On Steam and Brines 179 



of mercury, which is converted into a in k./c. 2 . The excess 

 of this above the atmospheric pressure multiplied by the 

 surface, IV, gives the extra load required : 



and this quantity b kilogrammes is the mechanical equivalent 

 of the fifth of a molecule of salt in so far as the raising of 

 the boiling temperature of water, or the resistance to steam 

 pressure, is concerned. 



In the case of the boiling saturated solution of salt when 

 steam is continued to be passed through and heat is lost, the 

 solution is diluted by the addition of the condensed steam to 

 the original quantity, W, of saturated water. This dilution 

 or addition of pure water to the saturated water, is accom- 

 panied by a fall of the temperature of ebullition, which is 

 very rapid at first, but becomes slower as the quantity of 

 condensed steam increases, tending ultimately towards the 

 boiling temperature of pure water at atmospheric pressure. 



The more concentrated the solution is, the more accentuated 

 are the specific properties of the dissolved salt, and they are 

 most pronounced in the saturated solution which approximates 

 to the condition of the liquefied salt, as the dilute solution 

 approximates to that of pure water. The specific nature of 

 the dissolved salt shows itself first in the maximum tempera- 

 ture to which the solvent water can be raised under a given 

 pressure, and then in the rate of fall of boiling temperature 

 with dilution. Different salts behave differently in these 

 respects. 



The uniformity observed in the physical properties of very 

 dilute solutions is due in part to our limited powers of per- 

 ception, and to arithmetical necessity. In proportion as the 

 number expressing the dilution becomes very great it tends 

 to occupy the whole field of view, and, consequently, to 

 obscure or obliterate the specific properties of the substance 

 dissolved. 



Similarly, in considering the trigonometrical functions of 

 angles, if we limit our contemplation to very small angles, we 

 can perceive no difference between the sine, the arc, and the 



