A procedure by finite difference method is described for calculating the temperature of mine air as it passes through a dry roadway. The accuracy of the calculation by this method is discussed, using the values of the exact solution by van Heerden. For an example, the calculation of air temperature is carried out when the temperature and volume of intakesairchange after one year from the start of ventilation.

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In this paper, the outburst of gas and coal has been studied, from the view point of geological structure in coal field.
The results obtained are as follows:
1) Geologically, the nothern district of Sorachi coal field including the collieries such as Sunagawa, Utashinai, Akabira etc. has the most complex structure, particularly with many faults, in Hokkaido coal field. In this district, a lot of weakened zones of coal seams and rock layers with high pressed and much quantity of free gas are observed.
2) It should be especially noticed that the blasting in the crossing structure is apt to be the over charged blasting and the bottom shock blasting, owing to the frequent changes of rock and coal strength in drifting. And even in the lower potential zones, the shock of the blastings mentioned above may give rise to the outburst of gas and coal.

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The object of this study is to develop the vertical screw conveyors for transportation of wet sand, mud, sludge material, coal or ores. As well known, the screw conveyors are widely used for conveying friable or granular materials in agricultural field, but they are not available for wet sand and mud.
In this paper we reported the results of experimental investigations which were carried out with dry and wet sand. The relations between the vertical 'velocity of a particle or the output of conveyor and many technical parameters, i. e. screw speed, inclination angle of the screw blade, pitch, friction coefficient between sand and screw or casing pipe etc. were, obtained
The most desirable parameters on constructions and operations of vertical screw conveyors for dry and wet sand were obtained. The results are useful for designs of the vertical screw conveyors.

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The size of make-up balls is one of the most important factors affecting capacity and grinding efficiency of ball mills. However, the size distribution of seasoned ball load which performs actual grinding work is establis hed by the relationship between ball size x and the rate of wear as well. Employing the thickness of film removed by wear per hour h(x) as the wear rate at size x, the author has derived eq.(1) which states that the distribution of number of balls in an equilibrium ball load is determined by h(x).
Previous studies which appear in references indicate that h(x) follows eq.(4).From eqs.(1) and (4) the distribution of the number of balls n(x) is n(x) =n_f/2kx^m (5) where nf is the number of make-up balls fed per hour, k and m are constants.
Eq.(9) derived from eq.(5) shows the size distribution of equilibrium ball load is determined by the wear film index m.And the value can be obtained when the size distribution of equilibrium ball load in an operating mill is measured. The index m in Yaguki No.3 mill with make-up balls rationed is found approximately zero by using eq.(17)(fig.1).This means equal film wear in equal grinding time.
Additional, equations on the equilibrium ball load for practical applications are also presented as follows. And it is expected that the control of ball mill operation will have more scientific means when the wear film indices are measured in mariy operating mills.
1) The procedure to calculate the start-up media is described (eqs.9 and 17 and fig.1).
2) Specific surface area is given.in eqs.(21) or (23).
3) Actual wear rate is obtained by eqs.(24) to (27).It was 4.2×10^-4cm/h in Yaguki No.3 mill.
4) Size of the individual ball reduces as indicated in eqs.(30) or (31), and the time required to reach equilibrium is given in eqs.(33) or (34).
5) After the condition of make-up balls is changed, the portion of remaining balls previously fed decreases as stated in eqs.(35) and (36) corresponding to weight and surface area respectively (fig.2).
6) Loss of weight of remaining balls per hour is given in eq.(37).

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The spectrophotometric determination of Aerofloat with ferroin has been investigated to determine the amounts of Aerofloat adsorbed on sulfide minerals.
Aerofloat is extracted from aqueous solution into nitrobenzene as ion pairs of Aerofloat and ferroin.
The absorbance of extract has a maximum at 514nm.and does not vary within an hour.The calibration curve obeys Beer's law.
The absorbance is constant in the pH range 2 to 10 and it is affected by the presence of monovalent anions of relatively large steric structure, such as NO_-3and ClO^-ions, but is not by the presence of divalent anions, subh as SO₄^2-, CO₃^2-and S^2-, which are often contained in flotation pulp of sulfid oees.
Therefore, the amounts of Aerofloat adsorbed on galena or chalcopyrite surface are easily determined from the difference between initial and equilibrium concentrations.But, when the decomposition of Aerofloat occurs in course of adsorption process, the amounts of adsorption can not be determined by this method.In this case, it can be estimated from the amounts of Aerofloat desorbed from sulfide mineral surface by treatment with sodium sulfide solution, because Aerofloat adsorbed on the surface is entirely desorbed by sodium sulfide.

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The potential and pH measurements of the S₂0^2-₃-H₂O system were carried out at 90°C by decreasing the pH of sulfate solutions (about lg-ion/l. S0^2-₄) containing dissolved sodium thiosulfate (1, 0.1 and 0.01mo1/l) by the aid of a rotating Pt electrode, a glass electrode and two reference electrodes (S. C. E.).
The results obtained were summarized in the potential-pH diagram (Fig. 4) and empirical potential-pH equations were presented and compared with those calculated at 100°C. It is considered that the measureed potentials corresponded to the potential for S₄0^2-₆/S₂O^2-₃ and that for S°/H₂S in the neutral region and acidic region where S₂O^2-₃decomposed, respectively.

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To investigate the reaction of the surface active agent to the electrode, the activation energy of the electrolytic deposition of lead was estimated by the relation between the electrode reaction velocity i and the overpotentialπ.
The experimental results were as follows;
1) The Tafel equation was applicable in the region of current density from 1 to 10mA/cm² in case of noaddition electrolyte.The electrolytes containing glue, gelatin or phenol show the same behavior as the no-addition electrolyte.However, the addition of KSCN elevates the applicable region of Tafel equation from 10 to100mA/cm².
2) The intervals of the Tafel line and its inclination measured at each electrolytic temperature increased with increasing amount of the added surface active agent in the electrolyte.
3) The activation energy increased with increasing amount of the added surface active agents.Most remarkable increase of activation energy was observed in the case of phenol addition.With the addition of 0.2g/l KSCN to the electrolyte, a maximum in activation energy was observed.These activation energy is dissipated when Pb ion passes through the double layer.It is satisfactory to consider that the surface active agent affects the formation of the double layer.
4) The shape of deposited layer was dependent on the kind of surface active agent.Glue and gelatin gavesmooth surfaces and phenol and KSCN gave the dendritic or needle like shapes.

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