The first organic acid known was vinegar (acetic acid), and for a long time all naturally occurring organic acids having a sour taste were regarded as identical with or as forms of vinegar. It was only during the second half of the eighteenth century that it was clearly ascertained that a variety of organic acids exist, perfectly distinct from acetic acid. _Glacial acetic acid_ was first obtained by Löwiz in 1789. Acetic acid, as a product of the destructive distillation of wood, was first obtained by Göttling in 1779. The acetic fermentation has been studied from very early times. Surmises as to the mode in which wine was converted into vinegar are to be met with in the works of Basil Valentine, Becher (1669), Lemery (1675), and Stahl (1667). Priestley, for a time, held the opinion that vinegar contained a vegetable acid air, but he subsequently discovered and corrected his error. The direct conversion of spirit of wine (ethyl alcohol) into acetic acid was studied by Lavoisier and Berthollet, who first clearly recognised that it was a process of oxidation. The quantitative composition of acetic acid was first established by Berzelius in 1814. Many of the acetates have been known from early times. _Verdigris_ is mentioned by Theophrastus, Dioscorides, and Pliny. _Zinc acetate_ was known to Geber, and _potassium acetate_ to Pliny, who mentions its use in medicine. _Ammonium acetate_ was also used in medicine as far back as the beginning of the seventeenth century, and was particularly recommended by the physician, Raymond Minderer. _Sodium acetate_ was prepared by Duhamel in 1736. _Lead acetate_ was known in the fifteenth century, and was styled by Libavius _saccharum plumbi quintessentiale_, in allusion to its sweet taste. What was called by the alchemists _lac virginis_ was a turbid solution of basic lead acetate, and it was frequently used in medicine, more particularly by Goulard in 1760. What we now call _acetone_ was first observed by Libavius, in 1595, and subsequently by Boyle, during the destructive distillation of lead acetate: its formation from other acetates was noticed by Trommsdorff, Derosne, and Chenevix, by whom it was termed pyroacetic spirit. Its true nature and composition were first ascertained by Liebig in 1831. The formation of tartar in the manufacture of wine has been known from the earliest times. It was regarded as, and originally styled, the _faex vini_. The word “Tartarus” is first met with in alchemistic literature in the eleventh century, and is the Latinised form of an Arabic word. Marggraf, in 1764, recognised that the tartar of wine contained potash; but tartaric acid itself was first isolated by Scheele in 1769.