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 than in the original vegetation. 
Reversion of Nitric 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 ( Versuchs St., III, 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°|, 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. & 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. : 
