APPENDIX. 



COLORIMETERS. 



A high grade colorimeter is a necessary adjunct of a Biochemical Labora- 

 tory, a number of important analyses being made by its use. 



Fig. 52. Duboscq's Colorimeter. 

 Inset shows construction of vernier scale. 



The best known instrument is that of Duboscq, which is shewn in fig. 52. 

 The standard solution is placed in one of the cups, B, and the unknown solution 

 in the other cup. The plungers, D, are either cylindrical hollow cups, closed 

 at the bottom, or, preferably, are made of a solid piece of optically clear glass. 

 They can be moved up and down by turning the screw E, which works on a 

 rack and pinion. The height of the bottom of the plungers from the bottom 

 of the cups, that is the depth of the solution used, can be read by means of a 

 scale and vernier at the back of the instrument. The standard is set at a given 

 height (say 15 mm.) and the height of the other plunger adjusted until exact 

 equality of tint is obtained. The light is reflected through the solutions from 

 A, which is either a mirror or a piece of opal glass. After passing through 

 the layers of the fluids on the two sides the light falls on to the prisms shewn 

 in K of fig. 53. These prisms are contained in the case marked J in fig. 52. 

 The light then passes through the eye piece as shewn. 



