C. Remigius Fresenius.

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The mercury compound which has been separated by ammonia is
dried and ignited (under a chimney with good draught). Should
a residue remain, this must be examined. If it consists of phos-
phates of the alkali-earth metals, the treatment with mercury and
nitric acid must be repeated; if, on the contrary, it consists of
magnesium oxide or of carbonates of the alkali-earth metals, it is
dissolved in hydrochloric acid, and the solution added to the fluid
containing the chief portion of the basic metals, which may then
be separated and determined in the usual manner. The following
method is often advantageously resorted to instead of the one
described : The filtrate from the mercurous phosphate is evaporated
to dryness, in a platinum dish, and the residue ignited, in a plati-
num crucible, under a chimney with good draught. If alkali
nitrates are present, some ammonium carbonate must be added
from time to time during the process of ignition, to guard against
injury to the crucible from the formation of caustic alkali. The
ignited residue is treated, according to circumstances, first with
water and then with nitric acid, or at once with nitric acid.

ft. If the substance contains iron but not aluminium, the
greater part of the iron is left undissolved with the mercurous
phosphate. The dissolved part is separatd from the other bases by
the methods given in Section Y. ; the iron in the undissolved part
is obtained, after ignition of the residue with sodium carbonate
and treating the ignited mass with water, as ferric oxide contain^
ing alkali (and generally also some phosphoric acid). This is dis-
solved in hydrochloric acid, and precipitated with ammonia.

y. If the substance contains aluminium, the process just given
cannot be used, as aluminium phosphate is not decomposed by
fusion with alkali carbonates, while aluminium nitrate, like ferric
nitrate, is decomposed by simple evaporation. In this case proceed
as follows ; Dissolve the substance in the least quantity of nitric



464 DET;:ILMIXATION. t135.

acid, precipitate hot with mercurous nitrate, add a little mercuric
nitrate, and then pure potash or soda, till a permanent red precipi-
tate appears. The precipitate contains no aluminium, and is to be
treated according to a or fi (H. ROSE, E. E. MUNKOE*).

I. From all Bases without exception,.

Apply SONNENSCHEIN'S method ( 134, Z>, /?), and in the filtrate
from the ammonium phospho-molybdate separate the bases from
the molybdic acid. As molybdic acid comports itself with hydro-
gen sulphide and ammonium sulphide like a metal of the sixth
group, it is best to precipitate metals of the sixth and also of the
fifth group from acid solution with hydrogen sulphide, before pro-
ceeding to precipitate the phosphoric acid with molybdic acid; the
latter will then have to be separated only from the metals of the
first four groups. This is done in the following manner : Mix the
acid fluid, in a flask, with ammonia till it acquires an alkaline
reaction, add ammonium sulphide in sufficient excess, close the
mouth of the flask, and digest the mixture. As soon as the solution
appears of a reddish-yellow color, without the least tint of green,
filter off the fluid, which contains molybdenum and ammonium
sulphide, wash the residue with water mixed with some ammonium
sulphide, and separate the remaining metallic sulphides and hydrox-
ides of the fourth and third groups by the methods which will be
found in Section V. Mix the filtrate cautiously "with hydrochloric
acid in moderate excess, remove the molybdenum sulphide accord-
ing to 128, d, and determine the metals of the first and second
groups in the filtrate.

This method of separating the phosphoric acid from basic radi-
cals is highly to be recommended ; especially in cases where a
small quantity of phosphoric acid has to be determined in presence
of a very large quantity of ferric and aluminium salts, as, for exam-
ple, in iron ores, soils, &c. As arsenic acid and silicic acid give,
with molybdic acid and ammonia, similar yellow precipitates, it is
necessary, if these acids are present, to remove them first.

As the separation of the basic metals from the large excess of
molybdic acid used is somewhat tedious, the best way is to arrange
matters so that this process may be altogether dispensed with.
Supposing, for instance, you have a fluid containing ferric iron,
aluminium, and phosphoric acid, estimate, in one portion, by cau-
tious precipitation with ammonia, the total amount of the three
*Amer. Journ. of Sci. and Arts, May, 1871; Zeittchr. f. anatyt. Chem., X, 467.



136.] BORIC ACID AND BORIC ANHYDRIDE. 465

bodies; in another portion the phosphoric acid, by means of
molybdic* acid ; and in a third, the iron, in the volumetric way.
The aluminium can then be calculated by difference. Attention
has already been called ( 135, A, y) to a method, often very con-
venient, which consists in precipitating the phosphoric acid together
with a small quantity of the iron and then determining in 'this
precipitate the acid and iron, as well as the aluminium carried
down. In this method the molybdic acid need be separated only
from the small quantity of iron and aluminium, and not from the
other bases, thus greatly simplifying the process.

136.

BORIC ACID (H S BO S ) AND BORIC ANHYDRIDE (B 2 O 3 ).
I. Determination.

Boric acid is estimated either indirectly or in the form of potas-
sium ~borofluoride.

1. The determination of the boric acid in an aqueous or alco-
holic solution cannot be effected by simply evaporating the fluid
and weighing the residue, as a notable portion of the acid volatil-
izes and is carried off with the aqueous or alcoholic vapor. This
is the case also when the solution is evaporated with lead oxide in
excess.

a. Mix the solution of the boric acid with a weighed quantity
of perfectly anhydrous pure sodium carbonate, in amount about 1-J
times the supposed quantity of B 2 O 3 present. Evaporate the mix-
ture to dryness, heat the residue to fusion, and weigh. The residue
contains a known amount of E"a 2 O, and unknown quantities of CO 2
and B 2 O 3 combined as sodium borate and carbonate. Determine
the CO 2 by one of the methods given in 139, and find the B 2 O,
from the difference (H. ROSE).

5. In the method a, if between 1 and 2 mol. sodium carbonate
(Na a CO 3 ) are used to 1 mol. B 2 O 3 and this can easily be done if
one knows approximately the amount of the latter present all the
carbonic acid i.s expelled by the boric acid. Hence we have only
to deduct the Na 2 O from the residue to find the B 2 O 3 . As the
tumultuous escape of carbonic acid may lead to loss, it is well, after
having thoroughly dried the residual saline mass, to project it in
small portions cautiously into the red-hot crucible. Results good
(F. G. SCHAFFGOTSCH).*

c. When the amount of acid is quite unknown, and an estima-
tion of carbonic acid in the residue is objected to, you may proceed

. Ann., cv. 427.



466 DETERMINATION. [ 136.

thus : Evaporate the solution of the acid with addition of a weighed
quantity of anhydrous neutral borax (sodium metaborate NaBO,)
free from carbonic acid to dryness, and heat the residue to redness
with great caution (on account of the intumescence) till the weight
is constant. The amount of neutral borax must be so adjusted
that it may not be entirely converted into common borax (2NaBO,
B a 3 ) (II. KOBE).

d. If a solution contains, besides boric acid, only alkalies or
magnesium, the acid may be determined, according to C. MARIG-
NAO,* in the following manner: Neutralize the solution with
hydrochloric acid, add double magnesium and ammonium chloride
in sufficient quantity to give at least 2 parts of MgO to 1 part of
B a O 9 , then add ammonia and evaporate to dryness. If on adding
the ammonia a precipitate is formed which does not redissolve
readily on warming, add more ammonium chloride. The evapora-
tion is conducted, at least towards the end, in a platinum dish, a
few drops of ammonia being added from time to time. Ignite the
dry mass, treat with boiling water, collect the insoluble precipitate
(consisting of magnesium borate mixed with excess of magnesium
oxide) on a filter, and wash with boiling water till the washings
remain clear with nitrate of silver. The filtrate and washings are
mixed with ammonia, evaporated to dryness, ignited, and washed
with boiling water as before.

The two insoluble residues are ignited together in the platinum
dish before used, as strongly as possible, and for a sufficiently long
time, in order to decompose the slight traces of magnesium chlo-
ride that might still be present. After weighing determine the
magnesium oxide, and find the boric acid from the difference.
The determination of the magnesium may be made by dissolving
the residue in hydrochloric acid and precipitating as ammonium
magnesium phosphate, or more quickly, and almost as accurately,
by dissolving in a known quantity of standard sulphuric acid at a
boiling temperature and determining the excess of acid with stand-
ard soda (comp. Alkalimetry).

Should a little platinum remain behind on dissolving the resi-
due, it must be weighed and subtracted from the weight of the
whole (unless the dish was wi-ighiMl first). Results satisfactory.
MARIGNAO obtained in two experiments 0*276 instead of 0-28.

2. If boric acid is to be determined as potassium borqfluoride,
alkalies only (preferably only potassa) may be present. The process
* Zeitschr. f. analyt. Chem., i, 405.



136.] BOEIC ACID AND BOKIC ANHYDEIDE. 467

is conducted as follows : Mix the fluid with pure solution of potassa,
adding for each mol. boric acid supposed to be present, at least 1
mol. potassa ; add pure hydrofluoric acid (free from silicic acid) in
excess, and evaporate, in a platinum dish, on the water-bath, to
dry ness. The fumes from the evaporating fluid should redden
litmus paper, otherwise there is a deficiency of hydrofluoric acid.
The residue consists now of KF,BF 3 and KF,HF. Treat the dry
saline mass, at the common temperature, with a solution of 1 part
of potassium acetate in 4 parts of water, let it stand a few hours,
with stirring, then decant the fluid portion on to a weighed filter,
and wash the precipitate repeatedly in the same way, finally on the
filter, with solution of potassium acetate, until the last rinsings are
no longer precipitated by calcium chloride. By this course of pro-
ceeding, the hydrogen potassium fluoride is removed, without a
particle of the potassium borofluoride being dissolved. To remove
the potassium acetate, wash the precipitate now with 84 per cent,
alcohol, dry at 100, and weigh. As potassium chloride, nitrate,
and phosphate, sodium salts, and even, though with some difficulty,
potassium sulphate, dissolve in solution of potassium acetate, the
presence of these salts does not interfere with the estimation of the
boric acid ; however, sodium salts must not be present in consider-
able proportion, as sodium fluoride dissolves with very great diffi-
culty. The results obtained by this method, are satisfactory. STRO-
MEYER'S experiments gave from 97'5 to 100*7 instead of 100.
When the amount of alkali salt to be removed is very large, the
saline mass left on evaporation should be warmed with the solution
of potassium acetate, allowed to stand 12 hours in the cold and
then filtered. In this way the quantity of potassium acetate
required will be much reduced. For the composition and proper-
ties of potassium borofluoride, see 93, 5. As the salt is very
likely to contain potassium silicofluoride it is indispensable to test
it for that substance ; this is done by placing a small sample of it
on moist blue litmus paper, and putting another sample into cold
concentrated sulphuric acid. If the blue paper turns red, and
effervescence ensues in the sulphuric acid, the salt is impure, and
contains potassium silicofluoride. To remove this impurity, dis-
solve the remainder of the salt, after weighing it, in boiling water,
add ammonia, and evaporate, .redissolve in boiling water, add
ammonia, &c., repeating the same operation at least six times.
Finally, after warming once more with ammonia, filter off the



468 DETERMINATION. [ 136.

silicic acid, evaporate to dryness, and treat again with solution of
potassium acetate and alcohol (A. STROMEYER).'* I was obliged to
modify STROMEYER'S method for effecting the separation of the
silicic acid, the results of my experiments having convinced me
that treating the salt only once with ammonia, as recommended by
that chemist, is not sufficient to effect the object in view.

II. Separation of Boric Acid from the Basic Radicals.

a. From the Alkalies.

Dissolve a weighed quantity of the borate in water, add an
excess of hydrochloric acid, and evaporate the solution on the
water-bath. Towards the end of the operation add a few more
drops of hydrochloric acid, and keep the residue on the water-bath,
until no more hydrochloric acid vapors escape. Determine now
the chlorine in the residue ( 141), calculate from this the alkali,
and you will find the boric acid from the difference.

E. SCHWEIZER, with whom this method originated, states that
it gave him very satisfactory results in the analysis of borax. It
will answer also for the estimation of the basic metals in the case
of some other borates. It is self-evident that the boric acid may be
estimated, in another portion of the salt, by I., 1, tf, or 2. If you
have to estimate boric acid in presence of large proportions of
alkali salts, make the fluid alkaline with potassa, evaporate to dry-
ness, extract the residue with alcohol and some hydrochloric acid,
add solution of potassa to strongly alkaline reaction, distil off the
alcohol, and then proceed as in I., 1, <?, or 2 (Auo. STROMEYER, loo.
cit.).

LuNGEf determined the soda in boronatrocalcite alkalimetri-
cally, by dissolving the mineral in normal nitric acid ( 215) and
titrating back with normal soda, till the tint of the litmus added
becomes violet.

o. From Calcium,.

Dissolve in hydrochloric acid in the heat, avoiding too lurirc ;m
excess, neutralize with ammonia and precipitate with ammonium
oxalate (LUNGE, loc. cit.).

c. From almost all otlier Bases except Alkalies.

The compounds are decomposed by boiling or fusing with
potassium carbonate or hydroxide ; the precipitated base is filtered
off, and the boric acid determined in the filtrate, according to I., 1,

*Annal. d. Chem. u. Pharm., c, 83. \Ib., cxxxviu, 53.



136. J BORIC ACID AND BOKIC ANHYDEIDE.

d, or 2. If magnesium was present, a little of this is very likely
to get irfto the filtrate, and if process L, 2, is employed upon
neutralizing with hydrofluoric acid, this separates an insoluble
magnesium fluoride, which may either be filtered off at once, or
removed subsequently, by treating the potassium borofluoride with
boiling water, in which that salt is soluble, and the magnesium
fluoride insoluble.

d. From the Metallic Oxides of the Fourth, Fifth, and Sixth
Groups.

The metallic oxides are precipitated by hydrogen sulphide, or,
as the case may be, ammonium sulphide,* and determined by the
appropriate methods. The quantity of boric acid may often be
inferred from the loss. If it has to be estimated in the direct way,
the filtrate, after addition of solution of potassa and some potassium
nitrate, is evaporated to dryness, the residue ignited, and the boric
acid estimated by I., 1, r7, or 2. In cases where the metal has been
precipitated by hydrogen sulphide from acid or neutral solutions,
the boric acid may also be determined in the filtrate in the absence
of other acids by L, 1, a or b or c, after the complete removal of
the hydrogen sulphide by transmitting carbon dioxide through the
fluid.

e. From the whole of the Fixed Basic Radicals.

A portion of the very finely pulverized substance is weighed,
put into a capacious platinum dish, and digested with a sufficient
quantity of hydrofluoric acid (which leaves no residue when evapo-
rated in a platinum dish) ; pure concentrated sulphuric acid is then
gradually added, drop by drop, and the mixture heated, gently at
first, then more strongly, until the excess of the sulphuric acid is
completely expelled. In this operation the boric acid goes off in
the form of fluoride of boron (B 2 O 3 + 6HF = 2BF, + 3H.O).
The basic metals contained in the residue in the form of sulphates
are determined by the appropriate methods, and the quantity of
the boric acid is found by difference. It is of course taken for
granted that the substance is decomposable by sulphuric acid.

* Boric acid cannot be separated completely from aluminium by precipitation
of the hydrochloric acid solution with ammonium sulphide or with ammonium
carbonate (WoHLER)- Ann, d. Chcm. u. Pharm.,, CXLI, 208; Zeitsclir. f\ analyt.
Cfiem., vi, 225.



470 DETERMINATION. [ 137.

131

3. OXALIC ACID.

I. Determination.

Oxalic acid is either precipitated as calcium oxalate, and esti-
mated after determination of the calcium in the latter as oxide,
carbonate, or sulphate; or the amount contained in a compound
is inferred from the quantity of solution of potassium permanga-
nate required to effect its conversion into carbonic acid ; or from
the quantity of gold which it reduces ; or from the amount of car-
bonic acid which it affords by oxidization.

a. Determination as Calcium Carbonate, d&c.

Precipitate with solution of calcium acetate, added in moderate
excess, and treat the precipitated calcium oxalate as directed in
103. If this method is to yield accurate results, the solution
must be neutral or slightly acid with acetic acid; it must not con-
tain salts of aluminium, chromium, or of the heavy metals, more
especially cupric or ferric salts ; therefore, where these conditions
do not exist, they must h'rst be supplied.

b. Determination by means of Solution of Potassium Perman-
ganate.

Standardize the solution of potassium permanganate, as directed
112, 2, a, cc, by means of oxalic acid ; then dissolve the substance
in about 150 c.c. water, or acid and water (sulphuric acid is the
best acid to use) ; add, if necessary, a further quantity of sulphuric
acid (about 6 or 8 c.c. strong sulphuric acid should be present), heat
to about 60, and then run in the permanganate, with constant
stirring, until the fluid just shows a red tint. Knowing the quan-
tity of oxalic acid which 100 c.c. of the standard permanganate
will oxidize, a simple calculation will give the quantity of oxalic
acid corresponding to the c.c. of permanganate used in the experi-
ment. The results are very accurate.

c. Detemnination from the reduced Gold (II. ROSE).

a. In compounds soluble in water. Add to the solution of the
oxalic acid or the oxalate a solution of sodium auric chloride, or
ammonium auric chloride, and digest for some time at a tempera-
ture near ebullition, with exclusion of direct sunlight. Collect the
precipitated gold on a filter, wash, dry, ignite, and weigh. 2 at.



137.] OXALIC ACID. 471

An. (197-2 X 2 = 394-4 correspond to 3 mol. C a O 3 (72 X 3 =
216).

/?. In compounds insoluble In water. Dissolve in the least
possible amount of hydrochloric acid, dilute with a very large
quantity of water, in a capacious flask, cleaned previously with
solution of soda ; add solution of gold in excess, boil the mixture
some time, let the gold subside, taking care to exclude sunlight,
and proceed as in a.

d. Determination as Carbonic Acid.

This may be effected either,

a. By the method of organic analysis ; or

ft. By mixing the oxalic acid or oxalate with finely pulverized
manganese dioxide in excess, and adding sulphuric acid to the mix-
ture, in an apparatus so constructed that the disengaged CO 2 passes
off perfectly dry. The theory of this method may be illustrated
by the following equation: H 2 C 2 O 4 + MnO 2 + H 2 SO 4 = MnSO 4
+ 2H,O+ 2CO,. Each eq. of oxalic acid hence affords 2 eq.
of carbon dioxide. For the apparatus and process, I refer to the
chapter on the examination of manganese ores, in the Special Part
of this work. Here I may remark that free oxalic acid must first
be prepared for the process by slight supersaturation with alkali
free from carbonic acid, and also that 9 parts of oxalic anhydride
(C 2 O 3 ) require theoretically 11 parts of (pure) manganese dioxide.
Since an excess of the latter substance does not interfere with the
accuracy of the results, it is easy to find the amount to be added.
The manganese dioxide need not be pure, but it must contain no
carbonate. This method is expeditious, and gives very accurate
results, if the process is conducted in an apparatus sufficiently light
to admit of the use of a delicate balance. Instead of manganese
dioxide, potassium chromate may be used (compare 130, 1, d\
and instead of estimating the carbonic acid by loss it may be col-
lected in a weighed soda-lime tube and the increased weight
noted (139, e)\ the latter method is always to be preferred in
the case of small quantities.

II. Separation of Oxalic Acid from the Basic Radicals.

The most convenient way of analyzing oxalates is, in all cases,

to determine in one portion the acid, by one of the methods given

in I., in another portion the basic radical, particularly as the latter

object may be generally effected by simple ignition in the air,



472 DETERMINATION. [ 138.

which reduces the salt either to the metallic state (e.g., silver oxa-
late), or to pure oxide (e.g., lead oxalate), or to carbonate (e.g.,
the oxalates of the alkalies and alkali-earth metals). In some
cases, as when bases are present which are reduced by carbonic
oxide, or where the resulting carbonate gives up its carbonic
either not at all or with difficulty on ignition, 'the estimation of
the base is more easily effected by simple fusion witli borax glass
(compare 139, II, c). The increase in weight of the platinum
crucible containing the borax glass after fusion corresponds to the
weight of the base present. The loss of weight corresponds to
the oxalic acid, or the oxalic acid and water, as the case may be.

If the acid and basic radical have to be determined in one and
the same portion of the oxalate, the following methods may be
resorted to :

a. The oxalic acid is determined by L, <?, and the gold separated
from the basic metals in the filtrate by the methods given in Sec-
tion Y.

b. In many soluble salts the oxalic acid may be determined by
the method I., a ; separating the basic metals afterwards from the
excess of the calcium salt by the methods given in Section V.

c. Many oxalates of metals which are completely precipitated
as carbonates or oxides by excess of sodium or potassium carbonate,
may be decomposed by boiling with excess of these reagents,
metallic oxide or carbonate being formed on the one, and alkali
oxalate on the other side.

d. All oxalates of the metals of the fourth, fifth, and sixth
groups may be decomposed with hydrogen sulphide or ammonium
sulphide.

138.
4. HYDROFLUORIC ACID.

I. DETERMINATION.

Free hydrofluoric acid in aqueous solution* is determined either
with standard alkali or as calcium fluoride ( 215). In the latter
case sodium carbonate is added in moderate excess, then the solu-

* In analyzing fluorides you must always avoid bringing acid solutions in
contact with glass or porcelain. If platinum or silver dishes of sufficient size
are not at hand you may sometimes use gutta-percha vessels or glass vessels
goated with wax or paraffin.



138.] ' HYDROFLUORIC ACID. 473

tion being boiled, calcium chloride is added as long as a precipitate
continues to form ; when the precipitate, which consists of calcium
fluoride and carbonate, has subsided, it is washed, first by decanta-
tion, afterwards on the filter, and dried ; when dry, it is ignited in
a platinum crucible ( 53) ; water is then poured over it in a plati-
num or porcelain dish, acetic acid added in slight excess, the mix-
ture evaporated to dryness on the water-bath, and heated on the
latter until all odor of acetic acid disappears. The residue, which
consists of calcium fluoride and acetate, is heated with water, the
calcium fluoride filtered off, washed, dried, ignited ( 53), and
weighed. As a control of the purity of the calcium fluoride, it is
well to convert it after weighing into sulphate. If the precipitate
of calcium fluoride and carbonate were treated with acetic acid,
without previous ignition, the washing of the fluoride would prove
a difficult operation. Presence of nitric or hydrochloric acid in the
aqueous solution of the hydrofluoric acid does not interfere with



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