Measuring the stresses and their variations on the wall of the lateral roads at the Sanyomuen anthracitemine near Mine City by means of photoelastic stressmeters and electrical resistance strainmeters, theauthors have investigated into the effect of progress of a longwall working upon the stress state in the roofand floor.
From these measurements, they have shown the magnitude and location of both the peak pressure infront of, and the lowest pressure to the rear of the caal face. They have also clarified the initial pressurebefore the mining was started as well as the recovery of pressure after the mining was over.

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With the progress and popularization of electronic digital computers, many enterprises in mining industryintroduce the machines and are making use of them in management and production control. in thefield of mine ventilation the possibility has come about in the analysis of ventilation networks by use ofthese machines.
One of us studied this problem several years ago. Including the improvement of previous study, wehave developed two general methods of the network analysis which were adopted two successive approximationprocedures and could be applied to any complicated ventilation system consisting of large number ofairways.
One of them is fit to use the computers of large capacity and is able to analyse the system consistingof some 100 airways, the other is very popular method on which Hardy Gross technique is applied and canaccomodate the system consisting of 250 airways by use of medium capacity computers.

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As a complement to their previous report, the authors give more detailed idea of the flotation rateprocess based on the 1st order kinetics. A graphical method of determining the distribution of the flotationrate constant K₁ is described starting from batch or continuous flotation test, and the significance of K₁ andits distribution is discussed in view that K₁ is a criterion of the floatative separation as well as of floatabilityof mineral particles in the actual flotation system. Some experiments are conducted both on free quartzcafioniccollector systems and free sulphide mineral-anionic collector systems to find their representative kineticbehaviours in flotation.

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In order to recover the coal concentrate of low ash content, the effect of humidity on the electrostaticseparation of coal were studied.
The relation between the critical electric intensity at which coal particles repell from an electrodeand the humidity of the atomosphere was obtained. The particles of high ash coal repell at lower electricintensity than those of low ash. However, both of them behave similarily in the extremely low or high humidity.
The electric discharge between electrodes as well as the adsorbed moisture on coal particles relatesclosely with the electrical charging of coal particles in an electric field. The electric discharge betweenelectrodes increases with increasing of the humidity. And the adsorbed moisture on coal particles also increaseswith increasing of the humidity. The high ash coal adsorbs more moisture than the low ash coal.
Furthermore, the behavior of coal particles in an electric field was discussed through the measurementof the electrical charge on coal particles in terms of the humidity and the heating temperature.
As a result, it was clarified that the separation is excellent in the 40-80% relative humidity of theatomosphere. And it was recognized that heating of feed has a bad effect on the separation.

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The extraction rate of lead oxide in the glassy lead silicates containing 0 to 65 mol SiO₂ has beenmeasured by using saturated solution of ammonium nitrate.
The activities of PbO in the silicates are calculated on the assumption that the lead oxide in thesilicate will obey Raoult's law when the extraction rate of lead oxide is 100%. It is found that these resultsindicate almost the same tendency as others.
The activities of PbO in ternary mixtures, containing one of various metallic oxides such as MgO, CaO, ZnO, BaO, TiO₂, Al₂O₃ and Fe₂O₃ in PbO-SiO₂ system, were obtained by using the above method. At constant PbO mole fraction, basic oxide tends to raise the activities of PbO in the range of compositionsinvestigated, whereas acidic oxides lower them.
Moreover, the activies of Cu₂O in the Cu₂O-SiO₂ mixture were calculated from the extraction rateof Cu₂O using KCN solution, which results indicate that Cu₂O-SiO₂ mixtures behave as an ideal solution.

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