1GO UKEA. 



might arise in the body from the union of two molecules of cyanic 

 acid and one of water : CO.NH+CO.NH+H 2 = (NH 2 ) 2 CO+CO 2 . 

 The final formation of cyanuric acid (CO.NH) 8 by the action of 

 heat on dry urea is further evidence in the same direction. On 

 the other hand there are a number of reactions resulting in the 

 production of urea, which leave but little doubt that urea, while 

 closely related to cyanic acid, is truly the amide of carbonic or 

 carbamic acid. Thus by the action of ammonia on phosgene 

 gas: COCl 2 -r-2NH 3 = CO(NH 2 ) 2 + 2HCl: of ammonia on 

 diethyl-carbonate : CO.(C 2 H 5 0) 2 + 2NH 3 = CO(NH 2 ) 2 + 2C 2 H 5 . 

 OH : reactions which are strictly analogous to the formation of 

 acetamide CH 3 . CO(NH 2 ) by the action of ammonia on acetyl 

 chloride CH 3 . COC1, and on ethyl-acetate CH 3 . COO (C 2 H 5 ). 



It is interesting to observe here that acetamide yields methylcyanide 

 by treatment with phosphorous pentoxide : CH 3 . CO (NH,) = CH 3 . 

 CN+H.O. 



Acetamide is also formed by the dry distillation of ammonium 

 acetate, the change being one of simple dehydration ; and this re- 

 action is one of general applicability, amides being formed by the 

 removal of one molecule of water from the ammonium salt of a 

 monobasic acid or of two molecules of water from that pf a dibasic 

 acid, e.g. ammonium oxalate yields oxamide. Now although urea 

 has not been formed by the dehydration of ammonium carbonate, 

 it is readily rehydrated into the carbonate by the action of acids, 

 alkalis, superheated water, or the urea ferment. Further, if instead 

 of operating on ammonium carbonate the ammonium salt of car- 

 bamic acid (see p. 151) be heated in sealed tubes to 140, or if it 

 be electrolysed with a rapidly commutated current, it loses a mole- 

 cule of water and is converted into urea. 



When the purely chemical facts above stated are applied to the 

 formation of urea in the animal body it is at once obvious that 

 urea might originate from some cyanic source, or from a simple 

 dehydration of ammonium carbonate or carbamate. A full dis- 

 cussion of the possibilities thus indicated lies outside the scope of 

 this work, but it may not be out of place to indicate, as briefly as 

 may be, the various views which have been put forward concern- 

 ing the probable way in which urea originates in the body. 1 



There is little reason for doubting that the larger part of the 

 nitrogen which leaves the body as urea was at one time a constit- 

 uent of the nitrogenous muscle-substance (see 484.) There is 

 equally no doubt, both from general considerations and from the 

 fact that no urea can ever be detected in muscles normally, that 

 the nitrogen does not make its exit from the muscles as ready- 

 made urea. Neither until recently had urea been obtained by 



1 The literature of the subject is very fully quoted in Bunge's Physiol. and 

 pathol. Chemistry, 1890. Lecture xvi. pp. 310-348. 



