Radiometric Measurements of Constants of Indicators. 



51 



should agree with each other very closely for all wave-lengths of light 

 if the cells are optically identical. Having made sure that the cells 

 are optically identical, they were heavily plated with gold to remove 

 any possibility of the solutions attacking the metals of the cell. It is 

 very important to keep the solutions perfectly clear when measurements 

 are being made, and the glass ends must be maintained absolutely clean. 

 Table 29 shows the optical identity of the two cells. Under cell A 

 and cell B are given the actual radiomicrometer deflections for various 

 wave-lengths of light. 



TABLE 29. Comparison of the two cells. 



Having discussed the principal parts of the apparatus, viz, the radio- 

 micrometer, spectroscope, source of light, and the cells, and having 

 shown how they meet the requirements demanded by work of this 

 character, it is desirable to consider next the general arrangement of 

 the various parts. 



ARRANGEMENT OF APPARATUS. 



The Nernst glower, lenses, prisms, and carriage for the cells were 

 mounted on an upright steel standard placed by the side and near 

 the end of the spectroscope next to the radiomicrometer. Parallel 

 light from the Nernst glower was made to pass, by means of a carefully 

 adjusted sliding carriage, first through one cell and then through the 

 other. The two cells could thus be made to occupy the same position 

 in the path of the light. The light transmitted by the solutions con- 

 tained in the cells was then deflected by means of a right-angle prism 

 and focused on the slit of the spectroscope si. Inside of the box 

 inclosing the spectroscope, and directly in the rear of slit si, was placed 

 another right-angle prism which reflected the light through a 4-inch 

 lens to the grating. The dispersed light was reflected back through 

 this same lens and focused on the slit of the spectroscope s 2 . The light 

 that emerged through slit s 2 was again brought to a focus on the June- 



