Physical properties of bentonites at room temperature used for green sand moulds and skin dry moulds for steel castings were described.
  The results are summarized as follows.
  (1) Suitability of testing methods applicable to bentonite for mould, particularly of the penetration test, the liquid limit test and the swelling test, were comparatively examined.
  (2) The physical properties of bentonite-water mixtures were found to be under an extensive influence of the inherent characteristics of the bentonite, but not influenced by the so-called fineness.
  (3) The physical properties of bentonite-water mixture with a water-to-bentanite ratio as low as normally employed for actual mould sands, the testing method for which is rather difficult to conduct, were found to be satisfactorily deductable from testing results on mixtures with high water-to-bentonite ratio, which are for readily obtainable by such testing method, the liquid limit test or swelling test.