An improved method for the employment of agar gel as a medium for diffusion meas- urements and a mathematical treatment of the data for the calculation of diffusion coefficients are described. Diffusion is allowed to proceed under controlled conditions into a column of agar gel held in a cell made of a 50-ml hypodermic syringe that has had the needle end of the barrel cut off. By means of a micrometer the gel is pushed from the cell, sectioned with a fine wire, and assayed. The use of arithmetic prob- ability paper affords a convenient means of plotting the data, making necessary cor- rection for the presence of the gel, and calculating diffusion coefficients. Advantages include the possibility of using mixtures and very dilute solutions. Coefficients ob- tained on some salts, sugars, amino acids, and proteins are in agreement with those obtained by free diffusion.
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