FORMIC ACID

HCHO 2 . Syn. Hydrogen Formiate . An organic acid, obtained by oxidizing many organic substances, and found in the red ant. Prep. Sugar, 1 part; water, 2 parts; binoxide of manganese, 3 parts; mix in a retort capable of holding fully 10 times the bulk of the ingredients, and add, cautiously, oil of vitriol, 3 parts, diluted with an equal weight of water; as soon as the first violent effervescence has subsided, heat may be applied, and the product collected and purified, as below. Formate of lead in fine powder is introduced into a long gla tube, one end of which is connected with an apparatus evolving sulphuretted hydrogen, and the other with a receiver. As soon as the salt is entirely decomposed (blackened) a very gentle heat is applied, and the distilled liquid collected; the product is, lastly, boiled for a minute or le , to expel any adhering sulphuretted gas. This furnishes chemically pure formic acid. From wood spirit, 1 part; bichromate of pota ium and sulphuric acid, of each 3 parts; the sulphuric acid, diluted with an equal weight of water, being gradually added last. A portion of wood spirit distils over with the acid, and may be again treated with bichromate of pota ium and sulphuric acid, when a fresh portion of formic acid will be produced. This proce yields a large product. Prop., purific., . The products of the above proce es are limpid and colourle ; the stronger ones fume slightly in the air, and po e an extremely penetrating odour. The acid obtained by the second proce boils at 209° Fahr., crystallises in brilliant scales below 32°, and has the sp. gr. 1·2353. Its vapour is inflammable, and burns with a blue flame. It is extremely corrosive, and rapidly destroys the texture of living organic substances. The products of the other proce es are very dilute, and po e the above properties in only a minor degree. They may all be purified and concentrated by saturating them with pure carbonate of sodium or of pota ium, and after subjecting the liquid to a gentle heat for a short time, and liberating the formic acid from the salt by means of dilute sulphuric acid, finally submitting the mixture to distillation, when the hydrated acid will come over perfectly pure. Formic acid reduces the salts of mercury and silver, and forms salts with the bases termed formiates. Formic acid is readily distinguished from acetic acid, which in many points it resembles, by heating it with a little solution of oxide of silver or mercury; the metal is reduced, and precipitated in a pulverulent state, while carbonic acid is extricated. The odours of the two acids also vary.