108 ANIMAL OXIDES WITH AZOTE NOT OILY. 



to form allantoin artificially. But it will be requisite in this 

 place to be somewhat more particular. 



Pure uric acid extracted from the excrements of serpents was 

 mixed with water* to the consistence of a thin pap. This mix- 

 ture was raised to the boiling point, and peroxide of lead in fine 

 powder was added by little and little. A reaction took place, 

 carbonic acid was given out with effervescence. The pap thick- 

 ened considerably unless water was added ; and the peroxide of 

 lead disappeared. More and more of this peroxide was cautious- 

 ly added, taking care to renew the water and to keep the whole 

 in a boiling heat till the mixture, by assuming a chocolate colour, 

 indicated that a slight excess of peroxide had been added. The 

 whole was then filtered while hot, and the matter on the filter was 

 repeatedly washed with boiling water. 



The filtered liquid was colourless, and on cooling deposited a 

 great number of hard brilliant crystals, which were colourless, or 

 had only a very slight tint of yellow. These crystals constitute 

 allantoin. The mother water by evaporation yields an addition- 

 al quantity of them. 



The liquid, after depositing the allantoin, having been evapo- 

 rated to the consistence of a syrup over the water-bath, yielded 

 on cooling long prismatic crystals of urea. The white matter 

 collected on the filter is oxalate of lead. If we wash it, mix it 

 with water, and pass through it a current of sulphuretted hydro- 

 gen, the oxalic acid freed from lead dissolves in the water, and 

 may be obtained in crystals. 



Thus the products of the reaction of uric acid and peroxide of 

 lead are allantoin, urea, oxalic acid, carbonic acid, and protoxide 

 of lead, and these are the only products. 



Wohler and Liebig compared the allantoin thus obtained with 

 a quantity of allantoin from the liquor of the allantois of a calf 

 which they had in their possession, and found the two to agree in 

 their characters and composition. 



The crystals are colourless and transparent Their primitive 

 form is a rhomboid. They are hard and their faces are very 

 brilliant. They are tasteless and do not alter the colour of lit- 

 mus-paper. At 68 allantoin is soluble in 160 times its weight of 

 water. But it is much more soluble in hot water, and crystal- 

 lizes while the solution is cooling. It does not combine with the 



* Ann. de Chim. et de Phys Ixviii. 228. 



