The action of a stream flowing from a nozzle 2mm. in diameter at the velocity of 100-300m/s in eroding solids is investigated. The effect on erosion of the distance from the nozzle and the angle of incidence of the stream is studied. Experiments show that the stream produces the most destruction when the streamis divided. The results can serve as a confirmation of the theory of the destructive action of cavitation, based on the multiple renewal of direct blows delivered to the surface of the solids by the liquid.

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In recent years there has been increasing interest in the development of new methods of breaking rock. Thermal rock fracture is one of the most effective new methods of rock fracture. New thermodrills, which were designed by the author, are now being tested and fracturing mechanism of rock is being investigated by experiments.
In this paper, the author examined the characteristics of thermal conduction in rock and thermalstresses in rock in case of thermal fracturing.
The following results were obtained;
(1)The most important factor in mechanism of thermal fracturing of rocks is the Biot number.
(2)We must design the thermodrill, of which jet velocity is maximum, while large velocity of jet gives the large Biot number.
(3)Rocks, which have large values of Youngs modulus and linear expansion coefficient, are desirable for thermal fracturing.

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In this paper, the authors described the relation between the weight variation and the spontaneous combustibility of coals.
Experiments were carried out at a constant heating rate by means of a highly sensitive thermobalance, and the weight variation of sample was measured as a function of temperature.
The oxidation process is composed of several stages, however, those stages partly overlap each other. Therefore, we divide them into four stages.
In the first stages the coal gains weight than original.In the second stage it loses weight.During the third stage which starts after the weight curve has passed through the minimum point, a sharp increase in weight is observed.In the fourth stage a rapid decrease in weight is observed.
Therefore, the authors conclude that the third stage must be able to show the susceptibility of coals for spontaneous combustion.Experiments have been made to research the various factors affecting the oxidation process and some interesting results have been observed.

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In starting of large conveyor occurs a Inogitudinal vibration of continuous media “belt”, which causes a remarkable variation of belt tension and a big surging of take up.When an electrically tensioning device is used, the theoretical and practical knowledge on its dynamic behavior is necessary.As a part of our research and experience on Akiyoshi long conveyor and, Utashinai high tension mine conveyor, in this paper the authors report results of our research on the dynamic behavior of large conveyors as follows.

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In order to apply some control systems successfully to the process considered, it seems neccessary in the first place to get enough informations about the characteristics of the object to be controlled.
In the previous report some investiaations were carried out on static characteristics of the object-that is, ball mill.
In the present paper some experimental data obtained by laboratory scale wet ball mill were discussed from the viewpoint of static as well as dynamic characteristics of ball milling process.
The main, conclusions can be summarized as follows.
i) The same relationships as previously presented were recognized among the variables feed rate F_MS, hold up H_s and grinding energy E. That is.
H_S ∝√F_MS
E ∝ H_S
ii) Indicial responses of some variables-discharge rate of each size fraction of the product, and the hold up were examined. The response curve of the latter variable could be well approximated by that of an element of first order.
iii) On the basis of the experimental data controllability of a typical closed grinding circuit was discussed. In this case it-was observed that the productivity of the grinding circuit and the stability of the control system could not be compatible.

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Some questionable problems on the chloride volatilization of pyrite cinder by heavy oil as fuel, was mainly discussed in labolatory experiment. And several series of experiment were carried out in order to clarify some problems. Optimum condition was obtained experimentally, and in this report describes some preliminary experimental work to effected of PH₂O, PH₂, Pco₂ and Po₂ in oil burning combustion gas. The results obtained can be summarized as follows.
The PH₂o and PH₂ in oil combustion gas extremely injurious to remove the copper. However, the existence of O₂ (>5%-vol.%) in the atmosphere is effective for decreasing those interference.

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The molten salts, sodium fluoride-barium fluoride-aluminum fluoride system, are known as “Hoopes' bath” in the electrolytic refining of aluminum.
The melting points and densities of this system were already reported by the author.
In this paper, the electrical conductivities of some compositions of the above-mentioned system were determined.
1) As a conductance cell of the molten fluoride salts, a platinum crucible combined with a platinized platinum wire was used.
To prevent errors due to polarization, we adopted
(i) An electrode of platinized platinum wire.
(ii) Resistances measured at 2, 500, 5, 000, 10, 000 cycles/sec were plotted against 1/√f and the linear extrapolations to infinite frequency were used.
Then we calculated both the electrical conductivities of the molten salts and the resistance of the lead wire by using the next formula;
R ∝ =R₀+K/k
2) The measuring value of the specific conductivity of the molten cryolite was 2.92 ohm^-1cm^-1 at 1, 050°C and 2.87 ohm^-1 cm^-1 at 1, 000°C.
3) The values of the molten mixtures of the ternary system NaF-BaF₂-AIF₃ are 5.0-1.0 ohm^-1cm^-1 at 1, 000°C and 950°C.
When the content of barium fluoride is kept constant, the specific conductivity decreases almost linearly with the increase of aluminum fluoride content, and when the content of barium fluoride increases, the conductivity decreases also.
4) The specific conductivity of the Hoopes' bath is 1.70 ohm^-1cm^-1 at 1, 000°C and 1.47 ohm^-1 cm^-1 at 950°C.
5) When we assume the formation of the compound NaBaAIF₆ and calculate the specific conductivities of these ternary molten salt mixtures, these values accord well with measured ones.
6) In this system, the following compositions show the comparatively low melting temperatures and have the same value as that of th, e Hoopes' bath.
NaF 50-57%, BaF₂ 30-40%, AIF₃ 8-18%
The densities of ihese salt mixtures also range between that of the anode alloy and the refined aluminum.

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