The _double tartrate of potash and soda_ was first prepared in 1672 by Peter Seignette, an apothecary of Rochelle, and was used by him in medicine. _Tartar emetic_ was discovered by Adrian von Mynsicht in 1631, and its true nature explained by Bergmann in 1773. _Racemic acid_ was first mentioned by a wine manufacturer named Kestner, and was recognised as an acid in 1819. Its relation to tartaric acid, with which it is isomeric, was first explained by Berzelius, who gave it its name. 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.