On Steam and Brines 175 



on pure water at the time and place, the saturated water will 

 mix with the free water, producing a resultant temperature 

 depending on the relative quantities of the saturated and 

 the free water. The case, then, of sodium nitrate, for instance, 

 in which the value of W (t T) is nearly constant, could be 

 represented by imagining the steam to condense at the tem- 

 perature of the boiling saturated solution of the salt so long 

 as solid salt is present, and the condensation temperature of 

 the steam remains constantly at the maximum. When the 

 solid salt has all disappeared, then the steam condenses at the 

 temperature at which it condenses in pure water. The two 

 portions of water, the saturated and the free, then mix, giving 

 the resultant temperature, depending on the relative quantities 

 and on the assumption that the heat of the saturated solution 

 is that which the water present in it would have if it had the 

 same temperature. 



In the cases where W (tT) is constant, we have Blagden's 

 law of the lowering of freezing-point applied to the raising of 

 the boiling-point of saline solutions ; both vary directly with 

 the concentration or inversely with the dilution. But in the 

 case of a saline solution following Blagden's law, when ice is 

 melted in the saturated solution already cooled to its freezing- 

 point, the solution is diluted and its temperature rises. The 

 rise of temperature is thus the same as would have been pro- 

 duced if the quantity of ice which has melted had been added 

 as pure water of o C. to the saturated solution at the initial 

 temperature of its freezing-point, and the two had been 

 mixed. 



The same is the case, mutatis mutandis, in the condensation 

 of steam by a saline solution. If the boiling temperature of 

 the stronger solution be t lt and steam be passed through it 

 until this temperature has fallen to 4, the temperature of 

 steam condensing on pure water being T, and if the quantity 

 of water in the stronger solution be W ly and in the weaker 

 W z , then we should have 



W l t,+(W z - W,}T = W 2 t,, 

 whence W l (/, -T)=W 9 (/, - T), 



the values of W(t T) are constant, which is the characteristic 



