A method has been described for removing iron oxide, silica, and alumina, existing as coatings and cementing agents on soil grains, preparatory to making petrographic studies of soil minerals. This method involves the reduction of the iron oxide by means of nascent hydrogen and its solution by oxalic acid, after which it is easily removed by washing. This treatment removes about 94% of the total Fe2O3 and small amts. of SiO2, A12O3, and TiO2. The treatment is rapid, and produces excellent soil separates for subsequent petrographic study, apparently does not attack the soil minerals, and allows attention to a large number of samples at one time.