Earths. The early alchemists recognised four "essences" or "elements." Of these earth was one. The term "element" had not, however, the same definite meaning then that it obtained amongst chemists of later times. The name was afterwards applied to such substances as were unacted upon by heat or by water. Since lime and other kindred bodies showed great resemblance to the ordinarily known earths, they also received the same title, but as they gave a basic solution in water they were distinguished as "alkaline earths." These were shown to consist of oxides of metals, and, although many of the substances previously called earths do not fall in this class of bodies, the term was restricted to infusible, insoluble oxides. At the present time the word is not of great usage in chemical literature, being applied to the oxides of certain metals which, though some occur plentifully, as calcium, barium, aluminium, are for the most part found in but small quantities, as cerium, lanthanum, iridium.