This explains why water can dissolve so many compounds. Water is a powerful solvent, it will eventually dissolve almost any substance. The total quantity of dissolved organic solids in water is its salinity. Most of the dissolved solids in seawater are salts that have been seperated into ions. In order to determine salinity, you can measure the chlorinity of the water.
Chlorinity is the measure of the total weight of chloride, bromide, and iodide ions in seawater.
Because the proportion of chlorinity to salinity is constant, marine chemists have devised this formula to determine salinity. In 1865, Johann Georg Forchhammer found that the ratio of major salts in samples of seawater from various locations was constant. This constant ratio is known as Forchhammer's Principle, or the Principle of Constant Proportions. The ocean appears in chemical equilibrium. This means the proportion and amounts of dissolved salts per unit volume of ocean are nearly constant.