1006 CYANOGEN COMPOUNDS. 



alloxan is poured drop by drop into a boiling solution of acetate 

 of lead, a granular very heavy precipitate of mesoxalate of lead 

 falls, while nothing remains in the acid liquor but the excess of 

 acetate of lead and pure urea. Both this and the preceding 

 acid may be separated and crystallized, and are powerful acids. 



Mycomelinic acid, C 16 N 8 H 10 O 10 , is formed on adding an 

 excess of ammonia to a solution of alloxan, and raising the mix- 

 ture to the boiling point. It is almost insoluble in cold water, 

 and is thrown down as a yellow gelatinous precipitate, which 

 becomes a yellow porous powder on drying. 



Parabanic acid, 2HO-|-C 6 N 2 O 4 , is one of the products of the 

 decomposition of uric acid or alloxan by nitric acid, discovered 

 by Liebig and Woehler. It is prepared by dissolving 1 part of 

 uric acid or alloxan in 8 parts of nitric acid of ordinary strength, 

 evaporating the liquor to a syrup, and allowing it to crystallize. 



It forms thin, transparent, six-sided prisms, of a very sour 

 taste, resembling that of oxalic acid. It is very soluble in water 

 and does not effloresce in the atmosphere nor by heat ; it is 

 partially volatile. 



Oxaluric acid, HO -f C 6 N 2 H 3 O 7 , is formed on adding am- 

 monia to a boiling solution of parabanic acid, or on supersatu- 

 rating with ammonia a solution recently prepared of uric acid 

 in nitric acid, which yields by evaporation crystals of oxalurate 

 of ammonia. The acid when separated is a brilliant white 

 powder, light and crystalline ; its taste is very sour, and it red- 

 dens litmus. Its aqueous solution is decomposed completely by 

 ebullition, and resolved into oxalic acid and oxalate of urea. 

 It is formed by the combination of the elements of parabanic 

 acid with 2 atoms of water. The crystallized acid contains the 

 elements of 2 atoms of oxalic acid and of 1 atom of urea, and 

 may be considered as uric acid in which the urile is replaced by 

 oxalic acid. (Liebig). 



Thionuric acid, HO + C 8 N 3 H 5 O 6 (S 2 O 6 ), is a bibasic acid pro- 

 duced by the simultaneous action of sulphurous acid and am- 

 monia upon alloxan. Liberated from thionurate of lead by 

 sulphuretted hydrogen, it crystallizes in very thin needles, is 

 persistent in air, very soluble in water, and has an acid taste. 

 It contains the elements of 1 atom of alloxan, 1 atom of am- 

 monia and 2 atoms of sulphurous acid. On heating thionuric 

 acid, 2 atoms of oxygen of the alloxan re-unite with 2 atoms of 



