The brown residue, obtained by heating oxamide for several hours in a sealed tube, has been shown to be paracyanogen. The chemical and physical properties and infra-red spectra have been compared with those of paracyanogen prepared by thermal decomposition of mercuric and silver cyanides. Some suggestions are put forward with regard to its structure.IN an attempt to grow large crystals of oxamide by slow sublimation a brown residue was found in the hot section of the sublimation tube. It was suspected that this was paracyanogen. The substance was therefore compared with paracyanogen from other sources. These compounds are little known and their structures are undetermined.Paracyanogen was first noticed by Guy Lussac (Annulen, 1816, 53, 139) during his experiments on heating mercuric cyanide, which led to the discovery of cyanogen. He considered the material to be mainly carbon with a small nitrogen content. Johnston