Place before a brisk fire a set of polished fire-irons, and beside them a rough unpolished poker, such as is used in a kitchen, instead of a bright poker. The polished irons will remain for a long time without becoming warmer than the temperature of the room, because the heat radiated from the fire is all reflected, or thrown off, by the polished surface of the irons, and none of it is absorbed. The rough poker will, however, become speedily hot, so as not to be used without inconvenience. Hence, the polish of fire-irons is not merely ornamental, but useful.
EXPANSION OF METAL BY HEAT.
Provide an iron rod, and fit it exactly into a metal ring: heat the rod red hot, and it will no longer enter the ring.
Observe an iron gate on a warm day, when it will shut with difficulty; whereas it will shut loosely and easily on a cold day.
EVAPORATION OF A METAL.
Rub a globule of mercury upon a silver spoon, and the two metals will combine with a white appearance; heat the spoon carefully in the flame of a spirit lamp, when the mercury will volatilize and disappear, and the spoon may then be polished until it recovers its usual luster: if, however, the mercury be left for some time on the spoon, the solid texture of the silver will be destroyed throughout, and then the silver can only be recovered by heating it in a ladle. Care must be taken to avoid the fumes of mercury, which are very poisonous.
A FLOATING METAL ON FIRE.
Throw a small piece of that marvelous substance, potassium, into a basin of water, and it will swim upon the surface and burn with a beautiful light, of a red color mixed with violet. When moderately heated in the air, potassium takes fire, and burns with a red light.
ICE MELTED BY AIR.