Mixtures of boron and carbon were heated at approximately 2000°C; the reaction products have been studied by x‐ray diffraction and by density and electrical measurements. The existance of a wide range of homogeneity of ``boron carbide'' has been established. No evidence of compound formation corresponding to B4C could be detected. Similarities between the structures of boron and ``boron carbides'' indicate that the latter may best be described as solutions of varying amounts of carbon in a slightly distorted boron lattice.