LIME.
Another very plentiful substance in the earth is lime. It is chiefly found in the form of three salts, the carbonate, sulphate and phosphate (CaCO₃) (CaSO₄) (Ca₃(PO₄)₂), respectively. The first is familiarly known as limestone. When crystallized, it appears as marble. The shades of marble are due to the tinting of metallic oxides, and sometimes to the presence of fossils. The most beautiful marble is obtained from Carrara, Italy, which has long been famous for furnishing the material used for statues. It is pure white. Pure black marble is found in some ancient Roman sculptures. Sienna marble is yellow. Italy furnishes one kind that is red. Verd-antique is a mixture of green serpentine and white limestone, while our beautiful Tennessee marble, used so profusely in the new Capitol at Washington, is a blended red and white.
Common limestone is almost entirely the product of minute animals[4] which lived in early geologic times. Ages before the Romans drove piles into the Thames, or the first hut was erected on the banks of the Seine, these little creatures laid the foundations which underlie London and Paris. They built the rocky barriers which gave to England the name Albion, derived from the white cliffs along her shore. It is a suggestive crumb of comfort for little folk, that the great tasks in the building of our earth have been performed by the smallest creatures.
The wide distribution of limestone is shown from the fact that it is found to be an ingredient in almost all waters. It is readily dissolved, as is seen in the numerous caves which are found in limestone regions.
When limestone is heated, the carbonic anhydride[5] is expelled, leaving quicklime. All are familiar with the manifold uses of this material. United with sand, it forms a silicate of lime, called mortar, which becomes harder with age. In the old stone mill[6] at Newport, R. I., which is of unknown antiquity, the mortar in some places actually protrudes beyond the stones, showing it to be more durable than the rock itself. The catacombs of Rome were excavated in a very soft kind of limestone, called calcareous tufa.
Sulphate of lime, also known as gypsum and plaster of Paris, is widely distributed. One beautiful variety is called satin spar, and another alabaster.
Great quantities of sulphate of lime are quarried for use in the arts and for agricultural purposes. Dr. Franklin was one of the first to discover its value in connection with crops, and is said to have sown it with grain on a side hill, so that when the wheat sprang up, observers were surprised to see written in gigantic green letters, “Effects of Gypsum!” I suspect he got the hint from Dr. Beattie, who sowed seeds so that their flowers formed the name of his son, to prove to the boy the existence of a God, from evidences of design in nature.