on Nuclei 'produced by Shaking Solutions. 267 



from gravitation), it is necessary to test a chemically dissolved 

 gas like hydrochloric acid or ammonia. Pure water was 

 first taken and the evanescence of the nuclei (say within 4 

 minutes) confirmed. Pure hydrochloric acid was then added, 

 and the persistence of the nuclei established, as shown by the 

 following example : — 



Time elapsed after shaking dilute HC1. 





Corona. 



| min. 



Strong". 



a = l°-6o 



10 „ 



Strong-. 





30 „ 



tr. 





15 hours. 



Distinct. 



"Weak. 



Tested with pure water again, the fleeting coronas per- 

 sisted somewhat longer (vanished in 10 minutes) than 

 before, showing that traces of HC1 still lingered in the clean 

 apparatus. On again adding HC1 the above results were 

 confirmed. 



Dilute ammonia was next tested in the same way. Great 

 care had to be taken after the vessel was thoroughly cleaned 

 to remove lingering traces of HC1. When this was done air 

 free from nuclei remained so above dilute ammonia inde- 

 finitely. No nuclei arise spontaneously from the liquid. 



On shaking the ammonia nucleus behaved like the nucleus 

 of dilute hydrochloric acid, or of sodic carbonate solution, 

 showing indefinite persistence apart from removal by gravity. 



With these experiments the indefinite persistence of nuclei 

 produced by shaking solutions, whatever be the original state 

 of aggregation of the solute, may be considered established. 

 It is finally necessary to inquire into the reasons. 



Cause of Persistence. — Inasmuch as the nuclei are equally 

 persistent, no matter whether the solute is gaseous or whether 

 it is liquid or solid, it is not permissible to accentuate Uhe 

 possible occurrence of solid residues as the cause of per- 

 sistence. At first sight one would be liable to conclude that 

 the persistent nuclei are loose molecular aggregates ; but 

 their size, which probably embraces many thousands of mole- 

 cules, is unfavourable to such an assumption. They cannot 

 owe their condensational activity to ionization, for the effect 

 is equally marked with the most pronounced hydrocarbon 

 and other insulators. Frictional electricity seems equally 

 negligible ; it would not account for the difference of be- 

 haviour of pure water and solutions ; for the electric field 

 within the receiver is a closed field. 



The endeavour must therefore be made to explain the 

 phenomenon in terms of surface-tension. If p r and p w be 

 the vapour-pressures corresponding to radii r and oo , T the 



