The phosphates, as well as the nitrates and potash, are the basis of an active industry. Instead of being obliged to go abroad for supplies, however, or to search everywhere for them at home, as in the c.•?se of nitrates and potash, the United States is easily able to supply phosphates for export from the large deposits in the rocks of Tennessee and Florida;, and also from old bones not large enough for buttons or other manu factured products. The need of phosphorus in foods was demonstrated in Wisconsin by feeding animals with rations deficient in phosphorus. It was found that the animals drew the phosphorus they needed from their own bones, which being thus weakened, were no longer able to sup port the body and the animal collapsed. Nor did they recover when fed a normal ration.
In spite of all the activities which depend directly on the fertilizer industry, the importance of fertilizers seems to be only in its earlystages. The demand is constantly increasing, and presents one of the greatest problems of modern chemistry and engineering. The supplies of phosphate rocks of the United States will last a long time, but those of nitrogen and potassium arc very limited compared with the probable demands of the future. The greatest source of new supplies seems to
be the air for nitrogen and the water of the ocean and the deposits of old salt lakes for potassium. Kelp and other large seaweeds as well as marsh grasses are among the best fertilizers, for they store up much potash derived from the sea. One of the chief difficulties in getting fertilizers from the air and the sea is the vast amount of energy needed for evapora tion, chemical changes, mechanical transportation, and deep mining. If power were sufficiently abundant and cheap, the supply of fertilizers might be indefinitely increased. In this respect, as in many others.the problem of increasing the world's production is closely connected with the question of power. This is true no matter whether we wish to use uncultivated rugged tracts, irrigate the fertile soil of the desert, improve the poor soil of humid and tropical regions, or restore the exhausted soil of the long-settled parts of the world. 1