Oxalic Acid
2 of the 6 encyclopedias on this shelf carry an entry for Oxalic Acid. Both are reproduced below, so you can see where they agree and where they differ.
The Encyclopedia of Founding (1892)
Important: Safety Warning
This page contains a formula or preparation using substances now known to be dangerously toxic, such as arsenic, mercury, lead, or cyanide compounds. Exposure to these substances can cause severe poisoning, permanent injury, or death.
In addition, this page describes trade processes that use dangerously toxic materials such as cyanide solutions, mercury amalgams, or strong acids. These processes require training, equipment, and precautions far beyond what the text describes.
This information has been left in for historical purposes but should not be acted upon.
This substance exists as binoxalate of potash in common sorrel and the rhubarb plant, which accounts for the acid taste common to those vegetables. As oxalate of soda it is found in the barilla plant, and as oxalate of lime in lichens. It is commonly prepared by the oxidation of sugar or starch with nitric acid: 1 part of sugar is dissolved in 8 parts of nitric acid and gently heated, when intense action ensues, with a copious disengagement of nitrous-acid fumes. The crystals obtained are sour and poisonous, resembling Epsom salts, for which they are often mistaken. Chalk or magnesia suspended in water acts as an antidote in cases of poisoning. This acid is extensively used in calico-printing, and is also employed as a test for the presence of lime. It also removes ink and iron stains from cloth by forming a soluble oxalate of iron, but the fabric suffers injury if the acid be not washed off immediately.
Collier's New Encyclopedia (1921)
in chemistry, { OHO + 2H2O, CO.HO a dibasic acid existing ready formed in plants, and produced by the simple oxidation of glycollic alcohol, or by acting on starch, sugar, or cellulose, with nitric acid, or fusion with caustic alkali. It is formed commercially by fusing sawdust with a mixture of soda and potash to 204°, decomposing the oxalate with lime, and the lime salt with sulphuric acid, and afterward recrystallizing. The solution has a strong acid reaction, and is highly poisonous. The antidote is chalk or magnesia. OXALIDACEÆ, the oxalid or woodsorrel family, an order of plants, alliance Geraniales. They are herbs, undershrubs, or trees, generally distributed throughout both the hot and the temperate regions of the globe; the shrubby species, however, are almost confined to the tropics. They are chiefly remarkable for their acid juice, containing binoxalate of potash. The order contains six genera and 325 species.
What Has Changed in the Last Century
The chemistry in both accounts still holds: oxalic acid is the dibasic acid H2C2O4, present in sorrel and rhubarb as the acid potassium salt, and it is still made industrially by nitric-acid oxidation y other routes rather than by the sawdust-and-alkali fusion Collier's described in 1921, which has long since been abandoned in favour of routes based on carbohydrate or ethylene-glycol oxidation and on carbon monoxide via dimethyl oxalate. The 1892 warning that the crystals resemble Epsom salts and are often mistaken for them reflects a real Victorian hazard; poisoning is now rare and treated in hospital with calcium salts and support for the kidneys, though chalk or magnesia remains sound first aid on the same principle of precipitating insoluble calcium oxalate. What the old entries could not say is that this same insoluble salt is the chief constituent of most human kidney stones, which is why dietary oxalate is now a routine clinical concern. Its old jobs of removing ink and iron stains and bleaching survive in domestic rust removers and wood bleaches.
Written for this edition, 2026.