PERSISTENCE AFTER SOLUTION. 



= 23 cm. in the cylindrical apparatus) decidedly above the fog limit, 

 so that a corona of appreciable size may appear. If this is dispelled 

 on admission of filtered air by evaporation, the second corona may be 

 obtained at a pressure difference (8/ = 2i cm. in the table) below the 

 fog limit, showing that large nuclei have been produced by evapora- 

 tion. In the data of table 38, or in curves 61 , 62, different intervals of 

 waiting are tested, these intervals referring to the time elapsed (i to 

 10 minutes) between the evaporation of the first corona and the con- 

 densation of the second. After 3 minutes about 25 per cent of the 

 nuclei persist and require smaller exhaustions to induce condensation 

 than the original nuclei. After 10 minutes about 5 per cent are left 

 (curve 60), though a greater number of observations are here desirable. 

 It should be noticed that without the preliminary condensation no con- 

 densation whatever would take place at the lower pressure difference. 



TABLE 38. Persistence in solution. Air nuclei. Fog chamber glass cylinder. 



23.2; 5/1 = 21.4. 



= always tested. 



\ Sufficient for complete subsidence. 



51. Occurrence Of water nuclei. An explanation of the phenomena 

 of the preceding paragraphs is not far to seek. Clearly the ions or 

 fleeting nuclei go into solution, and the result on reevaporation of the 

 fog particles is a solutional or water nucleus. Such a nucleus is ob- 

 viously larger than the original nucleus or ion which furnishes the 

 solute. Hence the condensation in the succeeding exhaustion must 

 first take place on these residual nuclei, and they are therefore apt to 

 capture all the available water. What makes the water nucleus stable 

 is either the solute, by which the vapor pressure is reduced on con- 

 tinued evaporation to a degree equal to the excess of vapor pressure 

 due to curvature, or possibly electrical potential may have a corre- 

 sponding effect. 



