The property of seawater used in induction salinometers to measure salinty is?

Answer 1

Induction salinometers measure the electrical conductivity of seawater. At a fixed temperature, the conductivity is approximately linearly proportional to salt concentration. The nature of the salt makes a difference, and sea salt composition varies somewhat around the world.

For chemical solutions other than seawater, conductivity generally increases with increasing concentration, but the factor relating conductivity to concentration depends upon the composition of the solution.

For a given concentration of salt near room temperature, conductivity increases about 2% for each degree Celsius of temperature increase because the viscosity of water decreases as the temperature rises. For solutions of strong acids, the temperature coefficient is nearer 1%/ degree. (The mechanism of conductivity in strong acid solutions differs from that in salt solutions.)

Temperature coefficients are smaller at elevated temperatures. Weird nonlinearities occur in aqueous solutions below 4 degrees C, as the water begins to freeze.

The temperature coefficient of seawater also depends slightly on the composition of the seawater. Commercial induction salinometers which calculate temperature corrections assume some standard composition of seawater, such as that found in Copenhagen bay. This may yield errors for seawater which has been concentrated by solar evaporation, such as in the Red Sea, or seawater which has been diluted by river water or ice melt.