A colorless, inflammable, poisonous gas, C2N2, with a
   peach-blossom odor, so called from its tendency to form blue compounds;
   obtained by heating ammonium oxalate, mercuric cyanide, etc. It is
   obtained in combination, forming an alkaline cyanide when nitrogen or a
   nitrogenous compound is strongly ignited with carbon and soda or
   potash. It conducts itself like a member of the halogen group of
   elements, and shows a tendency to form complex compounds. The name is
   also applied to the univalent radical, CN (the half molecule of
   cyanogen proper), which was one of the first compound radicals
   recognized.