SECT. XXX.--_Observations upon Pyro-tartarous Acid, and its Combinations with the Salifiable Bases[46]._ The name of _Pyro-tartarous acid_ is given to a dilute empyreumatic acid obtained from purified acidulous tartarite of potash by distillation in a naked fire. To obtain it, let a retort be half filled with powdered tartar, adapt a tubulated recipient, having a bent tube communicating with a bell-glass in a pneumato-chemical apparatus; by gradually raising the fire under the retort, we obtain the pyro-tartarous acid mixed with oil, which is separated by means of a funnel. A vast quantity of carbonic acid gas is disengaged during the distillation. The acid obtained by the above process is much contaminated with oil, which ought to be separated from it. Some authors advise to do this by a second distillation; but the Dijon academicians inform us, that this is attended with great danger from explosions which take place during the process. TABLE _of the Combinations of Pyro-mucous Acid, with the Salifiable Bases, in the Order of Affinity(A)._ _Bases._ _Neutral Salts._ Potash Pyro-mucite of potash. Soda soda. Barytes barytes. Lime lime. Magnesia magnesia. 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. antimony antimony. [Note A: All these combinations were unknown to the ancient chemists.--A.] SECT. XXXI.--_Observations upon Pyro-mucous Acid, and its Combinations._ This acid is obtained by distillation in a naked fire from sugar, and all the saccharine bodies; and, as these substances swell greatly in the fire, it is necessary to leave seven-eighths of the retort empty. It is of a yellow colour, verging to red, and leaves a mark upon the skin, which will not remove but alongst with the epidermis. It may be procured less coloured, by means of a second distillation, and is concentrated by freezing, as is directed for the citric acid. It is chiefly composed of water and oil slightly oxygenated, and is convertible into oxalic and malic acids by farther oxygenation with the nitric acid. It has been pretended that a large quantity of gas is disengaged during the distillation of this acid, which is not the case if it be conducted slowly, by means of moderate heat.