Since 1975, Standard Seawater has been provided by the Institute of Oceanographic Sciences in Wormley, England. Obviously, few if any volunteer monitoring groups will purchase Standard Seawater. Volunteers can practice their technique using a solution of ordinary table salt in water. Instruments should ideally be checked against another instrument that has been calibrated with a primary standard. By measuring the concentration of one major constituent, the salinity of a sample can be calculated.
Chlorinity is measured by titration in a fairly simple procedure.
First an indicator, potassium chromate, is added to a carefully measured volume of sample. This reagent produces a yellow color. Then silver nitrate solution of a standard concentration is added as the titrant. The silver reacts with chloride in the sample to form a white precipitate, silver chloride. Chloride concentration is calculated from the size of the sample and the concentration and amount of the silver nitrate used.