C. Remigius Fresenius.

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6. Decomposition by Fusion with Calcium Carbonate and
Ammonium Chloride.

DEVILLE * recommends fusing 1 part of the powdered silicate
with 0*3 to 0'8 part calcium carbonate, but I have not found the
process to answer with many silicates. L. SMITH f recommends
fusing 0*5 to 1 grm. of powered silicate with 1 grm. finely granu-
lated ammonium chloride (prepared by interrupted crystallization)
and 8 grm. pure calcium carbonate (obtained by precipitation
with ammonium carbonate with heat). Should the temperature
during fusion rise too high, however, a portion of the alkali
chloride may be lost by volatilization. SMITH employs crucibles
9 mm. high, 22 mm. wide at the mouth, and 16 mm. wide
at the base. The crucibles are fixed in a metal clamp or in the
iron plate of a special gas furnace, J and in such a manner that
about 15 mm. remains outside. Gentle heat is applied first to

*Journ.f. prakt. Chem., LX, 246.

t/6., LX, 246; also Chem. News, xxin, 222 and 234; Zeitschr. /. analyt.
Chem., xi, 85.

IZeitschr.f. analyt. Chem., xi, 87.

140.] SILICIC ACID. 519

the part t)f the crucible above the mixture, and is then gradually-
moved downwards, so that in about 5 minutes all the ammonium
chloride is decomposed. The heat is then increased and the
crucible kept at a bright-red heat for 40 to 60 minutes. By this
method of heating all fear of volatilization of alkali chloride is
avoided. After cooling, proceed with the semi-fused mass accord-
ing to y. SMITH states, however, that a solution of the total
alkalies may also be obtained by heating the ignited mass with
water for several hours, filtering, and washing the residue. From
this solution of alkalies, calcium chloride, and calcium hydroxide,
the calcium is precipitated by ammonium carbonate and a little

[Prof. J. L. SMITH'S METHOD in detail for separating alkalies :
Mix 1 part of the pulverized silicate with 1 part of dry ammo-
nium chloride, by gentle trituration in a smooth mortar, then add
8 parts of calcium carbonate ( u Qual. Anal." p. 87) and mix inti-
mately. Bring the mixture into a platinum crucible, rinsing the
mortar with a little calcium carbonate. Warm the crucible gradu-
ally over a small Bunsen burner until fumes of ammonium salts no
longer appear, then heat with the flame of- a Bunsen burner until
the lower three-fourths only of the crucible are brought to a red
heat. Keep this temperature constant from 40 to 60 minutes.
The temperature desired is that which suffices to keep in state of
fusion the calcium chloride formed by the reaction of ammonium
chloride with calcium carbonate. The mass, however, does not
become liquid since the fused calcium chloride is absorbed by the
large quantity of calcium carbonate present. If the silicate is
fused by application of too strong heat, disintegration of the mass
at the end of the operation with water cannot be effected. More-
over, too high a temperature causes volatilization of alkali chlo-
rides. Certain silicates e.g., those which contain much ferrous
iron may fuse when heated with the above mixture, even if no
higher temperature is employed than is necessary to effect decom-
position. If this occurs, it is better to repeat the ignition with a
new portion of the silicate, using 8 to 10 parts of calcium carbo-
nate. The mass contracts in volume during the ignition, and is
usually easily detached from the crucible. Boil it in a covered
porcelain dish, with 50- Y5 c.c. -water, half an hour, replacing water
lost by evaporation. Decant the solution from the residue upon a
filter, boil the residue a few minutes with water, and decant again


If the residue is now all in a finely disintegrated state, it may be
brought upon the filter and washed. But if, as is often the case, a
portion remains coherent or in a coarsely granular state, it must be
/educed to a line state of division by trituration with a porcelain
;>r agate pestle in the dish, and boiling with water again. By a
few repetitions of the trituration, boiling and decanting, allowing
the fine suspended portion to pass upon the filter each time, the
whole can usually be transferred to the filter in properly disinte-
grated condition in course of an hour. Next wash until a few drops
of the washings acidified with nitric acid give but a slight turbid-
ity with silver nitrate. The filtrate now contains the alkalies of
the silicate as chlorides together with calcium chloride and hydrox-
ide. It is not advisable to concentrate this filtrate in a glass vessel,
since it might take an appreciable quantity of sodium from the
glass. 'Precipitate, therefore, the calcium at once with ammonium
carbonate ; allow the precipitate to settle, and concentrate the
supernatant solution in a porcelain (or platinum) dish, decanting it
into the latter, portionwise if necessary, rinsing finally the precipi-
tate into the porcelain dish. When the whole is thus reduced to
about 30 c.c., add a little more ammonium carbonate and ammonia,
heat and filter into a platinum (or porcelain) dish, evaporate to
dry ness on a water-bath, expel ammonium chloride by ignition,
dissolve the residual alkali chlorides in 3 to 5 c.c. of water. A
little black or dark-brown flocculent matter usually remains undis-
solved, while the solution may still contain traces of calcium. Add
two or three drops of ammonium carbonate and ammonia, warm
gently, and filter through a very small filter into a weighable plati-
num vessel. Evaporate to dryness on a water-bath, heat to in-
cipient fusion of the alkali chlorides, and after cooling weigh.

Prof. SMITH'S method is the most convenient of all methods
for extracting alkalies from silicates, and is universally applicable,
except perhaps in presence of boric acid. When carried out as
here described, the results are sufficiently accurate in most cases.
If, however, the silicate is rich in alkalies, a loss amounting to
O'l or 0-2 per cent of the mineral is possible. If great accuracy
is desired in such cases, a repetition of the whole process may be
applied to the residue left by treatment of the ignited mass with
water. It need hardly be mentioned that unless care be taken to use
reagents perfectly free from soda, and to avoid the action of solu-

141.] CHLORINE. 521

tions on^lass, an amount of soda may be introduced from these
sources equal to O'l or 0*2 per cent of the silicate.]

. Decomposition with Hydrochloric or Sulphuric Acid
in Sealed Tubes (under Pressure), according to AL.


Many silicates, as well as aluminates, which are scarcely or not
at all attacked on being digested with hydrochloric or sulphuric
acid in open vessels, are completely decomposed on being heated
for two hours in sealed tubes to 200 to 210 with 25-per cent
hydrochloric acid or with a mixture of 1 part by weight of
water and 3 parts by weight of concentrated sulphuric acid. To
carry out the process introduce about 1 grm. of the finely elu-
triated or sifted substance into a tube of difficultly fusible Bohe-
mian glass sealed at one end and drawn out somewhat at the
other ; then add the acid, carefully seal the tube, enclose it in the
wrought-iroii tube of a metallic bath,f and heat in the manner
prescribed. After cooling, carefully open the tube, rinse out its
contents into a platinum or porcelain dish, and proceed as in
140, II, a. This method possesses the advantage over others
that any ferrous salt present is obtained in solution as such and
can be readily determined.

Second Group.



I. Determination.

Chlorine may be determined very accurately in the gravimetric
as well as in the volumetric way.J

a. Gravimetric Method. Determination as Silver Chloride.

Solution of silver nitrate, mixed with some nitric acid, is added
in excess to the solution of the chloride, the precipitated chloride
is made to unite by heating and agitating, washed by decantation

*Journ. f. prakt. Chem., LXXXI, 108, and LXXXIII, 455.

fSuch a bath is described and illustrated in the Journ. f. prakt. Chem.,
LXXXIII. 489, and in the Zeitschr. f. analyt. Chem., i, 55.

:f For the acidimetric estimation of free hydrochloric acid, see 215,


and filtration, dried, and ignited. The details of the process have
been given in 115, 1, a. Care must be taken not to heat the
solution mixed with nitric acid, before the nitrate of silver has
been added in excess. As soon as the latter is present in excess,
the silver chloride separates immediately and completely upon
shaking or stirring, and the supernatant fluid becomes perfectly
clear after standing a short time in a warm place. The determina-
tion of chlorine by means of silver is therefore more readily effected
than that of silver by means of hydrochloric acid.

I. Volumetric Methods.

a. By Solution of Silver Nitrate.

In 115, 5, we have seen how the silver in a fluid may be esti-
mated by adding a standard solution of sodium chloride until no
further precipitation ensues ; in the same way we may determine
also, by means of a standard solution of silver, the amount of hydro-
chloric acid in a fluid, or of chlorine in combination with a metal.
PELOUZE has used this method for the determination of several
atomic weights. LEVOL* proposed a modification which serves to
indicate more readily the exact point of complete precipitation.
To the fluid, which must be neutral, he added one tenth volume
of a saturated solution of sodium phosphate. When the whole of
the chlorine has been precipitated by the silver, the further addi-
tion of the solution of silver produces a yellow precipitate which
does not disappear upon shaking the vessel. FR. MOHR has since
replaced, with the most complete success, the sodium phosphate by
potassium chromate.

This convenient and accurate method requires a perfectly neu-
tral solution of silver nitrate of known value. The strength most
convenient is, 1 litre = 0*1 at. 01. I recommend the following
method of preparation : Dissolve 18*80 to 18*85 grin, pure fused
silver nitrate in 1100 c.c. water, and filter the solution if required ;
the solution is purposely made too strong at first. Now weigh off
r.victly four portions of pure sodium chloride, each of 0*10 to 0'18
grin., one after another. The salt should be moderately ignited,
not fused, powdered roughly while still warm, and introduced into
a small dry tube, that can be well closed. The weighing off is per-
formed by first weighing the filled tube, then shaking out into a
dry beaker the quantity required, weighing again, dropping a

* Journ.f. prakt. Ghem., j.x, 384,

141.] CHLORINE. 523

second portion into beaker No. 2, weighing again, and so on.
Each portion is dissolved in 20 to 30 c.c. water, and about 3 drops
of a cold saturated solution of pure normal potassium chromate

Fill a MOIIK'S burette (in very accurate analysis an EKDMANN'S
float should be used) with the silver solution, and run it slowly,
with constant stirring, into the light yellow solution contained in
one of the beakers. Each drop produces, where it falls, a red spot,
which on stirring disappears, owing to the instant decomposition
of the silver chromate with the sodium chloride. At last, how-
ever, the slight red coloration remains. Now ail chlorine has com-
bined with silver, and a little silver chromate has been permanently
formed. Read off the burette and reckon how much silver solu-
tion would have been required for O'l mol. sodium chloride, i.e.,
5 -85 grin. Suppose we have used to 0-11 sodium chloride 18*7
c.c. silver solution:

0-11 : 5-85 :: 18-7 : x\ x = 994-5.

Now, without throwing away the contents of the first beake* ,
make. a second and third experiment in the same manner, of course
always taking notice to regard the same shade of red as the sign of
the end. The results of these are reckoned out in the same way
as the first. Suppose they gave for 5'85 Nad 995*0 and 993-0
respectively, we take the mean of the three numbers, which is
994*2, and we now know that we have only to take this number of
c.c. of silver solution, and make it up to 1000 c.c. with 5 '8 water,
in order to obtain a solution of the required strength, i.e., 1000 c.c.
= 0-1 mol. Nad. But if 994-2 requires 5'8 water, 1000 requires
5 '83. Hence we fill a litre-flask (previously dried or rinsed with
a small portion of the solution) up to the " holding " mark with
the solution, add 5 -83 c.c. water, insert a caoutchouc stopper, and

The solution must now be correct ; however, to make quite
sure, we perform another experiment with it. To this end rinse
the empty burette with the new solution, fill it with the same and
test with the portion of salt in beaker No. 4. The c.c. used of
silver solution must now, if multiplied by 0*00585, give exactly the
weight of the salt.

Being now in possession of a standard silver solution, and being-
practised in exactly hitting the transition from yellow to the shade


of red, we are in the position to determine with precision chlorine
in the form of hydrochloric acid or of a metallic chloride soluble in
water. The fluid to he tested must he neutral free acids dissolve
the silver chromate. The solution of the substance is therefore,
If necessary, rendered neutral by addition of nitric acid or sodium
carbonate (it should be rather alkaline than acid), about 3 drops
of the solution of chromate added, and then silver from the burette,
till the reddish coloration is just perceptible. The number of c.c.
used has only to be multiplied by the atomic weight of chlorine
or the mol. weight of the metallic chloride and divided by 10,000
to give the amount of these respectively present.

If the operator fears he has added too much silver solution, i.e.,
if the red color is too strongly marked, he may add 1 c.c. of a solu-
tion of sodium chloride containing 5*85 in a litre (and therefore
corresponding to the silver solution), and then add the silver drop
by drop again. Of course in this case 1 c.c. must be deducted from
the amount of silver solution used.

The results are very satisfactory. The fluid to be analyzed
should be about the same volume as the solutions employed in
standardizing the silver solution, and also about the same strength,
otherwise the small quantity of silver which produces the colora-
tion will not stand in the same proportion to the chlorine present.
This small quantity of silver solution is extremely small, varying
between 0*05 and p l c.c. : the inaccuracy hereby arising even in the
case of quantities of chlorine differing widely from that originally
used in standardizing the silver solution is therefore almost incon-
siderable. If the amount of silver solution necessary to impart the
coloration always remained the same, we should have simply to
deduct the amount in question in all experiments, in order to
avoid this small inaccuracy entirely ; since, however, the greater
the quantity of silver chloride the more silver chromate is required
for visible coloration, this method of proceeding would not increase
the exactness of the results.

fi. By Solution of Silver Nitrate and Iodide of Starch
(PiSANi's method*).

Add to the solution of the chloride, acidified with nitric acid, a
Blight excess of standard solution of silver nitrate, warm, and filter.
Determine the excess of silver in the filtrate by means of solution

* Anital. d. Mines, \, s: 1 ,; L'KKH; and Kori-'s , r,,j, ,VA/,, > =/<///, 1856,751.

141,] CHLORINE, 623

of iodide* of starch (see p. 349), and deduct this from the amount
of silver solution used. The difference' shows the quantity of
silver which has combined with the chlorine ; calculate from this
the amount of the latter. Results satisfactory.

y. By Mercuric- Nitrate Solution (LIEBIG'S method,* par-
ticularly recommended for estimating chlorine in the chlorides in

aa. Principle of the method. Mercuric-nitrate solution causes
an immediate, dense, white precipitate in a solution of urea;
mercuric chloride, however, does not. On mixing a mercuric-
nitrate solution with an alkali chloride, mercuric chloride and
alkali nitrate are formed. Hence on adding sodium chloride to a
urea solution and then dropping in a dilute mercuric-nitrate solu-
tion a white cloudiness forms at the point where the drops fall,
but on shaking it disappears immediately so long as the mercu-
ric nitrate continues to react with the sodium chloride. The
moment the double decomposition is complete, however, an
additional drop of mercuric-nitrate solution causes a permanent
turbidity. Hence, if the volume and strength of the mercuric-
nitrate solution added be known, the chlorine strength of the salt
solution is also known, since 1 eq. of mercury in the mercuric
solution corresponds to 2 eq. of chlorine.

lib. Preparation of the mercuric-nitrate solution. As this
solution must be perfectly free from other metals, it is advisable
to prepare it from mercury oxide obtained by precipitating mer-
curic chloride with soda solution and thoroughly washing the
precipitate. 10'8 grin, of the dried oxide so obtained are dissolved
in nitric acid, the solution evaporated to a syrupy consistency,
and then diluted to 550 c. c. with water. The solution may also
be made by dissolving repeatedly recrystallized mercurous nitrate
in water, with the addition of some nitric acid, boiling, adding
strong nitric acid until red fumes no longer are evolved, evapo-
rating to syrupy consistency, and diluting with enough water to
yield a solution of approximately correct strength,

cc. Determining the strength of the solution. This is effected
by means of a sodium-chloride solution of known strength, pre-
pared according to LIEBIG by mixing 20 c. c. of a saturated (at

* Annal. d. Chem. u. Pharm., LXXXV, 297.


ordinary temperatures) solution of pure rock salt or chemically
pure sodium chloride, with 298 -4 c. c. water. Every c. c. of the
solution will contain 20 mg. of sodium chloride.

Of this solution measure 10 c. c. into a beaker and add 3 c. c.
of a urea solution containing 4 grm. in every 100 c. c.

Drop the mercury solution to be standardized from a burette
into the mixture, with shaking, until a just perceptible precipitate,
which fails to dissolve on shaking, forms.*

dd. Having thus ascertained how many c. c. of mercuric-
nitrate solution are equivalent to 10 c. c. of sodium-chloride solu-
tion (:= 0'2 grm. NaCl), the mercuric solution is applicable
for immediate use, if a little calculation is not objected to. If
this is rather avoided, dilute the mercuric solution so that every
c. c. may correspond to a given number of milligrammes of
sodium chloride or chlorine. LIEBIG dilutes the solution so that
1 c. c. corresponds to O'Ol grm. of sodium chloride.

ee. If the test-fluid is to be used for testing solutions which
contain much foreign salts or an excess of urea, add to 10 c. c. of
the sodium -chloride solution 3 c. c. of the urea solution and also
5 c. c. of a cold saturated sodium-sulphate solution before drop-
ping in the mercuric solution f . Results accurate.

d. Alkalimetrically (according to BOHLIG J). Add to the
solution, if necessary, potassium carbonate in not too great excess,
to precipitate the alkali earths, earths, or metallic oxides, dilute to
250 c. c., mix, filter, and determine the alkalinity of 50 c. c. of the
filtrate according to 220. To 125 c. c. of the filtrate in a 250-
c. c. flask add an excess of pure silver oxide, fill to the mark with
water and shake repeatedly, with exclusion of light. After a few
minutes filter through a dry folded filter, pipette off 100 c. c.
of the filtrate (corresponding to 50 c. c. of the original liquid),
and determine its alkalinity also. The difference in the c. c. of

* A mere opalcsccnce of the fluid is to be disregarded, as this depends upon
a trace of foreign metals, and has no bearing on the n-.-iciinn. as \\\\\\ be readily
seen from tue fact that the cloudiness is not increased by a further addition ot
the mercuric solution.

f The reason for this addition is that the mercuric nitrate and urea are more
readily soluble in pure water than in saline solution, hence the solvent powers of
the solutions should be as nearly alike as possible when standardizing and
performing the analysis, if accurate results are desired.

\ Zeitechr. f. analyt. Chem., ix, 314

141 J CHLORINE. 527

standard lacid used in the two determinations of alkalinity cor-
responds to the chlorine content of the solution. The result is
naturally correct only when another portion of the filtrate has
been tested and found free from chlorine. BOHLIG'S method is
particularly well adapted for technical purposes.

Of these volumetric methods of estimating chlorine, the first
deserves the preference in all ordinary cases. It is not, however,
applicable in urinalysis, because compounds of the silver oxide,
with coloring matters, etc. , are precipitated with the silver chloride
(C. NEUBAUER*). PISANI'S method (b, ft) is especially suited for
the estimation of very minute quantities of chlorine, but is not
applicable when, as in nitre analyses, large quantities of alkaline
nitrate are present (p.. 344).

II. Separation of Chlorine from the Metals.

a. In Soluble Chlorides.

The same method as in I, a. The metals in the filtrate are
separated from the excess of the salt of silver by the methods
which will be found in Section Y. Chlorides soluble in water may
also be completely decomposed by cold digestion with oxide or
carbonate of silver. Silver chloride is obtained, while the metal
combined with the chlorine is converted into oxide or carbonate
and either remains in solution or falls down with the silver chlo-
ride. Take care that no traces of oxide or carbonate of silver pa~o
into the filtrate.

Stannous chloride, mercuric chloride, platinic chloride, the
chlorides of antimony, and the green chloride of chromium, form
exceptions from the rule.

a. From stannic chloride, silver nitrate would precipitate,
besides silver chloride, a compound of stannic oxide and silver
oxide. To precipitate the tin, therefore, the solution is mixed with
concentrated solution of ammonium nitrate, boiled, allowed to
deposit, decanted, and filtered (compare 126, 1, Z), and the chlo-
rine in the filtrate is precipitated with solution of silver. LOWEN-
THAL, the inventor of this method, has proved its accuracy. f

* To apply this method to urine also, R. PRIBRAM (Zeitschr. f. analyt. Chem.,
ix, 428) heats 10 c. c. of urine with 50 c. c. of a solution of pure potassium
permanganate (1 or 2 : 1,000) to gentle boiling, filters off the brown flocks, washes
these, and determines the chlorine in the filtrate according to b, a.

\Journ. /. prakt. Chem., LXVI, 371.


fi. When 'mercuric chloride is precipitated with solution of
silver nitrate, the silver chloride thrown down contains an admix-
ture of mercury. The mercury is, therefore, first precipitated by
hydrogen sulphide, and the chlorine in the filtrate determined as
directed in 169.

y. The chlorides of antimony are also decomposed in the man-
ner described in /?. The separation of basic salt upon the addi-
tion of water may be avoided by addition of tartaric acid. The
antimonous sulphide should be tested for chlorine.

d. Solution of silver fails to precipitate the whole of the chlo-
rine from solution of the green chloride of chromium (PELIGOT).
The chromium is, therefore, first precipitated with ammonia, the
fluid filtered, and the chlorine in the filtrate precipitated as in I., a.

f. From platinic chloride silver nitrate throws down a com-
pound of platinous chloride and silver chloride (COMAILLE *). We
may either ignite the platinic chloride in a current of hydrogen
and pass the hydrochloric acid produced into solution of silver
(BONSDORFF), or we may evaporate the solution with sodium car-
bonate, fuse the residue in a platinum crucible, and determine the
chloride in the aqueous solution of the fusion. Or, thirdly, we
may (after TOPSOE f ) digest the moderately dilute solution in the
cold with zinc clippings till hydrogen ceases to escape, add ammo-
nia in excess, heat on a water-bath till the fluid is fully decolorized,
all the platinum being precipitated, and finally determine the chlo-
rine in the filtrate.

b. In Insoluble Chlorides.

a. Chlorides soluble in Nitric Acid.

Dissolve the chloride in nitric acid, without applying heat, and
proceed as in I., a.

fi. Chlorides insoluble in Nitric Acid (lead chloride,
silver chloride, mercurous chloride).

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