OXALIC ACID (_Acide oxalique_, Fr.; _Sauerkleesaüre_, Germ.); which is
the object of a considerable chemical manufacture. It is usually
prepared upon the small scale by digesting four parts of nitric acid of
specific gravity 1·4, upon one part of sugar, in a glass retort; but on
the large scale, in a series of salt-glazed stoneware pipkins,
two-thirds filled, and set in a water bath. The addition of a little
sulphuric acid has been found to increase the product. 15 pounds of
sugar yield fully 17 pounds of the crystalline acid. This acid exists in
the juice of wood sorrel, the _oxalis acetosella_, in the state of a
bi-oxalate; from which the salt is extracted as an object of commerce in
Switzerland, and sold under the name of salt of sorrel, or sometimes,
most incorrectly, under that of salt of lemons.
Some prefer to make oxalic acid by acting upon 4 parts of sugar, with 24
parts of nitric acid, of specific gravity 1·220, heating the solution in
a retort till the acid begins to decompose, and keeping it at this
temperature as long as nitrous gas is disengaged. The sugar loses a
portion of its carbon, which combining with the oxygen of the nitric
acid, becomes carbonic acid, and escapes along with the deutoxide of
nitrogen. The remaining carbon and hydrogen of the sugar being oxidized
at the expense of the nitric acid, generate a mixture of two acids, the
oxalic and the malic. Whenever gas ceases to issue, the retort must be
removed from the source of heat, and set aside to cool; the oxalic acid
crystallizes, but the malic remains dissolved. After draining these
crystals upon a filter funnel, if the brownish liquid be further
evaporated, it will furnish another crop of them. The residuary mother
water is generally regarded as malic acid, but it also contains both
oxalic and nitric acids; and if heated with 6 parts of the latter acid,
it will yield a good deal more oxalic acid at the expense of the malic.
The brown crystals now formed being, however, penetrated with nitric, as
well as malic acid, must be allowed to dry and effloresce in warm dry
air, whereby the nitric acid will be got rid of without injury to the
oxalic. A second crystallization and efflorescence will entirely
dissipate the remainder of the nitric acid, so as to afford pure oxalic
acid at the third crystallization. Sugar affords, with nitric acid, a
purer oxalic acid, but in smaller quantity, than saw-dust, glue, silk,
hairs, and several other animal and vegetable substances.
Oxalic acid occurs in aggregated prisms when it crystallizes rapidly,
but in tables of greater or less thickness when slowly formed. They lose
their water of crystallization in the open air, fall into powder, and
weigh 0·28 less than before; but still retain 0·14 parts of water, which
the acid does not part with except in favour of another oxide, as when
it is combined with oxide of lead. The effloresced acid contains 20 per
cent. of water, according to Berzelius. By my analysis, the crystals
consist of three prime equivalents, of water = 27, combined, with one of
dry oxalic acid = 36; or in 100 parts, of 42·86 of water with 57·14 of
acid. The acid itself consists of 2 atoms of carbon = 12, + 3 of oxygen
= 24; of which the sum is, as above stated, 36. This acid has a sharp
sour taste, and sets the teeth on edge; half a pint of water, containing
only 1 gr. of acid, very sensibly reddens litmus paper. Nine parts of
water dissolve one part of the crystals at 60° F. and form a solution,
of spec. grav. 1·045, which when swallowed acts as a deadly poison.
Alcohol also dissolves this acid. It differs from all the other acid
products of the vegetable kingdom, in containing no hydrogen, as I
demonstrated (in my paper upon the ultimate analysis of organic bodies,
published in the Phil. Trans. for 1822), by its giving out no muriatic
acid gas, when heated in a glass tube with calomel or corrosive
sublimate.
Oxalic acid is employed chiefly for certain styles of discharge in
calico-printing, (which see), and for whitening the leather of
boot-tops. Oxalate of ammonia is an excellent reagent for detecting lime
and its salts in any solution. The acid itself, or the bi-oxalate of
potash, is often used for removing ink or iron-mould stains from linen.
A convenient plan of testing the value of peroxide of manganese for
bleachers, &c., originally proposed by Berthier, has been since
simplified by Dr. Thomson, as follows. In a poised Florence flask weigh
600 grains of water, and 75 grains of crystallized oxalic acid; add 50
grains of the manganese, and as quickly as possibly afterwards from 150
to 200 grains of concentrated sulphuric acid. Cover the mouth of the
flask with paper, and leave it at rest for 24 hours. The loss of weight
it has now suffered, corresponds exactly to the weight of peroxide of
manganese present; because the quantity of carbonic acid producible by
the reaction of the oxalic acid with the peroxide, is precisely equal to
the weight of the peroxide, as the doctrine of chemical equivalents
shows.
OXIDES, are neutral compounds, containing oxygen in equivalent
proportion.
OXISELS, are salts, consisting of oxygenated acids and oxides, to
distinguish them from the HALOSELS, which are salts consisting of one of
the archæal elements; such as chlorine, iodine, bromine, &c. combined
with metals. See SALT.
OXYGEN _(Oxigène_, Fr.; _Sauerstoff_, Germ.); is a body which can be
examined only in the gaseous form; for which purpose it is most
conveniently obtained in a pure state by exposing chlorate of potash, or
red oxide of mercury, in a glass retort, or recurved tube, to the heat
of a spirit lamp; 100 grains of the salt yield 115 cubic inches of gas.
One pound of nitre, ignited in an iron retort, gives out about 1200
cubic inches of oxygen, mixed with a little nitrogen. The peroxide of
manganese also affords it, either by ignition alone in an iron or
earthen retort, or by a lamp heat in a glass retort, when mixed with
sulphuric acid. Oxygen is void of taste, colour, and smell. It possesses
all the mechanical properties of the atmosphere. Its specific gravity is
1·1026 compared to air 1·0000; whence 100 cubic inches of it weigh 33·85
grains. Combustibles, even iron and diamonds, once kindled, burn in it
most splendidly. It forms 21 parts in 100 by volume of air, being the
constituent essential to the atmospheric functions of supporting animal
and vegetable life, as well as flame.
The full development of this subject in its multifarious relations, will
be discussed in my forthcoming new system of chemistry.
OXYGENATED-MURIATIC, and OXYMURIATIC, are the names originally given by
the French chemists, from false theoretical notions, to chlorine, which
Sir H. Davy proved to be an undecompounded substance.