It has been proposed to replace fulminate by silver azoimide (Wdhler & Matter, Brit.
Wdhler, Ann., 1848, 67, p. 360).
This last process was much improved by Brunner, Wdhler, and especially by F.
Wdhler, Ann., 1850, 73, p. 219), the anhydrous acid being.
Wdhler repeated the experiment at GÃ¶ttingen in 1827, employing potassium alone as the reducing agent, he obtained it in the metallic state for the first time.
Wdhler oxidized potassium ferrocyanide to potassium cyanate by fusing it with lead or manganese dioxide, converted this cyanate into ammonium cyanate by adding ammonium sulphate, and this on evaporation gives urea, thus: K 4 Fe(NC)r-->K CNO--->NH4CNO->CO (NH2)2 It may also be prepared by the action of ammonia on carbonyl chloride, diethyl carbonate, chlorcarbonic ester or urethane; by heating ammonium carbamate in a sealed tube to 130-140° C.; by oxidizing potassium cyanide in acid solution with potassium permanganate (E.