Abstract
Soils, applied to this experiment, were all of reddish colour. (See Table 1) Of these soils, free iron oxide of which was previously removed by the extraction of Na_2S after TRUOG, colours were determined by the use of photo-colorimeter. Colour, so photometrically determined, was compared with that of original soil. The comparison of colour was made, in this case, depending on the purity and the dominant wave length. From the results of comparison (See Table 2,and Fig. 1), all soils decrease their purities, but not remarkably their dominant waves, except some soils (M902,903 & M907,908), by the removal of the free iron oxide. Colours of these soils were supposed mostly to be quite fundamental.
