nS UREA AND ITS ALLIES. [App. 



water be removed, the result is often spoken of as a diamide. Thus if 

 from ammonic carbonate, (NH 4 ) 2 CO 3 , two molecules of water, 2H 2 O, be 

 removed, carbonic acid being a dibasic acid, the result is urea; thus : 



(NH 4 ) 2 C0 3 - 2H 2 = (NH 2 ) 2 CO, 



which may be written either according to the ammonia type as 

 CO 



H 



or as CO 



two atoms of amidogen (NH 2 ) being substituted for two atoms of hy- 

 droxyl (HO). 



This connection between carbonic acid and urea is shewn by the fact 

 that ammonic carbonate may be formed out of urea by hydration, as 

 when urea is subjected to the specific ferment mentioned above. 

 Regarded then as a diamide of carbonic acid, urea may be spoken 

 of as carbamide. Bat the theoretical derivation of urea from ammonic 

 carbonate by dehydration cannot be realised in practice, whereas urea 

 can readily be formed from ammonic carbarnate, and Kolbe is inclined 

 to regard it, not as the diamide of carbonic acid, but as the amide of 

 carbamic acid. Ammonium carbamate, C0 2 N 2 H 6 minus H 2 0, gives urea, 

 CO, N 2 , H 4 which, if carbamic acid be written as CO, OH, NH 2 , may 

 be written as CO, NH 2 , NH,, one atom of amidogen being substituted 

 for one atom of hydroxyl, and not two, as when the substance is re- 

 garded as derived from carbonic acid. Drechsel's experiments indicate 

 a ready derivation of urea from ammonic carbamate. He has obtained 

 urea by the electrolysis of a solution of this salt with rapidly alternating 

 currents thus removing the elements of water from the carbamate by 

 such alternating processes of oxidation and reduction as may be supposed 

 to take place in the body. The reaction is expressed as follows : 



i. NH . CO . O . NH 4 + O - NH 2 . CO . O . NH 2 + H 2 O. 

 ii. NH 2 . CO . ONH 2 + H, = NH 2 . CO . NH 2 + H 2 O. 



Wanklyn and Gamgee 2 however, since urea when heated with a 

 large excess of potassic permanganate gives off all its nitrogen in 

 a free state and not in the oxidized form of nitric acid, as do all other 

 amides, conclude that it is not an amide at all, that it is isomeric only 

 and not identical with carbamide. 



It is important to remember that urea is also isomeric with ammonic 



(N 

 cyanate, C j Q-J^JJ and indeed was first formed artificially by Wohlei 



(1828) from this body. We thus have three isomeric compounds, am- 

 monium cyanate, urea, and carbamide, related to each other in such a way 

 1 Arch.f. Physiol. 1880, S. 550. 2 Journ. Chem. Soc. 2, Vol. vr. p. 25. 



