CHAPTER V. 



PROPERTIES OF THE NUOLEl I'UOUUCED JiY SHAKlNCi IJQUID.S. 



INTRODUCTION. 



1. Thermodynamic and clcrtiviiic liypotlienen. — When I first tMicoiiiitercd the 

 preseut kind of nucleatiun, tlie observation did not seem to me to \k' of mnch 

 interest or the occurrences unexpected. It was not until I had satisfied myself of 

 the extreme minuteness of the particles that I became convinced of theii- value as 

 a means of elucidating the phenomenon of condensation. Clearly the importance 

 of these nuclei is enhanced in pi-oportion as the means by which they are [)ro(luced 

 are similar. Lenard,' as I afterwards found, had met them incidentally in connec- 

 tion with his electrical investigations before, and treated them chiefly with reference 

 to their bearing on those phenomena. 



I first endeavored to explain the persistence of the nuclei produced by shaking 

 solutions, by pointing out that whereas the vapor pi-essure increases as the di'oplet 

 grows smaller by evapoi'ation, this pressui'e decreases again as the result of the con- 

 tinued concentration of the evaporating droplet, until a state of equilibrium is 

 reached. Afterwards, however, I was unable to look at this sti'aightforward 

 explanation without considerable misgiving, as it is not easy to agree that nuclei at 

 the same time so small and so nearly of a size as to pi'oduce shai'p coronas on pre- 

 cipitation could be produced by a random process of the kind in question. Not 

 enough is known, moreover, of the vapor pressure of such concentrated solutions as 

 those with which the evapoi-ation of the droplet terminates. 



From another point of view, it is not impossible that these nuclei may owe 

 their persistence to the occurrence, for instance, of an ion within them. In other 

 words, one may suppose that ions have been sepai'ated by the comminution due to 

 violent shaking, or have been separately enti'apped in the water nuclei observed. 

 Again, the results of the investigations on the electricity i)roduced by the attrition 

 (if I may call it so) of water in falling (Lenard, I. c), may have immediate relations 

 to the present phenomenon of persistence. In short, the theoretical bearing of the 

 experiments is not quite so simple as a first inspection had led me to infer. 



Considerations like these suggest an extended inquiry into the pi-operties of 

 nuclei produced by shaking very different solutions, and the present chapter is an 

 endeavor to bring together a number of relevant data. The results show, I think, 

 that the concentration hypothesis first mentioned has very powerful evidence in its 

 favor. 



' Lenard, Wicd. Ann. xlvi, pp. S95-S96, 1892, " Elcktricital der Wasserfiille." 



93 



