The initial objective of this investigation was the measurement of the isoelectric pH values of ß-lactoglobulin as a function of the ionic strength of the buffer solvent and the nature of added salt ions. In contrast to their experience with egg albumin, Cannan, Palmer, and Kibrick (4) found that the pH of a ß-lactoglobulin solution is independent of the concentration of added potassium chloride and is identical with the isoelectric pH value obtained by Pedersen ( 14). On the basis of these observations they suggested that the isoelectric pH values of this protein might prove to be independent of the ionic strength. Consequently we were somewhat surprised to find that the isoelectric pH of ß-lactoglobulin changed with the concentration of the acetate buffers in much the same manner that Tiselius and Svensson (21) had observed in the case of egg albumin.We then studied bovine serum albumin and found that this protein behaves similarly to egg albumin and ß-lactoglobulin. Finally, in an attempt to learn 1 Presented at the Twenty-second National Colloid Symposium, which was held under the auspices of the Division of Colloid Chemistry of the American Chemical Society at

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The method here described is a simplification of that developed by LINDERSTRBM-LANG and LANZ (1938). Principle.A reasonably linear specific gravity gradient is produced in a vertical measuring cylinder (200 cc) by mixing kerosene and bromobenzene in varying proportions. If a drop of a given solution is introduced under the surface, it will fall with diminishing velocity and finally come to rest a t a position in the cylinder where the specific gravity of the kerosene-bromobenzene mixture is equal to that of the drop in question.Before introducing the drop of the solution under investigation, other drops (standard drops) are introduced of potassium chloride solutions of accurately known specific gravity. NaturaUy these drops will also come to rest a t levels where their specific gravities are equal t o that of the surrounding medium. Plotting the positions of the potassium chloride drops as ordinates against the corresponding specific gravities as abscissae, a reasonably straight line is obtained in the coordinate system, from which it is possible, knowing the position of the drop of the unknown solution, to read the specific gravity of this solution with considerable accuracy. The specific gravity may also be calculated by linear interpolation.This simple principle is known from the above quoted paper by LINDERSTR0M-LANG and LANZ.

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