TIIK STUUCTlJi:)': OK TlIK NUCLEUS. 157 



methyl alcohol (24), ethyl alcohol (23), aiiiyl alcohol (24), which leaves out of 

 account the high value of h for ethyl alcohol and does not adet^uately account for 

 watei-. Cf. § 20. 



1 9. Ooniparima of the present and earlier values of absorption and of diffusion 

 velocity. — It is finally interesting to resume the comparison of absorption velocities 

 begun in Chapter V, § 9. This is now easily feasible by consulting table 25 and § 

 43 of that chapter, and table 12 of the present chapter. An introductory reduction, 

 however, is needed, since in table 12 the velocity measured is at once the actual 

 velocity of the nucleus, whereas in the preceding chapters k was computed as if all 

 the nuclei travelled in a single direction. As they necessarily travel in all direc- 

 tions, a rough compensation may be temporarily made by multi[)lying h by 6, oi- 

 preferably by the probability factor, IQ/n- 



The following are the diffusion velocities, « , as found from widely different 

 experiments. From the preceding volume,' in which the velocities of phosphorus 

 nuclei in ordinary atmospheric air were studied both by mechanical methods 

 (steam jet and absoi-ptiou tubes), and by the electrical condenser methods, the mean 

 value of ^=18 cm/niin. may be taken. Hence « = 90 cm/miu., nearly. The 

 number of particles was of tlie order of 10* to 10^ per cub. cm. of air. 



In Chapters II and III, by a I'ough method of comparing coronas of different 

 orders, the value of h for phosphorus and other nuclei present in saturated water 

 vapoi- to the average extent of 10* per cub. cm., the value ^ = .1 cm/min. was 

 ascertained. This is equivalent to « = .5 cm/min. 



This datum may be compared with the diffusion velocities of table 12 of this 

 chapter, in which fresh phosphorus and other nuclei were used, densely distributed 

 and tested in a variety of vapoi-s, alcoholic, hydrocarbon, etc. The usual values of 

 diffusion velocity lie between « = .5 cm/min. and « := .9 cm/miu., being thus of the 

 order of the preceding case. Water vapor itself did not admit of measurement. 

 The value estimated from the Alimentary advance seen immediately after the nuclei 

 enter, « = 80 cm/min., agrees moi-e closely with the case for atmospheric air at the 

 beginning of the pai-agraph. There is much in the behavior of water which is left 

 unexplained. When the nuclei are first introduced into the mixture of air and 

 saturated water vapoi', the aii' contact does not seem to be negligible. 



Finally the experiments on the evanesence of the luiclei pimluced by shaking 

 solutions lead to a series of values of h as follows. A few hundred nuclei per cub. 

 cm. were usually present after shaking the solutions, and less than 50 (usually) 

 after shaking pure water. 



For the saline solutions of 1-3 %, n ~ .25 ; for solutions of .01 %, n = .40 ; for 

 solutions of .0001 %, n = 10. For pure water h = 25 or even 50. 



For aqueous solutions of solid neuti-al oi'ganic solutes of 1 to 3 %, n = 8 ; for 

 solutions of .01 %, k = 3. The acid organic solutes, like tartaric acid, seem to 

 behave quite differently. The solutions of this body of 2 %, .02 %, and .0002 %, 

 showed diffusion velocities of «= .1, .1, and 1.0, respectively, thus evidencing uni- 

 foi-mly greater persistence of nucleation than even the saline bodies. 

 ' Experiments zaith Ionized Air; Smithsonian Contributions, 1901. 



