486 



PHYSIOLOGICAL CHEMISTRY 



solutions through which the light passes are regulated by raising 01 

 lowering the cups and are accurately indicated in millimeters on a 

 vernier scale at the back of the instrument. The standard solution is 

 placed at any convenient depth and the color of the solution to be ex- 

 amined is matched with it by raising or lowering cups. When the coloi 

 is of the same intensity as the standard the depth of the solution is 

 read. The amounts of the colored substance in solution are inversely 

 proportional to the depths of the columns of fluid. Thus if the standard 

 is set at 10 mm. and the solution under examination has the same coloi 



FIG. 153. DUBOSCQ COLORIMETER. 



density at 20 mm. the latter has just one-half the concentration of the 

 standard. 



A large number of other colorimeters have been devised and 

 may be used in place of the Duboscq. Most of these though less ex- 

 pensive than this instrument are also less accurate. The Hellige 

 colorimeter has been recommended, particularly for clinical de- 

 terminations by Myers and Fine. 1 Kober has devised a combined 

 colorimeter and nephelometer which may be obtained in this country 

 (see page 293). For merely approximate determinations the color 



1 Myers and Fine: Post-graduate, 1914-1915. 



