The methylene blue adsorption test measures the amount of methylene blue (MB) adsorbed on montmorillonite in bentonite. The test is one of the most important methods to estimate a quality of the bentonite. Therefore, the test is conducted by most of the bentonite companies such as mining companies, general construction companies and foundries. However, the detail procedures of the test vary among different companies. This study reports the differences in the amount of MB adsorbed on bentonite caused by the different procedures. We used the Mikawa montmorillonite which is the Clay Science Society of Japan (CSSJ) Reference Clay Sample JCSS-3102 Montmorillonite "Mikawa". The amount of MB adsorbed on bentonite dispersed in pure water with sulfuric acid was about 13% smaller than that in tetrasodium pyrophosphate (TSPP) solution. The amount of MB adsorbed on bentonite dispersed by boiling was about 9% larger than that by ultrasonic treatment. In the bentonite-dispersed solution, the initial amount of MB is normally about 75% to the amount of MB at the end point. When the initial amount of MB was < 50%. the amount of MB adsorbed on bentonite was about 5-7% smaller than when the initial amount was normal. To make halo around spots on a filter paper, various instruments (stirring glass rod, komagome pipette, and micropipette) and various filter papers (ADVANTEC No.131, No.2, No.5C and No.6) are used in the bentonite companies. First appearances of halo did not vary, but 1.5-2 mm width halo varied among the different instruments and filter papers. When the filter paper was No.2 or No.6, the 1.5-2 mm width halo was reached by about 4-6% smaller amount of MB than the other filter papers.

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