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Page:Popular Science Monthly Volume 1.djvu/496

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Indium resists oxidation up to a temperature somewhat beyond its melting-point, but at much higher temperature it oxidizes freely; and at a red heat it takes fire in the air, burning with a characteristic blue flame and abundant brownish smoke. It is readily attacked by nitric acid, and by strong sulphuric and muriatic acids. In diluted sulphuric and muriatic acids, however, it dissolves but slowly, with evolution of hydrogen. Oxide of indium is a pale-yellow powder, becoming darker when heated, and dissolving in acids with evolution of heat. The hydrated oxide is thrown down from indium-solutions by ammonia, as a white, gelatinous, alumina-like precipitate, drying up into a horny mass. The sulphide is thrown down by sulphuretted hydrogen as an orange-yellow precipitate, insoluble in acetic but soluble in mineral acids. The hydrate and sulphide of indium, in their relations to fixed alkali solutions more particularly, seem to manifest a feebly-marked acidulous character. Chloride of indium, obtained by combustion of the metal in chlorine gas, occurs as a white micaceous sublimate, and is volatile at a red heat, without previous fusion. The chloride itself undergoes decomposition when heated in free air, and the solution of the chloride upon brisk evaporation, with formation in both cases of an oxichloride.



WHETHER the human race is degenerating, and, if so, by what causes, are questions of much speculative interest to scientific thinkers, and of much practical interest to each father and mother in the community. The subject is complicated by many conditions. Physical health and vigor, and mental strength and power, are to a great degree a matter of hereditary transmission, over which the individual has no control. Yet, taking our natures as they are, we can renovate, reinvigorate, and advance them by attentive study of and conformity to the laws upon which health and vigor are based. I propose in the present article briefly to glance at the chief physical agencies—air, exercise, clothing, food, and rest—and at some of the mental and moral influences, by the bad or good employment of which the physical stock is deteriorated or improved.

Air.—Probably the inhabitants of the globe generally were never so thoroughly sheltered as at present. The house keeps off rain, dew, and the moistures from evaporation—certainly very desirable—but it also to a greater or less degree modifies the temperature and the quality of the air that we breathe.

Theoretically, air is admitted to be an agent conducive to life; prac-