Reagent grade potassium chloride usually contains sufficient water to hydrolyze some of the KCl so that crystals grown from it contain KOH unless they are treated with either HCl or Cl2. Thus crystals grown in platinum without pretreatment show the well‐known OH band. Crystals grown in silica do not show this OH band but they nevertheless contain a source of hydrogen as shown by the formation of theU2band on exposure to ultraviolet light. It is shown that such crystals have an absorption band at 187 m&mgr; and form bands at 193.5 and 360 m&mgr;, in addition to other bands previously recorded, on exposure to uv light. Various possible models for the centers responsible for these absorption bands are discussed, together with the photochemical reactions involved.