Abstract
The electron‐spin resonance of F centers in potassium iodide is observed at 293°K, 77°K, and 4°K. Additively‐colored crystals of several concentrations and x‐rayed crystals show the same resonance with g = 1.970 and a width of 213 gauss at maximum slope. The saturation of the absorption is measured. The resonances of F centers in potassium halides are compared.