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a weighed platinum vessel. Then bring the chief quantity of the
precipitate into the platinum dish and dry the whole to a constant
weight at 130 C.

If the quantity of potassium-platinic chloride obtained is very
small, the whole may be dissolved from the filter, evaporated and
dried in the same manner.*

The asbestos filtering-tube described on page 108, Fig. 68, is
generally to be recommended for filtering. The tube to be dried
is freed from water so far as possible by suction, and then inserted
into another, wider tube about 4 cm. shorter, which is fixed in the
air-bath shown on page 64, Fig. 38. Air is then slowly drawn
through the tube, while the air-bath is heated, towards the end at
130, for a long time. The air- current should enter the tube at the
wide end, and should be dried by concentrated sulphuric acid. After
the drying is effected and the tube weighed, the results may be readily
controlled by converting the potassium-platinic chloride into plati-
num. For this purpose dry hydrogen is passed through the tube
while it is moderately heated. After the decomposition is com-
plete, the potassium chloride is leached out with water, all the
water is removed by suction while the tube is being heated, and the
residual platinum weighed, 1 equivalent being equal to 2 equivalents
of potassium.

If a paper filter is used, this must first be dried at 100, weighed,
and then the loss of weight of an aliquot portion dried at 130
determined, from which the loss of weight of the entire filter at
130 may be calculated.

/?. Potassium salts of non-volatile acids (phosphoric acid, boracic
acid, &c.).



* When many successive determinations are to be made, especially in technical
analyses, much time can be saved by using Goocn's apparatus (see pp. 120, 121)
for washing and weighing the K,PtCl.



97.] POTASSIUM. 247

Make a concentrated solution of the salt in water, add some
hydrochloric acid, and platinic chloride in excess, mix with a toler-
able quantity of the strongest alcohol, let the mixture stand 24
hours, after which filter, and proceed as directed in a.

For properties of the precipitate see 68. This method, prop-
erly executed, gives satisfactory results. Still there is generally a
trifling loss of substance, potassium-platinic chloride not being
absolutely insoluble even in strong alcohol. In accurate analyses,
therefore, the alcoholic washings must be evaporated, with addition
of a little pure sodium chloride, at a temperature not exceeding 75,
nearly to dryness, and the residue treated once more with 80-per
cent, alcohol. A trifling additional amount of potassinm-platinic
chloride is thus obtained, which is either added to the principal
precipitate or collected on a separate small filter, and weighed by
dissolving from the filter and evaporating to dryness as above de-
scribed. The object of the addition of a little sodium chloride to
the platinic chloride is to obviate the decomposition to which pure
platinic chloride is more liable upon evaporation in alcoholic solu-
tion alone, than it is when mixed with sodium-platinic chloride.
The atmosphere of a laboratory often contains ammonia, which
might give rise to the formation of some ammonium-platinic chlo-
ride, and to a consequent increase of weight in the potassium salt.

As the collection of a precipitate on a weighed filter-paper is very
tedious, and, where small quantities are operated upon, inaccurate
as well, it is better, where the filter-tube is not used, to collect
small quantities of potassium-platinic chloride (up to 0'03 grm.) in
a very small, unweighed filter, dry, transfer the filter, wrapped up
around the precipitate, to a small covered porcelain crucible, and
slowly carbonize. The cover is then removed, the carbon burned,
and the crucible allowed to cool. A very small quantity of pure
oxalic acid is next added, the cover placed on, and heat applied, at
first gently, finally strongly. By the addition of the oxalic acid the
complete decomposition of the potassium-platinic chloride is greatly
facilitated, and which is not so readily accomplished by simple
ignition. Of course the oxalic acid may be replaced by a current
of hydrogen. The cooled contents of the crucible are treated with
water, the residual platinum washed out until the washings give no
cloudiness with silver-nitrate solution, then dried and weighed. As
a rule the washing may be accomplished by simple decantation.



248 DETERMINATION. [ 98.

5. Volumetric determination as Potassium Silicofluoride.

To the moderately concentrated solution of the potassium salt
in a beaker add a sufficiency of hydrofluosilicic acid,* and then an
equal volume of pure strong alcohol. If the potassium salt was
difficultly soluble (such as potassium platinic chloride), warm it
with the hydrofluosilicic acid before adding the spirit. The potas-
sium silicofluoride will separate as a translucent precipitate ; when
it has settled, filter, wash out the beaker with a mixture of equal
parts strong alcohol and water, and wash the precipitate with the
same mixture till the washings are no longer acid to litmus paper.
Put the filter and precipitate into the beaker previously used, treat
with water, add some tincture of litmus, heat to boiling, and add
standard, or, in the case of very small quantities, decinormal,
potassa or soda solution (215) till the fluid is just blue, and
remains so after continued boiling. The reaction is as follows :
(KF) a SiF 4 + 4KOH = 6KF + Si(OH) 4 , consequently 2 atoms
potassium in the standard solution correspond to 1 at. potassium
originally present and precipitated as potassium silicofluoride (Fie.
STOLE Af).

If the solution of the potassium salt contains much free acid,
particularly sulphuric acid, this is to be removed by heat before
adding the hydrofluosilicic acid. Small quantities of ammonium
salts are of no influence, but large quantities should be removed.
It need hardly be mentioned that other metals precipitable by
hydrofluosilicic acid must be absent. The results are satisfactory.
STOLBA obtained 99 '2 to 100 per cent. Potassium-platinic chloride
may be easily converted into potassium silicofluoride; hence, in
technical analyses, the potassium may be separated in the first
form, and then titrated as the latter (STOLBA, loo. cit.).

98.

2. SODITM.
a. Solution.

See 97, #, all the directions given in that place applying
equally to the solution of NaO.II and sodium salts.

* W. KNOP and W. WOLF use hydrofluosilicate of aniline instead. Zeitechr.
f. analyt. Chem., i, 471.

\Zeiischr.f. analyt. Chem., in, 298.



98.] SODIUM. 249

b.^ Determination.

Sodium is determined either as sodium sulphate, as sodium
chloride, or as sodium carbonate ( 69). For the alkalimetric esti-
mation of caustic soda and sodium carbonate, see 219 and 220.
We may convert into

1. SODIUM SULPHATE; 2. SODIUM NITRATE;

3. SODIUM CHLORIDE.

In general the sodium salts corresponding to the potassium salts
specified under the analogous potassium compounds, 97.

4. SODIUM CARBONATE.

Caustic soda, sodium hydrogen carbonate, and sodium salts of
organic acids, also sodium nitrate and sodium chlorate.

5. SODIUM SILICOFLUORIDE.

Sodium salts of acids soluble in dilute alcohol, excepting sodium
borate.

In sodium borate the sodium is estimated best as sodium sul-
phate ( 136) ; in the phosphate, as sodium chloride, or sodium
carbonate ( 135).

Sodium salts of organic acids are determined either, like the
corresponding potassium compounds, as chloride, or by preference
as carbonate. (This latter method is not so well adapted for
potassium salts.) The analyst must here' bear in mind, that when
carbon acts on fusing sodium carbonate, carbon monoxide escapes,
and caustic soda in not inconsiderable quantity is formed.

1. Determination as Sodium Sulphate.

If alone and in aqueous solution, evaporate to dryness, ignite
and weigh the residue in a covered platinum crucible ( 42). The
process does not involve any risk of loss by decrepitation, as in the
case of potassium sulphate. If free sulphuric acid happens to be
present, this is removed in the same way as in the case of potas-
sium sulphate.

"With regard to the conversion of sodium chloride, &c. , into
sodium sulphate, see 97, 5, 1. For properties of the residue,
see 69. The method is easy, and gives accurate results.
2. Determination as Sodium Nitrate.

Same method as described in 1. The rules and observations
are the same as those given under the estimation of potassium
nitrate ( 97). For properties of the residue, see 69.



250 DETERMINATION. [ 98.

3. Determination as Sodium Chloride.

Same method as described in 1. The rules given and the
observations made in 97, , 2, apply equally here. The fact
that sodium chloride is more difficultly volatilizable than potassium
chloride favors greater accuracy of results. For properties of the
residue, see 69.

The methods of converting sodium sulphate, chromate, chlorate,
and silicate into sodium chloride will be found in Part II. of this
Section, under the respective heads of the acids which these salts
contain.

4. Determination as Sodium Carbonate.
Evaporate the aqueous solution, ignite moderately, and weigh.

The results are perfectly accurate. For properties of the residue,
see 69.

Caustic soda is converted into the carbonate by adding to its
aqueous solution ammonium carbonate in excess, evaporating at a
gentle heat, and igniting the residue.

Sodium hydrogen carbonate, if in the dry state, is converted
into the normal carbonate by ignition. The heat must be very
gradually increased, and the crucible kept well covered. If iu
aqueous solution, it is evaporated to dryness, in a capacious silver
or platinum dish, and the residue ignited.

Sodium salts of organic acids are converted into the carbonate
by ignition in a covered platinum crucible, from which the lid is
removed after a time. The heat must be increased very gradually.
When the mass has ceased to swell, the crucible is placed obliquely,
with the lid leaning against it (see 52, fig. 42), and a dull red
heat applied until the carbon is consumed as far as practicable.
The contents of the crucible are then warmed with water, and the
fluid is filtered off from the residuary carbon, which is carefully
washed. The filtrate and rinsings are evaporated to dryness with
the addition of a little ammonium carbonate, and the residue is
ignited and weighed. The ammonium carbonate is added, to con-
vert any caustic soda that may have been formed into carbonate.
The method, if carefully conducted, gives accurate results; how-
ever, a small loss of soda on carbonization is not to be avoided.
If any residue soluble in water remains, dissolve it and add it to
the principal solution.



g 99.] AMMONIUM. 251

Sodium nitrate, or sodium chloride, may be converted into car-
bonate, by adding to its aqueous solution perfectly pure oxalic
acid in moderate excess, and evaporating several times to dryness,
with repeated renewal of the water. All the nitric acid of the
sodium nitrate escapes in this process (partly decomposed, partly
undecomposed) ; and equally so all the hydrochloric acid in the
case of sodium chloride. If the residue is now ignited until the
excess of oxalic acid is removed, sodium carbonate is left.

99-

3. AMMONIUM.

a. Solution.

Ammonia is soluble in water, as are all ammonium salts of those
acids which claim our attention here. It is not always necessary,
however, to dissolve ammonium salts for the purpose of determin-
ing the amount of ammonium contained in them.

1). Determination.

Ammonium is weighed, as stated 70, either in the form of
ammonium chloride^ or in that of ammonium platinic chloride.
Into these forms it may be converted either directly or indirectly
(i.e., after expulsion as ammonia, and re-combination with an acid),
Ammonium is also frequently determined by volumetric analysis,
and its quantity is sometimes inferred, from the volume of nitrogen.

We convert directly into

1. AMMONIUM CHLOKIDE. -

Ammonia gas and its aqueous solution, and also ammonium salts
of weak volatile acids (ammonium carbonate, ammonium sulphide,

&c.).

2. AMMONIUM PLATINIC CIILOKIDE.

Ammonium salts of acids soluble in alcohol, such as ammonium
sulphate, ammonium phosphate, &c.

3. The methods based on the EXPULSION OF AMMONIA from
ammonium compounds, and also that of inferring the amount of
ammonium from the volume of nitrogen eliminated in the dry
way, are equally applicable to all ammonium salts.

The expulsion of ammonia in the dry way (by ignition with
soda-lime), and its estimation from the volume of nitrogen elimi-
nated in the dry way, being effected in the same manner as the



252 DETERMINATION.

estimation of tlie nitrogen in organic compounds, I refer the stu-
dent to the Section on Organic Analysis. The process of estimating
ammonia by decomposing with a bromized solution of sodium liypo-
chlorite will be given under the Analysis of Soils, in the Special
Part. For the alkalimetric estimation of free ammonia, see 219
and 220; and for the calorimetric method based on the use of
NESSLER'S solution, see under the Analysis of Waters, 205.

1. Determination as Ammonium Chloride.

Evaporate the aqueous solution of the ammonium chloride on
the water-bath, and dry the residue at 100 until the weight re-
mains constant ( 42). The results are accurate. The volatiliza-
tion of the chloride is very trifling. A direct experiment gave
99-94: instead of 100. (See Expt. 15.) The presence of free
hydrochloric acid makes no difference ; the conversion of caustic
ammonia into ammonium chloride may accordingly be effected by
supersaturating with hydrochloric acid.* The same applies to the
conversion of the carbonate, with this addition only, that the process
of supersaturation mut bo conduced in an obliquely-placed flask,
and the mixture heated in the same, till the carbonic acid is driven
off. In the analysis of ammonium sulphide we proceed in the same
way, taking care simply, after the expulsion of the hydrogen
sulphide, and before proceeding to evaporate, to filter off the sul-
phur which may have separated. Instead of weighing the ammo-
nium chloride, its quantity may be inferred by the determination
of its chlorine according to 141, I (Comp. potassium chloride,
97, J, 3.)

2. Determination as Ammmiium-Platinic Chloride.
oe. Ammoniacal salts with volatile acids.

Same method as described in 97, 4, a * (potassium -pi atinic
chloride).

ft. Ammonium salts of non-volatile acids.

Same method as described 97, 4, ft (potassium-platinic chlo-
ride). The results obtained by these methods are accurate.

If you wish to control the results, f ignite the double chloride,

* GUNNING (Zeitechr. f. analyt. Chem., vii, 480) has pointed out that fluids
during evaporation may take up ammonia because of the presence of this in illu-
minating gas.

flf the ammonium-platinic chloride is pure, which maybe known by its color
and general appearance, this control may be dispensed with.



99.] AMMONIUM. 253

wrapped up in the filter, in a covered crucible, and calculate the
amount of ammonium from that of the residuary platinum. The
results must agree. If the double salt is in a filtering-tube, slowly
pass a current of air through it, while heating very carefully. If,
however, the salt is in a paper filter, it is best to transfer the pre-
cipitate, wrapped up in the filter, to the crucible, and continue the
application of a moderate heat' for a long time, then to remove the
lid, place the crucible obliquely, with the lid leaning against it, and
burn the charred filter at a gradually-increased heat (H. ROSE).

When the salt is pure, which may be known from its color and
general appearance, this control may be omitted. "Want of due
caution in respect to heating is apt to lead to loss, from particles of
the double salt being carried away with the ammonium chloride.
Very small quantities of ammoniurn-platinic chloride are collected
on an un weighed filter, dried, and at once reduced to platinum by
ignition.*

3. Estimation by Expulsion of Ammonia in the Wet Way.

This method, which is applicable in all cases, may -be effected
in different ways, viz. :

a. EXPULSION or THE AMMONIA BY DISTILLATION WITH SOLUTION
OF POTASSA, SODA, MILK OF LIME, OR MAGNESIA. Applicable in
all cases where no nitrogenous organic matters from which ammonia
might be evolved upon boiling with solution of potassa, etc., are
present with the ammonium salts. Magnesia is used in cases where
nitrogenous substances capable of yielding ammonia on boiling, are
present.

Weigh the substance under examination in a small glass tube,
three centimetres long and one wide, and put the tube, with the
substance in it, into a small, tubulated retort, a^ Fig. 81, contain-
ing a suitable quantity of moderately concentrated solution of
potassa or soda, milk of lime, or magnesia mixed with water, from
which every trace of ammonia has been removed by protracted
ebullition, but which has been allowed to get thoroughly cold again.
The further arrangement of the apparatus is shown by the cut. As
will be seen, the ammoniacal distillate does not come into contact with

*In a series of experiments to get the platinum from pure and perfectly
anhydrous ammonium-platinic chloride, by very cautious ignition, Mr. Lucius,
one of my pupils, obtained from 44 ! 1 to 44'3 per cent, of the metal, instead of
44-3.



254 DETERMINATION. [ 99.

cork or rubber and this is quite important, since otherwise thsee
might easily retain some of the ammoniacal fluid.




Fig. 81.

If you wish to determine volumetrically the quantity of ammo-
nia expelled, introduce the larger portion of a measured quantity
of standard solution of acid (sulphuric, hydrochloric, or oxalic,
215) into the receiver, the remainder into the U-tube; add to
the portion of fluid in the latter a little water, and color the liquids
in the receiver and U-tube red with 1 or 2 c. c. of tincture of lit-
mus. The cooling-tube must not dip into the fluid in the receiver ;
the fluid in the U-tube must completely fill the lower part, but it
must not rise high, as otherwise the passage of air-bubbles might
easily occasion loss by spirting. The quantity of acid used must
of course be more than sufficient to fix the whole of the ammonia
expelled.

When the apparatus is fully arranged, and you have ascertained
that all the joints are perfectly tight, heat the contents of the
retort to gentle ebullition, and continue the application of the same
degree of heat until the drops, as they fall into the receiver, have
for some time altogether ceased to impart the least tint of blue to
the portion of the fluid with which they first come in contact.
Before removing the heat, a strip of turmeric paper is fixed in
the tubulure of the retort; it must not turn brown. Then loosen
the stopper of the retort, allow to stand half an hour, pour the con-
tents of the receiver and U-tube into a beaker, rinse out with small
quantities of water, and determine finally with a standard solution



99.] AMMONIUM. 255

of alkali the quantity of acid still free, which, by simple subtrac-
tion, will give the amount of acid which has combined with the
ammonia ; and from this you may now calculate the amount of the
latter ( 220). Eesults accurate.* (Expt. No. 55.)

If you wish to determine ~by the gravimetric method the quan-
tity of ammonia expelled, receive the ammonia evolved in a quan-
tity of hydrochloric acid more than sufficient to fix the whole of it,
and determine the ammonium chloride formed, either by simple
evaporation, after the directions of 1, or, far preferably, as ammo-
nium-platinic chloride, after the directions of 2.

~b. EXPULSION OF THE AMMONIA BY MILK OF LIME, WITHOUT
APPLICATION OF HEAT. This method, recommended by SCHLOSING,
is based upon the fact that an aqueous solution containing free
ammonia gives off the latter completely, and in a comparatively
short time, when exposed in a shallow vessel to the air, at the com-
mon temperature. It finds application in cases where the presence
of organic nitrogenous substances, decomposable by boiling alkalies,
forbids the use of the method described in 3, a\ thus, for instance,
in the estimation of the ammonia in urine, manures, etc.

The fluid containing the ammonia, the volume of which must
not exceed 35 c. c., is introduced into a shallow flat-bottomed ves-
sel from 10 to 12 centimetres in diameter; this vessel is put on a
plate filled with mercury. A tripod, made of a massive glass rod,
is placed in the vessel which contains the solution of the ammonium
salt, and a saucer or shallow dish with 10 c. c. of the normal solu-
tion of oxalic or sulphuric acid ( 215) put on it. A beaker is now
inverted over the whole. The beaker is lifted up on one side as
far as is required, and a sufficient quantity of milk of lime added
by means of a pipette (which should not be drawn out at the lower
end). The beaker is then rapidly pressed down, and weighted
with a stone slab. After forty-eight hours the glass is lifted up,
and a slip of moist reddened litmus paper placed in it ; if no change
of color is observable, this is a sign that the expulsion of the ammo-
nia is complete ; in the contrary case, the glass must be replaced.
Instead of the beaker and plate with mercury, a bell-jar, with a
ground and greased rim, placed air-tight on a level glass plate, may
be used. A bell-jar, having at the top a tubular opening furnished
with a close-fitting glass stopper, answers the purpose best, as it

* [In thus estimating minute quantities of ammonia, the condensing tube
must "be of tin, since glass yields a sensible amount of alkali to hot-water vapor.J



256 DETERMINATION. [ 99.

permits the introduction of a slip of red litmus paper suspended
from a thread, thus enabling the operator to see whether the com-,
bination of the ammonia with the acid is completed, without the
necessity of removing the bell- jar. According to SCHLOSLNG, forty-
eight hours are always sufficient to expel O'l to 1 gramme of ammo-
nia from 25 to 35 c. c. of solution. However, I can admit this
statement only as regards quantities up to 0'3 grin. ; quantities
above, this often require a longer time. I therefore always prefer
operating with quantities of substance containing no more than 0'3
grin, ammonia at the most.

When all the ammonia has been expelled, and has entered into
combination with the acid, the quantity of acid left free is deter-
mined by means of standard solution of alkali, and the amount of
the ammonia calculated from the result ( 220).

c. INDIRECT METHOD ACCORDING TO FR. MOHR.^ In this method
a known quantity of alkali in excess, e.g., sodium carbonate, is
heated in aqueous solution with the ammonium salt until all the
ammonia has been expelled; the residual alkali is then volumetri-
cally estimated, and from the difference the equivalent quantity of
ammonia estimated. This method is of limited application, because
it can only be used with neutral ammoniacal salts in the absence
of organic matter.-)- It is, however, convenient and exact, and
may be conducted in an obliquely supported flask. As alkali, a
normal solution of soda or sodium carbonate (53*05 grm. anhy-
drous salt per litre) may be used. The boiling is stopped when the
escaping vapors cease to act on red litmus paper or turmeric paper.
4. Estimation by Expulsion of the Nitrogen in the Wet Way.

A process for determining ammonium by means of the azo-
tometer has been given by W. KNOI>. J It depends on the sepa-
ration of the nitrogen by a bromized and strongly alkaline solution
of sodium hypochlorite.

The simplest azotometer is that described by RUMPF.| It

* Lelirbucli der Titrirmethode.

\ Even organic matter free from nitrogen has a disturbing action, as when
boiled with alkali it forms humus-like acid decomposition products, which neu-
tralize the alkali. % ('hem. CenlralbL, 1800, 244.

This is prepared as follows : Dissolve 1 part of sodium carbonate in 15
parts of water, cool the fluid with ice, saturate perfectly with chlorine, keeping
cold all the while, and add stroug soda solution (of 25 per cent.) till the mixture
on rubbing between the fingers makes the skin slippery. Before using, add to
the quantity required for the scries of experiments bromine in the proportion of
2-3 grin, to the litre, and shake. || Fres. Zeit., vi, 398.



99.]



AMMONIUM.



257



consists of a burette of 50 or 100 c. c. stationed in a glass . Blinder
nearly filled with mercury, and connected by a stout caoutchouc
tube with a small bottle, a, Fig. 82 5 to which is fitted a soft, thrice-



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