C. Remigius Fresenius.

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149.] NITRIC ACID. 583

soda solution, is supported so that its open end is under the sur-
face of the liquid in B.

The solution of the nitrate in the flask is further concentrated
by boiling, and finally the lower end of the tube efgJi is brought
into the soda solution so that a part of the steam escapes through it.
After a few minutes the rubber tube at g is pressed together with
the fingers; if the air has been completely displaced from the
flask by boiling, the soda solution will rise suddenly in the tube as
in a vacuum, and a slight blow against the finger will be perceptible.
In this case the rubber tube at g is closed with a clamp and
the steam is allowed to escape through abed until only 10 c. c.
of fluid remain in the flask. The lamp is now removed and the
rubber tube at c is closed with a clamp, and the tube c d filled by
a jet of water. If an air bubble remains in the rubber tube at <?,
it must be removed by pressure with the fingers. The graduated
measuring tube is now brought over the upcurved end of the evo-
lution tube efg li so that the end rises in it 2-3 cm. The flask
must next be allowed to stand a few minutes until a partial vacuum is
produced in it, which is manifested -by a contraction of the rubber
tubes at G and g. A nearly saturated solution of ferrous chloride
is poured into a small beaker, the upper part of which is marked
so as to show the space occupied by 20 c.c. ; two other beakers
must also be at hand partly filled with concentrated hydrochloric
acid. The tube c d is now dipped into the ferrous- chloride solution,
and the clamp at c is loosened until 15-20 c.c. are drawn into the
flask. The ferrous chloride remaining in the tube is next removed
by drawing in a small quantity of hydrochloric acid in two suc-
cessive portions. Small bubbles may frequently be observed at
5, occasioned by evolution of hydrochloric gas caused by dimin-
ished pressure in the flask. They disappear almost completely so
soon as the pressure rises.

Heat is applied, at first very gently, until the rubber tubes at c
and g are slightly expanded ; then the rubber tube at g is held com-
pressed by the fingers, the clamp being removed, until the pressure
becomes stronger, when the gas is allowed to pass over to the grad-
uated tube. Toward the end of the operation heat is increased and
distillation continued until the volume of gas in the measuring
tube no longer increases. The hydrochloric gas, abundantly
evolved in the last part of the process, is absorbed with violence
by the soda solution with a peculiar clattering sound ; there is nc



584 DETERMINATION. [ 149.

danger, however, of breaking the evolution tube if care has been
taken to enclose the lower end with a rubber tube as above directed.

The measuring tube is brought into a large cylinder containing
cold water, best of 15-18 C., and by means of some suitable fix-
ture held wholly submerged in the same. The transfer is effected
with the help of a small porcelain dish filled with soda solution.

After 15-20 minutes, the temperature v of the water in the
cylinder is ascertained with a sensitive thermometer, and the state
of the barometer is also observed. Then the tube is taken hold
of at the upper end with a strip of paper or cloth, in order to avoid
imparting heat to it by direct contact of the hand, and drawn
up perpendicularly so far that the level of the fluids within and
without it exactly coincide, and the volume of the gas is read off.
From the data thus obtained, the volume which the dry gas would
occupy at C. and 760 mm. bar. pressure is to be computed. (See
pp. 160, 161, on Calculation of Analyses.) 1 c.c. N,O 2 at 0.
and 760 mm. bar. pressure corresponds to 0'002415 grm. N,O 5 .

A condition indispensable for the success of the operation is
the complete expulsion of air from the apparatus in the beginning.
When an abundant quantity of nitric acid is present in the sub-
stance, enough to produce about 80 c.c. nitrogen dioxide is a suit-
able quantity to use for its determination, and a somewhat larger
quantity of ferrous chloride and hydrochloric acid than above indi-
cated may be used. An unnecessary amount of these reagents
should, however, be avoided, since it is difficult to boil a small quan-
tity of nitrogen dioxide out of a large volume of liquid.

This method is easy to carry out and gives satisfactory results.

e. Methods "based on the conversion of Nitric Acid into
Ammonia.

On heating a nitrate in an alkaline fluid in which nascent
hydrogen is being evolved in sufficient quantity, all the nitric acid
of the nitrate is converted into ammonia,* from the volume of
which the quantity of nitric acid may be accurately determined.
FK. BoHULZBt was the first to base on this principle a method for
the estimation of nitric acid, and he was soon followed by

* Thr mm < Tsi.M lakes place in acid solution also, but is then only partial
(L. GMELIN; MARTIN).

f Chem. Centratol., 1861, 657 and 833.



149.] f NITRIC ACID. 585

W. WOLF,* HARCOURT,")* and SIEWERT. ;|: Later on BUNSEN,
and also HAGER, || modified both the methods and the apparatus.
SCHULZE effected reduction with platinized zinc ; W. WOLF, HAR-
COURT, and SIEWERT witli zinc and iron filings; BUXSEN with a
zinc-iron spiral. Zinc and iron appear to afford the most satis-
factory results, therefore I shall first describe HARCOURT'S process,
in which an aqueous potassa solution is used, and then describe
SIEWERT 's method, in which an alcoholic potassa solution is em-
ployed. If organic substances are present, these methods do not
afford good results (FRITHLING^). The reliability of the results,
however, is questioned even whqn organic substances are absent.
While the test-analyses afforded HAROOURT and SIEWERT uniformly
good results, WOLF (loc. cit.) states that the three following con-
ditions are essential for the success of the method : 1. The con-
version of nitric acid into ammonia must take place in the cold
(on heating, while the hydrogen is being evolved, some ammonia
is lost, most probably from the escape of nitrogen as such).

2. A copious and uniform evolution of hydrogen is necessary,
and is best secured by using zinc in conjunction with iron.

3. The potassa or soda must be dissolved in not less than 7 or
more than 8 parts of water. It will be observed that these con-
ditions are at direct variance with the directions given by HAR-
COURT. FINKENER ** rejects all the methods based on the above
principle, because, although all the nitric acid is decomposed, yet
all the nitrogen is not converted into ammonia. I have not studied

O

the methods sufficiently to give a decided opinion, but I must say
that in my laboratory the methods of HARCOURT and of SIEWERT
have generally given good results.

HARCOURT employs the apparatus shown in Fig. 110. Bring
the tube e into a vertical position by turning it half round in the
tubulure ; then run into it from a burette standard acid (more
than is sufficient to fix the ammonia) into <#, add a little litmus

* Ghem. Centralbl, 1862, 379; also Journ. f. prakt. Chem., LXXXIX, 93, and
Zeitschr.f. analyt, Chem., n, 401.

f Journ. of the Chem. Soc., xv, 385; also Zeitschr. f. analyt. Chem., ir, 14.

j Annal. d, Chem. u. Pharm., cxxv, 293.

Zeitschr. f. analyt. Chem., x, 414.

I Ib., x, 334.

\Landwirthsc7iaftl. Versuchsstat., vrn, 473.

** H. ROSE, Handb. d. analyt. Chem. , 6 Aufl. von FINKENER, n, 829,



586 DETERMINATION. [ 149.

tincture, turn the tube e back to its horizontal position, and let a
little more of the standard acid run into the bulbs. Kow remove




Fig. 110.

the flask #, while its stopper carrying the glass tube, and also the
small flask &, containing a little water, are allowed to retain their
position on the sand-bath unchanged. Into a introduce about 50
gnu. of finely granulated zinc and about 25 grm. of iron filings
(purified by first sifting and then heating in a current of hydro-
gen), add the weighed quantity of nitrate (for instance 0'5
potassium nitrate), 20 c. c. of water, and 20 c. c. of potassa solu-
tion of sp. gr. 1*3. That part of the sand-bath 0, directly
under #, is now heated until the contents of a boil. When the
bubbles of air and hydrogen pass quietly through the bulbs 0, a
loss of ammonia is not to be feared. As soon as distillation begins,
place the lamp so that also the contents of the flask J boil gently.
In this manner the fluid is by one operation distilled twice, and the
traces of potassa carried over from a are completely retained in b.
The end of each exit-tube, as a further precaution, is drawn out
and bent upwards in the form of a hook. The distillation re-
quires from 1 to 2 hours. It may be stopped when the hydro-
gen, which is evolved more freely as the potassa solution becomes
mre concentrated, has passed through the bulb-tube e for 5 or 10
minutes regularly. As soon as the fluid <?has receded to d on the
cooling of the apparatus, remove the rubber stopper from the small
tubulure/, and pass a stream of water through the condenser in
order to rinse the last traces of ammonia into the receiver. Once



149.] NITRIC ACID. 587

more "bring the tube e to a vertical position by a half- turn, rinse it
out with water, then remove it, and close the tubulure of the re-
ceiver with a cork. Finally remove the receiver, and rinse off the
outside of the lower end of the condenser, and proceed to titrate
the residual free acid. The metals remaining in a need only be
washed with water, diluted acid, and again with water, in order
to render them serviceable for a second determination. Metals
which have been once used evolve hydrogen more slowly
than do bright zinc and recently ignited iron, but the evolu-
tion of ammonia proceeds equally well in both cases. Metallic
chlorides and sulphates have no influence on the result. If
lead is present it appears advisable to add some potassium
sulphate.

SIEWEKT employed for every gramme of saltpetre 4 grm.
iron filings and 8 to 10 grm. zinc filings, and also 16 grrn. potas-
sium hydroxide and 100 c. c. alcohol of 0-825 sp. gr. By the
use of alcohol the danger of the boiling fluid receding is avoided.
The apparatus used by him consists of a 300- to 350-c. c.
flask with an evolution tube connected with the two flasks^ and (7,
arranged as shown in Fig. 111. These flasks have a capacity
of 150 to 200 c. c. each and contain
standard acid. The connecting tube b
is cut off obliquely at both ends; c
serves for the introduction of a strip of
litmus paper during the operation, and
after the latter is complete, for the
transference of the liquid from one
flask to the other at will. After put-
ting the apparatus together, the disen-
gagement of gas may be allowed to pro-
ceed first in the cold, or it may be
assisted from the beginning by the aid

of a small flame. After half an hour the ammonia formed begins
to pass over in proportion as the alcohol distils off. As soon as the
latter has completely disappeared from the evolution flask, apply
heat very cautiously (in order to drive off the last traces of am-
monia) until steam appears in the evolution tube ; or 10 to 15 c. c.
of alcohol are rapidly introduced once or twice into the evolution
flask and distilled off.




DETEfcM IN ATtOtf .



[ 149.



f. Method of estimating nitric acid from the loss of hydro-
gen, after FR. SCHULZE.*

On dissolving aluminium in potassa lye, a potassium-alumin-
ium compound is formed and hydrogen is evolved, the quantity




Fig. 112.

evolved corresponding to the weight of the aluminium dissolved.
If a nitrate is added to the mixture evolving the hydrogen, less
hydrogen is obtained than were no nitrate present, since part of
the nascent hydrogen serves to convert the N a O 6 of the nitrate

*Zeit8c7ir.f. analyi. Chem. t n, 300.



149.] NITRIC ACID. 589

into ammonia (K a O 6 + 16H = 2NH 3 + 5H a O), and the loss of
hydrogen is, of course, proportional to the quantity of N 3 O 6 con-
verted into ammonia. Since, according to FR. SCHULZE, this
conversion is complete when the process is conducted slowly
(FINKENER,* however, contradicts this), and since a small quan-
tity of N 2 O B is able to effect a relatively large deficit of hydrogen,
this method can be applied for the accurate determination of even
small quantities of nitric acid. The method cannot, according to
E. SCHULZE, f be used if organic matter is present, because then
the results are inaccurate. In such a case the substance must first
undergo the following preliminary treatment: Heat with dilute
potassa lye until all ammonia is expelled, add a concentrated solution
of pure potassium permanganate until the fluid retains a red color
even on continuous boiling during 10 minutes, then add a little
formic acid to decompose the excess of permanganate, present,
filter, wash, concentrate the filtrate, neutralize accurately with
dilute sulphuric acid, and then subject the fluid so obtained, and
concentrated by evaporation, if necessary, to the treatment to be
described below (FRANZ SCHULZE^:).

I shall first describe the apparatus used, resembling KNOP'S
azotometer || , and then the process.

The flask A (Fig. 112) has a capacity of about 50 c. c. Into
its neck is ground airtight the tube B, expanded above into a
bulb. A glass rod, <?, is ground to fit the lower opening of B>
which it closes perfectly ; it passes through the cork d, and is so
long that, when the cork is slid up to the end of 0, fluid may be
introduced into B by means of a pipette. For measuring the
gases there is used a tube, C, divided into 0*1 c. c. and connected
by means of a rubber tube with a tube, D, of similar size, but
plain. The tubulure f of the latter bears an arrangement for



*H. ROSE, Handb. d. analyt. Cfiem., 6. Aufl. von FINKENER, n, 829.

\Zeitschr.f. analyt. Chem., vi, 379.

\Zeitsclir.f. Chem. (N. F.). iv, 296; Zeit&clir.f. analyt. Chem., vn, 390.

Instead of this, RUMPF'S may be used (Zeitschr. f. analyt. Chem., vi, 399).

I Chem. Centralbl., 1860, 244. The original KNOP apparatus differs from the
modification here given in that the tube D is not provided with the lateral
tubulure. The removal of water from D is effected by suction into a flask. In
RAUTENBERG'S modification the tubes C and D are placed in a cylinder filled
with water, in order to enable the operator to better regulate the temperature of
the gases and estimate them.



590 DETERMINATION. [ 149.

allowing water to run off, as shown ; the upper end of the tube
is connected by means of a rubber tube ~k with the glass tube A,
which in turn is fitted into the cork inserted into the tubulnre a.
To perform a series of experiments, a rather large quantity of
aluminium filings is required from which any iron present has
been removed by means of a magnet. The first thing to be done
is to determine the weight of hydrogen evolved by a weighed
quantity of this aluminium powder on dissolving in potassa lye.
This preliminary experiment is absolutely indispensable, since
every kind of aluminium behaves differently in this respect. To
carry out this experiment, introduce a weighed quantity, say O'OTo
grm., of aluminium powder into A and add to it a little water.
On the other hand, introduce exactly 5 c. c. potassa lye into B
and place this on A, airtight. ]Now pour water into D until its
level stands exactly at the zero point in (7, and connect A with
the measuring- tube by inserting the tube A into the rubber
tube p. After again making sure that the water-level in C
and D is at the same height, and that it stands at zero in (7, note
the temperature of the room, and place A in a beaker of water
having the same temperature. Water is now allowed to run out
from n until the level of water in D stands exactly at a certain
height, say at 30 c. c., and the water has fallen in C to about the
mark 1. If both levels remain unchanged for some time, and
you are sure that all the parts of the apparatus are airtight, raise
the glass rod C slightly to allow the lye in B to flow into A. As,
on account of the lower level of fluid in D, the air in A is under
less pressure than is the air in B, or the free atmosphere, care
must be taken to again close the opening e airtight the moment
the fluid in B has almost run out, and when only just enough
remains to prevent free communication between A and B. The
volume of "liquid originally present in B (in this case 5 c. c.) is
subsequently to be deducted from the volume of gas in (7. In
the proportion in which the aluminium dissolves, and the hydrogen
is evolved, the level in C sinks, while that in D rises, and renders
necessary the withdrawal of more water through n, so that both
levels may remain about the same. When the evolution of gas
lias entirely ceased, and you are sure that the water in which
the flask A stands, as well as the air, are still at the same
temperature as at first, bring the level in D to the exact height in



149.] NITRIC ACID. 591

O, so tha*t the tension of gas in A. and C may correspond exactly
to the atmospheric pressure, and then read off the height of the
water in 0. This reading, minus the number of c. c. of fluid
which flowed from B into A, expresses the number of c. c.
of hydrogen evolved by the aluminium dissolved under the pre-
vailing circumstances of atmospheric pressure, temperature, and
tension of aqueous vapor. Reduce the measured volume to the
dry condition at and 760 mm. ( 198), calculate the weight of
this volume (1000 c. c. = 0'08988 grm.)of hydrogen, and ascer-
tain the weight of aluminium required to evolve 1 grin, of hydro-
gen by dividing the weight of the aluminium used by the weight
of the volume of hydrogen found. SCHULZE found this quotient
to be in one case 10*5042, i.e., this weight of aluminium evolved
1 grin, hydrogen (9*16 grin, absolutely pure aluminium evolve
1 grrn. hydrogen). Since 16 eq. of hydrogen (16-128) corre-
spond to 1 eq. of N 2 O B (108-08), 16-128 X 10-5042= 169-4117
grrn. of the aluminium in question correspond to 108-08 grin.

N,O V

Suppose, now we know the exact value of our aluminium,
we desire, on some occasion, to make a determination of ^ 2 O 5 ,
using the aluminium. We begin first by calculating how many
c. c. of hydrogen a certain weight aluminium, say 0*05 grm.,
will afford on the day the determination is about to be made,
i.e., at the temperature and atmospheric pressure prevailing on
that particular day, and which, it is assumed, will remain con-
stant throughout the process (to best insure this a room in which
the temperature remains constant is chosen). Let us assume we
obtained 58-4 c. c. as the number of c. c. of hydrogen correspond-
ing to 0'05 grm. of aluminium. Introduce the fluid, the nitric acid
of which is to be determined, and the volume of which may be
about 20 c. c., into the flask A, add a weighed quantity of alumin-
ium powder sufficient to insure at least 2 parts being present for
every 1 part of N 2 O B , connect the apparatus as detailed above,
and allow the potassa lye to flow into A , at first by drops. To insure
total conversion of N 2 O 6 into ammonia, in which case the hydrogen
deficit will correspond to the N 2 O B , the solution of the aluminium
must be so conducted that for at least one hour an evolution of
hydrogen is scarcely observable, and that from 3 to 4 hours are
required for the completion of the process. After making sure



592 DETERMINATION. [ 149.

that the barometer and thermometer stand as at the beginning of
the experiment, read off. Let us assume, taking one of SCHULZE'S
experiments as an example, that 0.15 grm. of the aluminium
powder and a definite quantity of potassium nitrate had been taken,
and had afforded 95*6 c. c. hydrogen. How much K a O; was pres-
ent? 0'15 grm. aluminium would have evolved 3 X 58*4 =
175-2 c.c. hydrogen; but we obtained only 95'6 c. c., hence the
hydrogen deficit would be 175 '2 95 -6 = 79*6 c. c., which
according to the proportion

58-4: 0-05: : 79-6: x = 0-06815 aluminium;
and further:

169-4117 : 108-08 : : 0-06815 : aj, = 0-04348 1STA-
(The 0-083 grm. of nitre added by SCHTJLZE contained 0-0443

N.O.).

g. Methods in which the Nitrogen of the Nitric Acid is sep-
arated and measured in the gaseous form.

These methods are more particularly suitable for analyzing
nitrates which are decomposed by ignition into oxide or metal and
oxides of nitrogen ; they will be found in the Section on the Ulti-
mate Analysis of Organic Bodies in 185. MARIGNAO employed
them to analyze mercurous nitrates. BKOMEIS analyzed nitrite,
<fec., of lead by a similar method, recommended by BUNSEN.* In
cases where it is intended to determine the water of the analyzed
nitrate in the direct way such methods are almost indispensable, f

If the nitrogen evolved on igniting a nitrate with finely divided
copper is to be estimated gravimetrically, the method recommended
i;i;> J may be employed.

h. The methods employed in determining the small quantities
of nitric acid occurring in natural waters will be described under
Water Analysis.



*Annal. d. Chem. u. Pharm., LXXII, 40.

i Sec :iK.i CM; us, Am. Journ. Set'., xxxvn, 350.
j Zeitechr.f. analyl. Chem., in, 393.



150.] CHLORIC ACID. 593



150.
2. CHLORIC ACID.

I. Determination.

Free chloric acid in aqueous solution may be determined by
converting it into hydrochloric acid by the agency of nascent
hydrogen (II., &), and determining the acid formed, as directed in
141 ; or by saturating with solution of soda, evaporating the
fluid, and treating the residue as directed in II. , a or c.

II. Separation of Chloric Acid from the Bases and
Determination of the Acid in Chlorates.

a. After BUNSEN.* When warm hydrochloric acid acts upon
chlorates, the latter are reduced ; as this reduction is not attended
with separation of oxygen, the following decompositions may take
place :



25 no ci 2 o 5 c 2 ci 2 o 5 sr C1 A 12C1

2HC1 | 4HC.I I 2H 2 6HC1 | J|* 8HC1 | ||* p 10HC1 } 5H 2 O

Which of these products of decomposition may actually be formed,
whether all or only certain of them, cannot be foreseen. But no
matter which of them may be formed, they all of them agree in
this, that, in contact with solution of potassium iodide, they liber-
ate for every 2 mol. chloric acid (IIC1O 3 ), or 1 mol. Cl a O 6 in the
chlorate, 12 at. iodine. 1522-2 of iodine liberated correspond
accordingly to 150-9 C1,O 6 . The analytical process is conducted
as described in 142, 1.

The test-analysis made by BUNSEN gave good results. Accord-
ing to FLNKENEE, f however, too little iodine is precipitated in this
method, hence he advises, in order to obtain correct results, to
boil 33 c. c. hydrochloric acid, 66 c. c. water, 10 grm. potassium
iodide, and 1 .c. c. aqueous solution of sulphurous acid five minutes
in a current of carbonic acid, allowing to cool in the current of
gas, and to then add this solution to the chlorate in a stoppered

* AnnaL d. Chem. u. Pharm., 86, 282.

f H. ROSE, Handbuch der analyt. Chem., 6. Aufl. von FINKENER, n, 612.



694 DETERMINATION. [ 150.

flask. The flask should have been previously filled with carbonic-
acid gas, then filled with the acid solution, tightly stoppered,
heated for 15 minutes in a water- bath, allowed to become perfectly
cold, shaken, the solution then diluted and the iodine liberated
estimated.

J. Heat the weighed chlorate with an excess of a solution of
ferrous sulphate in hydrochloric acid, and estimate the ferric chlo-
ride formed. The process is conducted according to the rules
given under 149, II, d, ft. 12 eq. of Fed, raised to Fe a Cl.
correspond to 1 eq. of C1,O 6 .

c. The conversion of chloric acid (and generally all oxygen
compounds of chlorine, excepting perchloric acid) may also be
accomplished in very dilute solution by nitrous acid or a nitrite,
preferably by neutral lead nitrite (II. TOUSSAINT *) . Mix the
dilute aqueous solution of the chlorate with a slight excess of lead-
nitrite solution, f acidulate with nitric acid, warm, and convert the
hydrochloric acid formed into silver chloride as in 141 , I, a.

If it is intended to apply this principle to the volumetric esti-
mation of chloric acid, introduce a very dilute solution of potas-
sium chlorate of known strength into a stoppered flask, add an
excess of silver nitrate, acidulate strongly with nitric acid, heat in
a water- bath, and then add, under frequent shaking (which pro-
motes the deposition of the silver chloride), the solution of lead
nitrite until a drop no longer causes a precipitate of silver chloride.
The lead-nitrite solution being thus standardized, it may be em-



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