"Teacher was very careful to show us that the rain- water is nearly pure, and contains no substances in solution. Such water could not feed the plant.
"It is only after it falls, and sinks into the soil, that the rain becomes useful to the plant. It is useful then because it dissolves the plant-food in the soil.""Teacher explained to us, too," said Willie, "that thissame rain, after passing through the soil, continues to sink down deep into the earth. It trickles through rocks of various kinds, and dissolves, on its way, all that is soluble.
"By and by the same water bubbles up out of the ground again, and forms a spring.
"Teacher says this spring water always contains some solid substances or other in a state of solution. "The waters of some springs contain such mineral substances as iron and sulphur in solution. These are known as mineral springs. The waters are usedas medicines."