Microscopic failures and displacements in rocks create a kind of microseismic vibrations, “rock noise”, according to the stress condition of surrounding rocks. The authors have made a series of researches concerning the microseismic method to predict rock failures. In order to apply this method to coal mines, thenoise-occurrence characteristics of coal were examined on several types of samples in laboratory.
Noise measurement in coal. mines was performed around the working face of the Ibaragi colliery in Johban district. The conclusions of this report are as follows:
1) The frequency range of noises, either 2-8kc/s or 16-32kc/s, is suitable for the method in coal seams. The noises in the latter range could be generally applicable.
2) The rate of occurrence of rock noise is the main factor to predict rock failure. Not only for the condition of increasing stress, but under constant load, this principle could be applied.
3) The possibility to assume the position and the types of failure in seams, is attained from thefrequency analysis of rock noise.
4) The rate of occurrence of rock noise along the coal getting face varies almost symmetrically. The middle part of long face is “silent”, whereas the both ends of face show high rate of occurrence of noise.
5) The rate of occurrence of rock noises in the gate road decreases rapidly according with the distance from the coal getting face. This trend corresponds to the result of rock pressure measurements.

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Recently the variation in stress in rocks has come to be measured, for the purpose of earth pressure control, using several kinds of stress meters or strain meters. The relationship among the measured value, the variation in stress and the present state of stress are complicated. Thus the authors have analyzed this relationship and have presented fundamental data for the interpretation and utilizatio n of the results of measurement.
Some of the results of stress measurement which have been carried out at some metal mines working massive ore bodies are introduced. It has been found from these measurements that the measurement of the variations in stress in pillars or rocks gives a useful data for earth pressure control, However, it is not yet possible to predict cavings merely from the results of measurement.

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The effects of decomposition temperature of ferrous oxalate and of formation temperature of zinc-ferrite on the rate of dissolution in dilute sulfuric acid were investigated.
Six species of zinc-ferrite were formed at 900 and 1, 190°C from the stoichiometric mixtures of ferric oxide, which was prepared by thermal decomposition of ferrous oxalate at 500, 700 and 900°C, and zinc oxide.
From the previous result that the rate of dissolution is approximately proportional to the surface area, pparent rate constant K (dependent on surface area) and rate constant κ(independent of surface area) of each specimen can be calculated.
Apparent rate constant K of zinc-ferrite, which was formed at 900°C, varies with the decomposition temperature of ferrous oxalate, but rate constant κ remains constant. This means that the difference of K arises mainly from surface area of zinc-ferrite, and that decomposition temperature of ferrous oxalate has no influence on the property of zinc-ferrite.
The zinc-ferrite, which was formed at 1, 190°C, dissloves with the rate lower than that of zinc-ferrite formed at 900°C. But, when κ were compared, k of zinc-ferrite formed at 1, 190°C are higher than those of zinc-ferrite formed at 900°C, except when the ferric oxide prepared at 500°C was used. This means that, considering the rate of dissolution per unit area, the zinc-ferrites, which were formed at 1, 190°C, dissolve more easily than those formed at 900°C.

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Studies were made on behaviors of lead sulfate and ferric oxide in the roasting with a weakly reducing atmosphere, furthermore, behaviors of artificially produced magnetite to dilute sulfuric acid were investigated.
A reaction product of lead sulfate with the reducing gases containing CO, CO₂ and N₂ (PCO/PCO₂=1/9, 2-8% CO) at 600°C was basic lead sulfate PbO %middot; EPbSO₄ final reaction products at 650°C and 700°C were metallic lead which was formed by equations (1) and (2).
2PbSO₄+CO=PbO · PbSO₄+CO₂+SO₂…(1)
PbO · PbSO₄+3CO=2Pb+3CO₂+SO₂…(2)
The reaction velocity equation for the reaction (1) obtained by this study is
P/Mri (1-³√1-x)=Kt
K is proportional, within a range of these experiments, to P^0.84_CO, andanenergy of activation of the reaction (1) is 7.9 kcal/mol. Therefore it is considered that the velocity-controlling step in the reaction (1) is a diffusional process of the reducing gas or the reacted gaseous products through a diffusional layer between the formed PbO · PbSO₄ layer and unreacted PbSO₄.
The sarrie velocity equation is applicable for the reduction of ferric oxide to magnetite and an energy of activation of the reduction is 9. 4 kcal/mol.
Artificially produced magnetite at relatively lower temperature (500°-700°C) is very soluble in dilute sulfuric acid, for instance, 10.4% of the magnetite was dissolved with 0.4N H₂SO₄ solution. Magnetite which was formed in a reducing atmosphere containing 0.7% of SO₂ is more soluble. 31.6% of the magnetite was dissolved with the same solution and the magnetite contained 6.3% of sulfur, but iron sulfide was not detected in the magnetite by an X-ray diffraction method.

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