Multiply chlorinity, the amount of chlorine in seawater, by 1.80655 to get this figure
[DOC] [TLE] c5 The Chemistry of Seawater [PAR] By examining figures 5.1 and 5.2 in your text you can see that there are two first-
order ... Six major ions make up > 99% of the salts dissolved in seawater: four .... 
by measuring the concentration of the chloride anion (the chlorinity of the water).