In the same way water in passing through manures takes up the soluble portions of the ash as fast as liberated by decomposition, and carries them into the soil below; or, if the water runs off from the surface, they accompany it. In either case they are lost to the manure. There is but a small quantity of ash exposed for leaching in recent manures; but, as the decomposition of the organic part proceeds, it continues to develope it more and more (in the same manner as burning would do, only slower), thus preparing fresh supplies to be carried off with each shower. In this way, while manures are largely injured by evaporation, the soluble inorganic parts are removed by water until but a small remnant of its original fertilizing properties remains. [What arrests their farther progress? What would be the effect of allowing these matters to filter downwards? What does evaporation remove from manure? Leaching?] It is a singular fact concerning leaching, that water is able to carry no part of the organic constituents of vegetables more than about thirty-four inches below the surface in a fertile soil. They would probably be carried to an unlimited distance in pure sand, as it contains nothing which is capable of arresting them; but, in most soils, the clay and carbon which they contain retain all of the ammonia; also nearly all of the matters which go to form the inorganic constituents of plants within about the above named distance from the surface of the soil. If such were not the case, the fertility of the earth must soon be destroyed, as all of those elements which the soil must supply to growing plants would be carried down out of the reach of roots, and leave the world a barren waste, its surface having lost its elements of fertility, while the downward filtration of these would render the water of wells unfit for our use. Now, however, they are all retained near the surface of the soil, and the water issues from springs comparatively pure. EVAPORATION removes from manure-- Carbon, in the form of carbonic acid. Hydrogen and oxygen, in the form of water. Nitrogen, in the form of ammonia. LEACHING removes from manure-- The soluble and most valuable parts of the ash in solution in water, besides carrying away some of the named above forms of organic matter. FOOTNOTES: [X] It should be recollected that every bent straw may act as a syphon, and occasion much loss of liquid manure. CHAPTER IV. ABSORBENTS. [What substances are called absorbents? What is the most important of these? What substances are called charcoal in agriculture? How is vegetable matter rendered useful as charcoal?]