THE DETERMINATION OF CHROMIC OXIDE IN SAMPLES OF FEED AND EXCRETA BY ACID DIGESTION AND SPECTROPHOTOMETRY

Abstract

Numerous aspects of the wet acidic digestion procedure for the assay of Cr2O3 in feed and excreta samples have been investigated; these included time and temperature of heating, the effects of sulphuric acid concentration, and the wavelengths at which optical densities are read. On the basis of the findings, modifications of the procedure have been adopted.As the optical densities of dichromate solutions, which are the end products of the digestion, are influenced by their sulphuric acid molarities, it is essential that such molarities be kept relatively constant. Reading of optical densities at 350 mμ permits a much greater sensitivity in the assay than does the use of a wavelength of 444 mμ. Standard curves with correlation coefficients of 1.000 between Cr2O3 concentration and optical density were obtained consistently, demonstrating a high degree of precision. When a 3-gram sample of feed and a 1-gram sample of excreta are employed, the observed ratio [Formula: see text] must be corrected as follows:Corrected ratio = (observed ratio × 1.110) − 0.045. This correction accounts for the background light absorption at 350 mμ attributable to the feed and excreta.The modified method was found to give comparable results to the sodium fusion technique with evidence of slight advantages over the latter.