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ABSTlXACTPartial equivalent volumes (v,) of the major salts in seawater have been mcasurcd over the salinity range from 30 to 40%, and a temperature range from 08 to 2X. 1NTRODUCTIONThis paper presents the results of the determination of the partial equivalent volumes of the major salts in seawater at temperatures and salinities common in the ocean. The partial equivalent volume ( Vl ) of a salt in seawater is defined as: where f7, is the increase in volume (V) of an infinitely large volume of seawater due to the addition of one equivalent (n) of salt 1. Several investigators (Wirth 1937 Owen and Brinkley 1941;Zen 1957) have reported partial volumes of various salts in pure water and in aqueous solutions of strong electrolytes; however, no data exist in the literature on the determination of the partial equivalent volumes in seawater.The experimental results contained in this paper can bc used to construct a density model of seawater by considering seawater as a two-component system containing sea salt and water, where sea salt is an appropriate mixture of the major salts in seawater. Lyman and Fleming's ( 1940) equivalent volume of sea salt derived from the density of seawater with the value detcrmined from a summation of the partial equivalent volumes of the individual salts. Recently, Cox et al. (1962) have been studying the density-conductance relationships of seawater. To estimate how this relationship is altered by slight changes in the relative composition of seawater, the partial equivalent volumes and partial equivalent conductances of the major salts in seawater must be known. Partial equivalent conductances of salts in seawater are currently being determined at Oregon State University ( Connors, personal communication). METHODS Sah investigatedThe partial volumes of the following salts were measured at various salinities and temperatures : NaCl, KCl, Na2S04, IGOd, MgSO .7H20, KIIC03, Ca(NO& *4&O, NaN03, KN03, Mg *Acetate. 4&O, and Na . Acetate. 3&O.The salts used were Baker and Adarnson reagent grade quality and were not further purified. Potassium bicarbonate and the hydrated salts were not dried before using because of the uncertainty in the composition and stability of the dried form. The remaining salts were dried at 15OC for at least 2 hr. The nondryable salts did not show noticeable deliquescence under laboratory conditions; therefore, the error introduced into the results because oE nondrying was estimated from the per cent of water (as an impurity) present in the salt when purchased. The significance of this error is illustrated for magnesium sulfate: At S = 34.46x0, T = 24.5C, the partial cquivalent volume of 'MgSO a 7&O is 64.42 * 0.20 52

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The activity of magnesium ions in seawater was determined from solubility data and found to be between the values determined by Platford and by Garrels and Thompson. Our value may result from extensive formation of magnesium sulfate ion pairs.