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Yol. 64 575°i mpractical, and extensions to higher temperatures were not possible. We infer from Fig. 1 that the two sets of curves would resolve themselves into single lines at the upper limits of the temperature range investigated.

A quantitative interpretation of the electrophoretic patterns of protein mixtures obtained with the aid of the Tiselius method is based, in part, on a knowledge of the specific refraction of the proteins to be analyzed. Since the patterns are recorded a t 0.5' and since no precise refractive index measurements of proteins at this temperature are available, an investigation has been made of the specific refractive increment of some purified proteins. A differential prism method, developed in this Laboratory,2 has been used in conjunction with the optical equipment of the electrophoresis apparatus. This permits data to be obtained under the same conditions as those encountered in the routine electrophoretic analysis of protein mixtures. The results of this investigation are presented in this report, ExperimentalThe proteins that have been studied in this research are listed in Table I. The egg albumin and &lactoglobulin were prepared in this Laboratory; the bovine serum albumin was obtained from the Armour Company, Chicago, and the samples of human serum albumin and y-globulin were kindly supplied by the Department of Physical Chemistry, Harvard Medical School.* In the case of egg albumin the purification procedure, including three recrystallizations, was that used by S@rensen and H6yrup' whereas @-lactoglobulin was prepared by a modification of Palmer's methods and was recrystallized four times. The modification consists of the removal of casein by the addition of solid ammonium sulfate to 40% saturation. The ammonium sulfate concentration of the filtrate was then increased to 55% saturation, the precipitate discarded and the ,c?-lactp;globulin prepared from the filtrate.Except for the egg albumin, which was kept as a paste in a concentrated ammonium sulfate solution, all of the protein samples were stored at 2' as dry powders until used. Salt-free solutions of the albumins were prepared by dialysis against distilled water. In the case of .the protein solutions containing neutral or buffer salts, a sample was dissolved in the appropriate electrolyte solution and then dialyzed against this solution.The concentrations of all of the protein solutions, except those dissolved in the sodium diethylbarbiturate buffers, have been determined from nitrogen analysis of weighed portions by the Pregl micro Kjeldahl method with the precautions recommended by Chibnall.E The factors for conversion of these results to a dry weight basis have been determined as follows. In the case of the albumins, weighed portions of a salt-free isoelectric solution were used for both the nitrogen and dry weight determinations.

The diffusion coefficients, in dilute aqueous solution, of some representative materials whose molecular weights range from 19 to 68,000 have been determined at several temperatures. The results indicate that the temperature coefficient for diffusion increases only slightly with increasing particle size and is less than that predicted by the Stokes-Einstein relation (assuming the diffusion radius to be independent of the temperature) only for solute molecules so small that the solvent, water, cannot be considered a continuum.

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