NUCLEI IN WET C0 2 . 109 



like nuclei this would imply the same degree of supersaturation. Hence, 

 if p t and p 2 be the vapor pressures of water before (20 C.) and after 

 exhaustion, and p = "j6 and p-dp be the corresponding pressures, the 

 occurrence of like supersaturation implies that 



Pi / P-P2- sp y = Pi / p-p 2 -dp' \ 7 ' 



p2^ P-Pi ' Pz^ P-Pi ' 

 where p 1 and y refer to C0 2 and where y is the heat ratio for air. Hence 



y ^ log (1 -(dp' + p 2 )/p) -log (1 -pjp) 

 y' log (1 - (dp +p 2 )/p) -log (1 -pjp)' 



y 



where the value for ^ = 1.10 as derived for direct experiment. 



To compute the value of the same ratio from the coronal experiment 

 it is necessary to know p 2 the vapor pressure on exhaustion and before 

 condensation ensues. This datum is unavailable, but it must be greater 

 than o and less than would correspond to the decidedly lower exhaustion 

 dp = 17 (for instance) than the one applied (dp = 28). Hence limits of 



the value of ~ may be computed by inserting p 2 = o and p 2 = o.2 respect- 



y 



lvely. The results are = 1.28, both for the superior and inferior limits, 



as would be otherwise evident. 



One may summarize these results as follows: Either the heat ratio of 

 carbonic acid, y', decreases in comparison with that of air, y, very rapidly 



y 



as temperature decreases, so that an average value of , = 1.3 instead 



y . . . . 



of = 1.1 is to be used in the preceding experiments; or the colloidal 



nuclei in wet C0 2 , though distributed in a way closely recalling the case 

 of air, are throughout smaller. 



71. Nucleation increases subject to a uniform law of equilibrium. The 



most interesting feature of the data for C0 2 is their repetition (under 

 higher exhaustion) of the behavior of air. In other words, the two curves 

 are closely parallel throughout their extent. This seems to imply that 

 both are primarily dependent, not on supersaturation or cooling or on 

 volume expansion, but on a common law of distribution of number with 

 size of aggregates, such as is given by the theory of dissociation. In 

 other words, a given drop of pressure of sufficient rapidity and from a 

 specific initial value in each case generates the same number of colloidal 

 nuclei, though it does not follow that the apparatus in all cases can 

 entrap them. This is even true in different apparatus of different degrees 

 of efficiency, as shown elsewhere. 



