122 VAPOR NUCLEI AND IONS. 



other things being equal. On the other hand, media of alcohol and water 

 require smaller exhaustion to precipitate an alcohol fog in corresponding 

 degree. The general character of the phenomena in all these several 

 cases are, however, the same. Their relation to each other when the 

 media are energized in like manner by the X-rays is also the same. 

 (Cf. fig. 56.) 



It does not follow, therefore, that wet coercible gases like carbon 

 dioxide and coal gas contain larger colloidal nuclei than wet air. The 

 apparent result would be quite the reverse of this. Neither can the 

 difference be explained in terms of the respective value of the ratio 

 of specific heats (y) ; for in relation to condensation, the order is air, coal 

 gas, carbon dioxide; in relation to y, air, carbon dioxide, coal gas. The 

 probable occurrence of large colloidal nuclei in media of alcohol and air 

 and relatively small colloidal nuclei in water and air seems to show that 

 the colloidal nuclei are primarily to be associated with the saturated 

 vapor, and that the gas involved is of secondary importance. It can 

 not be a question of mere solubility of gas in the vapor, for this is 

 strongest in water and carbon dioxide, in which there is no evidence of 

 large nuclei. The curves of distribution of number with size are again 

 such as to suggest a common law of equilibrium. 



The presence of strong odors (camphor, naphthalene, turpentine, etc.) 

 in the fog chamber is without an appreciable effect. Hence the col- 

 loidal nuclei can not be large molecules merely, and colloidal nuclei can 

 not be ascribed to chemical impurities in the gas. 



Continued slow exhaustion seems to be favorable to the growth of 

 fog particles and the formation of rain. 



Both for the energized and for the non-energized state, the graphs 

 for the same media, though referring to nuclei of widely differing sizes 

 (ions, colloidal nuclei), again terminate in the same asymptote, or end 

 in the same terminal corona. This is not identical for different media, 

 however, the corona being of lower order though denser for alcohol 

 and air, of higher order but thinner for water and air, for instance. The 

 number of nuclei caught {cat. par) in alcohol and air is much larger than 

 in water and air. When the limiting number of nuclei has been reached 

 by condensation, the system is powerless (in a given apparatus) to con- 

 dense on a greater number of nuclei, be they relatively large like the 

 ions or small like the colloidal nuclei. 



