Abstract
Previous investigators have shown that the binary systems involving the monocarbides of zirconium, columbium, tantalum, titanium, and vanadium are of the solid solution type, with the exception of 
which are almost completely insoluble in each other. In the present study it is shown that the mononitrides of zirconium, columbium, titanium, and vanadium, which have the same 
type crystal structure as the corresponding carbides, are also soluble in each other, with the exception of the pair 
. As in the case of the carbides, this exception can be explained on the basis of the atomic size rule governing the formation of solid solution. Furthermore, it is established that most of the binary systems formed by a carbide and a nitride are of the solid solution type, providing the atomic diameters of the metal atoms do not differ by more than about 15 per cent. The systems involving zirconium carbide with the nitrides were not investigated because zirconium carbide decomposed in a nitrogen atmosphere at high temperature.