We do not see the gases rising, but there are many ways by which we can detect them. If we wave a feather over a manure heap, from which ammonia is escaping, the feather having been recently dipped in manure, white fumes will appear around the feather, being the muriate of ammonia formed by the union of the escaping gas with the muriatic acid. Not only ammonia, but also carbonic acid, and other gases which are useful to vegetation escape, and are given to the winds. Indeed it may be stated in few words that all of the organic part of _plants_ (all that was obtained from the air, water, and ammonia), constituting more than nine tenths of their dry weight, may be evaporated by the assistance of decay or combustion. The organic part of _manures_ may be lost in the same manner; and, if the process of decomposition be continued long enough, nothing but a mass of mineral matter will remain, except perhaps a small quantity of carbon which has not been resolved into carbonic acid. [What remains after manure has been long exposed to decomposition? What gaseous compounds are formed by the decomposition of manures?] The proportion of solid manure lost by evaporation (made by the assistance of decay), is a very large part of the whole. Manure cannot be kept a single day in its natural state without losing something. It commences to give out an offensive odor immediately, and this odor is occasioned, as was before stated, by the loss of some of its fertilizing parts. Animal manure contains, as will be seen by reference to p. 100, all of the substances contained in plants, though not always in the correct relative proportions to each other. When decomposition commences, the carbon unites with the oxygen of the air, and passes off as carbonic acid; the hydrogen and oxygen combine to form water (which evaporates), and the _nitrogen is mostly resolved into ammonia, which escapes into the atmosphere_. [Describe fire-fanging. What takes place when animal manure is exposed in an open barn-yard? What does liquid manure lose by evaporation?] If manure is thrown into heaps, it often ferments so rapidly as to produce sufficient heat to set fire to some parts of the manure, and cause it to be thrown off with greater rapidity. This may be observed in nearly all heaps of animal excrement. When they have lain for some time in mild weather, gray streaks of _ashes_ are often to be seen in the centre of the pile. The organic part of the manure having been _burned_ away, nothing but the ash remains,--this is called _fire-fanging_. Manures kept in cellars without being mixed with refuse matter are subject to the same losses.