152 On Steam and Brines 



ascertain whether the salt, from which the ice could not be 

 entirely freed, was an essential part of the ice, or only an 

 inseparable adherent to it. The latter was shown to be the 

 case, and the ice, or crystalline body which freezes out of a 

 saline solution, to be really ice and nothing else, by showing 

 the identity of the temperature at which snow or pure 

 pounded ice of independent source melts in a saline solution, 

 and that at which ice forms on freezing a saline solution of 

 the same nature and concentration. 



It was natural to pass from the freezing to the boiling 

 temperature of solutions, and to use the temperature at which 

 steam condenses in the solutions as a measure of their boiling 

 temperature in the same way as the melting temperature of 

 ice had been used for indicating the freezing temperature. It 

 had also the advantage that no preliminary investigation was 

 necessary. There was no doubt that the steam produced by 

 a boiling saline solution was pure steam, there was no doubt 

 about the temperature of the boiling solution from which the 

 steam proceeded, and there was equally little doubt that the 

 steam so proceeding had the same temperature as the boiling 

 solution, because when steam is blown into such a solution it 

 is condensed until the solution has been heated to its boiling- 

 point. If the solution can condense outside steam, it neces- 

 sarily must be able to condense its own steam, for the two 

 substances are identical. 



These conditions are expressed in the following law: The 

 temperature at which steam condenses depends on tJte nature of 

 the medium in which it condenses; and the temperature at which 

 it is generated depends on the medium in which it is generated ; 

 and the temperature at which steam condenses in a given medium 

 is that at which it is generated in the same medium, the pressure 

 in all cases being the same. (191 6.) 



When the naked flame is used as source of heat it is very 

 difficult to obtain the exact boiling temperature of a brine, or 

 indeed of pure water. 



On the other hand, it is very easy to get results of any 

 desired degree of exactitude by using an abundant current of 

 saturated steam to boil the water or brine. Overheating is 



