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very strong heat is required in the current of hydrogen in
order to completely reduce the silver bromide. It will be
seen that one and the same portion of silver bromide and
chloride may be treated first as in a, and then, for control, as
in b. The difference found direct in a, and calculated in 5,

* Annul, d. Chem. u. Pharm., xciu, 80,



169.] * ACIDS OF GROUP It. 747

between the silver chloride and bromide, must be equal to
the silver chloride equivalent to it.

c. FR. MOHR* recommends precipitating the bromine 259
and a part of the chlorine by a known quantity of silver, and
then weighing the precipitate of silver chloride. It is seen
that this method will yield the same data for calculation as in

J. The known quantity of silver used for precipitating is
weighed either directly and is dissolved in nitric acid, or it is
added in the form of standard silver solution. This method
is more convenient than that given under &, but I do not con-
sider it quite so accurate, particularly if only small quantities
of bromine are present. It is assumed that from a weighed
quantity of silver the absolutely correct quantity of silver
chloride equivalent to it is obtained ; and this assumption
cannot be realized in practice. Errors to the extent of some
milligrammes cannot be avoided, hence the difference might
be calculated as bromine, even when none is present at all.
The method given under a is not nearly so likely to afford
errors, or at least to the same extent. Further, one can
ascertain without trouble whether, on carefully heating silver
chloride in a current of chlorine, any change in weight takes
place, and thereby rendering an error of 0*5 milligramme less
excusable than one of 2 milligrammes incurred by converting
2 or 3 grm. silver into chloride; and this is scarcely avoid-
able, particularly if a filter is used in the process, as is re-
quired in a partial precipitation, in which case the precipi-
tate always subsides less.

d. PisANi'sf method may be regarded as a modification 260
of <?, wherein a known quantity of silver solution is added in
slight excess, the precipitate filtered off, and the silver in the fil-
trate estimated with starch iodide (page 349). The precipitate is
weighed as in c. This method precludes partial precipitation.

e. Determine in a portion of the solution the chlorine 261
-(-bromine (by precipitating with silver), either gravimetrically

or .volurnetrically ; in another portion the bromine, either by
the colorimetric method ( 143, I., J, or or /?) or volumetrically
( 143, I., &, y). Calculate the chlorine from the difference.

* Annal. d. Chem. u. Pharm., xcm, 76.

f Compt. rend., XLIV. 352 ; Journ.f. prakt. Chem., LXXII, 266.



748 SEPARATION. [ 169.

The method is very suitable for an expeditious analysis of
mother-liquors.

f. Compare also 271 and 272.

2. CHLORINE FROM IODINE.

a. Add to the solution palladious nitrate, and determine 262
the precipitated palladious iodide as directed 145, I., a, /?.
Conduct hydrogen sulphide into the filtrate to remove excess
of the palladium, destroy the excess of hydrogen sulphide by
solution of ferric sulphate, and precipitate the chlorine finally
with solution of silver. It is generally found more simple
and convenient to precipitate from one portion the iodine, by
means of palladious chloride, as directed 145, I., #, /?, from
another portion the chlorine and iodine jointly with silver
nitrate, and to calculate the chlorine from the difference. If
you have no solution of palladious nitrate ready, and the
chlorine and iodine must be determined in one portion of the
solution under examination, add a measured quantity of a
solution of palladious chloride, determine the amount of chlo-
rine in this and in another exactly equal portion of the same
solution, and deduct it. The results are accurate. In the case
of fluids containing a large proportion of alkali chlorides to a
small quantity of iodide and such cases often occur the
iodide is concentrated by adding sodium carbonate to the fluid,
evaporating to dryness, extracting the residue with hot alcohol,
evaporating the alcoholic solution with addition of a drop of
solution of soda, and taking the residue up with water.

1). Proceed exactly as for the indirect determination of 263
bromine in presence of chlorine (255). The greatest care
must be taken that as little as possible of the mixed silver chlo-
ride and iodide adheres to the filter, for silver iodide dissolves
only very slightly in ammonia. Any particles of silver iodide
remaining attached to the filter may be saved by incinerating
the filter and evaporating the ash with a drop of nitric acid
and a drop of hydriodic acid. The loss of weight suffered by
the silver precipitate on fusion in chlorine multiplied by 2*569
gives the. amount of silver iodide present. The methods
given under 259 and 260 are also applicable. These methods
give still better results than in the separation of bromine from
chlorine, inasmuch as the difference between the atomic
weights of iodine and chlorine is far greater than the differ-






169.] ACIDS OF GROUP "ll. 749

ence between those of bromine and chlorine. Regarding the
concentration of the iodide, if necessary, see 262:

c. Liberate the iodine by nitrous acid, take it up with car- 264
bon disulphide, wash the latter, and then estimate the iodine

in it by sodium thiosulphate (p. 537, /3).

In this process the chlorine is determined either in the
fluid separated from the violet carbon disulphide, or with
greater accuracy by precipitating the chlorine -f- iodine in
a second portion with silver and deducting the weight of
silver iodide corresponding to the iodine already found from
the weight of the precipitate. A good and approved method.

If the quantity of iodine is small, the following method
may also be used with advantage for estimating it:

The carbon disulphide should be thoroughly washed, and
covered with a layer of water in a stoppered bottle. Add
drop by drop, with shaking, dilute chlorine water (of unknown
strength) till the coloration has just vanished and all the
iodine is consequently converted into IC1 6 . Separate the solu-
tion from the disulphide, add potassium-iodide solution insuf-
ficient excess, and determine the free iodine after 146. Six
parts of the iodine found correspond to 1 part originally pres-
ent. If the analyst would avoid the trouble of pouring off the
fluid from the disulphide, and of washing the latter, he may
transfer the mixture, after the addition of chlorine to decolora-
tion, to a somewhat narrow measuring cylinder, note the vol-
ume occupied by the iodine-pentachloride solution, take out
a portion with a pipette, and proceed as above directed.

Instead of carbon disulphide MOEIDE* uses benzene, while
RoGP:ut employs chloroform; and instead of nitrous acid,
the latter uses iodic acid for liberating the iodine, as pre-
viously recommended by LIEBIG, a dilute solution of the
reagent being added to the dilute fluid acidulated with sul-
phuric acid. From the equation 5HI + HIO S = 61 + 3H a O,
it follows that only | of the iodine found belonged to the
iodide originally present.

d. Determine in one portion chlorine and iodine as in 265
141, I., 5, ?, and in another portion the iodine alone as in

145, I., 5, y> ^> or e - The chlorine is found by difference.

*Compt. rend., xxxv, 789; Journ. f. prakt. Chem., LVIII, 317.
\Journ. de Pharm., xxxvn, 410.



750 SEPARATION. [ 169.

The method in 145, I., 5, tf (PISANI'S) is very rapid, and
still gives approximately accurate results in the presence of
small quantities of chloride; if much chloride is present,
however, the results are altogether inaccurate (see page 540).
The method in 145, I., &, y (REINIGE'S) cannot be em-
ployed if the solution contains any organic or other sub-
stances capable of reducing potassium permanganate. The
method in 145, L, &, e is inapplicable if the fluid contains
chlorates, nitrites, or nitrates.

e. For technical purposes the following method is also 266
suitable. It was recommended by WALLACE and LAMONT *
for the estimation of iodine in kelp. The kelp-lye is nearly
neutralized with nitric acid, evaporated to dryness, and the
residue fused in a platinum vessel to oxidation of all the sul-
phides. Treat with water, filter, add silver nitrate till the
precipitate appears perfectly white, wash, digest with strong
ammonia, and weigh the residual silver iodide. Finally
add to the weight of the latter the amount which passes into
solution in the ammonia; it is -g^g of the aqueous am-
monia (sp. gr. 0-89) used. See also 268, 271, and 272.

3. CHLORINE, BROMINE, AND IODINE FROM EACH OTHI:I:.

a. The three acid radicals are determined jointly in a por- 267
tion of the fluid by precipitating with solution of silver
nitrate ( 141, I., a or J, a). To determine the iodine, another
portion is precipitated with palladious chloride in the least pos-
sible excess ( 145, I., #, ft). The fluid filtered from the pre-
cipitate is freed from palladium by hydrogen sulphide and the
excess of the latter removed by means of ferric sulphate ; the
chlorine and bromine are then precipitated jointly either com-
pletely or partially with silver nitrate, and the bromine deter-
mined as directed 255.

If the compound contains a la rue proportion of chlorine to
a small proportion of l>romine, the iodine may l>e precipitated
also by palladious nitrate, as there is no danger, in that case,
of palladious bromide being coprecipitated. The filtrate is
treated as above.

These methods give accurate results; but they are appli-



*Clnm. Guz, 1859, 137.



169.] ACIDS OF GROUP II. 751

cable only if the quantity of iodide present is somewhat con-
siderable.

J. Mix the neutral dilute and cold solution containing alkali 268
iodide with alkali chloride or alkaki bromide, or both, with a
saturated neutral solution of thallium nitrate, stirring well till,
on repeated trial, you obtain a transient white precipitate
the first and permanent precipitate being yellow. It is best to
have the thallium solution in a burette, so that you can easily
add it by drops. If the white precipitate of thallium chloride
or bromide does not at once disappear on stirring, add more
water, but not an unnecessary quantity, or some of the thal-
lium iodide will remain in solution.

Allow to stand eight or twelve hours in a cold place, pour
off the clear fluid through a weighed filter dried at 100, wash
the filter a little so that no more water than necessary may
pass through the precipitate, turn the precipitate on to the
filter, wash with as little water as you can, dry at 100, and
weigh. Precipitate the chlorine and bromine in the filtrate
by silver solution. If they are both present, the mixed silver
precipitate is to be treated according to 255. Results quite satis-
factory (HtJBNERand SPEZIA,* and HUBNER and FuEKiCHsf).

c. Remove the iodine from the solution by carbon disul- 269
phide or chloroform, as in 264. In the fluid separated from

the iodized carbon disulphide determine the chlorine and bro-
mine as directed in 255, and in the iodized carbon disulphide,
the iodine as directed in 145, I., 5, f3. This method is
particularly recommended for the separation of small quanti-
ties of iodine, and in this respect is supplementary to 267.

d. Determine in a portion of the compound the chlorine, 270
bromine, and iodine jointly by adding a known quantity of
standard silver solution in slight excess, filtering and deter-
mining the small excess of silver in the filtrate by iodide of
starch (p. 349). The precipitate is weighed. Compare 263.

We now know the total of the chloride, bromide, and iodide
of silver and also tlio silver therein contained.

Determine the iodine separately as in 269, calculate the
quantity of silver iodide and of silver corresponding to the
amount found, deduct the .calculated amount of silver iodide
from the mixed iodide, chloride, and bromide of silver, that

*Zeitschr.f. analyt. Chem., xi, 397. -fib., xi, 400~~



SEPARATION. [ 169.

of the silver from the known quantity of the metal contained
in the mixed compound ; the remainders are respectively the
joint amount of chloride and bromide of silver and the quan-
tity of the metal contained therein ; these are the data for
calculating the chlorine and bromine (258).

e. On the fact that freshly precipitated silver chloride is 27J
converted into silver bromide by a solution of sodium
bromide, and that freshly precipitated silver bromide and
chloride are converted into silver iodide by potassium iodide
in solution, F. FIELD * has based the following method of
estimating all three halogens, if present, and combined with
metals : Introduce three weighed portions each into a stop-
pered flask, add to each about 30 c. c. water and an excess
of silver solution, shake vigorously, and thoroughly wash the
precipitates Nos. I, II, and III with water. Dry and weigh
No. I ; the weight represents the sum of the silver chloride,
bromide, and iodide present. Then digest No. II with
potassium-bromide solution, and No. Ill with potassium-
iodide solution, for 10 hours, taking care that the solutions
are dilute and not added in too great excess, and avoiding
warming, otherwise notable quantities of silver salts will be
dissolved. After II is washed, ignited, and weighed, it gives
the quantity of silver bromide and iodide ; while III finally
gives pure silver iodide. The calculation is as follows :

a. The difference between the equivalents of iodine and
chlorine ( 91*4) : eq. of silver chloride (= 143-37) : : dif-
ference between the weights of I and II : the silver chloride
contained in I.

ft. The difference between the equivalents of iodine and
bromine (= 46'9) : eq. of silver bromide (= 187*87) : : dif-
ference between II and III : silver-bromide content of II.
On deducting the silver bromide found from the weight of the
precipitate II, the silver-iodide content is obtained.

y. Finally on subtracting the silver chloride found in a,
together with the silver iodide found in y#, from the precipi-
tate I, the weight of the silver bromide is obtained. The
method is of interest theoretically. FIELD obtained quite
satisfactory results.

The method was later on thoroughly investigated by

* Quart. Journ. Chem. Soc., x, No. 39, 234; Journ. f. prakt. Chem., LXXIII,
404; also Chem. News, n, 325.



169.] ACIDS OF GROUP II. 753

0. HEJSCHKE,* and also by M. SiEWERT.f The former used a
1 : 48 potassium-bromide solution and a 1 : 34 potassium- iodide
solution, and digested with a moderate excess of solution for 1
hour. He obtained 5 f 248 and 5-206 grains of iodine instead
of 5-287; 3-313 and 3-349 grains bromine instead of 3-333,
and 1*477 and 1*496 grains chlorine instead of 1'503 grains.

SIEWEKT worked with both cold and hot solutions, but
obtained less satisfactory results. According to his investiga-
tions, the conversion of silver chloride into bromide is incom-
plete, and further, on boiling silver bromide with sodium-
chloride solution, silver chloride is found. The conversion
of silver chloride and bromide into iodide, however, he
found to be perfectly complete.

FIELD'S method, hence, can at most be used only when
relatively large quantities of all three halogens are present,
and when approximate results will suffice. The method is
absolutely inapplicable in the analyses of mineral waters % and
more particularly when only very small quantities of iodides and
bromides are present with comparatively large quantities of
chlorides.

f. H. HAGER'S method depends upon the fact that freshly 272
precipitated silver chloride is soluble in a boiling solution of
ammonium carbonate, while only traces of silver bromide dis-
solve in such a solution, and silver iodide is almost absolutely
insoluble. Regarding the details of this method, in which
the silver bromide and iodide are separated by ammonia, I
refer to the original paper. The method can be employed
only when approximate results suffice. In SONSTADT'S ]
method the iodine is precipitated as barium iodate. .

4. ANALYSIS or IODINE CONTAINING CHLORINE.

a. Dissolve a weighed quantity of the dried iodine in 273
cold sulphurous acid, precipitate with silver nitrate, digest the
precipitate with nitric acid -to remove the silver sulphite
which may have coprecipitated, and weigh. The calculation

* Zeitschr. f. analyt. Chem., vn, 434.

t Zeitschr. f. die gesammt. Naturwiss., 1868, No. 1; Zeitschr. f. analyt. Chem. t
vii, 469.

\ J. MITTEREGGER, however, employed it thus, using only 500 grm. of
mineral water. See Chem. Analyse des Radeiners Sauerbrun, by Dr. Jos. MIT-
TEREGGER, Vienna, 1872, published W. by BRAUMULLER, p. 5.

%Pharm. Centralbl., xn, 42 ; Zeitschr. f. analyt. Chem., x, 341,

| Qhem, News, xxvi, 173 ; Zeitschr. f. analyt. Chem., xn, 91,



754 SEPARATION. [ 169.

of the iodine and chlorine is made by the following equations,
in which A represents the quantity of iodine analyzed, x the
iodine contained in it, y the chlorine contained in it, and B
the amount of silver chloride and iodide obtained :

x + y = A
and



Now as



and



we have

ff- 1-8508^1
ym 2-1935

J. If you have free iodine and free chlorine in solution, deter- 274
mine in one portion, after heating with sulphurous acid, the
iodine as palladium iodide (145, I., #, /?), and treat another
portion as directed 146. Deduct from the apparent amount
of iodine found by the latter process, the actual quantity calcu-
lated from the palladium iodide ; the difference expresses the
amount of iodine equivalent to the chlorine contained in the
substance.

5. ANALYSIS OF BROMINE CONTAINING CHLORINE.
a. Proceed exactly as in 273, weighing the bromine in a 275
small glass bulb. Taking A to be equal to the analyzed bro-
mine, B to the silver bromide and chloride obtained, x to the
bromine contained in A, y to the chlorine contained in A, the
calculation is made by the following equations :

x + y = A
and

_ B- 2-34984^4
1-69444

1). Mix the weighed anhydrous bromine with solution of 276
iodide of potassium in excess, and determine the separated
iodine as directed 8 14(>.



169.] ACIDS OF GROUP II. ' 755

From these data, the respective quantities of bromine and
chlorine are calculated by the following equations. Let A
represent the weighed bromine, i the iodine found, y the
chlorine contained in A, x the bromine contained in A, then



= A

_i 1-5866 A

1-9907

BUNSEN, the originator of methods 4 and 5, has experi-
mentally proved their accuracy.*

6. CYANOGEN FROM CHLOEINE, BROMINE, OR IODINE.

a. Precipitate with solution of silver, collect the precipi- 277
tate upon a weighed filter, and dry in the water-bath until the
weight remains constant ; then determine the cyanogen by the
method of organic analysis ; the quantity of the chlorine, bro-
.mine, or iodine is found by difference.

b. Precipitate with solution of silver as in 277, dry the pre- 278
cipitate at 100 and weigh. Heat the precipitate, or an ali-
quot part of it, in a porcelain crucible, with cautious agitation

of the contents, to complete fusion ; add dilute sulphuric acid
to the fused mass, then reduce by zinc, filter the solution from
the metallic silver and silver paracyanide, and determine the
chlorine, iodine, or bromine in the filtrate, in the usual way
by silver. The silver cyanide is the difference. NEUBAUER
and KERNER| obtained very satisfactory results by this
method.

c. Precipitate with solution of silver as in 277, weigh the pre- 279
cipitate and heat it, or an aliquot part, with nitric acid of 1'2

sp. gr. in a sealed tube at 100 for several hours, or at 150
for one hour. The silver cyanide is completely decomposed^
while the chloride, bromide, and iodide are unaffected. Filter
the contents of the tube, wash the precipitate and weigh it,
the loss indicates the amount of silver cyanide (K. KRAUT;):).

d . Determine the radicals jointly in a portion by precipi- 280
tating with solution of silver, and the cyanogen in another
portion, in the volumetric way ( 147, I., 5 or c).

* Annal. d.'Chem. u. Pliarm. , LXXXVI, 274, 376. f lb. t ci, 344.

\ Zeitschr.f. analyt. Chem., n, 243.



756 SEPARATION. [ 169.

7. FERRO- OR FERRICYANOGEN FROM HYDROCHLORIC
ACID.

To analyze say potassium ferro- or ferricyanide, mixed with 281
an alkali chloride, determine in one portion the ferro- or ferri-
cyanogen as directed 147, II., g ; acidify another portion
with nitric acid, precipitate with solution of silver, wash the
precipitate, fuse with 4 parts of sodium carbonate and 1 part
of potassium nitrate, extract the fused mass with water, and
determine the chlorine in the solution as directed in 141.

8. SULPHUR (IN SULPHIDES) FROM CHLORINE.

The old method of separating the two radicals by means of a 282
metallic salt is liable to give false results, as part of the chlo-
rine may fall down as chloride with the sulphide. We, there-
fore, precipitate both as silver compounds, dry the precipitate
at 100, weigh it, and determine the sulphur in a weighed
portion ; or and this is usually preferred determine in a
portion of the solution the sulphur as directed in 148, 1., a, 5,
or <?, in another portion the sulphur 4- chlorine in form of silver
salts. If you employ a solution of silver nitrate mixed with-
excess of ammonia, for the determination of the sulphur, you
may, after filtering off the silver sulphide, estimate the chlo-
rine directly as silver chloride, by adding nitric acid, and, if
necessary, more neutral silver solution. In this case you must
take care that the silver sulphide is pure ; should it contain
calcium carbonate, which is not unlikely if calcium is present,
you remove this with dilute acetic acid. The weighed silver
sulphide should be reduced by hydrogen, and then weighed
again by way of control. To remove hydrogen sulphide from
an acid solution, in order that chlorine may be determined in
the latter by means of silver nitrate, II. ROSE recommends to
add solution of ferric sulphate, which will effect the separa-
tion of sulphur alone; the separated sulphur is allowed to
deposit, and then filtered off.



170.] ACIDS OF GROUP III. 757

Third Group.

NITRIC ACID CHLOEIC ACID.

I. SEPARATION OF THE ACIDS OF THE THIRD GROUP FROM THOSE

OF THE FIRST TWO GROUPS.

1TO.

a. If you have a mixture of nitric acid or chloric acid with 283
another free acid in a fluid containing no bases, determine in
one portion the joint amount of the free acid, by the aeidi-
metric method (see Special Part), in another portion the acid
mixed with the chloric or nitric acid, and calculate the amount
of either of the latter from the difference.

J. If you have to analyze a mixture of a nitrate or chlorate 284
with some other salt, determine in one portion the nitric or
chloric acid volumetrically ( 149, II., d, a, /?, or ;/, or II., e,
and 150), or the nitric acid by 149, II., &, /? ; and in
another portion the other acid. I think I need hardly remark
that no substances must be present which would interfere with
the application of these methods.

c. From the chlorides of many metals whose carbonates or 285
normal phosphates are insoluble, chlorates and nitrates may

be separated also by digesting the solution with recently pre-
cipitated thoroughly washed silver carbonate or normal silver
phosphate in excess, and boiling the mixture. In this process,
the chlorides react with the carbonate or phosphate silver
chloride and carbonate or phosphate of the metal with which
the chlorine was originally combined being formed, which
both separate, together with the excess of the silver carbon-
ate or phosphate, whilst the chlorates and nitrates remain in
solution (H. ROSE, CHENEVIX, LASSAIGNE*).

d. The estimation of an alkaline chlorate, in presence of 286
a chloride, may be effected also by precipitating one portion

at once, and another portion after gentle ignition, with solu-
tion of silver, and calculating the chloric acid from the differ-
ence between the two precipitates. Or, estimate in one por-
tion the chlorine content by means of silver solution, at once,

* Journ. de Pharm., xvj, 289; Pliarm. Centralbl., 1850, 121.



758 SEPARATION. [ 17Q

and in another portion after previous reduction of the chloric
acid with nitrous acid or ferrous hydroxide (150, II., c
and d).

e. Where you have sodium- or potassium nitrate in presence 287
of nitrate or carbonate, as for instance in the commercial
alkali nitrates, estimate in one portion the carbonate by stand-
ard acid ( 219),* in another portion the nitrous acid by



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