The direct chlorination of aromatic hydrocarbons, in the presence of a ferric chloride‐iron catalyst, proceeds smoothly to give nuclear‐chlorinated derivatives. Methyl side‐chains are retained, but larger alkyl groups, such as ethyl, isopropyl and n‐butyl, readily undergo cleavage by chlorinolysis. Halogenated alkyl side‐chains, such as CCI3 and C2Cl5, are usually not removed, though complete chlorination of the nuclei of compounds containing them cannot normally be achieved. In certain cases, one chlorine atom of a nuclear polychloro‐compound is susceptible to attack by alcoholic alkali.