ALLANTOIN. 107 



less they have been injured by having been in any degree over- 

 heated. The muriatic salt is decomposed at 2 12, in consequence 

 of the volatility of its acid, and the rest are easily destroyed by 

 a greater excess of heat. 



The salt formed by combination with nitric acid does not 

 yield oxalic acid, and does not become red when similarly treat- 

 ed with uric acid ; but assumes a brown colour, becoming gra- 

 dually darker till it is ultimately black. 



When the combinations with alkalies are evaporated they leave 

 small granular crystals. The only definite form observed was 

 that of flat hexagonal plates. But the primary shape of the crys- 

 tal could not be ascertained. On the cystic oxide calculus in 

 Guy's Hospital minute crystals nearly cubical were observed ; but 

 whether these were crystals of cystic oxide was not determined. 



Dr Prout subjected cystic oxide to an ultimate analysis, and 

 obtained, 



Carbon, 2 9 '8 7 5 or 6 atoms = 4'5 or per cent. 



Hydrogen, 5*125 or 6 atoms =0.75 



Azote, . 11*85 or 1 atom = 1*75 



Oxygen, 53*150 or 8 atoms 8*00 



100*00 15* 100* 



These numbers merely express the smallest ratios of the number 

 of atoms of each constituent which cystin contains. For no ex- 

 periments have been made to determine its atomic weight. The 

 analogy of uric oxide and urea would lead us to double the num- 

 ber of atoms of each constituent, and to represent the constitu- 

 tion of cystin by the following formula, C 12 H 12 Az 2 O 16 = 30. 



SECTION III. OF ALLANTOIN. 



This substance was first detected by Vauquelin and Buniva in 

 the liquor of the amnios of the cow, and was called by them am- 

 niotic acid* It was afterwards found that the liquor from which 

 it was extracted was not that contained in the amnios but in the 

 allantois. This induced chemists to change its name to allantoic 

 acid; and Wohlerand Liebig having found it incapable of neu- 

 tralizing alkaline bases changed that name to allantoin. 



An account has been given in the Chemistry of Vegetable 

 Bodies, (p. 212) of the method employed by Wohler and Liebig 



* Ann. de Chim. xxxiii. 279. 



