The Gallic acid, formerly called Principle of Astringency, is obtained from gall nuts, either by infusion or decoction with water, or by distillation with a very gentle heat. This acid has only been attended to within these few years. The Committee of the Dijon Academy have followed it through all its combinations, and give the best account of it hitherto produced. Its acid properties are very weak; it reddens the tincture of turnsol, decomposes sulphurets, and unites to all the metals when they have been previously dissolved in some other acid. Iron, by this combination, is precipitated of a very deep blue or violet colour. The radical of this acid, if it deserves the name of one, is hitherto entirely unknown; it is contained in oak willow, marsh iris, the strawberry, nymphea, Peruvian bark, the flowers and bark of pomgranate, and in many other woods and barks. SECT. XXXIX.--_Observations upon Lactic Acid, and its Combinations with Salifiable Bases[51]._ The only accurate knowledge we have of this acid is from the works of Mr Scheele. It is contained in whey, united to a small quantity of earth, and is obtained as follows: Reduce whey to one eighth part of its bulk by evaporation, and filtrate, to separate all its cheesy matter; then add as much lime as is necessary to combine with the acid; the lime is afterwards disengaged by the addition of oxalic acid, which combines with it into an insoluble neutral salt. When the oxalat of lime has been separated by decantation, evaporate the remaining liquor to the consistence of honey; the lactic acid is dissolved by alkohol, which does not unite with the sugar of milk and other foreign matters; these are separated by filtration from the alkohol and acid; and the alkohol being evaporated, or distilled off, leaves the lactic acid behind. This acid unites with all the salifiable bases forming salts which do not cristallize; and it seems considerably to resemble the acetous acid. TABLE _of the Combinations of Saccholactic Acid with the Salifiable Bases, in the Order of Affinity._ _Bases._ _Neutral Salts._ Lime Saccholat of lime. Barytes barytes. Magnesia magnesia. Potash potash. Soda soda. Ammoniac ammoniac. Argill argill. Oxyd of zinc zinc. manganese manganese. iron iron. lead lead. tin tin. cobalt cobalt. copper copper. nickel nickel. arsenic arsenic. bismuth bismuth. mercury mercury. antimony antimony. silver silver.