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IT is well known that the cations of many nitrogenous bases which cannot be directly titrated with alkali in aqueous solution submit to titration in the presence ofa suitable concentration offormaldehyde. This is true of certain ofthe cationic groups in the proteins and their hydrolytic products. In the case of the natural amino-acids and their peptides, the various cationic groups which may occur are (a) primary amino-groups, (b) the imino-groups of proline and hydroxyproline, (c) the guanidino-group of arginine and (d) the glyoxaline group of histidine. Only the first two types however react with formaldehyde to an extent sufficient to produce any profound change in their acidic properties. Birch and Harris [1930] first employed the hydrogen electrode to investigate the'nature of these changes. More recently, Levy [1933; 1935] has used the same method in an extensive study of the principles involved in the "formol" titration. It appears that the acid-base changes accompanying the addition of formaldehyde may be quantitatively described by an increase in the apparent hydrogen ion dissociation constant of certain cationic groups. Levy has shown that the constants of the cations of primary NH2 groups vary with the square of the concentration of formaldehyde above certain low limits of concentration. In the cases of proline and hydroxyproline on the other hand the change in the apparent dissociation constant is directly proportional to the formaldehyde concentration. The present paper is a report on an extension to egg albumin of the electrometric method of conducting formaldehyde titrations. The electrode behaviour of egg albumin solutions is decidedly less satisfactory in the presence of formaldehyde than in its absence. Nevertheless reproducible titration curves may be traced if occasional irrational observations and the electrodes responsible for them be rejected. The results meet the purposes of the present inquiry, though some features of the reaction remain obscure. It appears that the addition of formaldehyde is accompanied by an immediate readjustment of the acid-base equilibrium. This is followed however by slow secondary changes which persist for many hours and are accompanied by small but persistent changes in hydrogen electrode potential. In a period of one hour however these changes in potential are small in comparison with the large initial change. We have therefore ignored them and have accepted the substantially constant potentials observed during the first hour after the addition of formaldehyde. In doing so we believe that our curves faithfully reproduce the gross acid-base changes which accompany the usual process of formaldehyde titration. The method of calculation differs from that used in the first paper of this series [Kekwick and Cannan, 1936] only to the extent that the anion of form-

The effect of formaldehyde on the hydrogen ion dissociation curve of egg albumin