Mixtures of CuCI 2 and KC1 in molar ratios of Cu to K of from 0.5 to 1.0 were heated at 473 K in an air atmosphere, and then subjected to DTA analysis in the temperature range 293-773 K. A number of endothermic processes were observed, the extents of these depending on the molar ratio of Cu to K in the mixture.In the presence of potassium chloride, CuCI 2 forms complex compounds K2CuCI,, and KCuCI3 [1,2]. Phase diagrams of CuC12~uCI for specified contents of KC1 have been reported [3]. Similar data on the system CuCI2-KCI where copper(I) chloride is absent are not available. In the system CuC12-KC1, the transition of K2CuCI~ into KCuCI3 [4, 5] has been found to be possible within the temperature range 365-390 K.The present work involved thermogravimetric investigations of the system CuCI2-KCI in which the molar ratio of CuCI 2 to KCI was varied from 0.5 to 1.0 within the temperature range 293-773 K. Thermogravimetric investigations were supplemented by X-ray analysis. ExperimentalTo obtain the system CuCI2-KCI, dihydrous copper(II) chloride and potassium chloride (POCh Gliwice) were used. Weighed quantities of the two salts, in appropriate proportions, were dissolved in 100 cm 3 of distilled water and the solution was next evaporated to dryness at 343 K. The dry residue was crushed and ground. Powdered samples were roasted at 473 K for 2 h in an air atmosphere. After cooling down to room temperature, the samples were subjected to thermogravimetric and X-ray analyses.Mixtures with molar ratios of CuC12 to KC1 of 0.5, 0.614, 0.692, 0.768, 0.845, 0.922 and 1.0 were prepared as described above. Thermogravimetric analyses were made with a derivatograph (MOM, Budapest, Hungary) within the temperature John Wiley & Sons, Limited, Chichester Akad~miai Kiad6, Budapest