Earths
The solid matters of the earth, including rocks, etc., are composed principally of combustible elements, as aluminum, potassium, magnesium, calcium, and carbon, in combination with oxygen. The fact of the rarity of these metals in a free state is due to their extreme combustibility. The earths proper do not change vegetable colors; in acids they are soluble, and may be subsequently precipitated from their solutions by potash, soda, or ammonia. The alkaline earths, as barytes, strontia, lime, etc., are soluble in water, and have the property of neutralizing the strongest acids, and changing vegetable colors in general. The mineral elements composing the chief mass of soils are derived from the breaking-up of the various rocks by the action of heat, frost, air, and moisture, According to the composition of the rocks so will the soil be that is derived from them: clayey when from argillaceous rocks, calcerous from lime, and sandy from siliceous rocks, besides which must be included organic substances, a portion of liberated alkalies and alkaline earths, etc. See ALKALI.