on Isuclei produced by Shaking Solutions. 263 



in this conche that the nuclei which subsequently diffuse * 

 into and fill the whole vessel originate. They do not come 

 out o£ the benzol. 



To account for these couches, which occur more or less 

 frequently with all hydrocarbons and other volatile liquids, 

 it is necessary to consider the manner in which the nuclei are 

 introduced into the receiver. This is done expeditiously by 

 partially exhausting the receiver and allowing the inflowing' 

 air to pass over phosphorus, or glowing charcoal, or near a 

 sulphur flame. In the case of water vapour the nuclei after 

 entrance remain permanently apart. The nucleated air is 

 always homogeneous and the coronas regular. Semi-coronas 

 never occur. This indefinite suspension of nuclei means that 

 they remain small, diffuse relatively fast, and gravitate very 

 slowly. The phenomenon is very similar to the suspension 

 of particles of clay in water. The speed of subsidence is a 

 minimum. 



In case of the hydrocarbons &c. the occurrences are very 

 different. What goes on while the nuclei are being introduced 

 is not of course visible ; but the first exhaustion after nucleation 

 shows a horizontally graded distribution, in which the nuclei 

 are wholly confined to a narrow stratum, usually imme- 

 diately above the liquid, as already stated. The fog stratum 

 may, however, show itself at the top of the vessel, or even 

 between two hemispheres of clear non-nucleated air. Indeed 

 the air is rarely, if ever, nucleated uniformly. 



The distribution, therefore, is one of density ; and from the 

 relatively insignificant number of nuclei, it may be further 

 supposed that to influence the density of the strata, the nuclei 

 have been loaded on influx, almost without supersaturation, 

 even though the fog particles are small enough to remain 

 invisible. In such a case it is hardly probable that the nuclei 

 have remained individualized as in the case of water vapour ; 

 it is more probable that they grow by coalescence or cohesion, 

 until they are large enough to condense hydrocarbon vapour 

 with the minimum of supersaturation or none at all. This 

 again is remarkably like the subsidence of clay in hydrocarbon 

 liquids, in which, from the cohesion of particles, the precipi- 

 tation is, relatively speaking, instantaneous. 



It is not necessary, however, to assume loading. If the 

 nucleus diffuses slowly enough in organic vapours to virtually 



* The rate of diffusion (roughly, "015 centim./sec, upward in benzol 

 vapour, for instance) is the feature of these experiments on which I 

 am now at work. Incidentally one may note that the " granular " particles 

 in water vapour should diffuse much more rapidly than the " flocculent " 

 particles in benzol vapour, the nuclei being otherwise the same. 



