Limitations in our knowledge of the electrical conductivity of sea water are discussed. An empirical equation is presented which gives chlorinity aa a function of specific conductance and temperature at atmospheric pressure

Pollak, M. J.

English

Yale University

      P.O. BOX 208118 | NEW HAVEN CT 06520-8118 USA | PEABODY.YALE. EDU   JOURNAL OF MARINE RESEARCH The Journal of Marine Research, one of the oldest journals in American marine science, published important peer-reviewed original research on a broad array of topics in physical, biological, and chemical oceanography vital to the academic oceanographic community in the long and rich tradition of the Sears Foundation for Marine Research at Yale University.  An archive of all issues from 1937 to 2021 (Volume 1–79) are available through EliScholar,  a digital platform for scholarly publishing provided by Yale University Library at  https://elischolar.library.yale.edu/.  Requests for permission to clear rights for use of this content should be directed to the authors, their estates, or other representatives. The Journal of Marine Research has no contact information beyond the affiliations listed in the published articles. We ask that you provide attribution to the Journal of Marine Research.  Yale University provides access to these materials for educational and research purposes only. Copyright or other proprietary rights to content contained in this document may be held by individuals or entities other than, or in addition to, Yale University. You are solely responsible for determining the ownership of the copyright, and for obtaining permission for your intended use. Yale University makes no warranty that your distribution, reproduction, or other use of these materials will not infringe the rights of third parties.  This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. https://creativecommons.org/licenses/by-nc-sa/4.0/   THE USE OF ELECTRICAL CONDUCTIVITY MEASUREMENTS FOR CHLORINITY DETERMINATION1 BY M. J. POLLAK Chesapeake Bay Institute, The Johns Hopkins University ABSTRACT Limitations in our knowledge of the electrical conductivity of sea water are dis-cussed. An empirical equation is presented which gives chlorinity aa a function of specific conductance and temperature at atmospheric pressure. Determination of chlorinity of sea water by chemical analysis, while unsurpassed in accuracy, has always been a cumbersome tech-nique and one which generally involves a considerable time lag between sampling and availability of results. An alternative method of determining chlorinity, or salinity, is the measurement of electrical conductivity (specific conductance) as a parameter of chlorinity and of the simultaneously measured temperature. Proof of the basic soundness of this method is furnished by the extended use of the shipboard electrical salinity bridge described by Wenner et al. (1930). Its accuracy is considered comparable to that of the Knudsen method of chlorinity titration (± 0.02 %o of salinity). Since this instrument was designed for empirical calibration against samples of known salinity, the establishment of an exact relationship between specific conductance, .chlorinity, and temperature was not required. Increasing emphasis on in situ measurements that result in large quantities of data as well as the desirability of a sound basis of com-parison between different sets of specific conductance measurements lend importance to the need for a unique functional relationship between the variables involved. It is the purpose of this note to draw attention to certain limitations in our present knowledge of this relationship and to present an empirical approximation to it which may facilitate the use of this type of data. The basis for the conversion of most present-day oceanographic measurements of electrical conductivity is a table derived by Thomas et al. (1934) from their own experimental work which gives specific 1 Contribution No. 19 from the Chesapeake Bay Institute. This work was sup-ported by the Office of Naval Research (Geophysics Branch), the State of Maryland (Department of Research and Education), and the Commonwealth of Virginia (Virginia Fisheries Laboratory). 228 1954) Pollak: Chlorinity Determination 229 conductance as a function of chlorinity and temperature. From these data Jacobson (1948) developed an analytical function which, be-cause of the approximations involved, is unsuited for accurate work. The only other major investigation of the electrical conductivity of sea water was carried out by Bein et al. (1935). Since the objective of Bein et al. was a comparison of direct density measurements with !alues computed from various parameters, their data are presented m a form not readily adaptable to the problem at hand. The results obtained by Thomas et al. appear to contain errors from two sources. One of these, mentioned by the authors in a footnote, is the use of the Parker and Parker (1924) values for the specific conductance of a 0.1 demal potassium chloride solution (the reference standard for their conductivity measurements). Jones and Brad-shaw (1933) had found that these Parker and Parker values were low by 0.118% at 0°C, by 0.028% at 18°C, and by 0.028% at 25°C. It can be presumed that the resulting errors in the Thomas et al. measurements are of the same magnitude. The second source of errors is their use of Washburn pipet type conductivity cells. Jones and Bollinger (1931) found that in cells of this general design (Leeds and Northrup Co., 1924) there exists a capacitative shunt between parts of the cells of opposite polarity which results in resistance measurements that are lower than the true values. This so-called Parker Effect varies with the frequency, with the geometry of the cell, and with the resistance of the solution, but it always gives positive errors in conductivity. Although these errors in the Thomas et al. data are of unknown magnitude, it is apparent hat they are of opposite sign from those due to the reference standards used. Thus the total error in those data might be either positive or negative. Wenner et al. suggest that electrical conductivity may be a more accurate parameter of total salt content than of chlorinity alone. If this is the case, then the Thomas et al. data may reflect certain slight geographical differences not only in the conductivity-chlorinity re-lationship but in the chlorinity-salinity relationship established by Knudsen (1901). Minor anomalies of this nature are indicated, though not conclusively, by the works of Bein et al. and of Thompson and Wirth (1931). Jones and Bradshaw pointed out that absorbed carbon dioxide will increase the conductivity of a solution. Since dissolved CO2 varies over a considerable range in the sea, this effect may be a source of additional small errors in field measurements of specific conductance. Apparently the effect of pressure on the electrical conductivity of sea water has not been investigated, but it is a factor which cannot be 230 Journal of Marine Research (13, 2 ignored when dealing with in situ measurements at depths of several hundred meters. From analogy with other physical properties of sea water it appears likely that this effect would become significant at a depth which will depend on the degree of accuracy of the measure-ments. Despite the various gaps and uncertainties in our knowledge of the electrical conductivity of sea water, it was felt that the develop-ment of an analytical function relating specific conductance to chlo-rinity and temperature at atmospheric pressure would serve a useful purpose. The true physical relationship between these variables should be of the form C = f (T, H )11=0 , where C = specific conductance in mhos per cm3 (the dimensions used by Thomas et al. ; Jones and collaborators use the more conventional mhos per cm), T = tempera-ture in°C, and H = chlorinity in %o (halide concentration determined by titration). From a practical standpoint it is preferable to have a function giving Hin terms of C and T. Such an empirical function was derived from the basic experimental data of Thomas et al., and it is believed that it eliminates some slight discrepancies in their results which may well have been due to the above mentioned geographical anomalies. The simplest form of this relationship is where K1(T) = 721,392 + 24,597.IT and K:(T) = K1(T) X H K1(T) c-1.01 - K2(T)' 6 X 108 29.17T2 + 20.12T3 - 0.974T4 + 0.01584T6 5541 + 254.95T + 7.145T2 - 0.73T3 + 0.142T4 3,904,644 While these two parametric funct ions of temperature gave the best fit of the data, their complexity may be due partly to the use of the Parker and. Parker reference standards whose errors seem to vary rather unsystematically with temperature. In comparing chlorinities computed by means of this equation with the 61 titration values of the original data, the following results were obtained: in 32 cases the difference was 0.002 %o or less; in 22 cases it was between 0.003 and 0.005 %o ; and in the remaining 7 cases it varied from 0.007 to 0.027 %o. Because of the separation of variables, the above form of the equa-tion lends itself to compact, yet comprehensive, tabulation-one table for each of the three terms. By means of various manipulations it can 1954) Pollak: Chlorinity Determination 231 be put into other forms which might be more suitable for re:,;tricted ranges of the variables or for lower requirements in accuracy. It is a pleasure to acknowledge many fruitful discussions of the problem with D . E. Carritt and J. H. Carpenter of the Chesapeake Bay Institute. H.E.FERENCES BEIN, WILLY, H.-G. llrnsEKORK, LoT'l'E MoLLER 1935. Konstantenbest imrnungen des Meerwassers und Ergebnisse iiber Wllsser-kiirper. Veroff. Inst. Meeresk., Univ. Berl. N. F., A. Geogr.-naturwiss. Reihe, 28. 240 pp. JACOBSON, A. W. 1948. An instrument for recording continuously the salinity, temperature, and depth of sea water. Trans. Amer. Inst. elect. Engrs., 67: 714. JONES, GRINNELL AND G. M. BOLLINGER 1931. The measurement of the conductance of electrolytes. III. The design of cells. J. Amer. chem. Soc., 53: 411. JONES, GRINNELL AND B. C. BRADSHAW 1933. The measurement of the conductance of electrolytes. V. A redetermi-nation of the conductance of standard potassium chloride solutions in absolute units. J. Amer. chem. Soc., 55: 1780. KNUDSEN, MARTIN 1901. Hydrographical Tables. G. E. C. Gad, Copenhagen. 63 pp. LEEDS & NORTHRUP Cm,IPANY 1924. Apparatus for measuring conductivity of electrolytes. Catalog No. 48, Philadelphia. 32 pp. PARirnR, H. C. AND E. w. PARKER 1924. The calibration of cells for conductance measurements. III. Absolute measurements on the specific conductance of certain potassium chloride solutions. J. Amer. chem. Soc., 46: 312. THOMAS, B. D. WITH T . G. THOMPSON AND C . L. UTTERBACK 1934. The electrical conductivity of sea water. J. Cons. int. Explor. Mer, 9: 28. THOMPSON, T . G. AND H. E. WIRTH 1931. The specific gravity of sea water at zero degrees in relation to the chlorinity. J. Cons. int. Explor. ~Ier, 6: 232. WENNER, FRANK, E. H. SMITH, AND F. M. SOULE 1930. Apparatus for the determination aboard ship of the salinity of sea water by the electrical conductivity method. ,J. Res. U. S. Bur. Standards, Paper No. 223, 5: 711. 

The use of electrical conductivity measurements for chlorinity determination

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The use of electrical conductivity measurements for chlorinity determination

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