On Steam and Brines 181 



Let the temperature of the water in the tank be now 

 reduced to i i8 0- O3 C, at which temperature its vapour tension 

 is i '9 k./cm. 2 , and let steam of this temperature be condensed 

 in it. The volume of water in the tank increases while its 

 area expands in the same ratio, until the weight pressing on 

 its surface is at the rate of 1*9 k./cm. 2 , when the steam will 

 lift the cover and escape. The weight of the cover has 

 remained constant (= 100 kilogrs.), but the area exposed to 

 the atmospheric pressure has increased. The resulting area 

 and volume of water are given by the equation rg W= loo+W, 



TTr IOO 



whence Jr= =m. 

 0-9 



Again, let the temperature of the water in the tank be 

 reduced to i \6'2g C., at which temperature its vapour tension 

 is r8 k./cm. 2 , and let steam of this temperature be passed into 

 it. It will be condensed until the volume and surface of the 

 water have increased to such an extent that the total pressure 

 on its surface is at the rate of rS k./cm. 2 . As before, we find 

 the value of W, when this point has been reached, to be 



IOO 



77= 125, and so on. 



O'o 



In the principal table the pressure is reduced by 0*1 k./cm. 2 

 at a time, from 2 - o to ri k./cm. 2 , then by 0*01 k./cm. 2 down to 

 roi k./cm. 2 and by o'OOi down to rooi k./cm. 2 . The value of 

 W is inversely proportional to the difference of pressure, a A, 

 and becomes infinite when a A = o. On the other hand, it 

 diminishes rapidly at high temperatures and pressures, and 

 would become o when a A = oo . 



The table is carried upwards to a= 10 k./cm. 2 , and down- 

 wards to a=i'OOi k./cm. 2 . In these limits the value of W 

 varies from IIT to 100,000. 



The temperature of saturated steam rises at a slower rate 

 than its tension. Hence in our mechanical experiment with 

 pure water, when the area is increased by a given amount, 

 and the pressure per unit of area is correspondingly reduced, 

 the consequent fall of temperature depends on the actual 

 temperature, and is proportional to the reciprocals of the 

 figures representing the mean difference of tension per degree 



