1004 CYANOGEN COM POUNDS. 



In the artificial process for allantoin, 1 part of uric acid is 

 boiled in 2 parts of water, and the puce oxide of lead added in 

 small qualities so long as it changes colour. The liquid, filtered 

 boiling, and concentrated by evaporation, deposits allantoin 

 in crystals, which are purified by repeated crystallizations. In 

 the formation of allantoin, 2 atoms of the puce oxide of lead 

 lose the half of their oxygen, which, with 3 atoms of water, 

 produces 2 atoms of oxalic acid, 1 atom of allantoin and t 

 atom of urea : 



C 4 4 + N 2 C 4 =lat. Urile 1 

 2PbO + 2 H 3 3 + lat.Urea }=l at. uric acid. 



2 atoms of oxalate of lead + 1 at. of allant. + 1 at. of urea. 



Allantoin crystallizes in brilliant colourless prisms derived 

 from a rhombohedron. It is tasteless, neutral to test paper, 

 soluble in 160 parts of cold and in less boiling water. It dis- 

 solves in nitric acid ; the solution is decomposed by ebullition, 

 without the disengagement of ruddy fumes. It also dissolves 

 in a hot solution of an alkali or alkaline carbonate, and crystal- 

 lizes from these solutions without change. Allantoin contains 

 the elements of anhydrous oxalate of ammonia, minus 3 atoms 

 of water, which explains its conversion by boiling alkalies into 

 oxalic acid and ammonia. A solution of allantoin in 

 water at the boiling temperature, to which a few drops of 

 ammonia is added, gives a white precipitate with nitrate of 

 silver, of which the composition is expressed by C 8 N 4 H 5 O 5 -f- 

 AgO that is, 2 atoms of allantoin, C 8 N 4 H 6 O 6 , in which 1 atom 

 of water is replaced by 1 atom of oxide of silver. Allantoin 

 has also been named allantoic acid. 



ALLOXAN. 



Formula, C 8 N 2 H 4 O 10 . It is the erythric acid of Brugnatelli, 

 and was discovered by Liebig and Wcehler in the decomposi- 

 tion of uric acid. 



They recommend for its preparation, to add uric acid 

 gradually to nitric acid of 1.35, by which it is dissolved with 

 effervescence. " The action must be gentle, and, if heat be 

 applied, it must be done cautiously. As soon as crystals begin 



