Many other synthetical processes for the production of the acid or its salts are known. Hydrolysis of hydrocyanic acid by means of hydrochloric acid yields formic acid. Chloroform boiled with alcoholic potash forms potassium formate (J. Dumas, _Berzelius Jahresberichte_, vol. 15, p. 371), a somewhat similar decomposition being shown by chloral and aqueous potash (J. v. Liebig, _Ann._, 1832, 1, p. 198). Formates are also produced by the action of moist carbon monoxide on soda lime at 190-220 deg. C. (V. Merz and J. Tibicira, _Ber._, 1880, 13, p. 23; A. Geuther, _Ann._, 1880, 202, p. 317), or by the action of moist carbon dioxide on potassium (H. Kolbe and R. Schmitt, _Ann._, 1861, 119, p. 251). H. Moissan (_Comptes rend._, 1902, 134, p. 261) prepared potassium formate by passing a current of carbon monoxide or carbon dioxide over heated potassium hydride, KH + CO2 = KHCO2 and KH + 2CO = KHCO2 + C. A concentrated acid may be obtained from the diluted acid either by neutralization with soda, the sodium salt thus obtained being then dried and heated with the equivalent quantity of anhydrous oxalic acid (Lorin, _Bull. soc. chim._, 37, p. 104), or the lead or copper salt may be decomposed by dry sulphuretted hydrogen at 130 deg. C. L. Maquenne (_Bull. soc. chim._, 1888, 50, p. 662) distils the commercial acid, _in vacuo_, with concentrated sulphuric acid below 75 deg. C. Formic acid is a colourless, sharp-smelling liquid, which crystallizes at 0 deg. C., melts at 8.6 deg. C. and boils at 100.8 deg. C. Its specific gravity is 1.22 (20 deg./4 deg.). It is miscible in all proportions with water, alcohol and ether. When heated with zinc dust, the acid decomposes into carbon monoxide and hydrogen. The sodium and potassium salts, when heated to 400 deg. C., give oxalates and carbonates of the alkali metals, but the magnesium, calcium and barium salts yield carbonates only. The free acid, when heated with concentrated sulphuric acid, is decomposed into water and pure carbon monoxide; when heated with nitric acid, it is oxidized first to oxalic acid and finally to carbon dioxide. The salts of the acid are known as _formates_, and are mostly soluble in water, those of silver and lead being the least soluble. They crystallize well and are readily decomposed. Concentrated sulphuric acid converts them into sulphates, with simultaneous liberation of carbon monoxide. The calcium salt, when heated with the calcium salts of higher homologues, gives aldehydes. The silver and mercury salts, when heated, yield the metal, with liberation of carbon dioxide and formation of free formic acid; and the ammonium salt, when distilled, gives some formamide, HCONH2. The esters of the acid may be obtained by distilling a mixture of the sodium or potassium salts and the corresponding alcohol with hydrochloric or sulphuric acids.