﻿Nature of the Large Ions in the Air. 521 



the density of the vapour is small in comparison with the 

 density of the adsorbed moisture, the value of n found 

 necessary for the reduction of adsorption observations to a 

 common temperature might, therefore, possibly form a 

 criterion in determining the condition of the absorbed fluid. 



This question of: the condition of the adsorbed moisture is 

 even capable of somewhat more precise consideration, for in 

 the case of the large ions, and of uncharged drops of a similar 

 nature, which as shown by cloud condensation experiments 

 do not become unstable until the vapour becomes, at least, 

 slightly supersaturated, equation (1) becomes 



V_/1_1\^P 

 6 ~\a~ p'J de ' 



and no doubt the equation also holds for fluid adsorbed at a 

 plane surface. 



Patting p' = p + 8p with the sign of Sp undetermined, the 

 expression may be written 



7 \ p / per do \ p — o-J 



X' 



6 \ pi 



8 P 



or X p—o. 



P 



At atmospheric temperatures, as a is small compared with 

 p, we see, without requiring a knowledge of the density, 

 that when the vapour-pressure is that of saturation the 

 adsorbed fluid has a latent heat differing very little from 

 that of water. From the point of view of Laplace's theory 

 it is difficult to see how this conclusion could fail to carry 

 with it the inference that the difference in density is also 

 small. 



If it is experimentally found that (l/p)(dp/dO) m is equal to 

 {U¥)(dPld6) for all values of p, then 



A, o 



\ <T 



for all values of the vapour-pressure. 



If the adsorbed fluid is in the liquid state, little change, 

 I believe, occurs in its density as the vapour-pressure alters. 



