13'J THE 8TKU0TIIRK OF TUE NUCLEUS. 



If, as I interpret it, the loss of mielei in the lapse of time is due to absoiptioii 

 .it tlie soliil Willis (if the sjtherieal receiver, one may write foi- the al)Sorption ve- 

 locity, /•, the etinatiun k= — (R/'^n) (iln/dt), meaning that hii molecules are ab- 

 sorlied per stpiare centim. per second. Coniputini: I- in this way (essentially as a 

 logarithmic rate), one finds from all the saline solutions .-m important general 

 result: for the case of solutions of a few per cent (1 to 3), h is of the order 

 of .(t3 to .07 cm/min., though varying from solute to solute; for the .01 per 

 cent solutions, h is of the mean order of .08 cni/min. ; for the .0001 i>er cent solu- 

 tions, h is of the order of altout 1 to 2 cm/min. For oidinary distilled water 

 in glass vessels, k may reach over ."> cm/min., etc. Specific data are given in 

 table 24. Similar deductions may be made for the organic solvents (^Cf. Chapter 



\'l, cj r.»). 



It follows, therefore, in general, that not only does the number of nuclei pro- 

 duced b\ shaking {cuf. par.), increase with the concentration of the dilute .solution, 

 liut the apparent rate of decay diminishes, /. e., their jibsorption velocity decreases 

 with the strength of the .solution. I-'oi' ordinary distilled water, these velocities, 

 /'/ rrterred to tliri-e dimen-^ions, arc already beginning to approach the ionic veloci- 

 ties. Again, as the number of nuclei, //, is greater, they vanish more slowly, .so that 

 an a|)parent decay decreasing with the density of the nucleation is out of the <pies- 

 tion. The whole, therefore, constitutes an entirely new atid .sfiiking confirmation 

 of the isolated point of view taken throughout my woik.' 



44. Tlie iliennodyuainlc hypotlu^ix. — The inference is therefore tenable that 

 tiic nuclei shaken out of stronger solutions are larger. These nuclei are produced 

 by eva|H>iation from a larger iliametei', for the very dilute solutions must become 

 more concentrated, and it follows that the dimensions at which evaporation ceases 

 at the surface of a particle are larger for stronger than for weaker dilute solutions. 

 Naturally, a given degree of concentration is reached in a larger globule in the 

 former case as compared with the latter. The theory for the production of nuclei 

 here in question is thus at hand. A particle of absolutely pure water, }U'oduced by 

 shaking, will either vanish by complete evaporation, or it will grow and eventually 

 vanish by subsidence. If, however, the evai)orating globule is a solution, the in- 

 crement of vajior pi'essure at a surface of increasing convexity will gi'adually be 

 compen.sated by the decrement of v.-ipoi- picssnre due to the incicasing concentra- 

 tion of the solution. Hence, there must be a critical diameter at which the in- 

 creased vapor pressure due to surface tension just countei'l)alaiu'es the decreased 

 vapor pressure due to concentration. This is the stable diameter of the nucleus. 

 A smaller particle will grow because the concentration effect supervenes ; a larger 

 particle will evaporate because the effect of surface tension supervenes. 



In connection with tlie critical diameter, a critical density is also implied, 

 which varies naturally with the iliametei-. Thus, in the more concentrated solu- 

 tions, a lower density and larger diameter must occur than in the corresponding 

 case of staliility in the weaker solutions. If the particle is so small before evapo- 

 ration that, compatibly with the given supersaturation (pressure decrement), the 



' Cf. Experinifnts with Ionized Air, these contributions, y. 92, 1891. 



