Résumé : ARRHENIUS parameters have been determined for the solvolysis of a series of acid chlorides of polycyclic aromatic hydrocarbons in methanol‐acetone (1:1) (Table 11). The fact that the solvolyses were carried out at an average temperature (275°K)situated above the isokinetic temperature (estimated to be 220°K) explains why the sequence observed is the reverse of the one obtained in the case of the alkaline hydrolysis of the corresponding esters. Copyright © 1959 Verlag GmbH & Co. KGaA, Weinheim