The crossing galleries are classified into some types as the horizontal, vertical inclined and different level crossings. In all these cases, it is necessary to take care of the roof supports, because the stressconcentration in the crossing area is increased. Therefore, the authers performed some three dimensionally photoelastic experiments using the stress freezing method in order to investigate the fundamental problems of stress-concentration around the intersection part of crossing galleries.
In this paper, the authers report of all the relationships between the intersectional angle or the difference of level and the states of stress distribution around the crossing galleries, based on the result of these systematic experiments.

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Up to the present, the piston speed of the rock drill was obtained by drawing the tangent on the stroke curve, and the indicated energy was obtained from the area of the pressure-stroke diagram. These processes were very troublesome and easy to introduce errors.
Against these, we could measure the blow speed of the piston directly with the syncroscope which records an electro-magnetic motive power proportional to the piston speed, generated by making a coil attached to the piston traverse a uniform magnetic field.
If this motive power becomes an input to the wheatstone bridge of strain, gauges built in the internal pressure measuring pick-up of the cylinder, a mean value of an output is proportional to the indicated energy per unit time.
We could measure this value immediately with the galvanometer of the long period (8.6 spc).

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For the purpose of clearing up the effects of oxidation phenomenon of pyrrhotite, pyrite and marcasite. on their flotation properties, first of all, their oxidation properties were contrasted each other, next, the relation between prior oxidation in various conditions and flotation recovery was investigated. From this investigation, it was recognized, as a common tendency, that in xanthate flotation of iron sulphide minerals, their flotation recovery increases for a time in course of oxidation, and at a time when oxidation advanced to some extent, their recovery begins to decrease.
Considering also a connection with the knowledge obtained by the investigation on natural oxidation in water to the actual operation, the followings may be said.
a) There is a possibility that the particles of pyrrhotite and pyrite which begin to oxidize newly after grinding stage, and are considered to take the trend of quantity, are remarkably promoted in their floatability on xanthate flotation by acceleration of oxidation in water within a certain extent, for example, the increase. of aeration time.
b) Acceleration of oxidation in water is in danger of giving a fairly harmful effect on collection of pyrrhotite in the process of xanthate flotation attended by prior activation with copper sulphate. As a general rule, such danger is not brought on pyrite.

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In this study, the electrode potential of sulphide minerals, pyrite and galena, were measured at first in some electrolyte solution such as KCI, NaCI, KCN, NaOH or Na₂S with varying the electrolyte concentration ; and then the electrode potential and the floatability were also measured with varying pH value both in xanthate solutions and in solutions containing xanthate and KCN in order to discuss the relation between the electrode potential of sulphide minerals and their floatability.
In a solution of KCN, Na₂S or NaOH, the electrode potentials of pyrite and galena are much affected decreasingly with increasing of the electrolyte, concentration. Conversely, in a solution of NaCI or KCI the increase in electrolyte concentration makes a slight change of the electrode potential. In a xanthate solution with varying pH, the electrode potential of sulphide minerals changes from the potential governed by the xanthate ion to the potential governed by hydroxyl ion at the pH value prescribed by the xanthate concentration. Also, in the xathate solution containing potassium cyanide, it changes from the potential governed by xanthate ion to the potential governed by cyanide ion. The floatability of sulphide minerals remarkably decreases at pH value where the electrode potential changes.
From the experimental results, it was confirmed that the electrode potential of minerals relates closely with their floatability i, e. collection by xanthate and depression by alkali or cyanide.

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Most of the nickel ores imported to Japan are so-called “Garnierite Ores” from New Caledonia. For the effective extraction of nickel, l experimented on some properties of this ore and obtained the following results:
1) The principal constituents are Serpentine, Talc, Quartz.
2) Possible nickel-bearing minerals are Serpentine, Talc, Garnierite.
3) When the sample is heated
(i) At 130 & deg;C, adhered water is removed.
(ii) At 330 & °C, goethite loses its combined water.
(iii) At 654 & °C, serpentine loses its water and becomes amorphous.
(iv) At 816 & °C, decomposed serpentine changes to forsterite. Talc transforms into forsterite, also.

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A kinetic study has been made on the leaching of a sphalerite concentrate with sulphuric acid and oxygen under pressure.
The main results obtained are as follows;
(1) The leaching rate was increased with agitation speed and attained to some constant value.
(2) The rate was roughly proporiiOnal to oxygen partial pressure within the range examined (below 10 atm.)
(3) The rate was independent of sulphuric acid concentration within the range examined (5-20%)
(4) The rate was influenced by the particle size of the sample.
(5) The maximum rate was obtained at 100°C. Above 105°C the rate was decreased rapidly with the lapse of time by the layer of elemental sulphur produced. The activation energy below 100°C was 11.3°C kcallmole.
Besides these, some preliminary tests of leaching a zinc-bearing copper concentrate were carriedout with the intention of extracting zinc selectively. In these tests zinc was dissolved more easilythan copper and iron, but the selectivity was not satisfactory.

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