Note 5 — Chapter X · SODIUM CHLORIDE—BERTHOLLET'S LAWS—HYDROCHLORIC ACID

Owing to the fundamental property of salts of interchanging their metals, it cannot be said that sea water contains this or that salt, but only that it contains certain amounts of certain metals M (univalent like Na and K, and bivalent like Mg and Ca), and haloids X (univalent like Cl, Br, and bivalent like SO4, CO3), which are disposed in every possible kind of grouping; for instance, K as KCl, KBr, K2SO4, Mg as MgCl2, MgBr2, MgSO4, and so on for all the other metals. In evaporation different salts separate out consecutively only because they reach saturation. A proof of this may be seen in the fact that a solution of a mixture of sodium chloride and magnesium sulphate (both of which salts are obtained from sea water, as was mentioned above), when evaporated, deposits crystals of these salts, but when refrigerated (if the solution be sufficiently saturated) the salt Na2SO4,10H2O is first deposited because it is the first to arrive at saturation at low temperatures. Consequently this solution contains MgCl2 and Na2SO4, besides MgSO4 and NaCl. So it is with sea water.