The use of chemical potentials as indices of toxicity

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Abstract
Two main classes of toxic action exist. In one the effector are due to chemical reaction and in the other they are due to a physical mechanism. When an equilibrium exists between the external and internal cones. of substances exerting a physiological effect and when the physiological effect is a function of the external cone., it is justifiable to assume that the primary action is of a physical character. The existence of a direct correlation between solubility or vapour pressure and toxic cone. is a criterion of a physical mechanism., "Physiological effects due to a physical mechanism are generally measured when an equilibrium has been established between the cone. of the toxic substance in the phase, soln. or vapor, in which it is applied and the cone. in the phase or surface layer which is the seat of toxic action. Since the chemical potential of the toxic substance must be the same in all phases taking part in the equilibrium, the toxicities of physically toxic substances should be compared, not by the values of the toxic conc.;in the external soln. or vapor but by the values of the chemical potentials in these phases. Chemical potentials so detd. are identical with the chemical potentials as the actual point of attack within the organism. By this procedure the disturbing effect of phase distr. is eliminated from the comparison; of toxicities." "Using the activity function of G. N. Lewis as the chemical potential, when chemical reaction,is absent, though diverse chemical compounds exert the same toxic effect on a given organism at widely different cones. the activities corresponding to these cones. lie within a relatively narrow range. The differences in activity within this range are ascribed to the effect of chemical constitution.".