ALLANTOINE. 175 



composition, and the circumstance that we cannot find a more 

 appropriate position for it than amongst the nitrogenous products 

 of the metamorphosis of animal matters, we deemed it best to insert 

 it in this place. No rational formula can be assigned for it ; we 

 may, however, remark, that it exactly contains the elements of 4 

 atoms of cyanogen and 5 atoms of water. 



Combinations. The silver-compound, C 8 H 5 N 4 O 5 .AgO, is ob- 

 tained by mixing nitrate of silver with a boiling saturated solution 

 of allantoine, and then adding ammonia as long as a precipitate 

 continues to be produced : it forms a white powder which, when 

 examined microscopically, is found to consist of clear, perfectly 

 spherical particles. 



The lead-compound is obtained on boiling an aqueous solution 

 of allantoine with oxide of lead ; it is crystallisable. 



Products of its metamorphosis. Allantoic acid, C 10 H 7 N 4 O 9 , 

 which is obtained in the manner we have already described, occurs 

 as a tough, amorphous, white mass, soluble in water, but insoluble 

 in alcohol and ether, and forms soluble salts with the alkalies and 

 earths. (Pelouze.*) Attention has been drawn to the fact that this 

 acid contains exactly 3 atoms of water more than uric acid under the 

 older formula, (C 10 H 4 N 4 O 6 + 3HO=C 10 H 7 N 4 O 9 .) 



Preparation. On evaporating the allantoic fluid of the foetus of a 

 cow or the urine of a young calf to a thin syrup, without permitting it 

 to boil, and then allowing it to stand for a few days, we obtain crystals 

 of allantoine mixed with phosphate and urate of magnesia; by 

 stirring it with cold water and decanting, most of the viscid matter, 

 consisting of urate of magnesia, is removed, while the crystals of 

 allantoine and phosphate of magnesia rapidly sink to the bottom; hot 

 water extracts the allantoine, leaving the magnesian salt un dissolved; 

 the solution of allantoine is then decolorized with animal charcoal, 

 and evaporated till it recrystallises. 



Allantoine may also be obtained artificially from uric acid (see 

 " Uric acid") by boiling it with peroxide of lead, the products of 

 decomposition being oxalate of lead, urea, and allantoine ; when 

 the boiling fluid has been freed by filtration from oxalate of lead, 

 and allowed to cool, the allantoine separates in crystals. 



Tests. This body can only be recognised with certainty by an 

 accurate determination of its crystalline form, or by an elementary 

 analysis either of itself or its silver-compound. 



* Ann. de Chim. et de Phys. 3 S&-. T. 6, p. 69. 



