The solid material obtained upon freeze-drying sea water is not a true measure of salinity since it contains 9 or 10 % water of crystallization, the exact content being a sensitive function of temperature and humidity. The residual water is determinable with Karl Fischer reagent, although the method is not yet capable of yielding salinity with the precision hitherto obtainable through the Knudsen titration....
Barquist, Richard F., and A. V. Wolf. 1958. "A new method for direct determination for salinity." Journal of Marine Research 17, (1). https://elischolar.library.yale.edu/journal_of_marine_research/924