GENERATION, CONTROL, AND MEASUREMENT 



197 



For a horizontal beam of radiant energy the conventional cylindrical 

 filter cell with two vertical glass windows can be cooled very satisfactorily 

 with a cooling coil in the solution. In this case the heating occurs in a 

 vertical plane, and convection currents are induced. Acidulated copper 



100 



900 



Fig. 3-19. Spectral transmission of ferrous ammonium sulfate solutions in a 10-cm 

 path. The solutions were prepared in 2 per cent sulfuric acid at 30, 70, 150, and 300 g 

 per liter of sohition, as indicated on the solid curves. The upper dashed curve is for 

 water; the lower dash-dot curve is for 300 g per liter of solution exposed to the air for 

 2 weeks. {From Withrow and Price, 1953.) 



100 



80 



o 60 



z 

 < 



< 



40 



20 



300 



350 



400 



600 



650 



700 



450 500 550 



WAVE LENGTH, m/i 



FiG. 3-20. Spectral transmission of copper sulfate solutions in a 10-cm path length at 

 the concentrations indicated in grams per liter of solution made up in 0.5 per cent 

 sulfuric acid. (From Withroiv and Price, 1953.) 



sulfate solutions corrode copper, aluminum, tin, and lead tubing, but 

 stainless-steel, silver, or glass tubing may be used. 



2. Dye solutions and films. The three most useful classes of dyes for 

 the preparation of filters are the water- and alcohol-soluble basic, acid, 

 and direct, or substantive, dyes. Biological stains are of higher purity 



