20 FOFONOFF [chat. 1 



where rjw° is the entropy of pure water. Using the definition for the partial 

 entropy of water in sea-water 



djx drj 



we obtain 



' cT c^s 



Substitution from (47) yields 



(49) 



^w -V-' = 4rJ^T f -L ^ ds, (50) 



' ' c'T Jo I -r c's 



so that in terms of vapour-pressure lowering 



,,._^ _i?ln(l-r)+3--^^- (51) 



Values of -n have been tabulated by Robinson (1954) and by Wilson and 

 Arons (1955) using equation (47) and measured values of vapour-pressure 

 lowering. 



Given the vapour-pressure lowering and specific heat at atmospheric pressure, 

 we can make use of (42) and (20) to calculate ju. From (42), we have 



du. RT dr , ^ 



cs 5(1 —r) OS 



and from (20) 



By integration, the chemical potential difference /x, relative to an arbitrary 

 reference state Tq, sq, is 



/x = ^o + {T-To)i^^^+\^[\AT^T, + {T-To) ( 



ldA\ 



ds 



j: 



T' 



+ B{T,s)dT'dT. (52) 



T„ 



We cannot evaluate the linear function ijlo + {T - To){diJLldT)o in (52) as 

 both jLto and {d^ldT)o are arbitrary for any reference state To, so- 



Although present measurements of the lowering of vapour pressure are 

 sufficiently accurate for most purposes where total vapour pressure is required, 

 they are not consistent enough for use in (52). The fractional lowering of vapour 

 pressure, r, is approximately a linear function of salinity. Thus, the ratio rjS 



