A study has been made on the application of chemical exchange reactions to the problem of the concentration of the nitrogen isotope of atomic weight 15. We have investigated the exchange reactions involving ammonia as the gas phase and solutions of ammonia in water and alcohol, and of ammonium nitrate and ammonium sulfate in water as the liquid phase. The apparatus used consists of an efficient type of fractionation column previously described. It is found that the exchange reaction between ammonium nitrate solution and ammonia is probably the best of all of these for this purpose, except that ammonium nitrate solutions corrode our steel column so badly that their use is impractical in the present apparatus. The exchange between ammonium sulfate solutions and ammonia gas is shown to be more satisfactory for the purpose than any of the other combinations, and has been used to secure a 6½‐fold increased concentration of N15. Substantial amounts of nitrogen containing high concentrations of N15have been produced and these together with the efficient mass‐spectrometer method of analysis make possible a wide variety of studies.
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