PHYSICAL PROPERTIES OF SEA WATER 1 1 



The density of sea water depends upon three variables: temperature, 

 salinity, and pressure. These are indicated by using for the density the 

 symbol Ps.t?,p, but, when dealing with numerical values, space is saved by 

 introducing the symbol <Js,d.p, which is defined in the following manner: 



(Ts,^,p = (ps.O.p - 1)1000. (11,1) 



Thus, if ps,t>,p = 1.02575, <Ts,^,p = 25.75. The density of a sea-water 

 sample at the temperature and pressure at which it was collected is 

 called the density in situ and is generally expressed as da, 6, p. At atmos- 

 pheric pressure and temperature i>°C the corresponding quantity is 

 simply written <jt, and at 0° it is written o-q. The symbol t? will be used 

 for temperature except when writing at, where, following common 

 practice, t stands for temperature. 



At atmospheric pressure and at temperature of i?°C the density is a 

 function of the salinity only, or, as a simple relationship exists between 

 salinity and chlorinity, the density can be considered a function of 

 chlorinity. The International Commission, which determined the 

 relation between salinity and chlorinity and developed the standard 

 technique for determinations of chlorinity by titration, also determined 

 the density of sea water at 0° with a high degree of accuracy, using 

 pycnometers. From these determinations the following relation between 

 (70 and chlorinity was derived: 



(TO = -0.069 + 1.4708 CI - 0.001570 CP -f 0.0000398 CP. 



Corresponding values of o-q, chlorinity, and salinity are given in Knudsen's 

 Hydrographical Tables for each 0.01 per mille CI. 



In order to find the density of sea water at other temperatures and 

 pressures, the effects of thermal expansion and compressibility on the 

 density must be known. The coefficient of thermal expansion has been 

 determined in the laboratory under atmospheric pressure, and according 

 to these determinations the density under atmospheric pressure and at 

 temperature t? can be written in the form 



(Tt= (JQ- D. (II, 2) 



The quantity D is expressed as a complicated function of ao and tempera- 

 ture, and is tabulated in Knudsen's Hydrographical Tables. The values 

 of (Tt are widely used in dynamical oceanography. Knudsen's tables also 

 contain a tabulation of Z) as a function of at and temperature, by means 

 of which (To can be found if at is known (ao — at + D). This table is 

 useful for obtaining the salinity of a water sample the density of which 

 has been directly determined at some known temperature. 



The effect on the density of the compressibility of sea water of 

 different salinities and at different temperatures and pressures was 



