OPTICAL METHODS OF BORE-HOLE INVESTIGATION 329 



of different dimensions — from fractions of a micron to tenths of a millimetre 

 witli particles from 0.1 to 10 m/< being most freqnently encountered. 



Clay suspensions are classed as very turbid media. When light passes 

 through such a medium it is \\eakencd, mainly because of scattering and to 

 a negligible extent because of absorption. In this connection the attenuation 

 of a light iDeam by the clay suspension layers of various thickness was deter- 

 mined. 



Measurements were conducted on an CF-4 specrophotometer and consisted 

 of the following. An empty cylinder was placed in the path of the light 

 beam coming from the monochromator and the light intensity was noted. 

 Then in the path of the beam, in place of the empty cylinder, was placed 

 a cylinder with a layer of clay suspension of the required thickness, and 

 the width of the slit limiting the light beam was adjusted so that the light 

 intensity Avas the same as in the first case. The ratio of the slit width iii the 

 absence of the clay suspension to the slit width in the presence of the layer 

 of suspension, equal to the ratio of the strength of the light beam in air to 

 the light beam which has passed through the suspension, gives the quantity T 

 called tlie transmittance (a quantity the inverse of attenuation). The transmit - 

 tance is usually expressed in per cent. 



To obtain a layer of clay suspension of the necessary thickness (from 

 0.03 to 1 mm) cylinders from 4.03 to 5 mm in length were chosen. Part 

 of the cylinder was filled with a quartz plug of length 4 mm and the rest 

 with clay suspension forming the thin layer. 



Measurements were carried out with reference to an incandescent lamp 

 used in the spectrophotometer, and possessing wavelengths from 320 to 

 1100 m/Lt. The wavelength ■was determined from the position of the mono- 

 chromator prism. To improve the monochromatism there were fitted 

 filters of UFS glass for wavelengths of 300-400 ra/j,, and of OS-19 glass 

 for wavelengths of 600-1100 m//. 



Clay suspensions of different specific gravity {y — 1.2 — 1.02), obtained 

 by means of diluting the initial clay suspensions, were subjected to the 

 investigation. 



The investigations ^vere mainly carried out with clay suspensions prepared 

 from dark Buguruslanskian clay Avith the addition of 1 per cent NaoCOg*. 

 Data for this svispension are: viscosity 30 sec; specific gravity 1.2; water 

 yield 9 cm^; thickness of the crust 3 mm. The fractional composition of the 

 clay suspension is given in Table 1. 



* The sample of clay suspension was given by the clay suspensions laboratory of the- 

 Gubkin Moscow Petroleum Institute. 



