
y. AFTER PETTENKOFER.*

The principle of this simple and expeditious process consists in
mixing the carbonic-acid water with a measured quantity of stand-

*BUCHNEU'S neuesRepert., x, 1; Journ.f. prakt, Chem., LXXXII, 32; Annal
d. Chem. u. Pharm., 11, Supplement, i; Zeitschr.f. analyt. Chem., i, 92.



139..] CARBONIC ACID. 485

ard linje water (or, under certain circumstances, baryta water) in
excess. After complete separation of the calcium or barium carbo-
nate, the excess of calcium or barium in the fluid is determined in
an aliquot part by means of standard solution of oxalic acid ; the
difference gives the calcium or barium precipitated by the carbonic
acid, and consequently the amount of the latter present.

If a water contains only free carbonic acid, the analyst has only
to bear in mind if lime water is employed that the calcium car-
bonate formed is at first, as long as it remains amorphous, very
perceptibly soluble in water, to which it communicates an alkaline
reaction. Hence the unprecipitated lime in the fluid cannot be
estimated till the calcium carbonate has separated in the crystalline
form, which takes 8 or 10 hours, unless the mixture is warmed to
70 or 80. On this account it is generally best to use baryta
water (see " Analysis of Atmospheric Air").

If, on the contrary, a water contains an alkali carbonate or any
other alkali salt whose acid would be precipitated by lime or baryta,
a neutral solution of calcium or barium chloride must first be added
to decompose the same. This addition, too, prevents any incon-
venience arising from the presence of free alkali in the lime or
baryta water, or of magnesium carbonate in the carbonic acid
water; this inconvenience consists in the fact that oxalate of an
alkali or of magnesium enters into double decomposition with cal-
cium carbonate (which is seldom entirely absent from the fluid to
be analyzed), forming calcium oxalate and carbonate of the alkali
or of map-nesium, which latter will of course again take up oxalic
acid.

In the presence of magnesium salts in the carbonic acid water,
in order to avoid the precipitation of the magnesium, a little
ammonium chloride must also be added, but in this case heat must
not be applied to induce the calcium carbonate to become more
quickly crystalline, as ammonia would be thereby expelled.

In making the determination the first thing to be done is to
ascertain the relation between the lime- or baryta water and a
standard solution of oxalic acid. PETTENKOFER makes the latter
solution by dissolving 2 8647 grin, pure uneffloresced dry crystal-
lized oxalic acid to 1 litre ; 1 c.c. of this is equivalent to 1 mgrm.
carbonic acid. The lime water is standardized as follows : Measure
45 c.c. into a little flask which can be closed by the thumb, and
then run in from the burette the solution of oxalic acid till the



486 DETERMINATION. [ 139.

alkaline reaction has just vanished. During the operation the
flask is closed with the thumb and gently shaken. The end is
attained as soon as a drop taken out with a glass rod and applied to
sensitive turmeric paper * produces no brown ring. The first
experiment is a rough one, the second should be exact.

The analysis of a carbonic acid water (a spring water, for
instance) is performed by transferring 100 c.c. to a dry flask, add-
ing 3 c.c. of a neutral and nearly saturated solution of calcium or
barium chloride, and 2 c.c. of a saturated solution of ammonium
chloride, then 45 c.c. of the standard lime or baryta water ; close
the flask with an india-rubber stopper, shake and allow to stand 12
hours. The fluid contents of the flask measure consequently 150
c.c. From the clear fluidf take out by means of a pipette two por-
tions of 50 c.c. each, and determine the free lime or baryta by
means of oxalic acid, in the first portion approximately, in the
second exactly. Multiply the c.c. used in the last experiment by
3 and deduct the product from the c.c. of oxalic acid which .corre-
spond to 45 c.c. of lime or baryta water. The difference shows the
lime or baryta precipitated by carbonic acid, each c.c. corresponds
to 1 mgrm. carbonic acid.

The method is convenient and good ; it is especially to be
recommended for dilute carbonic acid water. When calcium sul-
phate or carbonate is present, as is almost always the case in spring
water, you must always before titrating await the conversion of the
amorphous calcium carbonate to the crystalline state, even if baryta
water is used (K. KNAPP J). Baryta water therefore possesses no
advantages over lime water for the analysis of spring waters.,

*For the preparation of this bibulous paper should be used, the ash of
which is free from carbonate of lime. Swedish filtering-paper answers best.
J. GOTTLIEB (Journ.f. prakt. Chem., cvu, 488; Zeitschr. f. analyt. C'?iem., ix,
251) prefers aqueous tincture of litmus, prepared from litmus first exhausted
with alcohol, and used in a very dilute state. E. SCHULZE and M. MARCKER
(Zeitschr. f. analyt. Chem., ix, 334) employ corallin or rosolic acid, which they
say is specially adapted for the purpose. The alcoholic solution is cautiously
neutralized with potassa and a drop or two of this tincture is added. F.
SCHULZE (Zeitschr. f. analyt. Chem., ix, 292) recommends alcoholic tincture of
turmeric.

f It is not admissible to use a filter (A. MULLER, Zeitschr. f. analyt. Chem.,
1,84).

\Annal. d. Chem. u. Pharm., CLVIII, 112; Zeitschr. f. analyt. Chem., x, 361.



139.] CARBONIC ACID. 487

II. Separation of Carbonic Acid from the Basic

Radicals, and its Estimation in Carbonates.

4

a. Estimation in Normal Alkali Carbonates and Alkali-earth
Carbonates.

If the salts are unquestionably normal carbonates, and there is
no other salt with power to neutralize an acid present, we may
determine the quantity of the ba&ic radical by the alkalimetric
method ( 219, 220, 223), and -calculate the amount of CO,
necessary to form with it normal carbonate.

5. Separation from Basic Metals in Salts which upon ignition
readily and completely yield their Carbonic Acid.

Such are, for instance, the carbonates of zinc, cadmium, lead,
copper, magnesium, tfec.

a. Anhydrous Carbonates. Ignite the weighed substance, in a
platinum crucible (cadmium and lead carbonates in a porcelain
crucible), until the weight of the residue remains constant. The
results are, of course, very accurate. Substances liable to absorb
oxygen upon ignition in the air are ignited in a bulb-tube, through
which a stream of dry carbon dioxide gas is conducted. The car-
bonic acid is inferred from the loss.

/?. Hydrated Carbonates. The substance is ignited in a bulb-
tube through which dried air or, in presence of oxidizable sub-
stances, carbon dioxide is transmitted, and which is connected with
a calcium chloride tube, by means of a dry, close-fitting cork.
During the ignition, the posterior end of the bulb-tube is, by
means of a small lamp, kept sufficiently hot to prevent the con-
densation of water in it, care being taken, however, to guard against
burning the cork. The loss of weight of the tube gives the amount
of the water -f- the carbonic acid ; the increase of weight gained by
the calcium chloride tube gives the amount of the water, and the
difference accordingly that of the carbonic acid. A somewhat
wide glass tube may also be put in the place of the bulb-tube, and
the substance introduced into it in a little boat, which is weighed
before and after the operation.

c. Separation from all fixed Basic Radicals, without exception,
in Anhydrous Carbonates.

Fuse vitrified borax in a weighed platinum crucible, allow to
cool in the desiccator, weigh, then transfer the well-dried substance
to the crucible and weigh ag.iin. The weights of both carbonate



488 DETERMINATION. [ 139.

and borax are thus ascertained. They should be in about the pro-
portion of 1 : 4. Heat is then applied, which is gradually increased
to redness, and maintained at this temperature until the contents
of the crucible are in a state of calm fusion. The crucible is now
allowed to cool, and weighed. The loss of weight is carbonic acid.
The results are very accurate (SCHAFFGOTSCH).

I must add that borax-glass may be kept in a state of fusion at
a red heat for J to an hour without the occurrence of any vola-
tilization, but that at a white heat (by igniting over the gas-bel-
lows), even in a few minutes, it suffers a decided loss.* A few
bubbles of carbonic acid remaining in the fusing mass are without
any influence on the result.

Instead of vitrified borax fused potassium dichromate may be
used, in the proportion of 5 to 1 of the carbonate (H. RosEf). The
heat applied in this case must be low, and great caution must be
used, or the dichromate will lose weight of itself4 The carbonic
acid may be expelled from alkali carbonates, by strong ignition
with ignited silica (H. ROSE).

d. Separation from all bases without exception. (Estimation
from the loss of weight.)

aa. Carbonates of Bases yielding Soluble Salts with
Sulphuric Acid.

The process is conducted in the apparatus illustrated by Fig. 93.

The size of the flask depends upon the capacity of the balance.
B may be smaller than A. The tube a is closed at b with a little
wax ball or a small piece of india-rubber tube stopped with half
an inch of rod ; the other end of the tube a is open, as are also both
ends of c and d. The flask B is nearly half filled with concentrated
sulphuric acid, free from oxides of nitrogen and sulphurous acid.
The tubes must fit air-tight in the corks, and the latter equally so
in the flasks. The weighed substance is put into A ; this flask is
then filled about one third with water, the cork properly insert CM 1,
and the apparatus tared on the balance. A few bubbles of air
are now sucked out of d, by means of an india-rubber tube. This
serves to rarefy the air in A also, and causes the sulphuric acid in
B to ascend in the tube c. The latter is watched for some time,

*Zeit*chr. f. analyt. Chem., i, 65. f Pogg. Annal., cxvi, 181.

\Z<it8chr.f. analyt. C/iem., I, 183. Pogg. Annal., cxvi, 686.




139.] CARBONIC ACID. 489

to ascertain whether the column of sulphuric acid in it remains
stationary, which is a proof that the apparatus is air-tight. Air is
then again sucked out of ^7, which causes a portion of the sulphuric
acid to flow over into A. The carbonate in the latter flask is
decomposed by the sulphuric acid, and the liberated carbonic acid,
completely dried in its passage through the sulphuric acid in J3,
escapes through d. When the evolu-
tion of the gas slackens a fresh portion
of sulphuric acid is made to pass over
into Ay by renewed suction through
d\ the operation being repeated until
the whole of the carbonate is decom-
posed. A more vigorous suction is
now applied, to make a large amount
of sulphuric acid pass over into A,
whereby the contents of that flask are
considerably heated ; when the evolu-
tion of gas bubbles has completely

j j FIG. 93.

ceased, the stopper on a is opened, and

suction applied to <$, until the air sucked out tastes no longer of
carbonic acid.* When the apparatus is quite cold it is replaced
upon the balance, and the equilibrium restored by additional weights.
The sum of the weights so added indicates the amount of carbonic
acid originally present in the substance.

If the flasks A and B are selected of small size, the apparatus
may be so constructed that, together with the contents; it need not
weigh above TO grammes, admitting thus of being weighed on u
delicate balance. The results obtained by the use of this apparatus,
flrst suggested by WILL and myself, are very accurate, provided
the quantity of the carbonic acid be not too trifling. Various
modifications of the apparatus have been proposed, principally in
order to make it lighter. See foot-note, p. 492.

If sulphites or sulphides are present, together with the carbon-
ates, their injurious influence is best obviated by adding to the
carbonate solution of normal potassium chromate in more than
sufficient quantity to effect their oxidation. If chlorides are pres-
ent, in order to prevent the evolution of hydrochloric acid, add to

* In accurate experiments it is advisable to connect the end b of the tube a
with a calcium-chloride tube during the process of suction, and to use an aspira-
tor or hydraulic air-pump instead of the mouth.



490 DETERMINATION. [ 139.

the evolution flask a sufficient quantity of silver sulphate in solu-
tion, or connect the exit tube d with a small prepared TJ-tube,
which is, of course, first tared with the apparatus, and afterwards
weighed with it. This U-tube is prepared in accordance with the
happy proposal of STOLBA by filling with fragments of pumice
which have been boiled with an excess of concentrated solution of
cupric sulphate, till the air has been expelled, and then dried and
heated to complete dehydration of the copper salt. If the U-tube
is only 8 cm. high and has a bore of 1 cm., it answers the purpose
very well. The outer end is provided with a perforated cork and
short glass tube. We apply suction to this by means of a flexible
tube, instead of to d.

fib. Carbonates of Bases yielding Insoluble Salts with Sul-
phuric Acid.

The method aa is unsuitable for these bases, because the
insoluble sulphate formed, e.g., calcium sulphate, partially protects
the still undecomposed portion of carbonate from decomposition.
The apparatus is hence modified as shown in Fig. 94.

The modification consists simply in the tube ab, which, as the
cut shows, is provided with a glass bulb, and is drawn out to a
fine point at the lower end.

The process is carried out as follows : The weighed substance
is introduced into A, with some water. The bulb-tube ab con-
tains dilute nitric acid (or, if substances are present which decom-
pose nitric acid, e.g., ferrous oxide, 10-per cent, hydrochloric
acid) in quantity more than sufficient to decompose the carbonate
present. The end b is closed by a well-kneaded piece of wax, or
with a short section of rubber tubing closed by a small piece of a
glass rod, in order to prevent the acid from running out. The
tip of the tube a should not, at first, dip into the water in A.
Place the apparatus on a balance and ascertain its tare, then care-
fully push the tube a down into the liquid until the tip nearly
reaches the bottom, then loosen the wax plug or open the rubber
tube for a moment, and allow some of the acid to run out, and
repeat this now and again until all the carbonate has been decom-
posed. Now heat the contents of A to incipient boiling, remove
the stopper from Z>, and draw the carbonic acid out of the
apparatus as detailed under aa ; after cooling, determine the loss
of weight.

It will be seen at a glance that the apparatus is susceptible of



139.] CARBONIC ACID. 491

a different construction ; for instance, the flask B may be omitted,
and the tube G connected instead with a calcium-chloride tube or





Fig. 94. Pig. 95.

a tube containing pumice-stone or asbestos saturated with sulphuric
acid ; or the substance to be decomposed may be placed in a small
tube arranged to stand upright at first, or suspended by a thread,
and which, after the apparatus is tared, may be upset or lowered
into the dilute acid ; the closure of the tube & may also be effected
by a pinch-cock, etc. Such modifications, if made judiciously,
affect the results but little, if at all. An apparatus of this kind,
modified by FR. MOHR, is shown in Fig. 95.

One of the most convenient apparatus is that proposed by
GEISSLER * and shown in Fig. 96. This consists of two parts, AB
and C. C is ground into the neck at a so as to fit airtight, yet
be readily removable, whereby A may be filled. C carries a
tube, fo, open at both ends, and ground to fit C watertight at c ;
by means of a movable cork, i, it is kept in proper position. In
other respects, the apparatus is arranged as shown in the cut.
The cork e must fit airtight, and so too must the tube d in the
cork e. The weighed substance to be decomposed is introduced
into A, water added to the extent indicated, and the substance
shaken to one side of the flask. C is now nearly filled with

* Journ.f. prakt. CJiem., LX, 35.

CALIFOfiNlA COLLEGE



492



DETERMINATION.



[ 139.



diluted nitric acid, or 10-per cent, hydrochloric acid, by means of
a t^j ^ette, having previously slipped the cork upwards, without, how-
ever, unseating &; the cork i is then slipped
down again, C inserted into A, 7? filled a
little over half full with pure concentrated
sulphuric acid, and J closed, with a wax
plug or a piece of rubber tubing and a
small piece of glass rod. After weigh,
ing, the decomposition is effected by
slightly lifting ~b and allowing acid to flow
into A from C. The carbonic acid escapes
8 through h into the sulphuric acid by
which it is dried, and passes from the
apparatus through d. When the decom-
position is complete, A is cautiously heated
to incipient boiling, J is then opened, and
the carbonic acid exhausted from the ap-
paratus at d by means of a small rubber
tube. After cooling, the apparatus is
weighed.*

If it is necessary to use hydrochloric
acid for decomposing the carbonate, the
escaping carbonic acid should be dried
with pieces of pumice-stone impregnated
with anhydrous cupric sulphate, which

retains both the water and hydrochloric-acid gas (STOLBAf).

Its preparation is described under aa. It is well to fill both limbs

* Other carbonic-acid apparatus effecting similar results by somewhat dif-
ferent modifications have been proposed by H. ROSE, FRITZSCHE, ROGERS (see
H. ROSE'S Handb. der analyt. Clem., 6. Aufl., n, 784), VOIIL (Annal d. Chem.
u. Pharm., LXVI, 247), M. ScHAFFNER(4/i/i<7J. de Chem. u. Pharm., LXXXII, 335),
WEUTHER (Modification of GEISSLER'S apparatus described above, Journ. f.
prakt. Chem., LXI, 99), T. D. SMITH (Chem. Gaz., 1855, 201), A. MAYER (Journ. f.
prakt. Chem., LXVII, 63), TH. SIMMLER (Journ. f. prakt. Chem., LXXI, 158), AL.
BAUER (personal communication), P. HART (Chem.' Gaz., 1859, 174), C. D.
BRAUN (Dingl. polyt. Journ., CLV,301), E. J. REYNOLDS (Chem. News, 1862, 143),
STOLBA (Zeitschr. f. analyt. Chem., i, 368), ULLGREN (ib., vnr, 46), JOHNSON
(ib., ix, 90), BUNSEN (ib., x, 403). and others. Johnson's method differs from
the usual one in that the apparatus is filled and acid saturated with carbonic
acid before beginning, and therefore docs not remove the carbonic-acid gas on
completing the analysis. In this method it is necessary, of course, to observe
that both air-pressure nd temperature are alike during both weighings.

\Dingl. polyt. Journ., CLXIV, 128; Zeitschr. f. analyt. Ch&m., i, 368.




Fig. 96.



139.] CARBONIC ACID. 493

of a light U-tube of a size to suit the apparatus. The tube remains
serviceable so long as one-third of its contents remains uncolored.
When employing a measured volume of standard acid accord-
ing to one of the methods described under d, Ib, the estimation
of the carbonic acid and the base may be effected in one operation
according to 139, II., &; this is often advantageous with pasty
precipitates. The standard acid is run in from a burette having a
fine point, into the bulb-tube of the apparatus, Fig. 94, first, how-
ever, closing the lip of the latter with a little tallow. After the
apparatus is tared it is warmed to melt the tallow, and the opera-
tion is then carried out (STOLBA*).

e. From all Bases without .Exception (Determination of Acid
from the Increase in Weight of an Absorption Apparatus).

This method, which was formerly seldom employed, has been
highly recommended by KoLBEf. I have striven, by utilizing
all the results recorded by G. J. MULDER, STOLBA, and KOLBE,
to make it as practical as possible, and for the last ten years I
have used it almost exclusively. The accuracy of the results
afforded by it is approached by but few others.

The apparatus I use has the arrangement shown in Fig. 97.
A is a 150- to 300-c. c. flask provided with a doubly perfor-
ated rubber stopper. is a twice-bent tube expanded at c to a
bulb ; it may be connected by means of a piece of rubber tubing,
bearing a pinch-cock, d, either with the funnel e, or with the
soda-lime tube, /*, which, in turn, is connected with the flask g
containing potassa solution. The tube A, also having a bulb, has
its lower end ground obliquely. The L r -tube i has a height of
17 cm. and a bore of 16 mm. ; only the lower bend contains some
calcium chloride. J The equally large U-tubes Jc and I contain
respectively calcium chloride and pumice copper sulphate (see
page 490). The smaller tubes, m, n, 0, and p, are 1 1 cm. high
and are 12 mm. bore; m contains calcium chloride, whereas n and

*Journ. /. prakt. Chem., xcvn, 312 ; Zeitschr.f, analyt. Chem., v, 208, and
Vi, 444.

f Annal. de Chem. u. Pharm., cxix, 130.

| It need scarcely be mentioned that all the calcium chloride must be free from
alkalinity, and should be tested for this. Any alkalinity is readily obviated by
adding a little ammonia to the calcium chloride solution before evaporating.



494



DETERMINATION.



[ 139.



<?, are filled with coarsely granulated soda-lime (about 20 grm.)
and the remaining T with coarsely granulated calcium chloride ;




Fig. 97.

the outer limb of p contains soda-lime, the inner calcium chloride.
i, &, I, and m serve to deprive the carbonic-acid gas of water
and hydrochloric acid; the soda-lime in n and o completely
absorb the carbonic acid, and the calcium chloride they contain
prevents any evaporation of water from the soda-lime (as this
becomes warmed during the absorption of carbonic acid) ; p serves
to prevent ingress of moisture into n and o from without. The
corks of n and o should be coated with sealing-wax. The other
tubes may be provided with perforated rubber stoppers or corks
coated with sealing-wax. The apparatus, once in order, may
serve for use for a long time, but before each new experiment,
it is necessary to renew the calcium chloride in *', and to refill n,
and occasionally o also.

After weighing the substance introduce it into -4, together



139.] CARBONIC ACID. 495

with a Uttle water ; then weigh n and 0, connect the various parts
of the apparatus, join 5 and e, close d, and apply suction by
means of a hydraulic air-pump or aspirator to the end of the tube
s, which is connected both with the U-tube r, containing a little
Water, and with p. The pinch-cock ^is in the meantime opened.
The apparatus may be known to be air-tight when the passage of
air-bubbles through the water in r soon ceases. As soon as this
occurs, fill e with dilute hydrochloric acid (or with nitric acid,
according to circumstances), and allow a little to flow into A by
cautiously opening d. Evolution of carbonic-acid gas begins at
once, and its rise noted by the passage of air-bubbles through
the water in r. When the evolution slackens, allow a further
quantity of acid to flow into A, and if the quantity of acid has
been properly adjusted the decomposition of the carbonate will be
complete on adding the last portion of acid, e is then rinsed with
a little water, which is allowed to flow into A, after which remove
0, connect d withy, and, cautiously opening d, draw a gentle cur-
rent of air continuously through the apparatus, while the con-
tents of A are heated to incipient boiling.

As soon as the carbonic acid reaches the soda-lime tubes these
become warm, and this progressive heating affords a good indi-
cation as to the extent to which the soda-lime has been saturated
by the carbonic acid. As soon as the soda-lime tubes have be-
come perfectly cold the larger part of the carbonic acid has been
absorbed, and if the current of air is slowly drawn through the
tubes 5 or 10 minutes longer all the carbonic acid will surely have
been removed from A, i, &, Z, and m. If the flask has been
properly and judiciously heated, but very little water will have
reached ?', so that the calcium chloride in its lower part will have
become moist, yet will not have quite deliquesced.

After the experiment is finished, stop the suction at s, and
remove and weigh n and o. The increase in weight will be the
exact expression of the carbonic acid present in the carbonate ex-
amined. The concordance and accuracy of the results leave
nothing to be desired.* The bases are retained perfectly pure
and completely dissolved in the hydrochloric (or nitric) acid.

In making a second test empty *, and recharge both it and n.



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