28 FOFONOFF [chap. 1 



The phenomenon of salt flux due to a temperature gradient is known as the 

 Soret effect. It has not been studied for sea- water but has been observed in 

 other solutions. Heat flow due to a concentration gradient (Dufour effect) has 

 not been observed in solutions (De Groot, 1952). 



Other transport phenomena can be analysed by methods similar to those 

 given here. Present knowledge of transport processes has been recently sum- 

 marized by Montgomery (1957). His compilation of transport coefficients is 

 reproduced in Table V. He points out that diflfusivities of nitrogen and oxygen 

 in sea- water may be uncertain by as much as 15%. The effect of pressure on 

 the transport coefficients is not available for sea-water. For pure water, thermal 

 conductivity increases slightly with pressure ; viscosity decreases with pressure 

 for temperatures under about 25°C and increases at higher temperatures 

 (Dorsey, 1940, table 86). 



6. Other Physical Properties of Sea-Water 



In addition to the properties which enter into the thermodynamical descrip- 

 tion of a sea-water system, there are a number of other properties of sea-water 

 that have been studied. Some of these, such as the optical and acoustical 

 properties of sea-water and properties of sea ice, are discussed in subsequent 

 sections and are, therefore, omitted here. Of the remaining properties, electrical 

 conductivity is important because of the increasing use of conductivity bridges 

 (salinometers) for determining the salinity of sea-water. 



The electrical conductivity in ohms per cubic centimetre has been measured 

 by Thomas et al. (1934) and Bein et al. (1935) for a range of temperatures and 

 salinities at atmospheric pressure. Their measurements show that conductivity 

 increases with both temperature and salinity. Recently, Hamon (1958) carried 

 out measurements on the effect of pressure on electrical conductivity. He used 

 a single sample of sea- water of chlorinity 19.7 %„ (salinity 35.5 %o) and made 

 measurements of the change of resistance of a cell filled with the sample and 

 sealed in a pressure bomb. Measurements were made over the temperature range 

 0°C to 20°C and pressures up to 100 atm. Hamon found that conductivity 

 decreased with pressure, the decrease being more rapid at lower temperatures. 

 He gave the fractional decrease of conductivity of 1.50 x 10"^ db"i at 0.5°C 

 and 0.82 x 10"^ db~i at 19.5°C, and estimated the accuracy of his results to 

 be about ±5%. 



The pressure dependence of electrical conductivity is of particular import- 

 ance in the development of conductivity bridges capable of measuring salinity 

 in situ. 



References 



Agamat, E.-H., 1893. Memoires sur I'elasticite et la dilabilite des fluides jusqu'aux tres 



hautes pressions. Ann. Chi?n. Phys., 29, 505-574. 

 Arons, A. B. and C. F. Kientzler, 1954. Vapor pressure of sea-salt solutions. Trans. Amer. 



Geophys. Un., 36, 722-728. 



