Alfred Henry Allen.

An introduction to the practice of commercial organic analysis : being a treatise on the properties, proximate analytical examination, and modes of assaying the various organic chemicals and preparations employed in the arts, manufactures, medicine ... online

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strong solution of alkaline carbonate. The liquid is filtered from
the residual carbonate of earthy-metal, acidulated with acetic acid,
and then precipitated with acetate of lead as above described.

Commercial Oxalic Acid is now so cheap that it is
rarely, if ever, purposely adulterated; nevertheless, various
impurities are frequently present, owing to careless manu-
facture or imperfect purification.

ORGANIC MATTERS other than oxalic acid are recognised
by the charring or darkening of the sample when heated.

FIXED MINERAL IMPURITIES are left as a residue on igniting
the sample in the air. If the ignited residue effervesce on
addition of dilute acid, an acid oxalate is present in the
sample. Very sensible quantities of lead and other heavy
metals are sometimes met with.*

present in oxalic acid in considerable quantity. The solution
of such samples gives a white precipitate of BaS0 4 on addition
of barium chloride. The same impurities are very common in
commercial ammonium oxalate.

Ozalates. These salts require but little special description.
The alkali-metals form three classes of oxalates, the potassium
salts having the formulae K 2 C 2 4 ,H 2 0; KHC 2 4 ,H 2 0; and
KH 3 (C 2 4 ) 2 ,2H 2 O. The acid salts are the least soluble. The
oxalates of most other metals are insoluble, or nearly insoluble,
in water. This is true of the oxalates of barium, strontium,
calcium, copper, magnesium, manganese, cobalt, nickel, zinc,

* In a sample of oxalic acid sold as specially purified for analytical purposes,
I found as much as 6*3 per cent, of oxide of lead.


lead, silver, &c. The first four of these retain 1 atom of water
on drying at 100 C. The remainder retain 2 atoms, with the ex
ception of the lead and silver salts, which are anhydrous.
Ferrous oxalate is but sparingly soluble, but ferric oxalate
is readily so, at least in presence of free oxalic acid ; hence the
use of oxalic acid for removing ink-stains and dissolving
Prussian blue. All the insoluble oxalates are soluble in
dilute nitric acid, but they are generally insoluble in acetic
acid. The determination of the oxalic acid may be readily
effected by the methods described on pages 236 and 237.

On ignition, oxalates of the metals of the alkalies and
alkaline-earths evolve carbon monoxide gas, and leave the
corresponding carbonates. These may sometimes be further
decomposed if the temperature be excessive (CaC 2 4 =CaO-f-
C0 + C0 2 ). Oxalates of the heavy metals, when heated to
redness in a close vessel, usually leave the free metal and
evolve carbon dioxide gas (NiC 2 4 =Ni+2C0 2 ). This re-
action occurs even at 100 C. in the case of gold ; hence, gold
is reduced from its solutions by boiling with an oxalate.

Pure oxalates do not char on ignition.


// 2 =(C 2 H 4 )

Succinic acid occurs ready formed in amber and in certain
lignites, is produced during the alcoholic fermentation of sugar,
and by the fermentation of malic acid and many other sub-
stances, especially under the influence of putrefying casein.
Succinic acid is also produced by the action of nitric acid
on the fatty acids and their glycerides, and it exists ready
formed in several plants.

Succinic acid bears the same relation to butylenic alcohol
that oxalic acid does to ethylenic alcohol (glycol), and may be
produced from butylenic alcohol by oxidation. It may also be
obtained by the deoxidation of tartaric or malic acid, which


contain respectively two and one atom more of oxygen than
-does suocinic acid.

Succinic acid may be obtained by the dry distillation of
,amber, the watery distillate being filtered while hot to sepa-
rate oil, when crystals of succinic acid are deposited on cooling,
and may be purified by boiling with nitric acid, followed by
recrystallisation from water.

Succinic acid crystallises in colourless, oblique rhombic
prisms or plates. When heated to 130 C. it emits suffocating
fumes and at 180 melts. When the heat is increased to 235
C. the acid boils and sublimes as succinic anhydride,
C 4 H 4 3 , which melts at 120 C. When heated strongly in
the air, succinic acid burns with a blue smokeless flame.

Succinic acid is soluble in about 13 parts of cold and 2J of
boiling water. It dissolves in alcohol and in ether, but is
insoluble in chloroform or benzene. Nitric acid, chlorine, and
chromic acid have no action on succinic acid. Permanganate
has no action on a cold acid solution, but hot permanganate in
presence of free alkali produces oxalic acid.

In its analytical reactions, succinic acid somewhat resembles
benzoic acid, but differs from it in not being precipitated from
a strong solution of its salts by hydrochloric acid ; in being
precipitated by ammoniacal chloride of barium even from a
dilute solution; and by being insoluble in chloroform, and
therefore not removable from an acid solution by agitation
with that liquid. Magnesium benzoate is soluble in alcohol,
but the succinate is insoluble.

Ferric chloride, if first treated with as much dilute ammonia
as it will bear without precipitation, precipitates from neutral
solutions of soluble succinates bulky brownish-red basic ferric
succinate. Benzoates, under similar circumstances, give a
flesh-coloured precipitate, and cinnarnates a yellow. The
precipitate may be filtered off, washed, and boiled with excess
of dilute ammonia. The filtered liquid, if mixed with barium
chloride and an equal bulk of alcohol, gives a white precipitate



of barium s u c c i n a t e. By the above combination of
reactions, succinic acid may be readily identified and separated
from other organic acids.* The process might possibly be
made quantitative. For such a purpose, sodium acetate should
be added to the liquid containing the iron precipitate, and
the whole boiled, the precipitate produced being first boiled
and then washed with dilute ammonia, the ammoniacal
liquid being then precipitated by alcohol and chloride of

For the determination of the succinic acid in wine
M. Maurnene recommends the following process : To 1 litre
of the sample add sufficient albumin or raw hide to precipitate
all the tannin. The filtered liquid is concentrated and treated
with hydrated oxide of lead till the colour is entirely removed.
The precipitate is boiled for a long time with a 10 per cent,
solution of ammonium nitrate, and the liquid filtered. The
filtrate is treated with sulphuretted hydrogen, the precipitate
filtered off, the filtrate concentrated to 100 c.c., and exactly
neutralised with ammonia. Perfectly neutral ferric chloride
is then added, the precipitate well washed, ignited, and the
residual Fe 2 3 calculated to succinic acid by multiplying the
weight found by the factor 1*978.

COMMERCIAL SUCCINIC ACID has usually more or less a brown
or yellow colour, and smells somewhat of the empyreumatic
oil of amber. It is not unfrequently adulterated with
sal-ammoniac, cream of tartar, oxalic acid,
boric acid, barium sulphate, &c. The incomplete
volatility of the sample will suffice to indicate the presence
of some of these, and the nature of the residue left on ignition
will show the kind of adulterant used. Cream of tartar
leaves potassium carbonate on ignition ; it has been found in
succinic acid to the extent of 50 per cent, of the sample.
Oxalic Acid and Sal-ammoniac are volatile on

* For methods of separating succinic acid from malic acid, see the latter
(pages 244 and 245).


ignition, but they may readily be recognised in the wet way, by
the formation of the insoluble oxalate of calcium and chloride
of silver. If a chloride be found in quantity by adding nitrate
of silver in presence of nitric acid, the presence of ammonium
must be proved before assuming the presence of sal-am-

FICTITIOUS SUCCINIC ACID has been prepared by adding a
little oil of amber to tartaric acid, sal-ammoniac, or acid sul-
phate of potassium.





This acid is contained in apples, pears, and most fruits used
for domestic purposes. It is usually prepared from rhubarb
stalks or mountain-ash berries.

Malic acid crystallises in groups of four- or six-sided prisms,
which are colourless and odourless, and readily fusible. Malic
acid is deliquescent and readily soluble in water, alcohol.
and ether. The aqueous solution has an agreeable acid taste,
and becomes mouldy on keeping. In contact with ferments,
especially putrid cheese, the solution of malic acid yields
succinic acid, C 4 H 6 4 , and acetic acid,' C 2 H 4 2 .
Sometimes butyric acid is produced.

When heated in a small retort to about 180 C., free malic
acid melts and evolves vapours of maleic and fumaric acids,
which crystallise on the cooler parts of the retort and receiver.
Fumaric acid, C 4 H 4 4 , forms slowly at 150 C., and mostly
crystallises in the retort, in broad, colourless, rhombic or
hexagonal prisms, which vaporise without melting at about
200 C., and are soluble in 250 parts of cold water, and easily
in alcohol and ether. Maleic acid, C 4 H 4 4 , is the chief
product if the temperature be suddenly raised to 200 C. This
body crystallises in oblique rhomboidal prisms, which melt at


130, vaporise at about 160 C., and are readily soluble in water
and alcohol. The behaviour of malic acid on heating is of
value owing to the few characteristic tests for this acid.

Native malic acid exerts a negative rotatory action on a ray
of polarised light.* By the action of hydriodic acid (in a sealed
tube), malic acid is converted into succinic acid. Nitric
acid and alkaline solution of permanganate oxidise malic acid.
Concentrated sulphuric acid darkens malic acid and malates
very slowly on warming. When boiled with dilute sulphuric
acid and bichromate of potassium, malic acid evolves an odour
of ripe fruit.

None of the malates are quite insoluble in water, but
few are soluble in alcohol. Solution of calcium chloride does
not precipitate malic acid or malates in the cold (distinction
from oxalic and tartaric acids); only in neutral and very con-
centrated solutions is a precipitate formed on boiling (citrates
are precipitated from neutral boiling solutions by calcium
chloride, unless the liquid is very dilute). The addition of
alcohol after chloride of calcium produces a bulky, white
precipitate of calcium malate, CaC 4 H 4 5 , even in dilute
neutral solutions. Thus, if the liquid be filtered first cold (to
remove oxalic and tartaric acids), and then boiling hot (to
remove citric acid), the malic acid can be precipitated on
addition of two volumes of alcohol. This precipitate may
contain calcium sulphate or succinate, but will be free from
formate,-)- acetate, benzoate, &c. On boiling the precipitate
with a moderate quantity of water, the malate will be dis-
solved, and tannate and sulphate left almost wholly behind.
The precipitate produced by calcium chloride and alcohol may
also be tested for malic acid (after drying it to get rid of all
trace of alcohol) by decomposing it with dilute sulphuric acid,
and boiling the filtered liquid with a small quantity of
potassium anhydrochromate (bichromate). If the liquid re-

* Artificial malic acid is inactive.

t If more than two volumes of alcohol be added, calcium formate may be


main yellow, succinic acid alone is likely to be present ; but if
a green colour is produced without any odour being developed,
citric acid is probably present either with or without succinic
acid. If the liquid acquires a green colour, and evolves an
odour of ripe fruit, malic acid is present, and possibly either
or both succinic and citric acids in addition.

Solution of acetate of lead precipitates malic acid, more
perfectly after neutralisation with ammonia, as a white
(and frequently crystalline) precipitate of lead malate,
PbC 4 H 4 5 , which, on boiling a few minutes, melts under the
liquid to a transparent, waxy semi-solid. This characteristic
reaction is obscured by the presence of other organic acids.
The precipitate is very sparingly soluble in cold water, some-
what soluble in hot water. Malate of lead is soluble in strong
ammonia, but is not readily dissolved by a slight excess.
(Distinction from tartrate and citrate.) Malate of lead dis-
solves in ammonium acetate, and on mixing the liquid
with two volumes of alcohol is reprecipitated. (Any suc-
cinate of lead remains in solution.) The precipitate may
be washed with a mixture of 2 measures of alcohol and 1 of

If the precipitate of malate of lead be treated with excess
of ammonia, dried on the water-bath, moistened and triturated
with alcoholic ammonia, and then treated with absolute alcohol,
only malate of ammonium dissolves ; ammonium citrate, tar-
trate, oxalate, &c., being insoluble in absolute alcohol. Malic
acid may be separated from other organic acids in solution by
adding ammonia in slight excess, and then 8 or 9 volumes of
strong alcohol, which precipitates all but the malate of
ammonium. The method may be conveniently applied to
the solution of the free acids obtained by suspending the lead
salts in water and passing sulphuretted hydrogen through the

If the alcoholic solution of ammonium malate be precipi-
tated by lead acetate, and the malate of lead obtained filtered


off, and washed with alcohol, dried at 100, and weighed, the
weight obtained, multiplied by 0'3953, gives the quantity of
malic acid present.

For the determination of malic acid in wine, 100 c.c.
should be precipitated with a slight excess of lime water ; the
filtrate is concentrated to one-half its bulk, and absolute
alcohol added in excess ; the precipitate, consisting of calcium
malate and sulphate, is collected on a filter, washed with proof-
spirit, dried, and weighed. If the calcium sulphate be next
determined by dissolving the precipitate in water, precipitating
the solution by barium chloride, and multiplying the weight
of barium sulphate obtained by '5837, the difference may be
regarded as calcium malate, 172 parts of which correspond
to 134 of malic acid.


French Acide Tartarique.

German Tartarsaure, Weinsteinsaure.

C 4 H 6 6 =H 2 r=H 2 (C 4 H 4 6 )"=(C 4

Tartaric acid occurs, either free or combined, in various
plants. The grape is the only source from which it is com-
mercially obtained, The deposit formed on the sides and
bottom of the vessels in which wine is manufactured consists
largely of calcium and potassium tartrates. After purifica-
tion, it is treated with chalk and calcium sulphate, by which
a nearly insoluble calcium . tartrate is produced, and this,
when decomposed with sulphuric acid, yields free tartaric acid,
which is obtained' in crystals by cooling the concentrated

Five distinct modifications of tartaric acid exist. Their
chief physical and chemical differences are as follow :
anhydrous, hemihedral, rhombic crystals, the aqueous solution


of which turns the plane of polarisation of a luminous ray to
the right. The crystals fuse at 135 C., have a density of
174 to T75, and are readily soluble in absolute and in aqueous

In the following article, ordinary tartaric acid and its
salts are always referred to unless some special prefix is

b. LuEVO-TARTARic, or ANTI-TARTARIC ACID, forms anhy-
drous, hemihedral, rhombic crystals, the aqueous solution of
which turns the plane of polarisation of a luminous ray to the

c. EACEMIC, or PARA-TARTARIC ACID, forms hydrated,
holohedral, triclinic crystals of H 2 T,H 2 O, which are optically
inactive. The crystals have a density of 1*69, and are soluble
in five parts of cold water, and with difficulty in cold alco-
hol. The calcium racemate is less soluble in water than
calcium dextro-tartrate, and is also distinguished by its
insolubility in acetic acid, and in chloride of ammonium

d. INACTIVE, or MESO-TARTARIC ACID : optically inactive,
but not resolvable in a. and b. acids.

e. META-TARTARIC ACID : produced by fusing the ordinary
variety. It is deliquescent and uncrystallisable. Its solution
and those of its salts are converted by boiling into those of the
ordinary modification.

When heated to 205 C., tartaric acid loses the elements of
water, and is converted successively into substances of the
formula C 8 H 10 O n ; C 4 H 4 O 5 ; and C 5 H 8 4 ; it ultimately car-
bonises and emits a smell resembling that of burnt bread
or sugar.

Tartaric acid is very soluble in water and alcohol, but

* Racemic acid can be prepared by mixing a. and b. tartaric acids, and can
be resolved into them by appropriate methods. According to Staedel, crystals
of natural acemic acid differ from the artificial product by not disintegrating on
exposure to air. Anhydrous artificial racemic acid is stated to fuse at 198,
and the natural at 201 C.


insoluble in ether. The aqueous solutions have the following
densities as determined by H. Schiff :

Percentage by weight of tartaric acid. Density at 15 C. (=59 F.)

33 11654

22 11062

14-67 1-0690

11 1-0511

7-33 1-0337

3-67 1-0167

Aqueous solutions of the acid (especially when dilute)
gradually decompose with growth of fungus. Cream of tartar
and other tartrates decompose when kept in a moist state.

Tartaric acid contains two atoms of hydrogen replaceable by
metals,* and hence forms two classes of salts. Few of the
metallic tartrates are readily soluble in water, and all are
insoluble in alcohol. The greater number of tartrates, except
tartrate of mercury, are soluble in ammonia.


1. Tartaric acid and tartrates are charred when heated with
concentrated sulphuric acid.

2. Soluble tartrates in neutral solution give white calcium
tartrate on addition of chloride of calcium. The precipitate
is nearly insoluble in cold water ; soluble in many ammoniacal
salts; soluble (after washing) in cold solution of sodium
hydrate, but reprecipitated on boiling; soluble in acids (in-
cluding acetic) ; and converted by heating with a neutral
solution of cupric chloride into insoluble cupric tartrate.
(Citrate of calcium yields soluble cupric citrate).

3. The reducing action of tartaric acid on solutions of silver
is an extremely delicate test when properly applied, but is
remarkably liable to failure if the proper conditions are not
carefully observed. The solution of tartaric acid, or the
tartrate of alkali-metal (all other metals being first removed),

* Two additional atoms are replaceable by alcoholic or acid radicals.


is rendered acid with nitric acid, excess of silver nitrate
added, and any precipitate filtered off. To the solution very
dilute ammonia is added until the precipitate at first formed
is nearly redissolved. The solution is again filtered, and the
filtrate heated nearly to boiling for a few minutes, when a
brilliant metallic mirror will be deposited on the sides of the
tube. Citric acid does not reduce silver under similar circum-
stances, except on continued boiling.

4. Tartaric acid prevents the precipitation of many metallic
solutions by alkalies, stable double tartrates being formed.
For the separation of heavy metals from tartrates, sulphu-
retted hydrogen or sulphide of sodium must be employed,
according to the metals present. The filtrate may be concen-
trated, and any barium, strontium, calcium, or magnesium
present thrown down by boiling with carbonate of sodium.
Aluminium is not separated by either of the above precipitants,
but the tartaric acid can be detected and estimated in the
solution without removing it.

5. The best method of determining tartaric acid by direct
estimation is to precipitate it in the form of potassium-
hydrogen tartrate (KHT). (For the properties of this salt, see
page 258.) When the free acid is to be determined, either
alone or mixed only with citric acid, no better process can be
employed than that described on page 264. For the deter-
mination of tartaric acid in tartrates, and in the various
natural and artificial products of tartaric acid manufactories,
the processes of Mr Warington, described on page 250, et seq.,
are by far the best.

6. Like the corresponding salts of other organic acids, the
tartrates of the light metals leave on ignition a residue of
carbonate or oxide of the contained metal, and by dissolving
this residue in standard acid and ascertaining the amount of
acid neutralised by titrating the excess with standard alkali,
an accurate estimation of the metal can be obtained, and if it
be known whether the tartrate was originally an acid or a


neutral salt, a determination of the tartaric acid itself is

7. Tartaric acid and acid tartrates neutralise alkalies
completely, and litmus affords a perfectly sharp indication of
the end of the reaction. Hence the ordinary processes of
alkalimetry are applicable to tartaric acid and tartrates.

The tartaric acid in tartrates of organic bases may generally
be determined by precipitation as acid tartrate of potassium.

The tartrates of the alcohol radicals are unimportant. Tar-
trate of ethyl may be decomposed by heating with alcoholic
potash, and the acid tartrate of potassium subsequently pre-
cipitated by adding excess of acetic acid. (See also page 142.)

COMMERCIAL TARTARIC ACID is liable to contain the same
impurities as citric acid, and is examined in a similar manner.
(See page 263, et seq.)

Tartaric Acid Liquors are the liquids resulting from the
decomposition of calcium tartrate by sulphuric acid. They
are of a very complex character, containing free tartaric acid,
sulphuric acid and sulphates of calcium, potassium, iron, and
aluminium, phosphates, and various organic acids and bodies
of an indefinite nature. Their analytical examination is
limited to the determination of the tartaric and free sulphuric
acid, and, in some cases, of the total organic acids.

The determination of the tartaric acid is best effected by
precipitation as the acid potassium salt. Acetate of potassium
is the best reagent for pure liquors, but is inapplicable in pre-
sence of iron or aluminium. Citrate of potassium is without
this objection, and is employed by Warington in the follow-
ing manner :

A quantity of liquor, containing from 2 to 4 grammes of
tartaric acid, and of 30 to 40 c.c. in volume, is treated with a
saturated aqueous solution of tripotassic citrate,* added drop
by drop with constant stiring. As soon as the free sulphuric

* Obtained by neutralising citric acid by pure potash or potassium car-


acid is satisfied, the precipitate begins to appear in streaks on
the sides of the glass. In presence of much sulphuric acid, a
fine precipitate of potassium sulphate will precede the forma-
tion of the acid tartrate, but is readily distinguished from it.
When the streaks begin to appear, 1 c.c. of citrate solution
is added for every gramme of tartaric acid supposed to be pre-
sent. A great excess should be avoided. Should a gelatinous
precipitate be formed, the experiment is repeated with a pre-
vious addition of some citric acid. After standing twelve
hours, the precipitate is collected on a small filter, washed two
or three times with a 5 per cent, solution of potassium chloride,
then with single washings of 50 per cent, and 70 per cent,
alcohol, and finally with 80 to 90 per cent, alcohol till the wash-
ings are no longer acid to tincture of litmus. The filter and
precipitate are finally transferred to a beaker, and the amount
of tartaric acid present is determined by titration with
standard alkali. Instead of washing the precipitate in the
above manner, a saturated aqueous solution of acid potassium
tartrate, containing 5 per cent, of potassium chloride, may be
employed, the washing being continued till the acidity of the
filtrate is no greater than that of the wash-water. A correc-
tion should in this case be applied for the acidity of the wash-
water retained by the filter.* The presence of potassium
sulphate in the precipitate is of no consequence, as it has no
neutralising power. Alum interferes, and, therefore, in pre-
sence of aluminium, the second method of washing is to be
preferred. Mr Warington's test experiments gave very satis-

Online LibraryAlfred Henry AllenAn introduction to the practice of commercial organic analysis : being a treatise on the properties, proximate analytical examination, and modes of assaying the various organic chemicals and preparations employed in the arts, manufactures, medicine ... → online text (page 21 of 32)