Ion-exchange (Kunin, '49; Nachod, '49), while used on an industrial scale for many years for water-softening, came into its own as a chemical, separation method during the period of 1943 to 1946 a t what is now th'e Oak Ridge National Laboratory. Ion-exchange column chromatography there made it possible to separate precisely the very small but highly radioactive masses of fission products, including those which are rare earths, and the method was soon shown to be the first means for quantitative separation of these notoriously inseparable elements (Tompkins, Khym, and Cohn, 47 ; Harris and Tompkins, '47; Ketelle and Boyd, '47; Tompkins, '49; Cohn et al., '48).
I n a certain sense, the degradation products of nucleic acidsthe purine and pyrimidine bases, their ribosides and desoxyribosides and the phosphate esters of the lattercan be considered as analogous to th,e rare earths in that they form mixtures which are sometimes ver;v difficult to resolve for analytical or preparative purposes (Leven?, ,31). Accordingly, a deliberate attempt was made to apply the same technique which had proved so successful in the inorganic field to the separation of these substances. While paper chromatographv, another iim-separation device of Work performed tinder Contract ~-7405-eug-26 for the Atomic Energy Cnmmission.