266 Dr. C. Barus on Spontaneous Nucleation and 



fused together would be undesirable for practical reasons. 

 To avoid these dilemmas experiments may be made with 

 water, in which the difficulties mentioned do not occur, and 

 a definite decision may be reached. 



Water.-, — If all precautions be taken to insure clean and 

 new apparatus and appurtenances and perfect filtration, the 

 air above the water, if free from nuclei, remains so inde- 

 finitely. Spontaneous nucleation does not occur. 



If a clean vessel free from nuclei is vigorously shaken so as 

 to comminute the water, nuclei are produced in considerable 

 quantity, as is evidenced by the strong coronas seen on ex- 

 haustion. But these coronas are short-lived, as shown by the 

 following table : — 



Time elapsed after shaking. Corona. 



All but absent. 



t 



mm, 



6 



» 



5 



>> 



3 



V 



2 



."> 



1 



V 



i 





•2 



V 



Ni 



3ne 



Faint corona, not measurable. Rain. 

 Corona, aperture, s=l 0, 45. 

 Strong corona lasting- 15 seconds. 



These nuclei are obviously water globules, which speedily 

 evaporate or subside, vanishing in a few minutes. 



Let a small quantity of sodic carbonate be added to the 

 water ; the result is a phenomenal increase in the persistence 

 of the nuclei produced by shaking, as for instance : 



Time elapsed after shaking. Corona. 



1 hour. Strong. s=l°'4 



2 „ „ 5 =l°-6 



3 „ „ s=0°-9 

 15 „ Just visible. 



15 „ Absent. 



15 „ (violent shaking.) Distinct, clear, small. 



The size and persistence depends on the violence of shaking, 

 the apertures varying from s = l°*4 to s = 2 o, correspondingly. 

 In the lapse of time the corona contracts, but may, in favor- 

 able cases, be seen much after 15 hours. 



The body in solution in this case is solid, and one is liable 

 to conclude that the nucleus in question is the solid residue 

 left after evaporation. This, as will presently be shown, is 

 not necessarily true ; the nucleus is liquid, being a more or 

 less concentrated solution both here and in the above ex- 

 periments with hydrocarbons, &c. 



To decide the question as to the cause of the indefinite 

 persistence of the nuclei produced by shaking solutions (apart 



