1) Definite quantity 
The chlorinity of water is defined as the mass of chlorine equivalent to the total mass of halogen contained in 1 kg seawater. It is determined by the Mohr-Knudsen titration, which however neglects fluoride. The halogen concentration of sea water can be expressed in terms of chlorosity which is the number of grams of chloride and chloride equivale...
Grams of chloride ions per 1000 grams of seawater 
noun a measure of the quantity of chlorine or other halides in water (especially seawater)
the quality, state, or degree of being chlorinous.