It has been shown (Garten, Weiss, and Willis 1957) that the acidity of carbon blacks is due to phenolic hydroxyls and two types of lactones. Those lactones which can be methylated by diazomethane were termed F lactones, whilst those that are not were termed N lactones.It was also shown (Garten and Weiss 1955) that the acidity of a carbon that had been activated in air at 800 "C and cooled in nitrogen increased after reduction, and this was taken as evidence for quinones in these carbons. Studebaker. et al. (1956) on the other hand suggested that since many carbon blacks are reduced b y sodium borohydride they also contain quinones. However it was observed (Garten and Weiss 1957) that the acidity of these carbons did not change on reduction, from which it was concluded " that either quinone groups are reduced beyond the hydroquinone stage or that a group other than quinone must be responsible for the oxidation of the borohydride ". It has recently been realized, however, that this conclusion is not necessarily valid and that the following mechanism for the oxidation of a carbon by air at about 400 "0 would reconcile Studebaker's work with our own and also with Hallum and Drushel's (1958) polarographic evidence for quinones. It is now postulated that the primary step in the oxidation of the carbon black during its production by the channel or roller processes is the formation of carbonyl and carboxyl groups as in (I). These groups are unstable when interconnected by conjugated double bonds and, as in the phthalein dyestuffs, revert to the more stable F lactone tautomer (11). IF' lactones have been shown to be