The Burning Sugar Cube: Still Unexplained? An "old standard" demonstration involves holding a sugar cuhe in a flame, where it melts hut does not burn. Another cube is rubbed with cigarette ashes, then held in the flame, where it burns steadily. The conclusion from these observations is that the ashes are functioning as s. catalyst in the combustion of the sugar. A wide range of powdered solids, other than cigarette ashes, may he used to product; a burning sugar cube. Among these are powdered Al, Sh, Zn, FeaOa,PhO, MnO?,graphite, talcum, instant coffee, nutmeg, cinnamon, and dirt. The effectiveness of such a wide variety of substances suggests that unquestioning application of the catchall explanation "catalysis" may not he justified. Rather, the demonstration seems to illustrate the effect of particle size on the rate of combustion. The heat probably melts a thin film of sugar which then coats the particles. The kindling temperature of the film of sugar is reached before the melting- mocess can dissipate the heat; hence the rapid burning- of the treated . cuhe. Perhaps other readers have examined this problem; we hope they will share their findings,
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Journal of Chemical Education
