332 



T. V. Shcherbakova 



300 



500 



\ 



700 



900 



IIOO 



Fig. 3. Dependence of attenuation of light, for light and dark driUing fluid, on the 

 thickness h of the layer of fluid and the wavelength A of the light. 



prepared from light and dark clays is apparently associated with the fact 

 that the particles of the two clays have different reflection coefficients. 



The values for the light transmittance shown in Figs. 1-3 were obtained 

 for the case when the angle 99 between the principal optical axis of the 

 photometer and the direction of the light beam was equal to zero. Scattering 

 of light at angles 99 differing from zero was investigated by Timofeeva on 

 particles from 3 to 20 /^ in milk solutions of low concentration and in rosin 

 suspensions (^). Figure 4 shows the curves obtained by Timofeeva for the 

 ratio of the intensity / of the light passing through the layer of suspension 

 to the intensity I^ of the light in air (i.e. values of the transmittance of the 

 hght) as a function of the thickness of the layer of suspension for various 9?. 

 As can be seen, for 99 = and at not very large layer thickness h the value 

 of the transmittance decreases according to an exponential law, i.e. just as 

 in the analogous case for a clay suspension. At angles 99 differing from zero 

 the value of the transmittance varies according to another law. In this case 

 for small h values of ///q are considerably less than for 99 = 0; the curve 

 has a maximum which is particularly sharply defined for 99 = 30 — 60°. 



It should be noted that in clay suspensions attenuation of the light with 

 change of wavelength is observed to a much smaller extent than in the 

 usual turbid media with small particle dimensions, in which attenuation 

 according to the Rayleigh law is inversely proportional to the fourth power 

 of the wavelength of the light (*>. Thus, in a clay suspension no significant 



