The miners sometimes meet some electric shocks of the static electricity charged by friction of rock dust flowed in the pipe against it's wall, and such shocks were experienced very often in use of the pipe of synthetic materials
This work was done as for declare the phenomena of charging of static electricity on the synthetic pipes undergoing the concrete conditions of coal mining, and then, to find out some appropriate measures to predict it easily,
In the experimental stands of laboratory the following materials were tested:
-small pipes of vinyl chloride used for rock dusting, -blasting wire rested nearby the small pipes abovementioned;-air pipes of vinyl used for local ventilation.
As a result of these studies the authors declared some general characteristics of static electricity charged in use of the pipes of synshetic materials as follows:
1) As the rock dusts flow in the pipe at velocity of 5m/s and the more this pipe is charged by static electricity, and we can sometimes see the sporks of electric discharge when the velocity of flowing dust surpasses 20m/s;
2) Blasting wiles rested nearby the pipes of vinyl chloride being used for rock dusting are probably induced to charge the static electricity in them, attaining the static voltage 4kV and the more. The short spark by this voltage can ignite the air-mixture of methane;
3) Air pipes of 250mm diameter are charged by static electricity when the rock dust of 41g/min. and the more at the velocity exceeding 5.3m/s, and this static charge growsup with the flowing speed of rock dusts.
The authors found out some appropriate countermeasures against such static electric charges and successfully experimented some ones of them in a laboratory

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In the previous paper, we pointed out that a remarkable reduction of cutting resistance of rock can be expected by the application of the ultrasonic vibration cutting method.
In this report, the results of the further investigations on this problem are described. As the first step, several kinds of rocks and “matsuiwa”, silicified woods, were cut by the vibrating bit, and then the rate of the reduction of cutting resistance was compared with their mechanical properties. Then the effect of the amplitude of vibrating bit and the water pouring on the cutting resistance and the wear of bit were studied. The results obtained from these studies are as follows.
1) The rate of the reduction of cutting resistance in the case of vibration cutting is dependent on the hardness of rock.
2) The rate of the reduction of cutting resistance increases with the increase of the amplitude of vibrating bit, but when the amplitude increases over a limit which seems to be an inherent value of the rock to the kinds of rocks, the rate of the reduction is approximately constant with the amplitude.
3) The cutting resistance in the case of wet vibration cutting process is remarkably low in comparison with the dry cutting.
4) The wear of bit increases as the amplitude of vibrating bit increases.

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Pyrrhotite, pyrite and marcasite, known generically as Iron Sulphide Minerals, have a similar chemical composition respectively, but on the other hand, each mineral is composed of a different crystal structure. Accordingly, as these minerals have a similar property respectively and at the same time, each shows cr quite different property, their flotation operation must be carefully done based on the particularity of their properties.
From these points of view, the author set about this study for the purpose of investigating and contrasting the flotation properties of pyrrhotite, pyrite and marcasite systematically considering the relation crystal structures.
In this report, for the purpose of comparing the flotation properties of these minerals fundamentally. “Flotation Properties with Xanthates”, “Effect of Activation with Copper Sulphate and Cupric Chloride” and “Effect of Depression with Soda Ash, Calcium Hydroxide, Sodium Cyanide and Starch” are investigated and. contrasted, under the same conditions made on three minerals, connecting with pH variation. The main results obtained are described in article 3.2, 3.3 and 3.4 of the text, and in Fig. 2 to Fig. 6. Thus, the author believes that more definite knowledge has been obtained about similar points based on similarity of chemical composition of pyrrhotite, pyrite and marcasite, and about different points which seem to be based on the difference of their crystal structures, in the flotation properties of these minerals.

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Anode potential-time curves have been determined for the selenide or telluride bearing copper anodes It was found that the potentials of these copper anodes were lower than that of electrolytic copper at the early stage of electrolysis. These differences of potentials increased as the temperature of the electrolyte was lowered and the current density was increased. As the electrolysis proceeds, the anode potentials raised for the sake of formation of anode slime. The composition of slime produced during electrolysis of the anode which contains copper selenide or telluride is different from that of original compound contained in anode.

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Sponge iron powder was prepared by reducing purified pyrites cinder with hydrogen which was obtained by removing As, Cu, Zn and silicate etc. from pyrites ore. The sponge iron was highly pure and its specific surface area was larger because of its porous structure than sponge iron ordinally used. The application of thus obtained iron powder for powder metallurgy, especially direct rolling to form thin sheet, was studied. Microscopic structure, magnetic and mechanical properties of the sheet were investigated. As for the magnetic property, average 6, 000 of maximum permeability and average 0.90 Oe of coercive force were observed. As for mechanical property, average 74 of Vickers hardness, approx. 20-24kg/mm² of tensile strength were obtained and deep drawing was excellent.

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