Abstract
According to the results of our research, hydrofluoric acid method was favourably compared to sodium carbonate fusion method for the determination of total iron, manganese and titanium in soils. Procedure of HF treatment is as follows : Take about 5 g of air dry fine soil (<2 mm) into an agate-mortar and crush it thoroughly. And then, take 200.0mg from it. Put it into a platinum-evaporating dish. Place it on a wirenetting asbestos in a draught. Add 5 ml of 1 : 5 H_2SO_4 and 5 ml of 40% hydrofluoric acid. Heat and evaporate gently to dryness, and ignite the evaporating-dish for a minuite to decompose the residue of organic matter. Repeat it until all the silicate would be decomposed. Usually, these two treatments should be enough. Evaporate it, but it should not be ignited this time, because the residue would become insoluble. Add 20 ml of 1 : 5 H_2SO_4 and boil it to dissolve the residue. Pale yellowish solution is obtained. Make it up to a definite volume. This solution is adapted directly to determine the total iron in soil by the titration with N/1OO standard mercurous nitrate. Further, it is applied to determine the total manganese and titanium colorimetrically. Procedure of Na_2CO_3 fusion was carried out as the usual method. Summary : 1. The crusibles used for Na_2CO_3 fusion were made of Pt, Ni and Al_2O_3,and among them Ni-crusible was suitable for the Na_2CO_3fusion. 2. This method (HF treatment-HgNO_3 titration method) was more convenient and rapid than the fusion method to determine the total iron in soils, and more reliable because iron and SiO_2 do not remain in Pt-evaporating dish.
