lOO ORGANIC AGRICULTURAL CHEMISTRY 



Urea occurs in considerable amounts in the urine of all ani- 

 mals. In man the amount is about 25 grams or one ounce per 

 day. It is present in urine in a much larger quantity than any 

 of the other nitrogenous constituents, all of which, as previously 

 stated, result from the metabolism of body protein or food pro- 

 tein, and they contain all of the nitrogen of the protein metabo- 

 lized. They are true excretion or waste products. 



Urea is a beautiful crystalline compound forming needle-like 

 prisms, melting at 132° C. It is readily soluble in water and in 

 alcohol. It may easily be isolated from urine, first as the nitric 

 acid salt, and this converted into free urea (Exp. XXXI). 

 When urea is heated with water to 180° C. or when it is 

 boiled with acids, hydrolysis occurs, and ammonium carbonate 

 is first formed, which then breaks up into ammonia and 

 carbon dioxide. 



/NH2 /ONH4 



0C< -h 2 H2O -> 0C< -> CO2 + 2 NH3 +H2O 



\NH2 \ONH4 



Urea Ammonium carbonate 



Probably ammonium carbamate (ammonium amino-formate) 

 is the intermediate product between urea and ammonium car- 

 bonate. This decomposition is the reverse of the reaction of 

 synthesis of urea from ammonia and carbon dioxide. The 

 importance of this decomposition is that it takes place natu- 

 rally due to the action of bacterial organisms, urea bacteria. 

 When urine undergoes fermentation, this reaction occurs and 

 the nitrogen of the urea, which is the nitrogen of the original 

 body or food protein, is thus set free in the form of ammonia. 

 This ammonia, which in some cases is useful as a plant food, 

 becomes readily converted by bacterial organisms into nitric 

 acid and its salts, in which form all plants can utilize it. 

 Thus, by these fermentation changes, nitrogen of urine, the 

 chief nitrogenous substance in ordinary manure, and which has 

 derived its nitrogen from the protein food, becomes converted 

 into forms directly available to plants. 



