Equations for the steady state were derived with regard to the multistage cascade enrichment of isotopes. For any column the procedure for calculating the flow rate was simplified by using the concept of the degree of equilibrium for the column terminal. A set of Type 1-5 glass cascade was set up on the basis of these equations. By using the CO2/di-n-butyl-amine (DNBA)/triethylamine (TEA) system and feeding the cascade with commerical cylinder-grade CO2

13C was enriched from natural abundance to 96.25 atom%

after a period of a little over 5 months operation. The cooler-condensers above the digestor

absorber and exchange column of each stage were cancelled in succession after accumulation of experi-mence from cascade operation. The structure of the cascade was thus simplified and its construction cost considerably decreased. An automation also became feasible

enabling the steady operation of the cascade for a long time.