C. Remigius Fresenius.

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ployed for estimating the chloric acid of solutions of unknown
strength. The author's test-analyses gave good results, which
were corroborated in my laboratory.

d. The reduction of chloric acid may also be simply effected by
ferrous hydroxide. Add a sufficient quantity of ferrous sulphate
to the solution of the alkali chlorate, supersaturate strongly with
chlorine-free potassa lye, boil for a long time, filter off the ferroso-
ferric hydroxide, wash, acidulate the filtrate with nitric acid, and

* Annal. d. Chem. u. Pharm., cxxxvii, 114; Zeitschr. f. analyt. Chem., v,

fTo prepare tliis, boil together 1 part plumbic nitrate, l\ part lead, and 50
part- water f,,r a i,,,m time, when tetrabasic lead nitrite (Pb[OH]NO 3 PbO)
]>!(( -ipitates us a white powder on rapidly cooling the at first yellow, then
colorless, solution. Suspend the nitrite in water and pass in carbonic acid until
the basic salt is entirely decomposed. The filtered solution may be preserved -
for a long time in completely filled bottles.

150.] CHLORIC ACID. 595

precipitate the chlorine with silver solution ( 141, 1, a. C. STEL-
LING *). According to my investigations it is advisable to bring the
filtrate up to 250 c. c., and to then test a portion of it for chloric
acid by adding, first, sulphuric acid to acidity, then a very small
quantity of indigo solution, and finally a little sulphurous acid.
When the indigo is no longer decolorized, and you are certain that
all the chlorate in the solution has been converted into chloride,
proceed to estimate the chlorine as silver chloride in an aliquot
part of the 250 c. c.

e. After SESTiNi.f To the concentrated aqueous solution of
the weighed chlorate add a piece of zinc and then some pure
dilute sulphuric acid, and allow to stand for some time (with O'l
grm. potassium chlorate half an hour is sufficient). By the nascent
hydrogen evolved the chloric acid is converted into hydrochloric
acid, which, after removal and rinsing of the zinc, is determined
according to 141. To use the volumetric method ( 141, 5, <*),
the sulphuric acid is first precipitated with barium nitrate, then the
zinc and excess of barium with sodium carbonate ; the liquid is
filtered and neutralized, then potassium chromate is added, and
finally standard silver solution.

f. The basic radicals are determined with advantage in a sepa-
rate portion, by converting the chlorate either by very cautious
ignition, or by warming with hydrochloric acid, into chloride.

The estimation of hypoMorous acid will be described in the
Special Part, article " Chlorimetry."

* Zeitschr. /. analyt. Chem., vi, 32.
f/6., i, 500.




only one basic or one acid radical i- present, the method
of its determination has been considered in the previou.- S
When more than one basic or more than one acid radical is ;
sent, the methods of separating and determining them will be
described in the present Section.

The separation of bodies may be effected in three ways: viz., //.
by direct analysis; J, by indirect analysis ; c,\>y estimation tj

By direct analysis, we understand the actual separation of rad-
icals or elements. Thus, we separate potassium from sodium by
platinic chloride ; copper from tin by nitric acid ; arsenic from
iron by hydrogen sulphide ; iodine from chlorine by palladious
nitrate ; carbon from potassium nitrate by water, &c., &c. In
direct analysis we render one body insoluble, while the others
remain in solution, or vice versa, or we volatilize one body, leav-
ing the others behind, or we effect actual separation in some other
manner. This is the mode of analysis most frequently employed.
It generally deserves the preference where choice is permitted.

"We term an analysis indirect if it does not effect the actual sep-
aration of the bodies, but causes, certain changes which enal>!<
to calculate their quantity. Thus, the quantity of potassium nnd
sodium in a mixture of compounds of the two may be determined
by converting them into chlorides, 'weighing the latter, ind deter-
mining the chlorine ( 152, 3).

Finally, if we weigh two bodies together, determine one of them,
and subtract its weight from that of the two, we shall find the
weight of the other body. In this case the second body is said to
be xtimated Tnj d(tf. /> /><<>. Thus, aluminium maybe determined
when its oxide is mixed with ferric <>\ide. by weighing the mix-
ture and determining the iron volumetrically.


/ I.M i-.\ i:\'i ION 01 BODIES.

Indirect an;dy-is and estimation by difference may be employed
in ;ni vi-c-dinij-ly lurjre number of cases; bnt their use is as a rule
only to he ivommcndcd where 1:000! methods of true separation
are wanting. Tin: .-jxviul cases in which they are preferable to
din-ft analysis '-;mnot be all foreseen; those alone are pointed
out wlii'-li ;m- of more frequent occurrence. As regards thecalcu-
lations required in indirect analysis, I have given general direc-
tion- under ; 'the Calculation of Analysis ;" wherever it appeared
judicious, I have added the necessary directions to the description
of the method itself.

I have retained our former subdivision into groups, and, as far
;> practicable, systematically arranged, first, the general separation
of all the bodies belonging to one group from those of the preced-
inn group.- : secondly, the separation of the individual bodies of one
group from all or from certain bodies of the preceding groups;
and finally, the separation of bodies belonging to one and the same
group from each other. I think I need scarcely observe that the
general methods which serve to separate the whole of the bodies of
one gmup from those of another group are also applicable to the

ration of every individual body of the one group from one or

ral bodies of the other group. It must not be understood that
the more special methods are necessarily in all cases preferable Jo
the more general ones. As a rule, it must be left to individual
chemists to decide for themselves in each special case which method
should be adopted. With respect to the general methods for sepa-
rating one group from another, I would observe that those adduced
appeared to me more adapted to the purpose than others, but
still there may l>e others that are equally suitable, and in special
cases even more so. A wide field is here open to the ingenuity
of the analyst.

The methods given for the separation of both basic and acid
radicals are generally based upon the supposition that they are in
the form of free acids or bases, or in the form of salts soluble in
water. "Wherever this is not the case, special mention is made of
the circumstance.

:n among the host of proposed methods, I have, as far as
practicable, chosen those which have been sanctioned by experience
and are distinguished for accurate results. In cases where two
methods were on a par with each other as regards these two points,
I have either given both or selected the more simple one. Methods


which experience has shown to be defective or fallacious have been
altogether omitted. I have endeavored to point out, so far as pos-
sible, the particular circumstances under which either the one or
the other of several methods deserves the preference.

Where the accuracy of an analytical method has been estab-
lished already, in Section IY., no furthur statements are made on
the subject here. Paragraphs of former Sections deserving par-
ticular attention are referred to in parentheses.

The extension of chemical science introduces almost every day
new analytical methods of every description, which are, rightly or
wrongly, preferred to "the older methods; the present time may
therefore be looked upon in this, as in so many other respects, as a
period of transition, in which the new strives more than ever to
overcome and supplant the old. I make this remark to show the
impossibility of always adding to the description of a method an
opinion of its usefulness and accuracy, and also to point out the
importance, under such circumstances, of a proper systematic
arrangement. I have in this Section generally arranged the vari-
ous analytical methods upon the bases of their scientific principles,
firmly persuaded that this will greatly tend to facilitate the study
of the science, and will lead to endeavors to apply known princi-
ples to the separation of other bodies besides those to which they
are already applied, or to apply new principles where experience
lias proved the old ones fallacious, and the methods based on them

I conclude these introductory remarks with the important cau-
tion to the student never to look upon a separation as successfully
accomplished before he has convinced himself that the weighed pre-
cipitates, c#<?., are pure and more particularly free from tliose
bodies from which it was intended to separate them.




First Group.



INDEX. The numbers refer to those in the margin.

Potassium from sodium, 1, 2, 6.

ammonium, 3, 4, 5.
Sodium from potassium, 1, 2, 6.

ammonium, 3, 4, 5.
Ammonium from potassium, 4, 5.
" sodium, 3, 4, 5.
(Lithium from the other alkalies, 7, 8, 9.)

1. Methods based upon the different degrees of Solubility
in Alcohol, of Sodium Platinic Chloride, and Potassium
Platinic Chloride.


It is an indispensable condition in tins method that the 1
two alkalies should exist in the form of chlorides. If, there-
fore, they are present in any other form, they must be first con-
verted into chlorides, which in most cases may be effected by
evaporation with hydrochloric acid in excess; in the case of
nitrates, the evaporation with hydrochloric acid must be
repeated 4 6 times till the weight of the gently ignited mass
ceases to diminish. In presence of sulphuric acid, phosphoric
acid, and boric acid, this simple method will not answer. For
the methods of separating the alkalies from the two latter acids
and converting them into chlorides, see 135 and 136. The
presence of sulphuric acid being a circumstance of rather fre-
quent occurrence, the way of meeting this contingency is given
below (2).

Determine the total quantity of the sodium chloride and
potassium chloride f (97, 98), dissolve in the least quantity

* Regarding the separation of caesium and rubidium from the other alkalies,
I refer to the " Analysis of Mineral Waters" in the Special Part.

f Never take the weight of the alkali chlorides without convincing yourself
of their purity by dissolving them in water, which should give a clear solution,
and testing the solution with ammonia and ammonium carbonate, which must
throw down no precipitate. It may be thought, perhaps, that a matter so simple
need not be mentioned here ; still I have found that neglect in this respect is
by no means uncommon.

600 SEPARATION. [ 152.

of water, and add to the fluid in a porcelain dish an excess of a
strong aqueous solution of platinic chloride as neutral as pos-
sible. Enough platinum solution should be added to convert
the sodium as well as the potassium into platinochloride. It
is best to use a solution of known strength and to calculate
roughly how much should be added. Evaporate on the water-
Itath nearly to dryness (the water in the bath should never
actually boil, and the sodium platinic chloride should not lose
its water of crystallization), treat the residue with alcohol of
In. in 0-86 to 0-87 sp, gr., cover the dish with a glass plate, and
allow to stand a few hours, with occasional stirring. If the super-
natant fluid is not deep yellow, this is a proof that the quantity of
platinic chloride used is insufficient. When the precipitate has
settled, pour off the clear fluid through a filter (preferably an
asbestos filter, 97, 4, a) and examine the precipitate most
minutely, if necessary, with the aid of a microscope. If it is
a heavy yellow powder (sufficiently magnified, small octahe-
dral crystals) it is the pure potassium-platinic chloride.* Then
transfer it best with the aid of the filtrate to the filter,
wash it with alcohol of 0'86 to 0'87 sp. gr., and proceed
according to 97, 4, a. (Instead of weighing the double
chloride or the platinum obtained from it, you may ignite gen-
tly in hydrogen, extract the potassium chloride with water,
and weigh this or titrate the chlorine in it by 141, I., J, a).
If, on the contrary, white saline particles (sodium chloride)
arc to be seen mixed with the yellow crystalline powder, pla-
tinic chloride has been wanting, the whole of the sodium chlo-
ride not having been completely converted into sodium platinic
chloride. In this case the precipitate in the dish must be
treated with some water, till nil the sodium chloride is dis-
solved, a fresh portion of platinic chloride is added, the whole
evaporated nearly to dryness, and the above examination
repeated. The quantity of the sodium is usually estimated
by subtracting from the united weight of the sodium chloride
and pota>Mimi chloride the weight of the latter, calculated
from that uf the potassium platinic chloride.

To make quite sure that the potassium lias completely sep-

* If small tesseral crystals are visible of a dark orange-yellow color, end

relatively lar-r >i/e. and appearing transparent by transmitted light, then the
double chloride contains lithium platinic chloride (jENzacii, Pogg. Ann., civ,

152.] BASES OF GROUP I. 601

arated, ft is advisable to add to the filtrate some water, some
more platinic chloride, and if the quantity of sodium is only
small, also some sodium chloride ; evaporate on the water-bath
nearly to dryness, at a temperature not exceeding Y5 (BISCHOF),
and treat "the residue in the manner just described. In order
to diminish the solvent action of the alcohol on .the potassium
platinic chloride, J ether may be now mixed with it. Should
this operation again leave a small undissolved residue of pota,^
sium platinic chloride, it is filtered off, best on a separate filter,
and first washed with alcohol and ether. As, however, this
remainder of the double salt is generally impure, dissolve it on
the filter with boiling water, evaporate with a few drops of pla-
tinic chloride, treat the residue with alcohol, and if any potas-
sium salt remains, determine it either with the principal quan-
tity or by itself.

If you are not satisfied with an indirect estimation of
the sodium, one of the following direct methods may be
employed, a. Evaporate the filtrate till the spirit has gone off,
dilute, digest the solution with small pure iron filings till the
platinum is all thrown down, filter, add chlorine water till the
ferrous is converted into ferric chloride, precipitate with ammo-
nia, filter off the ferric hydroxide, and determine the sodium
chloride in the filtrate, fi. Evaporate the filtrate, finally in a
porcelain crucible, to dryness, heat the residue to low redness
in a current of hydrogen, extract with water, and determine
the sodium chloride in the solution. For small quantities of
fluid this method will be found convenient, y. A. MITSCHER-
LICH recommends to mix the filtrate with sulphuric acid, evapo-
rate to dryness, ignite the residue, extract the sodium sul-
phate with water, and determine it according to 98, 1. These
methods, of course, yield the sodium salt in a pure condition
only when the separation of the potassium has been perfect.
They present the advantage that the sodium salt is brought
under one's eyes and may be tested after weighing.

Should the solution contain sulphuric acid, it may be in 2
presence of hydrochloric acid or of some volatile acid, convert
the alkalies first into normal sulphates ( 97, 98), and weigh
them as such. For the estimation of the potassium, one of the
two following methods may be used :

a. First convert the sulphates into chlorides and then pro-

602 SEPARATION. [ 152.

ceed as above. For this purpose barium salts were formerly
employed, or, better, an alcoholic solution of strontium chloride.
The barium sulphate, however, carries down considerable quan-
tities of alkali salt, and the strontium sulphate noticeable
quantities; hence the employment of these reagents, more par-
ticularly barium, cannot be recommended. II. ROSE advises
repeated ignition of the alkali sulphates with ammonium
chloride till the weight remains constant; this process is simple
and well adapted for small quantities ; no loss of alkali need be
feared if the heat is not unnecessarily raised. L. SMITH advises
the use of lead salts. Dissolve the alkali sulphate, precipitate
with pure neutral lead acetate, avoiding a large excess, add
some alcohol, filter, precipitate the excess of lead with sulphuric
acid, and evaporate to dryness with addition of sulphuric acid.
This method, when carefully conducted, yields excellent results.

/?. Precipitate the potash directly out of the solution of the
sulphates. R. FINKENER* gives the following process : To the
rather dilute solution of the salts in a capacious porcelain dish
add platinic chloride in quantity more than sufficient to throw
down all the potassium, evaporate on a water-bath down to a
few c.c., allow to cool, add, at first in small quantities, 20
times the volume of a mixture of 2 parts absolute alcohol and
1 part ether, with stirring; filter after a short time, and wash
the precipitate with alcohol and ether till the washings are
'colorless. If, when the alcohol arid ether are first added, a
strong aqueous solution of sodium sulphate separates, add some
hydrochloric acid till the fluids mix. Dry the precipitate con-
sisting of potassium platinic chloride and sodium sulphate,
heat with the filter in a porcelain crucible till the filter is car-
bonized, then in a current of hydrogen to scarcely visible
ivdnrss extract the residue with hot water, ignite the platinum
in the air, weigh and calculate from the weight the quantity of

The separation of potassium from sodium by platinic
chloride gives results which are fully satisfactory, and at all
event- far more exact tlian any method depending on another
principle; provided that the platinum solution is pure and the
operation.- have been carefully performed in accordance with
the directions. If you have any occasion to doubt the perfect

MI. KOSK, Handbuch </</ anaiyt. Ch, in., G. Anil, von Fl.NKENKH, II, 923.

152.] BASES OF GROUP I. 603

purity of *the weighed double salt, you may always dissolve it
in boiling water, evaporate with addition of a little platinum
solution, and re weigh the salt thus purified.

Where a series of analyses is being made, the potassium in
the potassium-platinic chloride may be volu metrically estimated.
For this purpose triturate it with double its quantity of pure
sodium oxalate (free from chlorides), heat the mixture in a
platinum crucible to fusion, leach the residue with watsr,
neutralize the filtrate nearly with acetic acid, determine the
chlorine in the alkali chloride with deciriormal silver solution
( 141, I., &, <*), and calculate 1 eq. of potassium for 3 eq.
chlorine. If the quantities of potassium-platinic chloride are
very small, moisten with a cencentrated solution of neutral
potassium oxalate, dry, ignite in a covered crucible, and pro-
ceed as above. The separated platinum, if weighed, will
afford a good control (F. MOHE *).


The process is conducted exactly as in #, when the alka- 3
lies are present as chlorides. See also 99, 2. If potassium
also is present, the precipitate produced by platinic chloride is a
mixture of ammonium platinic chloride and potassium platinic
chloride ; in which case the weighed precipitate is cautiously
ignited for a sufficient length of time, but not too strongly,
until the ammonium chloride is expelled, the gentle ignition
continued in a stream of hydrogen or with addition of oxalic
acid, the residue extracted with water, a few drops of hydro-
chloric acid added if oxalic acid was employed, and the potas-
sium chloride in the solution determined as directed 97, 3.
The weight found is calculated into potassium platinic chloride,
and the result deducted from the w r eight of the whole precipi-
tate : the difference gives the ammmonium platinic chloride.
The weighing of the separated platinum affords a good control.
The method is seldom employed, as that given in 2. yields more
exact results.

*Zeitschr. f. analyt. Chem., xn, 137.

604 SEPARATION. [ 152.

2. Methods based upon the Volatility of Ammonium
Salts and Ammonia.


a. The salts of the alkalies to be separated contain th# same 4
volatile add, and admit of the total expulsion of their water by

at 100, without losing ammonia (e.g., the chlorides).
Weigh the total quantity of the salts in a platinum crucible,
and heat, with the lid on, gently at first, but ultimately for
some time to faint redness ; let the mass cool, and weigh. The
decrease of weight gives the quantity of the ammonium salt.
If the acid present is sulphuric acid, you must, in the first
place, take care to heat very gradually, as otherwise you will
suffer loss from the decrepitation of ammonium sulphate ; and,
in the second place, bear in mind that part of the sulphuric
acid of the ammonium sulphate remains with the fixed alkali
sulphates, and that you must accordingly convert them into
normal salts, by ignition in an atmosphere of ammonium car^
bonate., before proceeding to determine their weight (compare
97 and 98). Ammonium chloride cannot be separated in
this manner from fixed alkali sulphates, as it converts them,
upon ignition, partly or totally into chlorides.

b. Some one or other of the conditions given in " a " is not
fulfilled, '

If it is impracticable to alter the circumstances by simple 5
means, so as to make the method a applicable, the fixed alkalies
and the ammonium must be determined separately in different
portions of the substance. The portion in which it is intended
to determine the potassium and sodium is gently ignited until
ammonium is completely expelled. The fixed alkalies are con-
verted, according to circumstances, into chlorides or sulphates,
and treated as directed in 1, 2, or 6. The ammonium is esti-
mated in another portion according to 99, 3.

3. Indirect JA ////*/*.

Of course, a great many of these may be devised; but the 6
following is i lie only one in general use.

I'oT.\irM I-'KoM SoDITM.

Convert both alkalies into neutral sulphates or chlorides


( 97 and 98), and weigh as such ; estimate the sulphuric acid
( 132) or chlorine ( 141); and from the amount of this cal-
culate the quantities of the sodium and potassium (see " Calcu-
lation of Analysis," 200*).

The indirect method of determining sodium and potassium
is applicable only in the analysis of mixtures containing toler-
ably large quantities of both bases ; but where this is the case,
the process answers very well, affording also, more particularly,
the advantage of expedition, if the chlorine in the weighed
chlorides is titrated ( 141, I., &).

Supplement to the First Group.

Lithium may be separated from potassium and sodium in the 7
indirect way, and by two direct methods :

a. Treat the nitrates or the chlorides, dried at 120, with a
mixture of equal volumes of absolute alcohol and anhydrous
ether, digest at least for 24 hours, with occasional shaking (the
salts must be completely disintegrated), decant rapidly on to a
filter covering the funnel, and treat the residue again several
times with smaller portions of the mixture of alcohol and ether.
Determine, on the one part, the undissolved potassium and
sodium salts ; on the other, the dissolved lithium salt, by dis-
tilling the fluid off, and converting the residue into sulphate.
This method is apt to give too much lithium, as the potassium
and sodium salts, especially the chlorides, are not absolutely
insoluble in a mixture of alcohol and ether. The results may
be rendered more accurate by treating the impure lithium salt,
obtained by distilling off the ether and alcohol, once more with
alcohol and ether, with addition of a drop of nitric or hydro-
chloric acid, adding the residue left to the principal residue,
and then converting the lithium salt into sulphate. If the
salts, which it is intended to treat with alcohol and ether, have
been ignited, however so gently, caustic lithia is formed in

Online LibraryC. Remigius FreseniusQuantitative chemical analysis → online text (page 54 of 69)