igog.] 



OF VARIOUS SALTS IN SOLUTION. 



197 



concave speculum mirror at M. M focuses the light on the slit of 

 the Rowland concave grating spectroscope, G being the grating and 

 C the focal curve of the spectrum. The prism arrangement was 

 designed by Dr. John A. Anderson. 



Fig. I. 



This apparatus was found to work very well for aqueous solu- 

 tions. Some evaporation took place at the higher temperatures, but 

 distilled water was added in proper quantity and mixed with the 

 solution so as to keep the concentration constant. By using troughs 

 of different lengths it was possible to vary the length of salt solution 

 through which the light beam passed from i to 200 mm. One 

 inconvenience was experienced at low temperatures ; moisture would 

 sometimes condense upon the exposed prism faces. To overcome 

 this an air blast was directed upon these faces and this helped very 

 materially to prevent the condensation of moisture. 



