228 C. Barus — Velocity and Structure of the Nucleus. 



less imagination, and it will therefore be chiefly referred to in 

 the following discussion. The nucleus is to be regarded small 

 enough that it is not symmetrically bombarded by the mole- 

 cules of vapor. Hence its velocity is conceived to be increas- 

 ingly larger as it is smaller, i. e., as the conditions favorable to 

 non-symmetrical bombardment increase. If too large it will 

 be stationary, apart from gravity ; if small enough, it must 

 eventually acquire the molecular velocities themselves. 



5. The relations of equilibrium here involved are peculiar 

 and need a more detailed elucidation. If vapor pressure 

 increases with increasing convexity, for capillary reasons, but 

 eventually decreases again as a result of the concentration 



1 



reached on evaporation, to a value nearly zero or at least below 

 the normal vapor pressure at a flat surface, it follows that as 

 the size of the drop continually decreases the vapor pressure 

 at its surface must pass through a maximum. The accompany- 

 ing diagram* is an attempt to represent the case graphically for 

 two given solutions, by making the vapor pressures the ordi- 

 nates, and the radii of the given droplet of solution the 

 abscissas. The line db indicates the normal vapor pressures. 

 All particles whose sizes taken from the curve l)m's' correspond 

 to the abscissas between s' and h therefore evaporate in the 

 lapse of time, those lying near the maximum, m', fastest, those 

 lying near s' or h with proportionate slowness, while the latter 

 are also lost by subsidence and may be dismissed from con- 

 sideration. On the other hand, a particle whose radius is 

 smaller than the abscissa corresponding to s' will grow so that 

 as' is the stable radius of the nucleus obtained by shaking the 

 given dilute solution. 



If the solution is weaker, the droplet shaken out of it will 

 have to evaporate further to reach the critical density of the 

 stable nuclear state, and the increment of vapor pressure due 

 to surface tension will also be larger or the maximum, m, will 

 be higher. The curve bms now represents the conditions and 

 is to be similarly interpreted. 



* The two curves should have been drawn preferably without intersecting. 



