( 610 ) 



vvliicli are coiitiiincd down lo ()^()5 helow lli(M'ri(iciil teinpemtiire '). 

 It would be very desirable (o investigate inorc (dosely in liow far the 

 disturbances mentioned sub c are eonnected with a disturbance in 

 the equation of state, or must be ascribed to 8|)ecial circumstances 

 of those experiments themselves (such as the difticult\- to determine 

 the moment at which begin condensation occurs). 



§ 4. The disturbances mentioned in § 3 apparently j)oint to the 

 fact that the substance in the neighbourhood of the critical point 

 occupies a smaller volume than would be expected according to the 

 special undisturbed ecpiation of state. In (Jomm. N". 88 p. 555 the 

 possibility is mentioned that these disturbances are connected with 

 ditferences of density which occur in the substance near the critical 

 state, as it is indicated by the mist (the blue opalescence) in the neigh- 

 bourhood of that state. The question was left aside whether those 

 differences of density are to be interpreted either as condensations 

 round condensation centres with an existence of their own (dust 

 according to Konowalow -), electrically charged particles "') a third 

 phase separated m small drops and for the greater part consisting 

 of an admixture), or sim|>ly as si)ontaneously formed ditferences of 

 density, either as accidental aggregations caused by molecular motion 

 and governed by the statistic equilibrium (Smoluchowski '), or because 

 small drops still have a })Ositive surface tension at temperatures 

 at which larger drops are no longer stable (Donnan ^). 



Whatever may be the cause of the blue mist, in all cases we may 

 expect a close relation between the compressibility and the occur- 

 rence of it. In order to form a better judgment about this matter 

 it was considered to be desirable to start an investigation of the 

 conditions of existence of this mist in a substance consisting of one 

 component in the neighbourhood of the critical point liquid-gas. For 

 an (►ptical research of these conditions of existence we refer to the 

 next communication. 



•) Nor can a similar disturbance be derived with certainly from Brinkman's 

 observations of carbon dioxide and methyl chloride, which observations, however, 

 are not continued so near to the critical point as those of comm. W. 88. 



^) D. Konowalow. Ann. d. Phys. (4) 10 (1903) p. 360. 



'^) Owing lo the highly penetrating radiation from the radio-active portions of 

 Ihe crust of the earth (Eve, Phil. Mag. (6) 12 (1906) p. 189) in the atmosphere 

 (Strong, Physik. ZS. 9 (1908) p. 170), or in the surroundings of the building 

 where the experiments are made, these particles would always be present to 

 almost the same amount. In the mean time it follows from the experiment of 

 FKiEDi-aNDER ZS physik. Ghem. 38 (1901) p. 385, on the stabiUty of the mist in 

 an electric field, that the particles which cause the opalescence are not charged. 



*) M V. S.MOLACHowsKi, Ann. d. Phys. (4) 25 (1908) p. 205. 



») F. G. DoNNAN. Ghem. News 90 (1904) p. 139. 



