CHAPTER 1 • Sea Water as an Electrolyte
Fig. 1.4. The major cations and
anions in sea water (Millero
1996)
1. Refractive Index
2. Sound Speed
3. Evaporation
4. Composition
5. Density
6. Chlorinity
7. Conductivity
±0.05
±0.03
±0.01
±0.01
±0.004
±0.0002
±0.0004
7
HCO]
B(OH)4
(1Due to the high precision, the salinity is presently determined from conductivity
measurements. These measurements are made relative to a sample of known conductivity (R = CSamplel CStd)' Since the S = 35.000 at a CI = 19.374 (Eq.l.7), the earlier conductivity measurements.as a function of CI were converted using S = 1.80655 CI. Since
the composition data for CI = 19.374 gives S = 35.171, 0.17 kg of carbonates and boric
acid are lost during the evaporation.
The Practical Salinity Scale of 1978 was developed from measurements made of the
conductivity of sea water of known CI (19.374) and S (35.000) relative to the conductivity of a given mass of KCl. This new scale breaks the CI-S relationship in favour of a
salinity-conductivity ratio relationship. All waters with the same conductivity ratio