The Acidity of Formaldehyde and the End- Point in the Formol Titration

Two factors are involved in a systematization of the form01 titration. The first of these factors is the titration constant of the amino acid in formaldehyde solution. This aspect has been discussed in a previous paper (4) for certain of the monoamino acids. The basic amino acids will be treated later. The second factor is the behavior of the solvent on the addition of strong alkali, just as the behavior of water in the same condition must be considered in the titration of weak acids. The present paper describes the titration of formaldehyde solutions with strong alkali and contains a discussion of the application of the data to the form01 titration. The acidity of commercial formalin is often ascribed to the presence of carboxylic acids, particularly formic acid, as impurities. Simple observations of the color changes of phenolphthalein in the titration of formalin with alkali show a distinct buffering power in its range (8.4 to 10) where carboxylic acids do not buffer. The same behavior is shown by pure formaldehyde solutions which do not contain carboxylic acids. It is evident that formaldehyde is itself a sufficiently strong acid to account for a measurable amount of alkali at the concentrations used in the form01 titration. The quantitative aspect of the reaction with alkali is dependent on the dissociation constant of the aldehyde and the determination of this constant should lead to useful formulations for calculating the alkali bound by formaldehyde, if this be desirable. In addition, the accuracy of the titration of amino acids is largely determined by the sharpness of the end-point, or by the steepness of the titration curves near the end-point. This in turn depends on the relative amounts of alkali bound by the amino acid and