The behavior of isothermal packed fractionating columns is deduced from their differential equation. The relation between rates of production and over-all fractionation is studied, as is the rate of approach to equilibrium. The results are illustrated by problems of isotope separation.

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A general theory of the optical rotatory power of liquids is developed. The method of C. G. Darwin, supplemented so that the fundamental quantities Sαβγ...† which appear there are related to the properties of the molecules comprising the medium, is followed. The optical properties of a molecule are given by a set of tensors σ′ αβγ.... The concept of deformation leads naturally to a simple relation between the σ′ αβγ...'s and the field acting on the molecule. The electrostatic field of the dipoles of the surrounding molecules is computed for the limiting cases of imperfect gases and dilute solutions, for molecules of simple geometrical configuration. This field is identified with the solvent field. For these idealized systems, the rotatory power of a molecule in various solvents is determined in terms of quantities characteristic of the solvents. The resulting equations are controlled by comparing with the behavior of actual liquids.

A further application has been made of the chemical exchange reaction between sulfur dioxide gas and a solution of sodium bisulfite to the problem of securing higher concentrations of sulfur of atomic weight 34. The exchange reaction was carried out in a series of counter-current fractionation columns which previously had been used for the separation of the nitrogen and carbon isotopes. Using three fractionation units in cascade arrangement, we have secured sulfur containing 25 percent S34 at a rate of 3.2 grams per day, and have produced sufficient material for a large number of tracer experiments.

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