The maximum concentration we can use and still have seawa,ter is approx- 

 imately c = 0.070, since salts precipitate out of sea,-wa,ter with 

 concentrations greater than this. 



Earned and Owen (1958) have tabulated da,ta on the relative partial 

 heat content of sodium chloride at 25°C. (The relative partial heat 

 content is the difference of the partial heat content of the salt at 

 concentration c from that at infinite dilution.) The data are shown 

 graphically in Figure lb. Near infinite dilution, the relative partial 

 heat content varies approximately as the sq.uare root of the concentration; 

 whereas between lO/oo and IQPJoo salinity, it varies linearly with the 

 concentration. Since sea salt is more tha,n 90/0 sodium chloride, the 

 choice of seawaters to be mixed (at 25 °C) was c = 0.01 a,nd c = O.O6, for 

 a final c of 0.035- 



The low tempera,ture concentration dependency of the heat of mixing 

 was determined from a series of mixing experiments performed at 2°C. 

 Ideally we would hope for a linear relationship between the partial 

 specific heat content of sea salt Yi and the concentration c; i.e., 



h^ - h^ + c h^ (1) 



si 2 



where ii = 12i 



Since seawater can be regarded as a two component system made up of water 

 and sea salt, the specific heat content at a temperature is: 



h (T, c) = (1 - c) h^ + ciig . (2) 



The concentration dependences of h and h can be rela,ted by the 



w s 

 Gibbs-Duhem equatxon 



8h 9h 



c ^ = -(1 - c) -^ = ch_ (3) 



9c oc 2 



Assuming (l-c) - 1 and integrating, we obtain 



h = h - V^ {h) 



w o 2 



Substituting equations (l)and {h) into equation (2) and neglecting terms 

 of order -greater than '2, we obtain 



2 h 



h = (1 - c) h + ch^ + — ^ — (5) 



^ ' o 1 2 



The coefficients h , h^ and h„ are functions of temperature; however, h 

 o 1 2 o 



will not be equal to the specific heat content of pure water since 



equation (l) is not valid for low concentrations. It is an empirical 



paramieter which can be evaluated for the range of concentration where the 



linear approximation holds . 



430 



