are identical or different contain from 1 to 5 carbon atoms such as methyl ethyl and tert butyl radicals for example 1 3 dimethyl 1 4 dimethyl 2 7 dimethyl 1 3 diethyl 2 7 di tert butyl 2 ethyl 6 tert butyl and the corresponding 5 6 7 8 tetrahydro derivatives the organic solvent forming part of the working solution is preferably a mixture of a nonpolar compound and of a polar compound the nonpolar compound is preferably chosen from petroleum cuts of boiling point higher than 140 u00b0 c predominantly containing aromatic hydrocarbons containing at least 9 carbon atoms such as trimethylbenzene isomers tetramethylbenzene isomers tert butylbenzene methylnaphthalene isomers and dimethylnaphthalene isomers the nonpolar compound is preferably chosen from saturated alcohols preferably containing from 7 to 11 carbon atoms such as diisobutylcarbinol 3 5 5 trimethylhexanol isoheptanol carboxylic acid esters such as methylcyclohexyl acetate marketed under the name of 34 sextate 34 heptyl acetate butyl benzoate and ethyl heptanoate phosphoric acid esters such as tributyl phosphate tri 2 ethylbutyl phosphate tri 2 ethylhexyl phosphate and tri n octyl phosphate and tetrasubsituted ureas such as tetra n butylurea 34 hydrogen peroxide equivalent 34 is intended to mean the quantity of hydrogen peroxide expressed in grams which one liter of working solution is capable of supplying at the end of the oxidation stage if the yield of this stage in the oxidizer 2 is 100 this potential mass concentration of peroxide corresponds to a molar concentration which is equal to the molar concentration of all of the reoxidized anthrahydroquinone forms in the working solution it depends on the one hand on the concentration of.