HYDRAZINE (DIAMIDOGEN), N2H4  or H2 N•NH2, a compound of hydrogen and nitrogen, first prepared by Th . Curtius in 1887 from diazo-acetic ester, N2CH•CO2C2H5 . This ester, which is obtained by the action of potassium nitrate on the hydrochloride of amidoacetic ester, yields on hydrolysis with hot concentrated potassium hydroxide an acid, which Curtius regarded as CIH3N6(CO2H)a, but which A . Hantzsch and 0 . Silberrad (Ber., 190o, 33, p . 58) showed to be C2H2N4(CO2H)2, bisdiazoacetic acid . On digestion of its warm aqueous solution with warm dilute sulphuric acid, hydrazine sulphate and oxalic acid are obtained . C . A . Lobry de Bruyn (Ber., 1895, 28, p . 3085) prepared free hydrazine by dissolving its hydrochloride in methyl alcohol and adding sodium methylate; sodium chloride was precipitated and the residual liquid afterwards fractionated under reduced pressure .