104 CONDENSATION OF VAPOR AS INDUCED BY NUCLEI AND IONS. 



the remainder having been dissipated during the first evaporation. This 

 agrees with the above results. The loss of nuclei in the lapse of time is 

 thereafter relatively slow, not more than one-half vanishing in the 

 ensuing 10 minutes. From the nature of the experiments it is idle to 

 endeavor to make out a numerical value for the rates, but they are of 

 the value of those obtained on shaking very dilute solutions, for instance. 

 Under the influence of radium, about the same number of water 

 nuclei occur after 10 minutes, no matter whether the initial dp 3 is 26.7 

 or 22.6. Temperature corrections would not modify the conclusions 

 drawn. When the fog is precipitated under the same exhaustions with 

 identically initial coronas (this is possible because the vapor nuclei are 

 efficient in the presence of the ions), on either ions or vapor nuclei, the 

 persistence of the water nuclei obtained on identical evaporation is 

 about the same. From this one may argue that the water nuclei which 

 persist, cat. par., are roughly independent of the nature of the original 

 nuclei. Finally in fig. 32, b, the persistence of water nuclei in successive 

 exhaustions is shown for comparison, the data being anticipated from 

 the next section. Water nuclei precipitated on ions vanish much more 

 rapidly than for the corresponding case of phosphorus nuclei. 



64. Summary. Fogs when characterized by identical initial coronas 

 evaporate naturally, or under compression, to about the same number of 

 residual water nuclei, no matter whether the precipitation takes place 

 on ions or on vapor nuclei. The method, however, is rough. In the most 

 favorable cases about one-half of the original number of ions are repre- 

 sented by the residual number of water nuclei. If the drop of pressure is 

 continually decreased the number of residual water nuclei caught 

 decreases with the pressure, rapidly below dp/p o.i to 0.2. In view 

 of the small amount of water precipitated and of the extremely filmy 

 coronas obtained as a consequence, measurement is difficult. There is a 

 lower limit to which the drop of pressure may be reduced unless a huge 

 fog chamber is constructed specially for these experiments. For small 

 exhaustions, coronas are liable to remain of the same type even though 

 dp /p decreases over wide ranges. 



The persistence of residual water nuclei is not appreciably different 

 when this precipitation of fog particles to be evaporated takes place on 

 ions or on water nuclei. It is, however, enormously different, cast, par., 

 from the case of phosphorus nuclei. It appears that this difference is 

 not of the nature of a time loss, but of a true evaporation loss. When 

 water nuclei are obtained from fog particles precipitated upon ions or 

 upon vapor nuclei, the chief loss of water nuclei accompanies each 

 evaporation of the fog particles, and over one-half of the total number 

 of ions may fail of representation in the number the nuclei present after 

 the first evaporation. This incidental observation will be systemat- 

 ically considered in the next section. 



