NJTnOOKXOrfl OnCAXIC Jr.VTTET^S OP THE ROIL. 277 



suppose that it is (joierated by the action of the alkali, 

 In fact, there are a large number of bodies whicli manifest 

 a similar dep<irtmcnt. Many substances which are pro- 

 duced from ammonia-compounds by heat and otherwise, 

 and called (onide^^ to whicli 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. Oxam,ide. Water. 



2 {N HJ C, 0, = 2 (IS" HJ C, O^ + 2 H,0 



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 add 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 nmide of malic acid. 



TJrea, 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 Ilumus.^ 



The organic nitrogen of humus may come from the albu- 

 minoids of the vegetation that has decayed upon or in the 



