A rapid method has been developed for the infra‐red spectroscopic analysis of simple mixtures of hydrocarbons. Through the construction of special equipment this method has been reduced to a routine procedure which can be carried out by comparatively inexperienced operators. The instruments built have proven sufficiently sturdy to be used for control work in plant operation. By basing the analytical method on an empirical calibration, the calculations involved have been reduced to a minimum. The instruments are relatively simple and permit the use of comparatively large spectral slit widths. This has eliminated the necessity for amplification of the thermopile output energy and for the determination of any continuous absorption curve. However, small spectral slit widths can be attained with the more versatile spectrophotometer if this should be required.