Caustic, burning, corroding:  a term applied to substances
     which eat away and burn any thing with which they are
     brought in contact.

In what state is Lime found in nature?

Never native, but combined with other substances;—­generally with an acid, and most plentifully with carbonic acid, as in chalk, marble, &c.  It is also found in vegetables, and is the basis of animal bones; it likewise occurs in the water of the ocean, and in that of all springs and rivers.  The method of procuring lime, from chalk, marble, limestone, oyster-shells, &c., has already been described in a former chapter.

What are the properties of Clay?

Argil, or pure clay, also called alumina, from its being the basis of alum, is soft to the touch, adhesive, and emits a peculiar odor when moistened;—­forms a paste with water, and hardens in the fire.  Its uses are so various and important, that it would have been almost impossible for man to have attained his present degree of civilization, if it had not been given him by nature in such abundance.  Its uses have already been described in the arts of brick-making, pottery, &c.  Besides these three principal primitive earths just described, there are seven others, having several properties in common, yet each possessing its different and specific properties, and evidently designed by nature for different purposes of utility.

     Specific, belonging to its particular species.

     Utility, usefulness.

What is a Volcano?

An opening in the surface of the earth, or in a mountain, from which are ejected smoke, flames, stones, lava, &c.  Beneath the outer crust of the earth inflammable materials appear to exist, which different causes excite into combustion.  Volcanoes are supposed to owe their origin to the metals and minerals which form the basis of earths and alkalies; and which, when ignited, expand,—­shake the rocky foundations,—­and sometimes, bursting through, produce all the destructive effects of earthquakes.  They break forth under the sea, as well as the land, and throw up mountains which rise above the level of the water.  During an eruption of Vesuvius, A.D. 79, three cities, Herculaneum, Pompeii, and Stabiae, were overwhelmed, and lay buried beneath the matter ejected from the volcano until within a few years, when excavations were made and many relics discovered;—­streets, houses, papyri, (manuscripts,) grain, fruit, bread, medicines, &c. &c., all in a remarkable state of preservation, have been found just as they were left by the terrified inhabitants at the time of the eruption!

     Eruption, an issuing or breaking forth with violence.

     Ejected, thrown out.

Are there many Volcanoes?