to be. Consequently, a voltage of - 1.6 was selected to be sure that measurements are made a t the top of the second oxygen plateau. Large quantities of salt can cause a much more serious difficulty. Orlemann and Kolthoff (8) reported that, in the presence of salt concentrations >0.5N, an anomalous current is produced which is much greater than accounted for by the diffusion current of oxygen alone. This anomalous current was enhanced by short, high drop times and high currents. Since the present technique employs extremely small drop times (about 0.25 second per drop) and high current (about 10 to 20 pa.), the effect described by Orlemann and IZolthoff is greatly accentuated.
ACKNO WLE1:lGMENT
The authors thank ’IValter A. Morgan for suggesting a circuit, which eliminated the voltmeter and the Humble Oil & Refining Co. for permission to publish this paper.
“Polarography,” 2nd ed., p. 552, Interscience, New York, 1952. (5) Kolthoff, I. M., Miller, C. S., J . Am. Chern. Soc. 63, 1013 (1941). ( 6 ) Marsh, G. A., ANAL. CHEM.23, 1427 (1951). (7) Moore, E. W.,Morris, J. C., Okun, D. A,, Sewage Works J. 20, 1041 (19481. - --, . (8) Orlemann, E. F., Ilolthoff, I. &I., J. Am. Chem. SOC.64,833 (1942). (9) Rand, RI. C., Heukelekian, H., Sewage and Znd. Wastes 23, 1141 (1951). (10) Seaman, W.,Allen, W.,Zbid., 22, \-
LlTERATURi CITED
(1) American Public Health Association,
New York 19, N. Y ”, “Standard Methods for the Examination of Water, Sewage, and Indusi,rial Wastes,” 10th ed., p. 254 1955. (2) Busch, A. W., Sawyer, C. N., ANAL. CHEM.24, 1887 (1952). (3) “Handbook of Chemistry and Physics,” 39th ed., p. 2022, Chemical Rubber Publishing Co., Cltrveland, Ohio, 19575s.
(4) Kolthoff, I. M., Lingane, J. J.,
912 (1950).
(11) Truesdale, G. A., Downing, A. L., Lawden, G. F., J . A p p l . Chem. 5 , 53
(1955).
RECEIVEDfor review June 9, 1958. Accepted December 1, 1958. Regional Meeting, ACS, San Antonio, Tex., December 1958.
Po arographic Determination of Dissolved Oxygen Study of Drop Time with Rapid-Dropping Mercury Electrode J. H. KARCHMER Humble Oil & Refining Co., Bayfown, Tex.
F A single capillary was used to study the effect of very small drop times at a constant mercury flow rate upon the polarographic current produced by dissolved oxygen in water. At first the capillary was mounted vertically, then horizontally, and finally its orifice was scratched and it was mounted vertically. This system provided for essentially the same mercury flow rate, but the horizontal electrode had a drop time 0.285 times as great as the vertical, and the scratched capillary’s drop time was 0.0263 times as great. Currents produced in the very low drop time regions were considerably less than predicted from the Ilkovic‘ equation. When the solutions are stirred, the effect on the current is less as the drop time decreases and the mercury flow rate becomes greater. The fundamental equations governing the drop times and mercury flow rate were studied and reduced to simple forms so that predictions involving mercury pressure, capillary length, capillary radius, and interfacial tension could be made in selecting capillaries of desired characteristics. The very rapid-dropping mercury capillary (
