The naturally occurring oxalates were long considered as identical with tartar. Oxalic acid was obtained by Scheele in 1776 by means of the action of nitric acid upon sugar. This acid was further investigated by Bergmann, who observed its decomposition by heat with the formation of a gas burning with a blue flame. The identity of the naturally occurring oxalic acid with that prepared from sugar was established by Scheele in 1784. The quantitative composition of oxalic acid was first ascertained by Dulong in 1815. Mucic acid was discovered by Scheele in 1780, and was studied by Fourcroy, who gave it the name it now bears. Pyromucic acid was also known to Scheele, and was observed by Hermbstädt and Houton-Labillardière. Camphoric acid was first recognised by Bouillon-Lagrange and Vauquelin. Suberic acid was discovered by Brugnatelli in 1787.
That gum benzoin yielded a product (benzoic acid) by sublimation was known in the sixteenth century. It was introduced into medicine by Turquet de Mayerne as flowers of benzoin. Scheele showed how this acid might be obtained by wet methods from gum-benzoin. It was detected in Peru-balsam by Lehmann in 1709. Rouelle found it in the urine of the cow and the camel. Liebig, in 1829, detected the difference between hippuric acid and benzoic acid. The characteristic acid in amber (succinic acid) was first detected by Pott in 1753.
Formic acid was first isolated by Wray in 1676. Lactic acid was discovered by Scheele in sour milk in 1780. For a time it was regarded as impure acetic acid, until it was detected in muscle juice by Berzelius, and its individuality established. Its true composition was ascertained by Mitscherlich and by Liebig in 1832. Citric acid has been known since the thirteenth century, but it was first definitely isolated by Scheele in 1784. Apple juice was used in medicine in the sixteenth century, and the soda salt of its characteristic acid (malic acid) was prepared by Donald Monro in 1767.
It was known to the ancients that extract of gall nuts acquired a black colour when mixed with a solution of iron vitriol; and Boyle and Bergmann ascribed this phenomenon to the presence of a peculiar acid. Gallic acid was first isolated by Scheele in 1785, and its composition established by Berzelius in 1814. Tannic acid was definitely recognised as distinct from gallic acid by Seguin in 1795.
Mellite, or honey-stone, is mentioned in mineralogical treatises in the sixteenth century. That it consisted of the alumina salt of a special acid (mellic acid) was shown by Klaproth in 1799.
Prussian blue was accidentally discovered in 1710 by a dyer named Diesbach. Its mode of manufacture was first made known by Woodward in 1724. The peculiar reaction by which it was obtained was made the subject of investigation by many chemists of the period without any decisive result. Scheele observed that, when the salt which occasioned the blue colour with vitriol was distilled with sulphuric acid, a volatile acid, inflammable and soluble in water, was obtained. This acid received from Bergmann the name of acidum cœrulei berolinensis, or “Berlin-blue acid,” subsequently shortened by Guyton de Morveau to prussic acid. Scheele also prepared the cyanides of silver and ammonium. That prussic acid was free from oxygen was established by Berthollet. Anhydrous prussic acid was first obtained by Von Ittner, who first established its highly poisonous nature. Bolim, in 1802, had previously observed the presence of prussic acid in oil of bitter almonds, the poisonous character of which was known to Dioscorides. Porret first definitely isolated potassium ferrocyanide, and subsequently discovered the thiocyanates, the quantitative composition of which was ascertained by Berzelius in 1820. That prussic acid was a compound of hydrogen and cyanogen was established by Gay Lussac in 1815.
Cyanic acid was discovered by Wöhler in 1822, in which year also L. Gmelin discovered the ferricyanides.
Fulminating mercury was first prepared by Howard in 1800, and fulminating silver by Brugnatelli in 1802. These were recognised by Liebig, in 1822, to contain a peculiar acid, which he termed fulminic acid, and which he showed to have the same composition as the cyanic acid discovered by Wöhler. Uric acid, so named by Fourcroy, was discovered in gall stones by Scheele in 1776. Urea was first definitely isolated by Fourcroy and Vauquelin in 1799, and was synthetically prepared by Wöhler in 1828.
The bitter principles of plants and their medicinal virtues early attracted attention, but the first attempt to isolate them was made by Fourcroy and Vauquelin in the case of the Peruvian bark, long known for its power as a febrifuge. In 1806 Vauquelin obtained quinic acid. Cinchonine was first isolated by Gomes in 1811.
The chemical nature of opium was the subject of numerous inquiries in the early years of the nineteenth century. In 1805 Sertürner detected the existence of meconic acid, and in 1817 that of morphine, which he recognised as an alkaloid. Narcotine was discovered by Robiquet in 1835. The investigation of other bitter substances was undertaken by Pelletier and Caventou, who in 1818 discovered strychnine, brucine (1819), and veratrine (1820).