The large slabs of rock salt, with which their country abounds, were employed by them instead of stones, in building their dwellings, the pieces being easily cemented together by sprinkling the joints with water, which, melting the parts of the two surfaces that opposed each other, formed the whole, when dry, into one solid block. Does Rock Salt undergo any preparation before it is used? Yes; when taken from the earth it is dissolved in cold water, and afterwards drawn off into salt-pans, and refined in the same manner as the sea salt. What is Coal? A hard, black, sulphurous and inflammable substance, dug out of the earth, serving in many countries as fuel. It is common in most of the countries of Europe and America. In some parts of the United States, it is found in beds having an area of several thousand square miles. From what is Coal supposed to have originated? Its origin is supposed to be derived from gigantic trees which flourished in the swamps and forests of the primeval earth. These having been torn away from their native bed, by storms and inundations, were transported into some adjacent lake, river, or sea. Here they floated on the waters until, saturated with them, they sank to the bottom, and being buried in the lower soil of adjacent lands, became transformed into a new state among the members of the mineral kingdom. A long interment followed, during which a course of chemical changes, and new combinations of their vegetable elements, converted them to the mineral condition of coal. _Primeval_, original, existing before the flood. _Gigantic_, extremely large, greater than the usual size. _Interment_, burial under the ground. _Elements_, the several parts or principles of which bodies are composed. What is a Coal Mine? A subterraneous excavation, from which coal is obtained. Do the terms Coal and Charcoal signify the same substance? No; Charcoal is an artificial fuel, made in imitation of coal, by burning wood covered with earth so as partially to exclude the air. It is used for various purposes, as the making of gunpowder,[7] polishing brass and copper, &c., and when a clear and bright fire is required, as it burns with little or no smoke; it is dangerous, however, for one to remain many hours in a close room with a charcoal fire, as the fumes it throws out are hurtful, and would destroy life. Charcoal, in fact, is the coaly residuum of any vegetables burnt in close vessels; but the common charcoal is that prepared from wood, and is generally black, very brittle, light, and destitute of taste or smell. It is a powerful antiseptic, unalterable and indestructible. [Footnote 7: See Chapter XII.] _Residuum_, the remaining part, that which is left. _Antiseptic_, that which prevents putrefaction. What is Iron?