We have discovered several new are deposits in our mine area by means of electrical prospecting, chiefly S. P. method and secondarily resistivety method.
Some interesting phenomena were found about the effects of over burden, topography, underground water, advance of developing of an are body, etc.
Especially, electric coring was effective for interpretation of negative centres.

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Specimens and “Twaki” sandstone of the Joban Colliery were made in cylindrical forms, cooled by submerging them within the vessel in the liquid air, and immediately after examined their tensile and compressive strengths.
Results of these tests show us that both strengths at low temperatures about 100°Cbelow the freezing point are remarkably larger, even six times, than those at the normal condition.

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The mixture of FeS, NaCl was roasted at various temperature from 300°C to 600°C in N₂atomosphere, and then was leached with water. The soluble Fe was traces. The mixture of Fe₂O₃, NaCl, S was roasted at various temperature from 300°C to 600°C in air, and then was leached with water. The soluble Fe was traces.
The FeS was rosted at various temperature from 300°C to 600°C in air, and then was leached with water. The soluble Fe was 0.1 0.3%.
The mixture of FeS, NaCl, S was roasted at various temperature from 300°C to 600°C in air, and then was leached with water. The soluble Fe increased to 400°C, and at 450°C decreased a little, and at 500°C increased extremely, and at abovd 500°C decreased again. Namely the maximum points of solubility were shown at 400°C and 500°C. When the roasting time was varied from 10 min. to 120 min. at 400°C and 500°C, in the former case the soluble Fe increased till 30 min., and after 30 min. decreased a lithe, but in the latter case the soluble Fe increared rapidly till 30 min. and after 30 min. decreased extremely.
Reaction formula can be shown as follows:
2NaCl+r/2S₂+2O₂=Na₂SO₄+Cl₂
FeS+Cl₂=FeCl₂+r/6S₆
→r/2S₂…(at 400°)
FeS+3/2Cl₂=FeCl₃+r/6S₆
→r/2S₂…(at 500°)

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