A Colour Reaction of Formaldehyde with Proteids and its Relation to the Adamkiewicz Reaction.

More thani a year ago I observed that the addition of a trace ot formaldehyde to acetic acid, which had beeni deprived by distillation' of its power to give, with sulphuric acid, Adamkiewicz'st reaction for proteids, restored to it its chromogenic power in a very markecd degree. As would be expected, it was found that the acetic acid was Inot essenitial, the formaldehyde, proteid anid sulphuric acid givinig by themselves an idenitical reactioni. Oni iincreasinig the quanitity of formaldehyde the reactioni failed after a certaini percenitage of it had been reached. The explaniationi of this apparent anomaly was found in the presenice of small quanitities of oxidisinig substanices (niitrous acid, ferric salts) in the ordinary sulphuric acid employed. Pure sulphuric acid and pure formaldehyde3 produce nio colour reaction with proteids, but after the addition of small amounts of oxidisinig substanices to the acid the reactioni is obtainied, provided that the amount of formaldehyde is very small. Wheni the amount is sufficienitly increased, its strotng reducinig power towards oxidising agenits is exerted anid prevenits the occurrenice of the reactioni. Three possibilities presenit themselves in regard to the action of formaldehyde oni proteids in the presence of oxidising agenits: (i) The proteid is oxidised first, anid its oxidation-product interacts with formaldehyde to produce the colour reaction.. This possibility was excluded by