Acidum Formicum. Formic Acid.
CH2O2 = 46.016.
Formic acid may be prepared by heating together glycerin and oxalic acid, or from the sodium formate produced by the action of carbon monoxide on sodium hydroxide or soda-lime. It contains about 25 per cent. of real acid, HCOOH, and is a colourless liquid with a pungent odour. Specific gravity, 1.06. When neutralised with sodium hydroxide, an excess of solution of mercuric chloride added, and the mixture warmed, the weight of mercurous chloride precipitated should correspond to about 25 per cent. of formic acid (10.23 parts of mercurous chloride representing 1.0 part of the anhydrous acid). The acid should be free from chlorides, sulphates, and oxalates, and should yield no residue on evaporation. After dilution and neutralisation with sodium hydroxide, the solution should have no pungent or empyreumatic odour. Formic acid of a higher degree of concentration is obtainable in commerce. This is caustic and gives rise to painful burns. An acid (Acidum Formicum Concentratum) containing 80 per cent. of real formic acid is used in the preparation of an effervescent formic bath.
Action and Uses.—Formic acid resembles acetic acid in its action, except that it is more irritating and volatile. The acid and its salts are employed internally as diuretics; more recently a tonic action upon muscle tissue has been attributed to these substances, and they have therefore been employed in convalescence and debilitated conditions, also in cardiac weakness and muscular rheumatism. There is a lack of reliable evidence to show that the acid and its salts act as suggested. In cases of muscular rheumatism formic acid and the formates are injected intramuscularly; injections of 1 mil (15 minims) of a 1 in 50 solution of the, acid are employed, a small quantity of cocaine being previously injected to alleviate the pain produced. Formic acid is used to neutralise sodium bicarbonate in some forms of effervescent medicinal baths. It may be administered internally well diluted with water or alkaline aerated water, or as the alkali formates.
Dose.—1 to 6 decimils (0.1 to 0.6 milliliters) (2 to 10 minims).
- Balneum Formicum Effervescens, B.P.C.—EFFERVESCENT FORMIC BATH.
- Formic acid (80 per cent.) and sodium bicarbonate are allowed to interact in water at from 30° to 35°, the formic acid being in excess. Used as an invigorating bath.