Spectrophotometric Analysis 



55 



solvent only; a photometer for adjusting the relative intensity of 

 the two beams; a spectrometer with prism and eye piece arranged 

 so that portions of the spectra of the light from the two beams are 

 observed juxtaposed in the field of the eye piece. The spectrum 

 of the beam which has passed through the dye solution will be 

 found deficient in those portions which have been absorbed by the 

 dye, and the degree of the deficiency at any position in the spec- 

 trum may be measured by determining the degree to which the 

 intensity of the light of the second spectrum must be reduced in 



TABLE 2 



RELATIONS BETWEEN THE SYMBOLS AND UNITS AND DEFINITIONS OF THE TERMS* 



I = lo- 10-kcd. 



Ix)gio lo/I = kcd = E. 



*For further discussion of this subject consult Erode (1943), Gibb (1942). 



order to obtain an equal intensity in the two fields observed by the 

 eve. 



The shutter of the eyepiece may be partially closed so that only 

 a narrow spectral range is visible ; this allows the eye to concentrate 

 on the matching of two small fields, each of which appears uniform 

 in color. The instrument is provided with a screw drum, calibrated 

 in wave lengths, by means of which the prism may be rotated in 

 such a manner as to bring light of any desired wave length into 

 the center of the field of vision. 



