334 



T. V. Shcherbakova 



where B^ and B^ are the vahies of the brightness of the white and dark 

 backgrounds in air; 

 B^. and B^, are the values of the brightness of the white and dark 

 oroimrls in a turbid medium. 



100 



K 10 



)/-= I- 01 



y- 1-02 



^=1-07 



1-20 



h, cm 



Fig, 5. Dependence of loss of contrast on the thickness of the layer of suspension, 

 the specific gravity y of the suspension, and the wavelength X of the light. 



To determine the reduction in degree of contrast in drilhng fluid, coefficients- 

 of loss of contrast were determined for layers of clay suspension of various 

 thickness. Determinations were made with an FM-2 photometer in the 

 following manner. 



With the aid of the photometer the brightness of the white ground (a sheet 

 of white paper) B^^, and B^ in the presence of a layer of clay suspension 

 and without it was compared in turn with the brightness of the dark ground 

 (black paper) B^. and 5^ with and without a layer of clay suspension in 

 front of it. In each of these cases the brightness of the white and dark grounds 

 was obtained in units of light flux from a standard, for which a baryta disk 

 (reflection coefficient 91 per cent) was used. 



