They give the biuret and xanthoproteic reactions, and form salts with both acids and bases.
The diketotetrahydrotriazoles, or urazoles, are formed by condensing urea derivatives with hydrazine salts, urazole itself resulting by the action of urea or biuret on hydrazine or its salts.
When heated above its melting-point, it yields ammonia, cyanuric acid, biuret and ammelide.
Urea may be recognized by its crystalline oxalate and nitrate, which are produced on adding oxalic and nitric acids to concentrated solutions of the base; by the white precipitate formed on adding mercuric nitrate to the neutral aqueous solutions of urea; and by the so-called "biuret" reaction.
Biuret (allophanamide), NH 2 CO NH CO NH 2, is formed by heating urea; by the action of ammonia on allophanic ester; and by heating urea to 140° C. and passing chlorine into the melt at 140-150° C. (J.