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07 May 1976
Vol 192, Issue 4239

About The Cover

Spheres-within-sphere structure of a fly ash agglomerate collected from the electrostatic precipitator of an operating coal-fired electric plant. The formation of these aluminosilicate plerospheres (hollow spheres packed with smaller spheres) probably results from rapid differential heating of a noncombustible coal fraction and subsequent evolution of gas from thermal decomposition and dehydration (about × 2660). See page 553. [G. L. Fisher, D. P. Y. Chang, and M. Brummer, University of California, Davis]