If we took 1000 grams of seawater and evaporated all the water, we would have 3.47g of dissolved solids, on the average. Rule of constancy of composition - The ratio of major elements in the oceans' salt is amazingly constant. This was established by the Challenger expedition, and is called the rule of constancy of composition. They are chlorine, sodium, sulfur, magnesium, calcium, and potassium. Salinity is usually measured in parts per thousand or ppt .
Percent is parts per hundred.
The chloride ion mass is proportional to the salinity, and chloride was commonly measured in the past and converted to salinity. There are also many minor constituents in seawater. Sea Water Density a. Density is affected by temperature, salinity, and pressure. However, in most cases seawater is considered incompressible, so not greatly affected by pressure.