318 T. V. Shcherbakova 



voltage on the grid of one of the triodes. A 300 [aK microammeter (MKA) is 

 connected across the measuring diagonal of the bridge. The switch P per- 

 mits selection of one of three values for the amplification factor of the ampli- 

 fier — 1100, 5500 and 27,500 (positions 1,2 and 3 respectively). 



The power unit contains sources of supply for the photomultiplier and 

 the amplifier. A voltage of 725 V, obtained from a twin rectifier assembled 

 about the two valves L^ and L^ (type 2Ts2S), is used for the photomultiplier 

 supply. The voltage is stabilized by an electronic stabilizer assembled about 

 the 6P6S valve L-^^- The comparatively low supply voltage for the photo- 

 multiplier is chosen with the object of obtaining a low value for the intensity 

 of the dark current (of the order 10~^°A). 



The supply to the anode circuits of the direct -current amplifier is obtained 

 from a rectifier, assembled as a full-wave rectification circuit about the 

 5Ts4S valve L^. 



Just before the measurement, with a completely darkened photomultiplier, 

 the current intensity in the anode circuit of the right-hand half of the 6N8S 

 valve is adjusted by means of the rheostats iJgg and R^^ so that the measur- 

 ing instrument indicates zero. If light falls on the cathode of the photo- 

 multiplier, the balance of the bridge is upset and a current begins to flow 

 through the MKA instrument. The instrument readings /„ will be propor- 

 tional to the intensity of the luminescent radiation reaching the cathode of 

 the photomultiplier. 



In order to ensure that it is possible to compare the readings obtained at 

 different times for different settings of the instrument, with the readings 

 /„ due to luminescent radiation from the sample of petroleum under inves- 

 tigation, the readings /^ from a standard are determined. The standard 

 used is a mixture of luminophors giving out a bluish -white light. The ratio 



— ^ is taken as the quantity defining the relative intensity of the luminescent 



radiation. 



By putting into the light path a filter transmitting a narrow region of the 

 visible spectrum (in the range 420-640 m/^), it is possible to determine the 

 intensity of the radiation in any part of the spectrum. Thus, by using a green 



filter, it is possible to measure the relative intensity —of the green light 



{X = 530 vafi) in the luininescent radiation. 



By means of a set of filters the complete spectral characteristics of the 

 radiation (the dependence of intensity of the radiation on wave length) 

 from the sample under investigation can be obtained. 



When using light filters, tlie absorption coefficient of the filter must be 



