C. Remigius Fresenius.

Quantitative chemical analysis online

. (page 62 of 69)
Online LibraryC. Remigius FreseniusQuantitative chemical analysis → online text (page 62 of 69)
Font size
QR-code for this ebook


curic salt, sodium acetate is mixed with the fluid, immediately
before the addition of the solution of chloride of sodium. In
the East India mint the silver is separated and weighed as
chloride.*

b. MERCUEOSUM FROM MKBCURICUM, COPPER, CADMIUM, AND
LEAD.

Mix the very dilute cold solution with hydrochloric acid
as long as a precipitate (rnercurous chloride) forms ; allow this
to deposit, filter on a weighed filter, dry at 100, and weigh.
The filtrate contains the other metals. If you have to analyze
a solid body, insoluble in water, either treat directly, in the
cold, with dilute hydrochloric acid, or dissolve in highly dilute
nitric acid, and mix the solution with a large quantity of water
before proceeding to precipitate. Care must always be taken
that the mode of solution is such as not to convert mercurous
into mercuric compounds. If lead is present the washing of
the mercurous chloride must be executed with special cure
with water of 60 70, till the filtrate ceases to be colored with
hydrogen sulphide. As an additional security, it is well to
test at last whether the weighed mercurous chloride leaves no
lead sulphide behind on cautious ignition with sulphur in a
stream of hydrogen.

c. MERCUROSUM AND MERCURICUM FROM COPPER, CADMIUM,
AND (but less well) FROM BISMUTH AND LEAD.

If mercury is present as a mercuric compound, or partly 145
in a mercuric and partly in a mercurous compound, it is pre-
cipitated according to 118, 2, by means of hydrochloric acid
and phosphorous acid as mercurous chloride. The precipitate,
particularly when bismuth is present, is first washed with water
containing hydrochloric acid, then with pure water, till the
washings are no longer colored with hydrogen sulphide (II.
RosEf). In the presence of lead, the remarks in 144 must
be attented to.



* Chem. Centralbl, 1872, 202.
\Pogg. AnnaL, ex, 534.



163.] * BASES OF GROUP V. 689

d. The method of separating lead from silver, copper,
and bismuth by highly concentrating the nitric-acid solution,
adding hydrochloric acid and alcohol, and washing the lead
chloride with alcohol, is not to be recommended. It is inferior
to 146 in accuracy.

2. Methods based upon the Insolubility of Lead
Sulphate.

LEAD FROM ALL OTHER METALS OF THE FIFTH GROUP.

Mix the nitric acid solution with pure sulphuric acid in not 146
too slight excess, evaporate until the sulphuric acid begins to
volatilize, allow the fluid to cool, add water (in which, if there
is a sufficient quantity of free sulphuric acid present, the mer-
curic and bismuth sulphates dissolve completely), and then
filter the solution, which contains the other metals, without
delay from the undissolved lead sulphate. If it is feared that
the residue no longer contains enough free sulphuric acid, add
some dilute acid to it before adding the water. Wash the
precipitate with water containing sulphuric acid, displace the
latter with alcohol, dry, and weigh ( 116, 3). Precipitate
the other metals from the filtrate by hydrogen sulphide. If
silver is present in any notable quantity, this method cannot
be recommended, as the silver sulphate is not soluble enough.
In this case you may follow ELIOT and STORER,* viz., mix the
solution with ammonium nitrate, warm, precipitate the greater
portion of the silver with ammonium chloride, evaporate the
filtrate, remove the ammonium salts by ignition, and in the
residue separate the small remainder of the silver from the
lead with sulphuric acid as just directed. For the separation
of lead from bismuth, on the above principle, H. EOSE f gives
the following process as the best. If both oxides are in dilute
nitric acid solution, as is usually the case, evaporate to small
bulk, and add enough hydrochloric acid to dissolve all the
bismuth ; the lead separates partially as chloride. Should a
portion of the clear fluid poured off become turbid on the
addition of a drop of water, you must add some more hydro-

* Proceedings of the American Academy of Arts and Sciences, Sept. 11,
I860, p. 52 ; Zeitschr. f. anatyt. Chem., I, 389.
\ Pogg. AnnaL, ex, 432.



690 SEPARATION. [ 163.

chloric acid, till no permanent turbidity is produced unless
several drops of water are added. The turbid fluids should
all be returned, and the glasses rinsed with alcohol. Add
now dilute sulphuric acid, allow to stand some time with stir-
ring, add alcohol of 0'8 sp.gr., stir well, allow to settle
for a long time, filter, wash the lead sulphate first with alco-
hol mixed with a small quantity of hydrochloric acid, then
with pure alcohol. Determine it after 116, 3. Mix the
filtrate at once with a large quantity of water, and proceed
with the precipitated basic bismuth chloride according to
120, 4.

3. Methods based upon different deportment with.
Cyanide of Potassium (FRESENIUS and HAIDLEN*).

a. LEAD AND BISMUTH FROM ALL OTHER METALS OF THE
FIFTH GROUP.

Mix the dilute solution with sodium carbonate in slight 147
excess, add solution of potassium cyanide (free from sulphide), .
heat gently for some time, filter and wash. On the filter you
have lead and bismuth carbonates (containing alkali) ; the fil-
trate contains the other metals as cyanides in combination with
potassium cyanide. The method of effecting their further
separation will be learnt from what follows. In very accurate
analyses bear in mind that the filtrate generally contains traces
of bismuth, which may be precipitated by ammonium sulphide.

J. SILVER FROM MERCURICUM, COPPER, AND CADMIUM.

Add to the solution, which, if it contains much free acid, 148
must previously be nearly neutralized with soda, potassium
cyanide until the precipitate which forms at first is redissolved.
The solution contains the cyanides of the metals in combina-
tion with potassium cyanide as soluble double salts. Add
dilute nitric acid in excess, which effects the decomposition of
the double cyanides ; the insoluble silver cyanide precipitates
permanently, whilst the mercuric cyanide remains in solution,
and the cyanides of copper and cadmium redissolve in the
excess of nitric acid. Treat the silver cyanide as directed
115, 3. If the filtrate contains only mercury and cadmium,
precipitate at once with hydrogen sulphide, which completely

*Anual. d. Chem. u. Pharm., XLIII, 129.



163.] BASES OF GROUP V. C91

throws down the sulphides of the two metals ; but if it con-
tains copper, you must first heat with sulphuric acid, until the
odor of hydrocyanic acid is no longer perceptible, and then
precipitate with hydrogen sulphide ( 119, 3).

c. COPPER FROM MERCURICUM AND CADMIUM.

Mix the solution, as in , with potassium cyanide until the 149
precipitate which is first thrown down redissolves ; add some
more potassium cyanide, then hydrogen sulphide water or
ammonium sulphide, as . long as a precipitate forms. The
cadmium and mercury sulphides are completely thrown down,
whilst the copper remains in solution, as sulphide dissolved in
potassium cyanide. Allow the precipitate to subside, decant
repeatedly, treat the precipitate, for security, once more with
solution of potassium cyanide, heat gently, filter, and wash
the sulphides of the metals. To determine the copper in the
filtrate, evaporate the latter, with addition of nitric and sul-
puric acids, until there is no longer any odor of hydrocyanic
acid, and then precipitate with hydrogen sulphide ( 119, 3).

d. ALL THE METALS OF THE FIFTH GROUP FROM EACH
OTHER.

Mix the dilute solution with sodium carbonate, then with 150
potassium cyanide in excess, digest some time at a gentle heat,
and filter On the filter you have lead carbonate and bismuth
carbonate (containing alkali); separate the two metals by a
suitable method. Add to the filtrate dilate nitric acid in
excess, warm gently till the cuprous sulphocyanate first pre-
cipitated with the silver cyanide has redissolved, and filter
off the undissolved silver salt, which is to be determined as
directed 115, 3. Neutralize the filtrate with sodium car-
bonate, add potassium cyanide, and pass hydrogen sulphide in
excess. Add now some more potassium cyanide, to redissolve
the copper sulphide which may have fallen down, and filter
the fluid, which contains the whole of the copper, from the
precipitated sulphides of mercury and cadmium. Determine
the copper as directed in c, and separate the mercury and cad-
mium as in 145 or 158.



C92 SEPARATION. [ 163.

4. Methods based on the Formation and Separation
of insoluble Basic Salts.

a. BISMUTH FROM COPPER, CADMIUM, AND MERCURICUM (also
from the basic radicals of the first four groups, with the excep-
tion of ferric iron).

Precipitate the bismuth as basic chloride according to 120, 151
4, and throw down the copper, &c., in the filtrate by hydro-
gen sulphide. Results thoroughly satisfactory (II. ROSE*).

b. BISMUTH FROM LEAD AND CADMIUM.

Separate the bismuth according to 120, 1, c, as basic 152
nitrate, and precipitate the lead and cadmium in the filtrate
by hydrogen sulphide. Results very satisfactory (J. LowEf).

c. BISMUTH AND COPPER FROM LEAD AND CADMIUM.
Separate the bismuth after 120, 1, <?, as basic nitrate, then

heat the dish on the water-bath till the normal copper nitrate
is completely converted into bluish-green basic salt and no
blue solution is produced on addition of water. Allow to cool,
treat with an aqueous solution of ammonium nitrate (1 in 500),
filter, wash with the same solution, and separate in the solution
lead from cadmium ; in the residue copper from bismuth.
Results very satisfactory (J. LOWE, loc. cit.).

5. Method based upon the Precipitation of som<e of
the Metals by Ammonia or Ammonium Carbonate.

COPPER FROM BISMUTH.

a. Mix the (nitric acid) solution with ammonium carbonate 1 53
in excess, and warm gently. The bismuth separates as car-
bonate, whilst the copper carbonate is redissolved by the excess
of ammonium carbonate. As the precipitate, however, gen-
erally retains a little copper, it is necessary to redissolve it,
after washing, in nitric acid, and precipitate again with amnio-
n in in carbonate; the same operation must be repeated a third
time if required. Some solution of ammonium carl innate may
be added to the water used for washing. Apply licat to the
filtrate that the ammonium carbonate may volatili/r, acidify
cautiously with hydrochloric acid, and determine the copper
as cuprous sulphide ( 119, 3). The oxide of bismuth thus

*Pogg. Annul., ex, 430. \Journ.f. prakt. Chem., LXXIV, 345.



163.] - * BASES 0-1* GROUP V. 693

obtained is quite copper-free, but a little bismuth passes into
the copper solution, hence the separation does not give such
exact results as that in 114 (H. ROSE*).

j3. Add some ammonium chloride to the solution and
drop the latter gradually into dilute ammonia. The bismuth
is hereby precipitated as bismuth .oxy chloride, while the
copper remains in solution as an arnmoniacal double salt
(BERZELIUS). Wash the precipitated bismuth salt with dilute
ammonia, dissolve it in dilute nitric acid, and determine
according to 120. The copper is determined in the ammo-
niacal solution. In this method, also, it is advisable to pre-
cipitate twice, as in a.

b. COPPER FEOM CADMIUM.

Add an excess of ammonium carbonate. Cadmium car- 154
bonate precipitates, while copper remains in solution with
some cadmium. On exposure to air, now, the dissolved cad-
mium precipitates, while the copper still remains in solution
(STROMEYER). The solution is to be treated as in 153.
The separation is more convenient, but less accurate than in
149 or 159.

c. LEAD AND SILVER CHLORIDES may be separated by 155
ammonia, which dissolves the latter, but not the former.
Care must be taken that the silver chloride be freshly pre-
cipitated with exclusion of light. From the ammoniacal solu-
tion precipitate the silver by nitric acid. It is necessary to
test the filtrate from the silver chloride with hydrogen
sulphide to ascertain whether any weighable quantities of
silver have been retained in solution by the agency of the
ammonium salts.

6. Method based on the Precipitation of the Copper
as Cuprous Sulphocyanate.

COPPER FROM CADMIUM (and the metals of Groups I. -IV.,
comp. 132).

Pecipitate the copper according to 119, 3, 5, as cuprous 156
sulphocyanate (Rivoi), and the cadmium from the filtrate as

*Pogg. Annal, ex, 430.



694 SEPARATION. [ 163.

sulphide. Results good (II. ROSE). Palladium may also be
separated from copper in this way



7". Method based upon the different deportment of
the Chrovnates.

BISMUTH FROM CADMIUM.

Precipitate the bismuth as directed 120, 2. The filtrate 157
contains the whole of the cadmium. Concentrate by evapora-
tion, and then precipitate the cadmium by the cautious addi-
tion of sodium carbonate, as directed 121, 1, a (J. L6wE,f
W. PEARSON Jj. The results given are satisfactory

8. Method based upon the different deportment of
the Sulphides with Acids.

a. MERCURICUM FROM SILVER, BISMUTH, COPPER, CADMIUM,
AND (but less well) FROM LEAD.

Boil the thoroughly washed precipitated sulphides with 158
perfectly pure moderately dilute nitric acid. The mercuric
sulphide is left undissolved, the other sulphides are dissolved.
No chlorine may be present, and it is necessary that the mer-
curic sulphide should be pure, that is, free from finely divided
mercury, which, as is well known, is precipitated when mer-
curous salts are treated with hydrogen sulphide. G. v. RATH
employed this method, which is so universally used in qualita-
tive analysis, with perfect success for the separation of mer-
cury from bismuth.

b. COPPER FROM CADMIUM.

Boil the well-washed precipitate of the sulphides with 159
dilute sulphuric acid (1 part concentrated acid and 5 parts
water), and, after some time, filter the undissolved copper sul-
phide, to be determined according to 119, 3, from the solu
tion containing the whole of the cadmium ( A. W. HOFMANN [)

9. Methods based upon the Volatility of some of iiiQ
Metals, Oxides, Chlorides, or Sulph'n1<* at a high Tsmr
perature.

a. MERCURY FROM SILVFR, LEAD, COPPER (in gene, i i, TM
the metals forming non-volatile chlorides).

* Annal. d. Chem. u. Phann , CXL, 14-1 ; Zeitschr.f. analyi. Ghem^ V, 40&

\Journ.f. prakt. Chem., IAII, 469. \Phil. Mag., xi 204.

%Pogg. Annal., xcvi, 322.

| Annal. d. Chem. u. Pharm. t cxv, 286.



163.] BASES OF GROUP V. 695

Precipitate with hydrogen sulphide, collect the precipi- 160
tated sulphides on a weighed filter, dry at 100, weigh, and
mix uniformly. Introduce an aliquot part into the bulb D




Fig. 116.

(Fig. 116), pass a slow stream of chlorine gas, and apply a
gentle heat to the bulb, increasing this gradually to faint
redness. The excess of chlorine escaping from E during
the operation may be conducted into a flue or into a carboy
containing moist slaked liine by connecting the carboy with
G. First sulphur chloride distils over, which decomposes
with the water in E and F '; then the mercuric chloride
formed volatilizes, condensing partly in E, partly in the hind
part of 0. Cut off that part of the tube, rinse the sublimate
with water into E, and mix the contents of the latter with
the water in F. Mix the solution with excess of ammonia,
warm gently till no more nitrogen is evolved, acidify with
hydrochloric acid, and then determine in the fluid filtered
from the sulphur, which may still remain undissolved, the
mercury as directed in 118, 3. If the residue consists of
silver chloride alone, or lead chloride alone, you may weigh
it at once ; but if it contains several metals, you must reduce
the chlorides by ignition in a stream of hydrogen, and dis-
solve the reduced metals in nitric acid, for their ulterior
separation. Bear in mind that, in presence of lead, the sul-
phides and the chlorides must be heated gently in the chlo-



696 SEPARATION. [ 163.

rine and hydrogen respectively, otherwise some lead chloride
might volatilize.

If it is intended to determine the mercury by the difference
instead of directly, the apparatus may be greatly simplified,
but in this case great care must be exercised in drying the
sulphides at 100. It is hence advisable to use the method
only when the mercury contains a very small quantity of
another metal. "Weigh the dried precipitate every half -hour
and consider the lowest weight as the correct one. Then
ignite an aliquot part of the precipitate in a current of hydro-
gen in a crucible provided with a perforated cover, or in a
tube with a porcelain boat. The method is applicable when
only one other metal is present besides mercury. Calculate
from the residue in the crucible or boat how much the entire
precipitate, dried at 100, would have yielded ; then calcu-
late the result into sulphide in which form the substance
was contained in the dried precipitate and from the differ-
ence find the mercury sulphide. On ignition in hydrogen,
silver sulphide yields metallic silver and cupric and cuprous
sulphides. If lead is present the latter method is inappli-
cable, because lead sulphide too readily loses weight in a cur-
rent of hydrogen ( 83,/).

In alloys or mixtures of oxides the mercury may usually
be determined with simplicity from the loss on ignition in the
air or in hydrogen.

b. BISMUTH FROM SILVER, LEAD, AND COPPER.

The separation is effected exactly in the same way as that 161
of mercury from the same metals (160). The method is more
especially convenient for the separation of the metals in
alloys. Care must be taken not to heat too strongly, as other-
wise lead chloride might volatilize; nor to discontinue the
application of heat too soon, as otherwise bismuth would
remain in the residue. AUG. YOGEL * gives 360 to 370 as
the best temperature. Put water containing hydrochloric
acid in U- tubes, which serve as receivers (Fig. 116), and
determine the bismuth therein according to 120.



Zeiischr.f. analyt. Chem., xin, 61.



163.] BASES OF GKOUP V. 697

10. Precipitation of one Metal in the Metallic
State l>y another or the lower Oxide of another.

a. LEAD FKOM BISMUTH.

Precipitate the solution with ammonium carbonate (116, 162
1, a and 120, 1, #), wash the precipitated carbonates, and
dissolve in acetic acid in a flask ; place a weighed rod of pure
lead in the solution and nearly fill up with water, so that the
rod may be entirely covered by the fluid; close the flask and
let it stand for about 12 hours, with occasional shaking.
Wash the precipitated bismuth off from the lead rod, collect
on a filter, wash, and dissolve in nitric acid ; evaporate the
solution and determine the bismuth as directed in 120. De-
termine the lead in the filtrate as directed in 116. Dry the
leaden rod and weigh ; substract the loss of weight which
the rod has suffered in the process from the amount of the
lead obtained from the filtrate (ULLGEEN *). PATERA f
recommends precipitating from dilute nitric solution, wash-
ing the precipitated bismuth first with water, then with
alcohol, transferring to a small filter, drying and weighing.
If it is feared that the finely divided bismuth has undergone
oxidation, it is well to fuse it with potassium cyanide
(120,4).

b. CUFKOUS COPPER FROM CUPRIC COPPER.

Cuprous copper may be accurately determined in the 163
presence of cupric copper by means of a solution of silver
nitrate. The action of this solution on cuprous oxide was
first studied by H. BOSE.:): According to HAMPE, who
further studied the subject with the greatest care, the action
proceeds as follows, sufficient dilution and a very gentle heat
being implied :

3Cu,0 + 4AgNO, + a?H f O = (4CuON,O 6 + 3H 2 O) +
2CuNO, + 4Ag + (x - 3)H a O.

Add to the mixture of the very finely divided oxides 200
times its weight of water and an excess of perfectly pure and

*BERZELIUS' Jahresber., xxi, 148. \Zeitschr.f. analyt. Chem., v, 226.
%Journ.f. prakt. Chem., LXXI, 412. Zeitschr.f. analyt. Ckem., xin, 207.



G93 SEPAKATION. [ 163.

neutral silver nitrate, heat to 40, allow to stand for three
days, filter, wash, dissolve in nitric acid, and determine the
silver as a chloride. Every 4 eq. of silver found represent
6 eq. of cuprous copper present. Now determine the total
copper in a second portion of the substance, and thus ascer-
tain the cupric copper by the difference.

11. Separation of Silver by Cupellation.
CUPELLATION was formerly the universal method of deter- 164
mining SILVEK in alloys with COPPER, LEAD, etc. The alloy is
fused with a sufficient quantity of pure lead to give to 1 part
of silver 16 to 20 parts of lead, and the fused mass is heated,
in a muffle, in a small cupel made of compressed bone-ash.
Lead and copper are oxidized, and the oxides absorbed by the
cupel, the silver being left behind in a state of purity. One
part by weight of the cupel absorbs the oxide of about 2 parts
of lead ; the quantity of the sample to be used in the experi-
ment may be estimated accordingly. This method is only
rarely employed in laboratories ; * I have given it a place
here, however, because it is one of the safest processes to
determine very small quantities of silver in alloys, f Regard-
the details of the method, I refer to the Special Part,
"Determination of Silver in Galena."

12. Methods depending on the Volumetric Estima-
tion of one Metal.

a. COPPER OF CUPROUS COMPOUNDS IN PRESENCE OF CUPRIC
COMPOUNDS.;):

Dissolve the substance, if necessary in a current of car- 165
bonic acid, in hydrochloric acid, and determine the cupric
chloride by means of stannous chloride as in 119, 4, d\ in
a second portion of the substance determine the total copper

*For details of this process consult Bodemann and KerVs Assaying,
translated by GOODYEAR ; or Notes on Assaying, by P. DE RICKETTS.

f Compare MALAGUTI and DUROCIIEH, Comp. rend., \\i\, ;sj) ; DINGLER
cxv, 276. Also W. HAMPE, Zeitfichr /. analyt. Chem., xi, 221.

J The method of COMMAILLK (Comp. rend., LVI, 309) can no longer be
relied upon, since STAB ( Untermcliungen uber die Gesetze der chemischen Propor-
tions, von J. 8. STAB, translated by ARONSTEIN, Leipzic, 1867, p. 8(5) has
shown that the finely divided silver thrown down by ammoniacal solution of
cuprous chloride dissolves largely in ammonia with access of air.



164.] METALS OF GKOUP VI.

according to one of the methods given in 119. It is of
course evident, from the statements on page 380, that cu-
prous copper may be determined in the presence of cupric
copper by means of ferric chloride.

5. SILVER IN PRESENCE OF LEAD AND COPPER.

Small quantities of silver may be estimated by PISANI'S
method, 115, II.

Sixth Group.

GOLD PLATINUM TIN ANTIMONY (ANTIMONIC ACID) AESE^
OUS ACID ABSENIC ACID.

L SEPARATION OF THE METALS OF THE SIXTH GKOUP

THOSE OF THE FIKST FlVE GEOUPS.

164.

INDEX. (The numbers refer to those in the margin.)

Gold from the metals of Groups III. I., 166, 171.
Group IV., 166, 169, 171.
" silver, 169, 188.
" mercury, 169, 182.
" lead, 169, 194.
" copper, 169, 171.
bismuth, 169, 171, 194.
" cadmium, 169, 171.

Platinum from the metals of Groups I. III., 166, 172.

Group IV., 166, 170, 172.
silver, 170, 188.

" mercury, 170, 172.
" lead, 170.

" copper, 170, 172.

bismuth, 170, 172.

" cadmium, 170, 172.

Tin from the metals of Groups I. and II., 166, 175, 18L
' Group III., 166, 175.

zinc, 166, 168, 173, 175.

manganese, 166, 168, 175.

nickel and cobalt, 166, 168, 173, 175, 180.
" iron, 166, 168.

silver, 167, 168, 173, 180.
" mercury, 167, 168, 173.

" lead, 167, 168, 173, 180.

copper, 167, 168, 173, 175, 180.
bismuth, 167, 168.
cadmium, 167, 168, 173, 175.



700 SEPARATION. [ 164

Antimony from the metals of Groups I. and II., 166, 178.
" Group III., 166.

zinc, 166, 168, 174.
" manganese, 166, 168.

nickel and cobalt, 166, 168, 174, 179, 180.
" iron, 166 ? 168, 178.

silver, 167, 168, 174, 180.
mercury, 167, 168, 174, 176, 189.
lead, 167, 168, 174, 180, 191.
copper, 167, 168, 174, 178, 180, 192.
bismuth, 167, 168.
cadmium, 167, 168, 174.
Arsenic from tlie metals of Group I., 166, 178, 184, 186, 187.

II., 166, 177, 178, 184, 186, 187, 190.
III., 166, 185, 186.

zinc, 166, 168, 177, 183, 184, 186, 187.
manganese, 166, 168, 177, 183, 185, 186, 187.
nickel and cobalt, 166, 168, 177, 179, 180, 183, 184, 185,

186, 187.

iron, 166, 168, 177, 178, 183, 185, 186.
silver, 167, 168,177, 180, 186.
mercury, 167, 168, 186, 189.
lead, 167, 168, 177, 180, 183, 184, 186, 190.
copper, 167, 168, 177, 178, 180, 183, 184, 185, 186, 192,

193.

bismutli, 167, 168, 177, 186.
cadmium, 167, 168, 177, 184, 185, 186.

A. General Methods.

1 . Method based upon the Precipitation of Metals
of the Sixth Group from Acid Solutions by Hydro-



Online LibraryC. Remigius FreseniusQuantitative chemical analysis → online text (page 62 of 69)