ANIMAL ACIDS CONTAINING AZOTE. 



of water. It would appear from this, that when parabanic acid 

 is united with oxide of silver it parts with two atoms of water, 

 which are replaced by two atoms oxide. Hence the acid united 

 with the oxide of silver contains no hydrogen, but is composed 

 of C 6 Az 2 O 4 = 12. 



No other parabanate but that of silver is known. Whenever 

 the acid is placed in contact with a soluble base it is converted, 

 under the influence of the most gentle heat, into oxaluric acid. 

 When heated with other acids it undergoes no alteration. Nor 

 is it altered when its aqueous solution is boiled. 



SECTION V. OF OXALURIC ACID. 



This acid also was discovered by Wb'hler and Liebig in 

 1838,* during their important examination of uric acid and its 

 compounds. 



Parabanic acid, the preparation of which was given in the 

 preceding section, is very soluble in caustic ammonia, and the 

 solution is perfectly neutral. If it be raised to the boiling point, 

 and then left to itself, it concretes on cooling into a white mag- 

 ma composed of small needles. This substance is oxalurate of 

 ammonia. If, to a hot concentrated solution of this salt in wa- 

 ter, we add sulphuric or muriatic acid, and cool the mixture as 

 quickly as possible, oxaluric acid falls in a white crystalline 

 powder. It may be purified by^ washing it in cold water, as it 

 is but little soluble in that liquid. 



Its solution has a decidedly acid taste, reddens litmus paper, 

 and neutralizes the bases. The neutral oxalurates, when dis- 

 solved in water, precipitate nitrate of silver in white flocks, which 

 dissolve in boiling water, and crystallize on cooling in long silky 

 needles. 



Neither" oxaluric acid nor oxalurate of ammonia throw down 

 any precipitate when dropped into dilute solutions of salts of 

 lime. But, if we add an excess of ammonia, a white gelatinous 

 precipitate falls, soluble in a great deal of water. 



If we boil free oxaluric acid in water till no crystals are de- 

 posited on cooling, the acid is completely decomposed. The so- 

 lution is very acid. When concentrated, it first deposits crys- 

 tals of oxalate of urea and then pure oxalic acid. 



When oxaluric acid is decomposed by oxide of copper, the 

 volumes of azotic gas and carbonic acid gas obtained are to each 

 other as 1 '. 3, as is the case with parabanic acid. 

 * Ann. de Chim. et de Phys. Ixviii. 276. 



