URINE 



509 



the same optical field and with a degree of accuracy of about i per 

 cent. The later type of the Duboscq colorimeter with cylinders instead 

 of prisms movable is to be preferred, particularly as this type may be 

 readily adapted to the comparison of cloudy solutions or suspensions, 

 the instrument thus modified being called a nephelometer (see Fig. 94, 

 page 295). In this later form of colorimeter the depths of the colored 

 solutions through which the light passes are regulated by raising or 

 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 color 



FIG. 161. BOCK BEN-EDICT COLORIMETER ILLUSTRATIONS FROM MYERS. "PRACTICAL 

 CHEMICAL ANALYSIS OP BLOOD,"* ST. Louis, 1921. 



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 color 

 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. Among these are the Kriise 

 model of the Duboscq, the Hellige, the Bock-Benedict and the Kober. 

 A simple colorimeter, costing only about one dollar, has been devised 

 and used with considerable success by Peebles and Lewis. 1 It is 

 claimed to compare favorably in accuracy with other colorimeters and 

 to be applicable to clinical and student use. A relatively cheap 

 although accurate colorimeter has been developed by Bock and Bene- 

 dict 2 in which the place of costly prisms is taken by mirrors (See Fig. 

 161). Kober has devised a combined colorimeter and nephelometer 



1 Peebles and Le\ns: /. Am. Ifed. Ass'n., 70, 679, 1918. 



* Bock and Benedict: Jour. Biol. Chem., 33, xix, 1918; 35, 227, 1918. 



