Feb., 1Y62
COMMUNICATIONS TO THE EDITOR
I 7 2626
THE DIELECTRIC CONSTANT OF WATER BETWEEN Oo AND 40° Xir: In recent reviews on dielectrics112it has been pointed out that considerable disagreement exists as to the dielectric constant of water and its temperature coefficient. On the basis of the careful investigation that was made of possible bridge and cell errors, the data of Malmberg and Maryotta seem to be preferred to the earlier work of Wyman and Ingalls4 who used a resonator method. These two sets of data differ in absolute value by as much as 0.5% and have quite different temperature coefficients. Recently, Owen and co-workers,6using a resonance technique, have reported dielectric constants of water from 0 to 70'. Their results are in fair agreernent with those of Malmberg and Maryott except for the temperature coefficient. The a,bsolute value and the temperature coefficient of Owen agree almost exactly with the unpublished data of Lees.6 Our results, obtained by a bridge method involving a new design of dielectric cell, agree well with those of Owen and of Lees at all temperatures but only approach those of Malmberg and Maryott at the higher temperature. The measurements were carried out on an improved Cole-Gross capacitance-conductance bridge' equipped with a calibrated General Radio Type 1422-CC variable capacitor. The cell was designed for absolute measurements and consisted of concentric Pyrex cylinders with electrodes formed by fusing a platinum film onto the surface of the glass. The inside electrode contained an extended guard ring on each side of the working electrode with a gap of less than 0.2 mm. The outside surface of the cell was completely shielded by a silver coating. The cell constant of 4.594 pf. was determined with the cell filled with dry nitrogen and corrected to vacuum. Water of specific conductivity 6-8 X o h m s 1 cm.-1 was obtained by passing distilled water through a mixed bed ion-exchange resin. Since a scrupulously clean cell was found essential for reproducible results, the cell was (1) R. H. Cole, Ann. Rev. Phys. Chem., 11, 149 (1960). (2) J. 13. Hasted, "Progress in Dielectrics," Vol. 3, Heywood and Co., Ltd., London, 1961, p. 103. (3) C. G. Malmberg and A. A. Maryott, J. Research Natl. Bur. Standards., 56, 1 (1956). (4) J. Wyman, Jr.. and E. N. Ingalls, J . Am. Chem. Xoc., 60, 1182 (193 8). ( 5 ) B. B. Owen, R. C. Miller, C. E. Milner and H. L. Cogan, J . Phys. Chem., 65, 2065 (1961). (6) W. L. Lees, Dissertation, Department of Physics, Harvard University, 1949. (7) R H. Cole and P. N. Gross, Jr., Rev.Sci. Instr., '20,252 (1949).
383
100 50 25
10 6 5 Frequency, kc. Fig. 1.-Capacitance in pf. ((31,this research; CZ,ref. 3) us. reciprocal frequency; 0 this research, d Malmberg and Maryott, measured values; 0 Malmberg and Maryott, corrected values.
cleaned with chromic acid solution and thoroughly leached. The results are comDared in Table I with the data of other workers. TABLE I Temp., 'C.
DIELECTRIC CONSTANTS O F WATER This Ref. 6 Ref. 3
Ref. 4
research
0 20 25 40
87.90 80.20 78.37 73.19
87.90 80.18 78.36 '73.15
87.74 80.10 78.30 73.15
88.15 80.36 78.54 73.35
We estimate that the error in our results is no more than i~0.04unit in the dielectric constant and can be attributed to the uncertainty in determining the cell constant. In Fig. 1 is shown the frequency dependence of a typical measurement as compared to that reported by Malmberg and Maryott. Because of the use of water of such low conductivity and wider spacing between electrodes (4 mm.), our frequency curve is essentially flat up to about 100kc./sec. An extrapolation of the slight curvature to infinite frequency to eliminate electrode polarization effects is not necessary in our case in view of the accuracy claimed. At 500 cps., C1 is higher than the value at 10 kc./sec. by only 0.06%. A detailed report of this work will be published when cells of varying cell constant have been investigated thoroughly. Acknowledgment.-The authors are indebted to Professor R. H. Cole for the use of his equipment and for many invaluable discussions and suggestions. This work was supported by the U. S. Atomic Energy Commission under Contract AT(30-1)2727. METCALFRESEARCH LABORATORY BROWNUNIVERSITY GEORGEA. VIDULICH PROVIDENCE 12, REIODEISLAND ROBERT L. KAY RECEIVED DECEMBER 21, 1961
