“NITROGENOUS ORGANIC MATTERS OF THE SOIL. 277 
suppose that it is generated by the action of the alkali, 
In fact, there are a large number of bodies which manifest 
a similar deportment. Many substances which are pro- 
duced from ammonia-compounds by heat and otherwise, 
and called amides, to which allusion has been already 
made, p. 276, are of this kind. Oxalate of ammonia, when 
heated to decomposition, yields oxamide, which contains 
the elements of the oxalate minus the elements of two 
molecules of water, viz., 
Oxalate of ammonia. Oxamide. Water. 
tt) a) = BN. AO OW 2 2 EO 
On boiling oxamide with solution of potash, ammonia 
is reproduced by the taking up of two molecules of water, 
and passes off as a gas, while oxalate of potash remains in 
the liquid. 
Nearly every organic acid known has one or several 
amides, bearing to it a relation similar to that thus sub- 
sisting between oxalic acid and oxamide. | 
Asparagine, a crystallizable body found in asparagus 
and many other plants, already mentioned as an amide, is 
thought to be an amide of malic acid. 
Urea, the principal solid ingredient of human urine, is 
an amide of carbonic acid. Uric acid, hippuric acid, gua- 
nine, found also in urine; kreatin and kreatinine, occurring 
in the juice of flesh; thein, the active principle of tea and 
coffee; and theobromin, that of chocolate, are all regard- 
ed as amides. 
Amide-like boaies are gelatine (glue), the organic sub- 
stance of the tendons and of bones, that of skin, hair, 
wool, and horn. The albuminoids themselves are amide- 
like, in so far that they yield ammonia on heating with 
solutions of caustic alkalies, 
Albuminoids a Source of the Nitrogen of Humus.— 
The organic nitrogen of humus may come from the albu- 
minoids of the vegetation that has decayed upon or in the 
