* Vitrescent sparks. l. 229. When flints are struck against other flints they have the property of giving sparks of light; but it it seems to be an internal light, perhaps of electric origin, very different from the ignited sparks which are struck from flint and steel. The sparks produced by the collision of steel with flint appear to be globular particles of iron, which have been fused, and imperfectly scorified or vitrified. They are kindled by the heat produced by the collision; but their vivid light, and their fusion and vitrification are the effects of a combustion continued in these particles during their passage through the air. This opinion is confirmed by an experiment of Mr. Hawksbee, who found that these sparks could not be produced in the exhausted receiver. See Keir's Chemical Dict. art. Iron, and art. Earth vitrifiable.

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