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(6) KOLTHOFF AND SANDELL: A Textbook of Quantitative Inorganic Analysis, p. 591. The Macmiilan Company, New York (1936). (7) (a) LANGER AND MEGGERS: Bur. Standards J. Research 4,711 (1930). (b) LINDAND LIVINGSTON: J. Am. Chem. SOC.64, 94 (1932). (8) LATIMER:Ozidation States of the Elements and their Potentials i n Aqueow Solutions, p. 322. Prentice-Hall, New York (1940). (9) LEIGHTON AND FORBES: J. Am. Chem. SOC.62,3139 (1930). (10) LIVINGSTON: J. Phys. Chem. 44, 601 (1940). (11) MOELWYN-HUGHES: Kinetics of Reactions i n Solution, pp. 170-98. Oxford University Press, London (1933). (12) ROLLEFSON AND STOUGHTON: J. Am. Chem. SOC.61, 2634 (1939). (13) SCHNEIDER: 2.physik. Chem. B28, 311 (1935). (14) SPEALMAN AND BLUM:Univ. Calif. Pub. Physiol. 8,147 (1937).
THE MAGNITUDE OF T H E SURFACE CONDUCTIVITY AT AQUEOUS-GLASS INTERFACES’ H. L. WHITE, FRANK URBAN,
AND
BETTY MONAGHAN
Departments of Physiology and of Biological Chemistry, School of Medicine, Washington University, Saint Louis, Missouri Received July S, 19.40
McBain and coworkers in 1929 (9) and 1930 (8),using alternating current, obtained for the specific surface conductivity of polished and unpolished glass in various concentrations of potassium chloride values ranging from 4.3 x lo-* to 2.1 X lo-’ mhos. White, Urban, and Van Atta (19), on the other hand, reported a much smaller value (2.2 X 10-e mhos) for the specific surface conductivity of unpolished Pyrex glass in 5 X 10-4 M potassium chloride, the measurements being made on small glass capillaries with direct current. The measurements were later repeated with A.C. on glass powders (15) and in unpolished Pyrex glass slits (14);values about twice those previously reported with D.C. were obtained. Still more recently (17), D.C. measurements on small capillaries have been repeated, using a vacuum tube in place of the original condenser arrangement; the results confirmed our original D.C. measurements. McBain and Foster (7), however, have again reported values approximately twenty times as great a9 those obtained in this laboratory on the same kind of material, i.e., unpolished Pyrex surfaces and with the same solutions. 1 The experimental work of this paper was carried out in 1935. Publication has been deferred to permit an attempt, through correspondence and a visit by one of US (B. M.) to McBain’s laboratory, to reach a conclusion mutually acceptable to both groups of workers; this attempt has not been successful.
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AT AQUEOUS-GLASS INTERFACES
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We have, therefore, determined to reinvestigate the problem, duplicating the apparatus and technique employed by McBain and Foster, except where a departure seemed desirable or essential. Again our previous value ww confirmed. EXPERIMENTAL
Resistance measurements were carried out with a five-dial Gray Wheatstone bridge, the coils of which were accurate to 0.025 per cent. The A.C. current w m supplied by a Leeds and Northrup 1000-cycle motor generator. The end point was determined by a Leeds and Northrup tunable double telephone receiver. The conductivity cell (figure 1) was modelled after that described by McBain and Foster (7), with the addition of an extra
