A Manual of the Chemistry of the Carbon Compounds

THE CARBON COMPOUNDS. 201
OXALYL COMPOUNDS,
OXALIO ACID C8O2(OH)a.
This important compound exists in many plants (Oxalis, Eumex,
and Rheum species), as potassium or calcium salt. Its sodium-salt
is obtained synthetically by passing carbon dioxide over sodium heated
to 360°:—
2CO2 + Na, = C8O4Naj
The some salt is produced by the action of a high temperature upon
sodium formate;—
HCO.ONa CO.ONa
HCO.ONa CO.ONa
Oxalio acid is an oxidation-product of glycol and glycollic acid;
but also many other compounds, belonging to the group of fatty
substances, yield oxalic acid as the final product of the action of
nitric acid, Many of these bodies are also converted into oxalic acid
by fusing them with caustio potash,
Acetic acid is oxidized to oxalic acid by heating it with a strongly
alkaline solution of potassium permanganate.
Pure oxalio acid is best obtained by heating one part of cane-sugar
with eight parts of nitric acid as long as red fumes are given off.
The acid, crystallizing out on cooling, ts purified by recrystalltzation
from boiling water:
Commercial oxalic acid is produced by fusing saw-dust with a
mixture of caustio potash and soda in the proportion of one equivalent
of the former to two of tlie latter, The solution of the mixed
alkalis having been evaporated to about 1"35 specific gravity, saw-dust
is introduced so as to form a thick paste, which is placed on iron
plates in thin layers and gradually heated, the mass being kept
constantly stirred. During this process water is in the first instance
given off; the mass then swells up and disengages inflammable gases,
consisting of hydrogen and hydrocarbons, an aromatic odour at the
same time being evolved. After the temperature has been maintained
at 200° for one or two hours, tie whole of the woody fibre is decomposed
and the moss is entirely soluble in water. It contains, however,
only from 1—4 per cent, of oxalic acid and about 05 per cent, of
formic acid. The mass is now exposed still longer to the same temperature,
care being taken to avoid any charring, which would cause
a loss of oxalic acid. When perfectly dry it contains the maximum
quantity of oxalic acid, viz. 28—30 per cent, of C2O4H, + 2H,O, but
no acetic acid, and very tittle more formic acid than" before. The
product, which is a grey powder, is in the next place treated with