Abstract
Of six soils (see Table 2), derived from various parent materials, amounts of easily soluble magnesium were determined in the following way. Ten or five grams of air dried soils were extracted by 0.05 N, HCl (GEDROIZ's solution for extracting exchangeable constituents); of the extract, the amount of MgO was determined by the use of electric photometer. After removed from R_2O_3 as well as calcium and acidified with acetic, the extracts were coloured by the additions of titan yellow solution, NaOH, glycerin and starch; and so developed colour was applied to electric photometer, and percentages of transmittance (see Table 3) were determined by green filter. Refered to a transmittance-concentration curve (Plate 1), the amount of MgO was calculated (Table 4). From the results of Table 4,the following facts were observed : easily soluble magnesium was much, in general, in the soils, except alluvial soils, rich in total magnesium; and a ratio of total magnesium to easily soluble magnesium was comparatively high in same soils, poor in total magnesium, soluble in conc. HCl.
