This paper describes the use of a fully automated Fourier‐transform infrared spectrophotometer system to scan the composition of bulk slices of CdxHg1−xTe for the range 0.15<x< 0.35 and its calibration to analytically determinedXvalues. The most useful correlation established is for thentype, between the 300 K IR cuton defined by the zero‐transmission intercept of a line tangent to the transmission curve at 1/eof its maximum and the composition parameterXas determined by wet chemical analysis. The overall prediction accuracy of trueXis better than 0.005. Other cuton definitions, implementation pitfalls, andXcorrelations with bothp‐type transmission and 300 K carrier concentration are also discussed.