Featured on the Cover: April 1999
The yellow cascading precipitates are lead iodide, made from potassium iodide and lead nitrate. In the article "Using Large Glass Cylinders To Demonstrate Chemical Reactions" (pages 528-530), Wobbe de Vos describes a demonstration for observing the formation of precipitates. In a 0.5- or 1-liter glass cylinder almost completely filled with water a slow precipitation reaction involving two soluble salts occurs by adding a sample of one salt directly to the water and then placing some of the second salt in a filter inside a funnel that has been placed on top of the cylinder. Whereas setting up the experiment takes only a few minutes, the reaction may go on for an hour or more, displaying a slow but continuous formation process. The same set up can be used for a variety of redox, complex formation, and other reactions that produce a visible effect. The photographs of the reaction were provided by Rembrandt Dijkema and Koert Oskam. The cover was designed by Betsy True.

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