( 622 ) 



c. If would be of interest to investigate whether for a single 

 substance in the neighbourhood of the, critical point an increase of 

 viscosity is found as has been noted by Ostwald ^) for a liquid 

 mixture in the neighbourhood of the critical point of separation 

 from measurements of Stebutt, and has been further determined 

 by Friedlander (see p. 611). Perhaps the increase of the viscosity 

 and the size of the light-scattering particles (§ 1) might be brought 

 into relation, and so also the colour of the scattered light. 



d. We could not ascertain an influence of RöNTOEN-rays on 

 the blue mist in ethylene. An investigation might be made as to 

 whether the «-rays or the emanation of radium exert an influence 

 on the mist. 



e. FtJCHTBAUER ^) investigated a mixture of iso-butyric acid and 

 water in the neighbourhood of the critical point of separation ultra- 

 microscopically ; he did not succeed in dissolving the cone of light. 

 Nor could we ascertain ^) the presence of separate light-scattering 

 particles in the mist for a mixture of amylene-aniline with the 



objective Homog. Imm. — , eye-piece 4, condenser AA (Zeiss) and 



1 Ci 



as source of light an electric arc lamp (30 Ampère) or solar light 

 (10 Dec. '07), We consider a repetition of this experiment with 

 more intense solar light and with more precautions taken to keep 

 the temperature of the mixture that is ultramicroscopically examined, 



particles per cM^, Au deviation from the average refractive index ^ ), and if we 

 express Au in terms of the deviation in density according to Lorentz-Lorenz, and 



if according to Smoluchowski we write 1~ = — " / „{bp\ (r = number of 



vv. 



Uy/o 



molecules in the light-scattering particle), in which ( ^- 1 for Vq = xh can be 



developed as -^^\^M{T-Tk) (Suppl. W. 6, May '03), we find at T-Tk = OJö 



for ethylene SD = 0.00075. 



Although our measurement is but preliminary, it leads us to conclude that, at 

 least as far as the order of magnitude is concerned, the intensity of the light 

 scattered by the blue mist in a single substance in the neighbourhood of the 

 critical state agrees with the hypothesis of Smoluchowski, that light is due to 

 differences in density caused by molecular motion and governed by statistical equi- 

 librium. [Note added in the English translation]. 



1) W. Ostwald. Lehrbuch der allgemeinen Chemie 11 2 (2te Aufl. p. 684). 



2) Ghr. Füchtbauer, Zeitschr. physik. Ghem. 48 (1904) p. 552. 



^) We express our hearty thanks to Prof. M. de Haas of -Delft for his kindness 

 to lend us his ultramicroscopic apparatus. 



