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 Chimie, tome xxii., p. 415, he gave the chemical process in the formation of specular iron.

In 1809, the same year that he discovered the law of volumes, Gay-Lussac was elected Professor of Chemistry at his alma mater—the École Polytechnique, Paris—and remained at the great military school for twenty-three years. In 1832 he transferred to the same chair in the Jardin des Plantes.

In 1823 he published a memoir on the dynamics of earthquakes, in which he says that "the earth, so many centuries old, still preserves an internal force, which raises mountains, overturns cities, and agitates the entire mass. Most mountains, in issuing from the bosom of the earth, must have left vast cavities, which have remained empty, at least unless they have been filled with water and gases."

The existence of alkaline metals was prophesied by Lavoisier in 1793; and potassium and sodium were discovered by Davy in 1807, by means of the voltaic pile; and in the following year Gay-Lussac discovered a new process which yielded both potassium and sodium more abundantly than the voltaic pile. This was by the action of white-hot iron on the hydroxides of potassium and sodium. No doubt the brilliant researches of Davy stimulated Gay-Lussac and his collaborates Thénard, and in their Recherches Physico-Chimiques (1811) are to be found many remarkable observations on the action of the voltaic pile which Napoleon had constructed for