One of the world's newest and most modern electrolytic zinc plant has been in operation at Akita City, Japan since Janualy 1954. The plant was designed, built, and is operated by the Mitsubishi Metal Mining Company, Ltd.
This plant is unusual in that it treats a wide variety of concentrates, which ae particularly high in copper in comparison with feed to other electrolytic zinc plant. The plant, in 1956, has a rated capacity of 25 metric tons of special high grade zinc.
The DORCO Fluo Solids process is successfully applied for roasting the concentrates.
The exhaust gas is washed by a Peabody scrubber and sent through an underground pipe to the Fertilizer plant 600 meters away. Hydrometallurgically a low density and low acid process is used. The entire system is designed to be continuous and mechanized. Continuous double leaching, 2-stage washing by Oliver filters, and continuous 3-stage purification process precede electrolysis. The zinc slab produced is certified to be more than 99.997 per cent pure.

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In this report, a four probe methode of resistivity measurement is described, and the relation between electric resistivity of pyrrhotite and temperature at which they were formed is mainiy discussed.
The results obtained by the measurement are as follows:
(1) The resistivity of pyrrhotite varies from 10^-3 ohm. cm to 10^-1 ohm. cm as Harvey described, and is smaller than the value reported by J. J. Jakosky.
(2) The variation of the resistivity of pyrrhotite with temperature is given by the following formulaρ=A·eKα/T.
where ρ is resistivity, A, K, and a are constants and 1' is absolute temperature (K°)
(3) The frequency curve of resistivity of pyrrhotite from pyrometasomatic deposits, has two peaks. On the other hand, the pyrrhotite from so-called hydrothermal deposits has one peak.
(4) It can be said that there is some qualitative relationship between the types of frequency curves and temperature at which they were deposited. This relation, therefore, may be applied to the geothermometer, inspite of necessity of further researchs.
(5) It seems that there is no correlation between resistivity and difference of level hight.The resistivity of pyrrhotite in skarn probably of high temperature forming is higher than that of pyrrhotite of lower temperature forming.

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The authors have carried out researches on the mechanism of the failure appearing in the rock around an underground opening, and have got results as follows. There appear two types of failure, tensile and compressive, when the theoretical maximum tensile and compressive stresses, determined on the basis of elastic rocks, reach values, 1.5-2 times the tensile strength and about 1.1 times the compressive strength respectively. The former failure grows into a tensile crack extending vertically, while the latter into a number of shearing fractures. Lastly the progress of the failures has been discussed, considering the results above mentioned and the mechanical properties of rocks, and somewhat a new concept about the progress of the failure has been presented.

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For the quantitative estimation of the workability of the coal face, the authers studied the friability of coal, and already introduced some experimental formulas which explain the relations between the cutting resistance and the friability of coal.
In order to apply these results to the coal face working underground, we invetigated how the cutting speed, rake angle and setting angle of the cutting edge influence upon the cutting resistance. These experimental studies have enabled us to estimate the rope pull and the power of coal planer required to coal seam cutting.
Furthermore we discussed, with some reasonable assumptions, on the other resistances of driving coal planers caused by the loading of broken coal and some subsidiary frictions.

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Recently the Tromp's partition curve has been applied to evaluate the classification performance in the form of a classification diagram (size-partition curve). Its basal principle is the same as the partition curve for gravity separation. In handling practically the classification diagram, however, it is insufficient to construct it with the conventional methods used for the gravity separation, because of some particular difficulties such as, for instance, the inaccuracy of testing sieves and sizing work.
The authors had observed empirically the above fact, and contrived a graphical. method to construct the partition curve. This method is based on the properties of the cumulative weight curve. From the tangents of the cumulative weight curves of feed and two products (underflow and overflow), three weight-distribution curves are obtained, from which the partition curve is derived graphically. To get partition curve with the correction of void-filling material, the equation Z_o=Z_o(1-ω) is used, in which Z_o and Z_o are the distribution factor to overflow before and after the void correction respectively and w is the distrtbution percentage of water to un derflow.
The partition curves obtained with this method are practically accurate except at their both ends. This method can naturally be used for the gravity separation as well, and is expected to be useful to reduce the number of the gravity fractions in sink-float analysis.

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The electric conductivity of molten lead silicates of various composition, 20 to 60 mole SiO₂, was determined at the temperature ranging 800 to 1, 150°C. The conductivity increased with rising temperature and with increasing PbO-content. There are two discontinuities in the conductivity-composition curve; each corresponds to the composition of 2PbO·ESiO₂ and PbO·ESiO₂ respectively, the fact showing the presence of these compounds even in the melt. The conductivity of some samples was also studied while heating from the solidto the melt. The appearance of melt was shown by sudden change in the logarithm of conductivity-reciprocal of absolute temperature curve.

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