Spontaneous Combustion.
Mix a small quantity of chlorate of potash with spirit of wine in a strong saucer; add a little sulphuric acid, and an orange vapor will arise and burst into flame with a loud crackling sound.
Inequality of Heat in Fire-Irons.
Place before a fire a set of polished fire-irons, and beside them a rough, unpolished poker, such as is used in the 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.