ALUMINA—Al₂O₃.
This material is found both alone and in combination with silica. It forms an important ingredient in alum. Crystallized, it furnishes some of our most rare and beautiful gems, the color of which depends upon the metal combined with them.
The ruby is red, the emerald green, the topaz yellow, the sapphire blue.
Slate rocks consist largely of this material, and clay is a compound of alumina with siliceous anhydride. Among the first earthy substances utilized by man was clay. We find remains of pottery even as far back as the stone age[7]. The ingenuity of man seems to have been displayed constantly and successfully in the ceramic[8] art, the art of making pottery. Note the accounts given by Prescott, in his “Conquest of Peru and Mexico,” and the Cesnola collection of Cypriote remains[9] exhibited in the Metropolitan Museum in New York City.
History is repeating itself by renewing the ancient enthusiasm for decoration of china and earthen ware. Bricks made from clay are found to rival granite in durability, and surpass it in resistance to heat, as was proven in the great fires of Boston and Chicago. It will be observed from the symbol of alumina that it is largely composed of the metal aluminum. If this could be readily liberated from the oxygen with which it is combined, the world would be immensely enriched.
Every clay bank or clayey soil contains it in great quantities. Next to oxygen and silicon, it is the most abundant element in the earth. Note its valuable properties. It is but two and one-half times heavier than water, as bright and non-oxidizable as silver, malleable, ductile, tenacious, and can be welded and cast. Who will lay the world under obligation by doing with alumina what has been done with iron ores, cheaply liberate the oxygen?
TESTING FOR IRON WITH A BORAX BEAD.—THE COMPOUNDS OF IRON WITH BORAX GIVE A BOTTLE GREEN COLOR.
In this brief enumeration of earth materials, we have intentionally omitted the forms of carbon. They constitute no insignificant portion of the earth’s crust, but belong to the class of organic substances. We introduce, however, an illustration showing one of the shapes in which is cut the diamond—that most costly of all forms of matter,—crystallized carbon.