on Nuclei produced by Shaking Solutions. 265 



of the air above. The following are typical data ; s is the 

 aperture * : — 



Time of Diffu- 



15 rnin. 



30 min. 



60 min. 



2h. 40 min. 



3h. 



6h. ! 



sion, upward. 

 Corona 



Film, 5 cm. 

 high. 



Partial, 

 faint. 



Full, faint, 

 diffuse. 



Strong, 

 s=l°-8. 



Strong, 

 s=2°'25. 



Strong i 

 s=3°-4. j 



15 h. 



Intense. 



6 = 3°'l. 



If the evaporation is accelerated, after shaking, as in a warm 

 bright room, the saturated condition may be reached in two 

 hours or less. Usually the coronas of the first hour, though 

 full, are too faint for measurement. On successive exhaustions, 

 the intense coronas vanish by passing through three-quarter, 

 half, quarter coronas, &c, in turn. 



Persistent Liquid Nuclei. 



Hydrocarbons, Sfc. — Nuclei obtained by vigorously shaking- 

 all the volatile liquids examined above, showed no tendency 

 to vanish until removed by gravity. I will cite special 

 instances at random bearing on this remarkable behaviour. 

 Coronas produced by precipitating gasoline vapour on the 

 nuclei produced by shaking the liquid, were observed with 

 undiminished strength 7 minutes and 30 minutes after shaking, 

 and might have been seen after an indefinitely longer time. 

 The average apertures were s = l°'4, corresponding to the 

 diameter of particle ^ = '0029 centim. In petroleum the 

 coronas were observed strongly an hour after shaking; in 

 benzol similarly intense 5 min., 30 min., 44 min., and 60 min. 

 after shaking ; they were distinct 3 hours after but absent 

 next day, about 15 hours after. In carbon bisulphide the 

 coronas due to shaken nuclei coalesce with the coronas due to 

 spontaneous nuclei, so that they persist indefinitely. 



From the excessively volatile character of these liquids 

 persistence, even beyond a few minutes, would be impossible 

 if the liquids were quite pure. For the small drops would 

 evaporate and the large drops subside. Consequently the 

 droplets must be solutions obtained by concentrating the 

 impurities throughout the continued evaporation of the liquid 

 by the addition of nuclei, &c. It is difficult to keep these 

 liquids quite pure in an apparatus of which rubber tubing f 

 is an essential part. Apparatus made entirely of glass parts 



* Source of light and goniometer are on opposite sides of the receiver, 

 each 2*5 metres distant. The aperture s subtends the central white disk 

 of the normal corona. If d is the diameter of particle, d— "00144/5 centim. 

 nearly. 



t Rubber tubing- through which carbon bisulphide has been passed 

 will furnish nuclei to precipitate water vapour for days after. Fresh 

 tubing must therefore be provided for each new experiment. 



