PHYSICAL PROPERTIES OF SEA WATER 13 



coefficient for pure water. Thus, for sea water of salinity 35.00 °/oo the 

 coefficient at 0° and atmospheric pressure is 51 X 10"^, and at 20° it is 

 257 X 10~®, whereas the corresponding values for pure water are 

 — 67 X 10~^ and 207 X 10""^. The minus sign shows contraction. For 

 sea water of salinity 35.00 °/oo and temperature 0° the coefficient at 

 atmospheric pressure is 51 X 10~^, and at a pressure of 4000 decibars it 

 is 152 X 10-^ 



Thermal Conductivity. The thermal conductivity is defined as 

 the amount of heat in gram calories which, per square centimeter per 

 second, is conducted through a surface if the temperature gradient at 

 right angles to the surface is one degree centigrade per centimeter. For 

 pure water at 15°C the coefficient equals 1.39 X 10~^. The coefficient is 

 somewhat smaller for sea water and increases with increasing temperature 

 and pressure. This coefficient is valid, however, only if the water is at 

 rest or in laminar motion (p. 17), but in the oceans the water is nearly 

 always in a state of turbulent motion in which the processes of heat 

 transfer are completely altered. In these circumstances the above 

 coefficient of heat conductivity must be replaced by an ''eddy" coefficient 

 which is many times larger and which depends so much upon the state 

 of motion that effects of temperature and pressure can be disregarded. 



Specific Heat. The specific heat is the number of calories required 

 to increase the temperature of 1 g of a substance 1°C. When studying 

 liquids, the specific heat at constant pressure, Cp, is the property usually 

 measured, but in certain problems the specific heat at constant volume, 

 Cv, must be known. 



The specific heat of sea water is somewhat lower than that of pure 

 water and decreases somewhat with increasing temperature. Thus, at 

 atmospheric pressure, the specific heat of sea water of salinity 34.85 °/oo 

 equals 0.941 at a temperature of 0°C, and 0.932 at a temperature of 20°C. 

 The specific heat increases somewhat with increasing pressure. At 4000 

 decibars it equals 0.970 for water of salinity 34.85 °/oo and temperature 

 0°C. 



The specific heat at constant volume, Cv, is somewhat less than Cp at 

 atmospheric pressure. The ratio Cp/cv for water of salinity 34.85 °/oo 

 increases from 1.0004 at a temperature of 0° to 1.0207 at 30°. The effect 

 of pressure is appreciable, and for the same water at 0° the ratio is 1.0009 

 at 1000 decibars and 1.0126 at 10,000 decibars. 



Latent Heat of Evaporation. The latent heat of evaporation of 

 pure water is defined as the amount of heat in gram calories needed for 

 evaporating 1 g of water, or as the amount of heat needed for producing 

 1 g of water vapor of the same temperature as the water. Only in the 

 latter form is the definition applicable to sea water. The latent heat of 

 evaporation of sea water has not been examined, but it is generally 

 assumed that the difference between that and pure water is insignificant ; 



