Thus, the chlorine content is a directly determinable quantity, while salinity is a quantity ob- 

 tained by multiplying the chlorine content by some standard coefficient. 



In oceanography, we must deal not only with the chlorine content or the salinity, but also with 

 densities, which depend on them and on temperature. The physical methods of determining density 

 are either inaccurate or too complex, while the chemical determination of chlorine content is very 

 simple and does not require special knowledge of chemistry. Assuming that the salt content of sea 

 water is constant, it is not difficult to determine both density and specific volume from the chlorine 

 content. 



In oceanographic research, we study, chiefly, the differences in the salinity and density of 

 sea waters both in time and in space, not their absolute values. Therefore, we are not so much 

 concerned with how accurately we determine salinity and density by the chlorine content, as how 

 accurately we determine their differences. Hence, we can assume not only that the salt composi- 

 tion of ocean waters is constant, but that the salt composition of the waters within each separate 

 ocean basin is constant, although it may differ from that of the ocean waters. Consequently, 

 Knudsen's formula and the relationships stemming from it can be used in investigating the dynamics 

 of sea wateiynot only for the ocean, but also for most of the enclosed seas. 



LITERATURE: 62, 73, 157. 



Section 4. Specific Gravity, Density and Specific Volume 



The density of sea water at constant pressure is a function of both salinity and temperature. 

 At the same temperature, it is exclusively a function of salinity and in oceanography is called spe- 

 cific gravity. In practice, specific gravity is expressed in two ways: 



1. the specific gravity of sea water at 0° relative to distilled water at 4° (s- I 



2. specific gravity of sea water at 17. 5° relative to distilled water at the same temperature 



In oceanography, density and specific gravity differ in that temperature is taken into consid- 

 eration in the case of density. In other words, density is the specific gravity of sea water at a 

 given temperature (t) relative to distilled water at 4° (s-j. 



Since the density of sea water varies within small limits, Knudsen introduced the following 

 notations to limit the number of signs: 



a = (s — l\ 1, 000 is the natural specific gravity at 0°, 



\ 4 / 



p = (s — '- 1) 1,000 is the natural specific gravity at 17.5°, 



^17.5 \ 17.5 / 



a, = (s — - ij 1, 000 is the natural density. 



The magnitudes 3, CI , u^ and p^^ ^ are different expressions of the same amount of chlo- 

 rides or chlorine content. Therefore, having determined one of these four values, the other mag- 

 nitudes are determined in the process. 



10 



