THE FORMOL TITRATION OF BACTERIOLOGICAL MEDIA

Abstract

The formol titration devised by Malfatti1 (1908), Sorensen (19072, 19083, and by Henriques and Sorensen4 (1909) for the titration of the ammonia and amino acids of urine has been more or less modified by bacteriologists for the titration of media and cultures. Ammonium chloride reacts with formaldehyde to produce hexamethylentetramine and hydrochloric acid. Amino acids and polypeptides react with formaldehyde to produce acid methylene derivatives which are stronger acids than the amino acids from which they are derived. The increase in acidity may be titrated against a standard alkali solution and serve as a measure of the amino acids and ammonia present in the sample.Sorensen (1907, 1908) pointed out that the reaction of amino acids with formaldehyde is a reversible one. A considerable excess of formaldehyde is required to effect complete conversion of the amino acids into their methylene derivatives, and, since water is a product of the reaction, the presence of too much water serves to throw the reacti...