In a previous paper (Barnes, '29) it was reported that the electrical potential of frog skin is modified by several biological dyesespecially by eosin. The experiments described below were designed to determine the electrical activity of biological stains at the junction of salt solutions and various oils. Beutner and Loxner ('30) have related the basophilic and acidophilic nature of oil mixtures (indicated by stainability with dyes) to the sign of phase boundary potentials produced in these artificial systems. Dean ('40) has published a brief report indicating that eosin establishes a positive charge and methylene blue a negative charge on a thin film of oil but he did not state the concentration of the dye. It is hoped that further detailed investigation of the electromotive activity of dyes widely used in biology will contribute to the theory of staining of tissues (cf. Conn, '40). Iloreover, the experiments reported below afford support for the general theory of phase boundary potentials (cf. Beutner, '13, '33).
METHOJX
The "oil" ernployecl in the model (guaiacol, cresol, nitrobenzene, triacetin or other substances) was contained in a glass cup 1.5 em. wide and 2.2 cm. high (termed the "oil cell") placed in a 200 cc. beaker containing 150 cc. of 0.7% XaC1 to which known amounts of aqueous solutions of the dyes were added. A U-tu6e filled with 0.7% NaCl made contact with the oil at the bottom of the cup and was connected to an aga; bridge containing 0.7% NaCl leading to a beaker of 0.7% NaCl into which dipped one Ag-AgC1 electrode. An agar bridge containing 0.7% NaCl connected the central vessel containing the oil cell and the dye to a third beaker of 0.7% NaCl into which dipped the second Ag-AgC1 electrode. The electrodes lead to the E.M.F. posts of a Leeds and Northrup vacuum tube amplifier (for high resistance circuits) serving as the iinll instrument for a second potentiometer reading to