As shown in the previous study on the corner fracturing in rock which was reported in the Journal of the Mining and Metallurgical Institute of Japan, Vol.83, No.952, Aug. 1967, the authors clarified already that the corner fracture was not developed essentially in a brittle rock-like material. But it has been reported that the corner fracture is produced actually in metals and in some kinds of plastics.
Therefore, in this study, in order to complete the studies on the corner fracture, a plastic material (polymethyl methacrylate) was used as the test material in which the corner fracture was expected to produce, and the stress condition in it in case of blasting with two free faces was analysed by means of the method same as that used in the previous study.
The results obtained in this study are as follows;
(1) It was clarified both theoretically and experimentally that the corner fracture was developed in the plastic material.
(2) There was the difference between the stress distribution in a rock caused by an explosion and that in a plastic material. Therefore, the pattern of the crack produced in the plastics was different from that in the rock.
It suggests us that, when the plastics was used as the model material for the studies on rock blasting, the results obtained might be analysed very carefully.

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At present, one of the most urgent problems of deep level mining in Japan is to improve its hot air conditions so that miners can do efficient work healthfully. As everybody knows we can deal with such environments by increasing the quantity of air in circulation or by applying air cooling equipment to such workings. In order to take measures to meet these situations and put in practice an optimum ventilation, it is indispensable to estimate underground air temperature and to judge the general effect of the estimation quickly and correctly about various ventilation plans which may be suggested in a mine.
The author has studied for several years on an air temperature forecast technique in underground. Making these studies complement and apply to real underground temperature problem, the technique was developed to calculate the mean air temperature for voluntary lapse of time and the temperature amplitude for the steady periodic variation of surface atmosphere. The model used in this study is adopted the mechanism of heat transfer between air current and surrounding rock and is disregarded other minor factors. This paper gives a general procedure to forecast the air temperature in an intake ventilation system. The procedure consists of many same iterative computation, so that the utilization of a digital computer is effective.

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In the previous paper the author had chance to present one part of my studies on the dynamic behavior of large conveyors, which treats mainly the dynamic tension during acceleration.
In this paper the author wants to treat the characteristics of an electrically tensioning device, which is not widely known to us. One of the most important problems of power take up is how to choose its proper tensioning speed for the kinds of belts. The author has studied the movement of power take up mathematically, and made clear its designing points.

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Applicability of vacuum volatilization process has been investigated for the complex sulfide ore which is generally known as “Black Ore”. An attempt has been made to recover lead and zinc sulfides by volatilizing them from black ore concentrate under a reduced pressure and simultaneously to obtain copper enriched concentrate as a residue. In addition, a new trial has also been made on the recovery of metallic lead and zinc by means of direct reduction. of gaseous lead and zinc sulfide with metallic iron and a mixture of calcium oxide and carbon. After the removal of excess sulfur by preliminary treatment, the concentrate was heated under reduced pressures of 10-1, 1 and 10mmHg in order to determine the volatilizing ratio of these sulfides. In this case, volatilization of lead sulfide proceeds prior to that of zinc sulfide. Recoveries of lead and zinc sulfides were more than 95% for PbS and more than 99% for ZnS, respectively. It is possible to obtain the respective sulfide of high purity separately without any intermixing if the temperature of condenser is well controlled.
In case that metallic iron or a mixture of calcium oxide and carbon is used as a reducing agent, gaseous lead and zinc sulfides can be directly reduced to metals at the temperatures more than 950-1100°C depending on the reduced pressures applied. Metallic lead and zinc can be recovered separately. Recoveries of these metals were 90-97% for lead, and 89-100% for zinc and the purities of these metals obtained were more than 95% for lead and more than 99% for zinc, respectively. When the concentrate is treated under a less reduced pressure, it is necessary to volatilize at higher temperature as compared with the case of high vacuum. presure, in order to obtain satisfactory results for removal and recovery of these metals. In this case, however, a reducing atmosphere should be maintained to avoid the oxidation of condensed metals and metallic iron which is used as a reducing agent.
The residue obtained in this process is corresponding to the concentrate of copper enriched or lowgrade matte, and can be used as a raw material of ordinary copper smelting.

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On the electrolytic process of zinc, Co⁺⁺ must be removed from the zinc sulfate solution beccuse of its harmful effects to the current efficiency.
Removal of Co⁺⁺ by the zinc dust, is not always satisfactory. So, copper ion and arsenous acid are added with zinc dust, or β-naphthol is used.
I studied the mechanism of the Co⁺⁺ removal from the zinc sulfate solution and found the favorable zinc dust which could successfully deposit the cobaltic ion, and which contained small amount of antimony and lead.

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Thermodynamic properties of molten Sn-Fe system were estimated by e. m. f. measurements employingsolid electrolytes. The e. m. f. of following oxygen concentration cells were measured at the temperature range of 900-1250°C.
Fe·EFeO /ZrO (+CaO)/ Sn-Fe·FeO
From these experimental results, it has been found, (1) the activities of tin and iron in molten Sn-Fe system had large positive deviation from Raoult's Law, (2) the Sn-Fe alloy solution in the field of homogeneous liquid phase was confirmed to nearly be a regular solution, (3) the present data for activity of iron in Sn-Fe alloy solution were in a good agreement with the calculated values which were derived from the phase diagram as a regular solution using heat of fusion of iron, and also these obtained values were not so far different from the presented values by Davey, (4) the present experimental results gave some support to the liquidus line in the range of 900-1180°C determined by Campbell, Wood and Skinner on the Sn-Fe phase diagram.

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Vapor pressures of zinc and cadmium in liquid copper-zinc and copper-cadmium alloys have been measured by means of the transportation method.
Activities calculated for copper-zinc alloy show considerable negative deviations from Raoult's law. The following equation derived from activities determined is well realized in the measured temperature range from 850°Cto 1200°C.
RTlnγ_Zn=-6400N²Cu±90
From this relation, both of the activity coefficients of copper and zinc atinfinite dilution are estimated to be 0.11 at 1200°C. Heats of mixing are exothermic and show a parabolic curve having a maximum of about -1.6kcal/mole at N_zn=0.5. From the above equation and the uniformity of a-function, it is considered that the liquid copper-zinc alloy shows the behavior of regular solution in the range of N_zn=0 to 0.6.
Owing to the high vapor pressure of cadmium, the measurements were limited in the ranges of composition from 0.40 to 0.85 in N_Cd and of temperature from 600°Cto 650°C for copper-cadmium system. Calculations of activities were extended to total range of Cu-Cd binary system by extraporation. Activities thus obtained agreed well with the values reported by previous investigators and also agreed well with the values estimated from liquidus. Free energies of mixing and excess free energies were also in good agreement with the other data, but not the heats of mixing.

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The study of the recovering titanium from Ilmenite by the Nitrofluor process was undertaken. Complete disintegration of the Ilmenite was achieved within two hours in a nonaqueous HF-NO₂ azeotrope boiling at 52°C. During decomposition the complex metallic compounds produced, the most of titanium dissolved in the azeotrope while iron was selectively precipitated.
For further isolation of the complex compounds, titanium bearing compound was heated in argon or argon-azeotrope vapor atmosphere and pure TiF₄ or nitrosylium penta [hexa] l fluoro titanate was cbtained respectively by selective volatilization.
The fundamentals of recovering components of the azeotrope which are chemically consumed during this process were studied.
Although this research has shown that the Nitrofluor process is superior to recovering not only titanium but also berylium, zirconium and many other elements from their minerals, further fundamental investigation is necessary to establish these process.

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