Abstract: Base-exchange determinations were made on selected clays of the montmorillonite-illite group to test this method as an analytical tool for the analysis of mixed-layer aggregates. The relatively rapid manganese method developed by Bower and Truog was used and its precision determined on monodisperse, monomineralic fractions and monodisperse fractions of prepared mixtures of illite and montmorillonite. The particle size range 1–0.25 micron was chosen for all determinations exclusive of those on bulk samples.
To establish end members, determinations were made on a series of illites, fine-grained muscovite and both natural and synthetic montmorillonites.
In order to test the validity of this method, determinations were made on mixed-layer aggregates on which illite-montmorillonite percentages had been determined by other workers using x-ray techniques and chemical analysis.