Spectrographic analysis, usually restricted to low concentrations of one element in another, may be extended to the whole range of the Ni-Co system when the purpose of the analysis is the determination of the diffusion coefficient of the solid metals. This is appropriate because the error of the spectrographic estimation is of the same order as the sampling error which arises from the disappearance of the original interface between the two metals. A solution method was used, and samples of about 20 mg from successive layers of the metal were analysed.
