This paper deals with the results of chemical pre-treatment of effluents from Chip Washing by coagulation. Three different, most frequently used coagulants i.e. calcium hydroxide, aluminium sulphate and ferric chloride were applied. Influence of single and simultaneous dosage of the reagents was investigated. Fully randomized block systems were applied in the factorial variance analysis and final approximation analytic-empiric mathematical equations with application of the central point method were formulated.