ALLOXANE OR ERYTHRTC ACID. Ill 



SECTION IV. OF ALLOXANE OR ERYTHRIC ACID. 



This remarkable substance was discovered in 1819 by Dr Gas- 

 pard Brugnatelli ;* but succeeding experimenters were unable to 

 succeed in forming it till it was discovered again in 1838 by 

 Wohler and Liebig, who gave a minute detail of the process 

 which they followed.f 



The substances formed by the action of nitric acid on uric acid 

 vary with the strength of the nitric acid and the temperature. 

 Alloxane is the compound obtained when the nitric acid is con- 

 centrated. If we put into cold nitric acid of the specific gravity 

 1 -425 dry uric acid, a strong effervescence takes place, a good 

 deal of carbonic acid is disengaged together with some nitrous 

 acid, and when the gases cease to be evolved, the liquid assumes 

 the state of a thick bouillee consisting of small prismatic crystals. 

 The mother water contains ammonia. A gentle heat determines 

 the evolution of pure azotic gas. The mass contains nothing 

 but ammonia, and the small crystals, which consist of pure al- 

 loxane. 



If in this experiment we employ a great excess of nitric acid, 

 and if we boil it with the crystals, on allowing the matter to cool, 

 long straight prismatic crystals are formed, having a very strong 

 resemblance to oxalic acid. 



If we employ nitric acid of the specific gravity 1'55, alloxane 

 is still formed ; but a portion of the uric acid undergoes other 

 modifications. Small masses of it become brown or black as if 

 charred, and the colouring matter which is developed is not easily 

 removed from the crystals. 



Wohler and Liebig employed the following process for pre- 

 paring alloxane. The most concentrated fuming nitric acid is 

 mixed with the ordinary acid of commerce so as to form a liquid 

 having a specific gravity from 1 45 to 1 '5. This mixture is put 

 into a very shallow porcelain evaporating basin, and then is ad- 

 ded to it by little and little at a time half its weight of dry uric 

 acid ; every portion added being mixed very carefully with the 

 nitric acid. On every addition an effervescence takes place, and 

 care must be taken to wait till the effervescence is over, and 

 the liquid cold, before any more of the uric acid be added. 



By this process we obtain a mass almost solid, consisting of 

 brilliant and transparent crystals. It is poured upon a very 



* Ann, de Chim. et de Phys. viii. 201, | Ibid. Ixviii. 240. 



