Values of thermal conductivity, dynamic viscosity, heat capacity, density, and Prandtl number for seawater and its concentrates are given. The data on which these recommended values are based are the most reliable available and cover a wide range of both temperature and concentration.

The concentration of seawater samples is normally defined by a single term, either salinity or chlorinity. This is possible since for all practical purposes the relative composition of seawater is constant. This docs not imply that all samples have the same composition but merely that all ions are present in the same ratios and that the only variation is the amount of pure water present. Thus, if the concentration of any one ion is measured, the amount of all the other ions can be accurately found by calculation.

Salinity was originally defined as the weight in grams of the dissolved inorganic matter in 1 kg of seawater after all bromide and iodide have been replaced by an equivalent amount of chloride and all carbonate has been converted to oxide. Chlorinity is in effect the halide concentration of seawater. The two are related by

S‰ = 1.80655 Cl‰ (1)

(The symbol ‰ denotes parts per thousand of seawater.) Chlorinity and salinity are now more accurately found by measuring the ratio of the electrical conductivity of the unknown sample to that of a "standard seawater" sample.