In the polar areas the melting of sea-ice and of ice formed by precipitation lowers the density of the seawater and causes a difference of level which sets up streaming movements towards the equator.
Further Physical Properties of Sea-water.---The laws of physical chemistry relating to complex dilute solutions apply to seawater, and hence there is a definite relation between the osmotic pressure, freezing-point, vapour tension and boiling-point by which when one of these constants is given the others can be calculated.
The internal friction or viscosity of seawater has also been shown by E.
FLUORINE (symbol F, atomic weight iv), a chemical element of the halogen group. It is never found in the uncombined condition, but in combination with calcium as fluor-spar CaF2 it is widely distributed; it is also found in cryolite Na3A1F6, in fluor-apatite, CaF 2.3Ca 3 P 2 O 8, and in minute traces in seawater, in some mineral springs, and as a constituent of the enamel of the teeth.
Considerable alarm was created about the year 1887 by the failure of two or three large structures of Portland cement concrete exposed to seawater, both in England and other countries.
In his researches on the bleaching compounds of chlorine he was the first to advance the view that bleaching-powder is a double compound of calcium chloride and hypochlorite; and he devoted much time to the problem of economically obtaining soda and potash from seawater, though here his efforts were nullified by the discovery of the much richer sources of supply afforded by the Stassfurt deposits.