SECT. 1] 



PHYSICAL PROPERTIES OF SEA-WATER 



11 



Eckart estimated random errors in measurements of specific volume to be 

 about + 2 X 10"'* nil/g and systematic errors probably greater than + 2 x 10~'^^ 

 ml/g for sea-water. Both formulas (25) and (27) give the same value for specific 

 volume within the limits of error given by Eckart. Over the major part of the 

 range of temperature, pressure and salinity encountered in the ocean, the 

 difference in specific volume from the two formulas is less than 5 x 10"^ ml/g. 



Fig. 1. A comparison of equations of state of sea-water, ax (Kjiudsen, 1901) and as 

 (Eckart, 1958). Values of the differences 104(o:/f — «£:) are shown as functions of 

 temperature (°C), salinity (%o) and pressure (db). 



However, the difference increases rapidly at the limits of the range. For ex- 

 ample, at atmospheric pressure the difference increases from 5 x 10^^ nil/g at 

 18°C to 30 x 10-5 ml/g at 30°C for sea-water of 35%o salinity. The difference 

 between the two formulae for various temperatures, pressures and salinities is 

 shown in Fig. 1. 



Although the specific volumes do not differ greatly, the two formulae pro- 

 posed for the equation of state of sea-water indicate that some of the derived 

 properties, such as the coefficient of thermal expansion, are seriously in doubt. 

 Even for pure water, which has been studied more intensively, the thermal 



