FORMIC ACID was first prepared by distilling red ants (Lat. formica) . It occurs in some mineral waters, in animal se cretions and in muscle. Its reputed presence in stinging nettles has been controverted. It is the first member of the series of aliphatic monobasic acids (q.v.), distinguished from the other members of the series by certain characteristic properties. For example, it shows an aldehydic character in reducing silver salts to metallic silver, it does not form an acid chloride or an acid anhydride, and, by the abstraction of the elements of water from the acid. carbon monoxide is produced, a reaction which finds no parallel in the higher members of the series. Finally, formic acid is, as is shown by the determination of its affinity constant, a much stronger acid than the other acids of the series. Its formula is or H.COOH. It may be prepared artificially by the oxidation of methyl alcohol and of formaldehyde ; by the rapid heating of oxalic acid (J. Gay-Lussac, 1831) ; but best by heating oxalic acid with glycerin at a temperature of Ioo—IIo° C (M. Berthelot, 1856). In this reaction a glycerol ester is formed as an intermediate product, and undergoes decomposition by the water which is also produced at the same time.
Formates are produced by the action of moist carbon mon oxide on soda lime at C (V. Merz and J. Tibirica, A. Geuther, 188o). An interesting process for sodium formate, due to Bredig and Carter (1915), consists in reducing solution of sodium bicarbonate with hydrogen at 7o° C under 6oatmos. pressure in presence of a palladium catalyst. Sodium formate is manufactured by absorbing carbon monoxide by caustic soda at 120-130° C under a pressure of 8 atmospheres.
Concentrated formic acid is prepared by dissolving sodium formate in an equal weight of 9o% formic acid, and then distil ling the mixture with concentrated sulphuric acid in copper vacuum pans (M. Goldschmidt, 1894) . Anhydrous formic acid results when the lead or copper salt is decomposed by dry sul phuretted hydrogen at 13o° C. Formic acid is a colourless, sharp smelling liquid, which crystallizes at o° C, melts at 8.6° C, and boils at 100.8° C. Its specific gravity is 1.22 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° C, give oxalates and carbonates of the alkali metals, but the magnesium, calcium and barium salts yield carbonates only. The free acid, when slightly warmed 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 formates are mostly soluble in water, those of silver and lead being the least soluble. The calcium salt, when heated with the calcium salts of higher homologues, gives alde hydes. The esters of the acid may be obtained by distilling a mix ture of the sodium or potassium salts and the corresponding alco hol with hydrochloric or sulphuric acids.
Formamide, H.CO.NH2, is obtained by heating ethyl formate with ammonia, by heating ammonium formate with urea to 140° C, or by heating ammonium formate in a sealed tube for some hours at 23o° C. It is a liquid which boils in vacuo at i so° C, but at 192-195° C under ordinary atmospheric pressure with partial decomposition into carbon monoxide and ammonia.