278 HOW CROPS FEED. 



soil. In their alteration by decay, a portion of nitrogen 

 assumes the gaseous form, but a portion remains in an in- 

 soluble and comparatively unalterable condition, though 

 in what particular compounds we are unable to say. The 

 loss of carbon and hydrogen from decaying organic mat- 

 ters, it is believed, usually proceeds more rapidly than the 

 waste of nitrogen, so that in humus, which is the residue 

 of the change, the relative proportion of nitrogen to car- 

 bon is greater thnn in the original vegetation. 



Reyersion of IVitric Acid and Ammonia to inert Forms. 

 — It is probable that the nitrogen of ammonia, and of ni- 

 trates, which are reducible to ammonia under certain con- 

 ditions, may pass into organic combination in the soil. 

 Knop ( VersucJis St., Ill, 228) found that when peat or 

 soils containing humus were kept for several months in 

 contact with ammonia in closed, vessels, at the usual tem- 

 perature of summer, the ammonia, according to its quan- 

 tity, completely or in part disappeared. There having been 

 no such amount of oxygen present as would be necessary to 

 convert it into nitric acid, the only explanation is that the 

 ammonia combined with some organic substance in the 

 humus, forming an amide-like body, not decomposable by 

 the hypochlorite of soda used in Knop's azometrical anal- 

 ysis. 



Facts supporting the above view by analogy are not 

 wanting. When gelatine (a body of animal origin closely 

 related, to the albuminoids, but containing 18 instead of 

 15° Id of nitrogen) is boiled with dilute acids for some 

 time, it yields, among other products, sugar, as Gerhardt 

 has demonstrated. Prof. T. Sterry Hunt was the first to 

 suggest {Am. Jour. Sci. d Arts, 1848, Vol. 5, p. 76) that 

 gelatine has nearly the composition of an amide of dextrin 

 or other body of the cellulose group, and might be regard- 

 ed as derived chemically from dextrin (or starch) by the 

 union of the latter with ammonia, water being eliminated. 

 viz.: 



