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The cover shows the catalytic oxidation of ammonia. This sparkling demonstration is discussed in the article by Vladimir A. Volkovich and Trevor R. Griffiths. The cover image was produced by Mike Hoyland using a slightly modified version of the demonstration. Concentrated ammonia is placed in a 20-L flask. Chromic oxide is heated to faint red heat in a steel crucible that has been silver-soldered to a steel tube. The crucible is placed in the flask and a sliding disk attached at the other end of the steel tube covers the neck of the flask and supports the crucible near the bottom of the flask. A rubber bulb connected with tubing to the steel tube is gently squeezed and the "sparkling" reaction begins! Additional squeezes of the bulb blow more chromic oxide into the ammonia vapor and sustain the reaction. See the article for more details and important safety information.