ANIMAL ACIDS CONTAINING AZOTE. 



4 Atoms carbon, = 3 or per cent. 27 '9 

 8 atoms hydrogen =1 ... 9*3 

 1 atom azote, =1-75 ... 16-3 



5 atoms oxygen. =5 ... 46*5 



10-75 100 



But 10-75 does not at all agree with the atomic weight of py- 

 ruric acid, as deduced from the analysis of the two pyrurates 

 above stated, namely, 17 '5.* 



SECTION IV. OF PARABANIC ACID. 



This acid was discovered by Wcihler and Liebig in 1838.f 

 They prepared it in the following way : Uric acid was dissolv- 

 ed by means of heat in eight times its weight of moderately 

 strong nitric acid, and after all evolution of gas had ceased, the 

 solution was evaporated. At a certain point of concentration, 

 it deposits colourless, lamellar crystals, Sometimes the whole 

 liquid concretes into these crystals, and sometimes they do not 

 appear till after an interval of some time. These crystals con- 

 stitute the parabanic acid of Wb'hler and Liebig. They may 

 be purified by a second crystallization. 



The crystals are six-sided prisms, colourless and transparent, 

 they have a strong acid taste, similar to that of oxalic acid. But 

 parabanic acid is more soluble in water than oxalic. The crys- 

 tals do not effloresce though exposed to the heat of 212. They 

 preserve their shape and transparency, but assume a red colour. 

 When exposed to a stronger heat they melt ; one portion is su- 

 blimed while another is decomposed with the disengagement of 

 hydrocyanic acid. 



When the cold solution of parabanic acid is mixed with ni- 

 trate of silver, a white pulverulent precipitate falls, which is very 

 much increased by the cautious addition of ammonia. The last 

 formed portion of this precipitate is gelatinous. 



When this acid is decomposed by oxide of copper the volume 

 of azotic gas evolved is to that of the carbonic acid gas as 1 : 3. 

 Hence it follows that the atoms of azote and carbon in the acid 

 are to each other as 1 : 3. 



Wohler and Liebig analysed parabanate of silver in order to 

 ascertain the atomic weight of the acid. This salt is insoluble 

 in hot water; but, like most of the salts of silver, it dissolves in 



* Ann. de Chim. et de Phys. xiii. 155. f Ibid. Ixviii. 273. 



