ABSORBING POWER AND FLUORESCENCE OF RESORUFIN. 



29 



To test this law the coefficient of absorption, /3, was calculated from 

 observations taken with cells of different inside thickness, the measurements 

 of these cells being made with great care. 



The larger cell was measured with micrometer calipers. Thickness of 

 glass = a, fi (Fig. 24). Outside thickness of that part of the cell used for 

 transmission = C. Inside thickness = T. 



T = C (a+jS) = 2.o5 cm. 



In the case of small cell (Fig. 25), calipers could not be used to measure 

 the thickness of glass. The cell was placed under a traveling microscope 

 to measure the average inside thickness of the top. The outside thickness 

 at the points indicated in the figure was measured with calipers. 



T=T'-\-(n m) = i.oj5 cm. 



It was assumed that the thickness of glass from top to bottom of cell re- 

 mained constant, since broken pieces of the same glass varied not more than 

 0.01 mm. 



To determine the transmission, the cell containing the resorufin was 

 placed in front of slit D (Fig. 22), care being taken that no direct light 

 from S should strike the cell, and light from the block of magnesium car- 



Fig. 24. Fig. 25. 



bonate, in front of slit D (not shown in the figure), was transmitted through 

 it. The reading of C was taken to get the relative intensity, /, of the light 

 transmitted for different wave-lengths. After each observation the cell 

 containing resorufin was removed and an identical one filled with absolute 

 alcohol put in its place. The reading of C in this case gave the intensity of 

 the incident light before absorption, I . From these observed values of 7~o 

 and /, together with the thickness of the absorbing layer, the coefficient 

 of absorption was computed. If the loss by reflection may be regarded as 

 the same for the cell containing resorufin as for that filled with alcohol and 

 the difference must be extremely small it will be seen that the influence of 

 reflection is to introduce a factor, 1 R, in the case of both settings, and that 

 this factor will disappear when the ratio is taken. 



As a check upon these results a different method of observation was 

 used. Keeping D (Fig. 22) constant, the reading C\ was taken for the 

 light alone. A reading of Ci was then taken with alcohol in front of C and 

 resorufin in front of D. 



Q 



= Incident light (7 ) 



C2 

 D 



= Transmitted light (/) 



