What substances are used for food, clothing, or domestic purposes that are not manufactured by the aid of iron? Ingot or billet steel is rated at about one cent per pound; the hair-springs of watches are worth several thousand dollars per pound; what makes the difference in their value? What are the qualities that give to gold its value? Would all the gold mined in the United States pay the national debt at the end of the Civil War? What causes have led to the increasing price of copper during the past few years? What is the market price each of copper, silver, steel rails, and aluminium to-day? FOR STUDY AND REFERENCE Obtain specimens of the following iron ores: Hematite, brown hematite, magnetite, carbonate, and pyrites. Note the color and physical appearance of each; scratch the first four with a very hard steel point and note the color of the streak. Obtain specimens of pig-iron, cast iron, wrought iron, and cast steel; note carefully the fracture or "break" of each; how does cast iron differ from wrought iron? Obtain specimens of the following copper ores: Malachite, azurite, chalcopyrite, and red oxide; wet a very small fragment with an acid and note the color when it is held in the flame of an alcohol lamp or a Bunsen burner; dissolve a crystal of blue vitriol (copper sulphate) in water and note what occurs if the end of a bright iron wire be dipped in the solution. Name the various uses to which nickel, tin, lead, and aluminium are put. Consult the chapters on these subjects in any cyclopaedia. [Illustration: TRANSPORTING SUGAR-CANE, CUBA] [Illustration: SUGAR-CANE GROWING IN CUBA] [Illustration: HAVEMEYER SUGAR-REFINERY, BROOKLYN, N.Y.] CHAPTER XIV SUGAR AND ITS COMMERCE The term sugar is applied rather loosely to a large number of substances characterized by the quality of sweetness. In a few instances the name is given to certain mineral salts, such as sugar of lead, but in the main the sugars are plant products very similar in chemical structure to the starches. They are very closely connected with plant growth, and even in animal life, starchy substances are changed to sugar in the process of digestion. Although sugar does not sustain life, it is necessary as an adjunct to other food-stuffs, and it is probably consumed by a greater number of people than any other food-stuffs except starch and water. Three kinds of sugar are found in commerce, namely--_cane_-sugar, _grape_-sugar, and _milk_-sugar. Cane-sugar occurs in the sap of the sugar-cane, sorghum-cane, certain of the palms, and the juice of the beet. Grape-sugar is the sweet principle of most fruits and of honey. Sugar of milk occurs in milk, and in several kinds of nuts.