AN EVALUATION OF THE TOLUIDINE BLUE TEST FOR THE ASSESSMENT OF ALLOPHANE AND IMOGOLITE

概要

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Toluidine blue (TB) is absorbed on negatively charged colloids and exhibits a characteristic color change from blue to purplish red (metachromasis). A procedure to test the metachromasis of TB was applied to two sets of soil samples derived from volcanic ash, which differed in their horizon, clay mineral composition and nature and content of humus. The results showed that the absence of TB metachromasis can be used to diagnose the predominance of allophane and imogolite with low SiO_2/Al_2O_3 ratios in B horizon samples, and also in Al or Ap horizon samples when these samples are pretreated with H_2O_2. The metachromasis of TB which was observed in the presence of relatively small amounts of layer silicates made the assessment of allophane and imogolite difficult in a few Ap horizon samples. The absence of TB metachromasis can also be used as an indication of @andic@ soil properties, when the test is applied to samples without H_2O_2 pretreatment.
社団法人日本土壌肥料学会の論文