A special refrigeration apparatus was constructed to simulate freezing of sea water under natural conditions. Ice thus obtained, as well as the residual waters, were studied to ascertain the effect of freezing upon the sulfate/chlorinity ratio. This ratio was found to be greater for salts retained by the ice than for the original water. An equivalent decrease in the ratio occurred for the residual water. The ratio in the ices varied considerably and was a function of the rate of formation of ice and the temperatures of exposure. Maximum ratios were obtained at - 8° C and - 45° C. Minimum ratios were obtained at about - 25° C.