The possibility of deriving the equilibrium constants for the higher deuterium substitutions from the isotope exchange coefficient is examined with the aid of calculations on the ammonia and methane reactions with water. If the experiment is carried to solutions at equilibrium with water containing as much as 25 percent D2O and the error in a single measurement does not exceed 1.0 percent the second constant is determined to within 10 percent of the correct value. As a standard of comparison against which the experimental results may be examined to advantage, an equation is developed showing the relation between the equilibrium constant for the first substitution and the exchange factor at higher deuterium fractions, subject to the assumption that each successive substitution of D for H produces the same frequency shift. The evaluation of frequency shifts from exchange data is considered.
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