Chlorinated thymotic or carracrotic acid is prepared by passing chlorine to saturation into an aqueous solution of the mono-potassium salt of the acid, dissolving the precipitate in caustic potash, filtering, acidifying the filtrate with hydrochloric acid, extracting the solution with ether, and evaporating off the ether.ALSO:Carboxyl groups are introduced into oil of thyme or other essential oil by heating with continuous passage of carbon dioxide and gradual introduction of metallic sodium. The product may be separated out by pouring the mixture into dilute hydrochloric acid, or the mixture may be poured into water saturated with carbon dioxide and extracted with ether to obtain a "soda-insoluble fraction" leaving an aqueous residue which is precipitated with strong hydrochloric acid to yield a "soda-soluble fraction." A CH2OH group may be added to oil of cloves or other essential oil by heating a caustic soda solution of the oil with formaldehyde, neutralizing the product with dilute acetic acid and filtering off the mass which separates. Fennel oil may be treated with potassium permanganate solution, acidified with sulphuric acid and extracted with ether. The various products are dispersed into the atmosphere to act as disinfectants. The disinfecting action of these and various other disinfectants, mainly consisting of essential oils or their constituents or of hydroxy carboxylic cyclic acids and their derivatives, is increased by treatment of the substances with ultra violet light, with or without the simultaneous supply of oxygen or ozone, or the air in which the disinfectants have been dispersed may be so treated.ALSO:Germs and other micro-organisms in the air are destroyed by finely dispersing in the air one or more of the following classes of substances of low vapour tension, viz. hydroxy carboxylic acids of iso- or heterocyclic, mono- or poly-cyclic character and with or without side chains on the nucleus; ethers and esters of such acids; substances obtained by chemical treatment of essential oils so as to add hydroxyl and/or carboxyl groups thereto; ethers and esters of such compounds; halogen derivatives of any of the foregoing substances; also terpinols, eugenol methyl ether, cinnamic aldehyde, cinnamic acid, geraniol, safrol, isosafrol, and citral. Active substances specified are salicylic, p-hydroxy benzoic, cresotic, hydroxydimethyl-benzene carboxylic, o- and p-thymotic, o- and p-carvacrotic, and hydroxyisoamyl-benzene carboxylic acids, chlorination products of these acids, methyl and propyl esters of p-hydroxy-benzene carboxylic acids, 8-hydroxy-quinoline-7-carboxylic acid and its methyl, propyl, isopropyl and isobutyl esters, b -naphthol-o-carboxylic acid, the methyl ester of hydroxy-naphthol-o-carboxylic acid, and chloro-hydroxy-methyl-isopropyl-benzene-carboxylic acid. The substances may be dispersed, in liquid or solid form or in solution, by spraying, volatilizing or smouldering. Solvents, when used, may be of high or low vapour tension and may be themselves disinfectants, the use of alcohol and acetone being referred to. The active substance may be dispersed in separate small portions, or a solvent may first be dispersed alone and then in admixture with the active disinfectant. The efficiency of the active disinfectants may be increased by treating them before or during dispersion with ultraviolet light, with or without the simultaneous supply of air, oxygen or ozone, or the air in which the disinfectants are dispersed may be so treated. The use, as disinfectants of substances of high vapour tension is also referred to, alcohol, n-propyl alcohol, benzene and ethyl acetate being specified. Chlorinated thymotic, or carvacrotic, acid is prepared by passing chlorine to saturation into an aqueous solution of the p mono-potassium salt of the non-chlorinated acid, dissolving the precipitate in caustic potash, filtering, acidifying the filtrate with hydrochloric acid, extracting the solution with ether and evaporating off the ether. Carboxyl groups are introduced into oil of thyme or other essential oil by heating with continuous passage of carbon dioxide and gradual introduction of metallic sodium. The product may be separated out by pouring the mixture into dilute hydrochloric acid, or the mixture may be poured into water saturated with carbon dioxide and extracted with ether to obtain a " soda insoluble fraction " leaving an aqueous residue which is precipitated with strong hydrochloric acid to yield a " soda-soluble fraction. " A CH2OH group may be added to oil of cloves or other essential oil by heating a caustic soda solution of the oil with formaldehyde, pouring the product into dilute acetic acid to neutralize it, and filtering off the mass which separates. Fennel oil may also be treated with potassium permanganate solution, acidified with sulphuric acid and extracted with ether.