“The consumption of coal,” says the United States Geological Survey, “is a measure of the industrial activity of a people, for as yet coal is the main source of mechanical energy. In this respect the United States is the foremost nation, its average annual consumption of coal for all purposes being about five tons per capita. Prior to the present war in Europe the consumption of coal per capita in England, Belgium and Germany was about four tons, in Russia a quarter of a ton, and in France about 1.6 tons.” Marvelous forms of labor-saving machinery have been introduced to facilitate the loading and unloading of coal. The principal form of apparatus for transferring coal either to or from a vessel is the “bridge tramway plant,” which consists of long steel bridges mounted side by side on suitable rails so that they can be moved into place over the hatchway of a vessel. Huge buckets, which load and unload themselves, are carried on a “trolley,” suspended from the bridge, and transfer coal at high speed from the vessel to the stock pile or railway cars, or _vice versa_. The cost of loading coal by this method is only a cent or two a ton. Another ingenious device is the “car-dumper.” This powerful machine picks up bodily from the railway track a car loaded with a hundred tons of coal, overturns it, and discharges its contents into the hold of a vessel; after which it returns the car to the track. It is capable of handling fifty cars an hour. It is equipped with special apparatus to prevent the coal from being discharged too violently, and thus being badly broken up. PREPARED BY THE EDITORIAL STAFF OF THE MENTOR ASSOCIATION ILLUSTRATION FOR THE MENTOR. VOL. 6, No. 6, SERIAL No. 154 COPYRIGHT, 1918. BY THE MENTOR ASSOCIATION, INC. [Illustration: COURTESY POPULAR SCIENCE MONTHLY CHARGING COAL IN A MODERN GAS PLANT] _THE STORY OF COAL_ _Coal Products_ FOUR The story of the coal products forms one of the most romantic chapters in the history of applied science. The marvels of fairyland are surpassed by the achievements of the modern manufacturer in obtaining from mere black rocks dug out of the ground not only heat and light, but a bewildering variety of useful gases, liquids and solids--drugs, chemicals, dyestuffs, and so forth.