In the systematic analysis of mixtures, cadmium is detected as a yellow or orange sulfide. When copper is .fresent, alkali cyanide is added to the solution, which contains [Cu(NH s ). ] 2 and rCd(NH s ).r-2 , until the colour is eliminated, and only then is hydrogen sulfide passed through the solution to form the yellow precipitate of cadmium sulfide [1]. Some laboratories do not give students mixtures of cadmium and copper, in order to avoid the use of cyanides, which ue extremely poisonous. Many authors have tried to develop methods for the detection of cadmium in the presence of copper without the use of an alkali cyanide (see Ref. 2 for a complete list of references).A method developed in our laboratory is based upon the difference between the solubilities of acetylacetonates of copper and cadmium. According to Ben-Bassat and Frydman-Kupfer [3] the complex [Cu(acetylacetoneh] is insoluble in a basic solution. However, centrifugation done by the author did not quantitatively eliminate the [Cuf acetylacetonerg] from its mixture with [Cd (acetylacetoneh], as was demonstrated by the appearance of a dark precipitate when H:aS was passed into the clear solution. A good separation was obtained when the edge of a piece of filter paper was dipped into the solution of the acetylacetonates. The soluble chelate of cadmium migrated on to the filter paper together with the solvent, while the insoluble copper chelate was left behind. The colourless filter paper was then treated with gaseous hydrogen sulfide and a clear yellow cadmium sulfide appeared immediately. These results are in agreement with the assumption of Pollard et al., [4], who showed that the movement of many cations depends not only on the complexes formed, but also on their solubilities in the solvent used.The qualitative separation of inorganic salts by paper chromatography by use of organic solvents, is well known. Increasing interest in the use of chelating agents for inorganic chromatographic separation is shown in the great number of articles publiahed (see ref. 5 for a list of references). Several authors [4,5,6] used acetylacetone in the solvent mixtures in order to separate various cations by paper chromatography.An attempt has been made here to develop a simple experimental technique for the paper separation of cadmium from copper, so that first year undergraduates would be able to use it without any difficulty and without apparatus (Procedure I). The medium of analyars twate r}, together with the reagent (acetylacetone), serve as the developing solvent. Hydrogen sulfide supplied from a semi-micro "Kipp", serves as the detector. A very small piece of filter paper is used (6 x 1 cm3), and \he process takes
