It is well known that KCNS reacts with ferric iron and produces the lovely pink red colour. By the use of this colour reaction, there have been many methods^<(1)(2)(3)> of determining the acidity of soils ; the methods have been always owing their fundamental ideas to the fact that this reaction becomes intense with an increase of soil acidity. The test, here reported, depends also upon the above fact, and has somewhat speciality in its simplicity of procedure. The procedure was as follows : KCNS-test paper. ・・・・After immersed in the solution (30 gm of KCNS sol. in 500 cc of ethyl alcohol), filter paper (7 cm. in diam., No.6 by TOYO-ROSHI;CO.) was kept to dryness. Extracting solution. ・・・・0.05N solution of HCL ; reagent used by GEDRCIZ for extracting exchangeable bases in the soils. Method.・・・・2.6 gm of air dried soil, in a test tube, were added with 13 cc of extracting solution and settled for one hour occasionally shakened. After the settling, the content was filtered. One drop of the filtrate was brought carefully to be settled on the center part of the test paper, and was kept to dryness. (see Fig. I.) If developed, the pink colour was examined and classified into the following four grades after its intensity. [table] Results : Of forty four soils, the following results were got. (see Table. 1) Almost all the applied soils except those of volcanic ash origin, (such as Nishigahara 1,2 & 3 and Misotsuchi) showed this reaction. 2) The podsolic soils, whose bases were considered to have been leached out, showed intense reaction. 3) Of ground-water soil types, all samples, except one of G horizon of Brown lowland soil and the other of A horizon of Meadow soil showed generally this reaction. These exceptions were considered to be due te the volcanic ash nature for the former and the severe leaching ("Rookyu-ka" in Japanese) for the latter. Anyhow we may conclude that the more the soils become deficient in bases or acidic to some extent the more the reactions become intense. This conclusion may be accepted after the results of experiments shown in Table. 2. In this experiment ; alluvial soils of River Arakawa were applied after being treated in three ways : 1) electrodialyzed for about 100 hours, brought to be deficient in bases and acdidified, 2) non-treated, and 3) added with CaO in an exchangeable form. Among the reactions of these three samples, that of 1) was stronger, of 2) medium and of 3) more feeble. There was observed a tendency of soils to show this reaction more intensively after the degree of deficincy of bases.
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