he authors already reported the studies on the strength of various rocks in high temperature, and in this paper we described the experimental results about the same problems in case of other experimental conditions and also the strength of rocks in minus temperature. For three kinds of such typical rocks as granite, andesite and sandstone, the results are as follows;
(1) It can be considered that the strength of rocks is not affected directly by three parameters which are “temperature increasing speed” from 30°C per 10min. to 100°C per 10min., “duration of constant temperature heating”, “duration of constant temperature after instant heating”. But the strength of granite is affected by the heating duration, that is, the amount of heating energy absorbed.
(2) The strength in instant cooling in water from hot conditions is less than that in gradual cooling in a furnace.
(3) In minus temperature the strength of rocks is obviously increased.
In case of thermal fracturing of rocks, we must consider those results together with.

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For the purpose of contributing to a rational design of rib pillars, the stress in rib pillars has been analyzed by the finite elements method as well as photoelastic experimets. From this analysis, the influences of geometrical conditions of open spaces and pillars upon the stress state and the stress concentration in pillars have been cleared out.
To show some of them, the stress concentration at the corner of an opening is raised as the ratio of the radius of curvature at the corner to the width of the opening, γ/α, decreases. A greater value of γ/α, no greater than 0.25, is preferable. The maximum stress is from 1.3 to 1.6 times the average stress in the pillar when γ/α=0.25, while it is from two to three times that when γ/α=0.1. If either the thickness of α pillar is not uniform or a pillar bends, a greater stress concentration may take place in the pillar than that which will appear in a pillar of uniform thikness, equal to the effective thickness of the former pillar.

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The object of the present paper is to obtain the basic informations for the extent which thin placer on the horizontal seafloor is sucked by the straight suction pipe.
On the assumption that placer is as the mono-layer on the horizontal seafloor and the suction pipe being perpendicular to the seafloor sucks up placers and water, the basic relation on the sucked extent is theoretically induced.
The experimental results in a small sized model can be represented by x_e/l-1/2=kF^2/3, _??_Where k=1.2 on the smooth floor of plastics and k=1.5 on the rough floor of abrasives cloth (AA#80 and AA#180).
On thin placer the experimental results by the model accord with a following empirical relation: x_e/l-1/2=0.8 (l/h) 0.2F^2/3The size distribution of placer using in this experiment is between 100×10^-6m and 1000×10^-6m, in this range of the size distribution, xe is very loosely related to the size of placer.
In these relations, the nomenclature is as follows, F: modified Froud number g: acceleration of gravity h: thickness of thin placer (h<l, h<L) L: distance between floor and entrance of suction slot l: opening width of entrance of suction slot V: average velocity in entrance of suction slot xc: extent that placer was sucked up ps: density of placer ρ: density of water φ: angle of repose between placer and floor

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An experimental study of the breaking strength and energy laws of single particle crushing under slow rate of loading in a coarse size range was carried out by using spheres made of borosilica glass and 4 kinds of minerals.
The sphere diameters ranged from 0.5 to 3.0cm and the rate of loading was 3t/min for borosilica glass specimens and was 0.3t/min for 4 kinds of minerals. A summary of experimental results was follows, I) as illustrated by equation (10) the elastic strain energy per unit mass of specimen stored up to breaking (E/M) is proportional to 5/3 power of breaking strength, II) similarly E/M is proportional to (-5/m) power of particle size and is calculated the equation (15), where m is the Weibull's coefficient of uniformity, III) as illustrated by equation (17) the index of the Lewis' general equation of energy laws can be calculated from the relation of n=(m+5)/m, IV) the status of fracture was of mainly transcrystalline.

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Reactor grade zirconium is required to keep hafnium content below 0.01%(as metal ratio).
However, zircon (ZrSiO₄), a major source of zirconium, contains about 2.5% hafnium (as metal ratio), and it is extremely difficult to remove 99.7% of hafnium for the material, because of similar chemical properties of zirconium and hafnium.
From the authors experience on the industrial production of about 600 tons hafnium-free zirconium oxide (ZrO₂) by the hexone extraction process, the following results were obtained.
(1) In the step of feed preparation, the zirconium concentration of about lmol/l and ammoniumthiocyanate (NH₄SCN) of 1.2-1.3mol/l revealed a good result for the extraction steps which follow.
(2) In the step of hafnium extraction, the thiocyanic acid concentration in hexone is preferred at about 2mol/l. Flow ratio (solvent/feed) should be about 2, and 15 to 17 stages of extraction are required.
(3) In the step of zirconium stripping, a desirable stripping solution is 4N hydrochloric acid. Flow ratio should be about 1/5 and 15 stages of stripping are required.
(4) In the step of hafnium scrubbing, a scrubbing solution of 6N sulfuric acid, is preferred. Flow ratio should be about 1/4 and 6 stages of scrubbing are required.
Control of impurities in the hexone after the scrubbing step is particularly important in order to limit the hafnium content to 0.01/0 or less. The content of impurities must, therefore, be reduced below 3mg/100ml.(at metal oxide).
(5) The theoretical explanation for their separation was made by the equilibrium studies on the solvent extraction system and it was in good agreement with the results of practical operation.
(6) For the separation of zirconium and hafnium, the prevention of decomposing thiocyanic acid is a factor of particular importance. Concerning this, the effects of extraction atmasphere, temperature, iron content were investigated which led to the prevention of the decomposition.
(7) Special equipment is required for satisfying the extracting conditions, and it is to be adapted for the continuous counter-current extraction in thenon-oxidizing atomospher. The equipment should resist against the highly corrosive mixture of acid such as hydrochloric acid and thiocyanic acid. A new extraction equipm-ent of jet system which meets all these requirements was developed.

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The magnesia dependence of reducibility on garnierite was studied by mesuring the properties of synthesized nickel ortho-silicate. The principal conclusions are as follows:-
(1) Nickel ortho-silicate was synthesized and its properties was investigated. It has the olivine structure and indicates a close approach to ideal behaviour of a solid solution with forsterite as fayalite does. However the free energy change for the reaction 2NiO+Si0₂=Ni₂SiO₄ is assumed to be the value of-0.5kcal/mole at 1, 400°C sintering a pellet of intimately mixed NiO and Si0₂ at 1, 400°C for instance, requires more than 100hr. to obtain a single phase of nickel olivine. But whenever the system contains the MgO, most of the NiO becomes easily combined as a Ni₂SiO₄ in the magnesium olivine which crystallizes at an early stage, because the free energy change for the reaction 2MgO+Si0₂=Mg₂SiO₄ is given a value of -15. 12kcal /mole at 1, 400°C a solid solution of Ni₂SiO₄ and Mg₂SiO₄, for instance, can be prepared easily by sintering a pellet of intimately mixed NiO, MgO and Si0₂ at 1, 400°C 15hr.
(2) When the green garnierite is sintered in air at 1, 400°C the sintered garnierite has a structure of olivine which is proved to be an uniform solid solution of (Mg, Ni)₂SiO₄ from well difined x-ray diffraction peaks, and excess silica is separated from ortho-silicate, meta-silicate is not formed.
(3) Nickel oxide, if combined with SiO₂ as nickel ortho-silicate, does not behave for free oxide, as can be assumed from the fact that the reduction therefrom in the solid state is for more difficult to accomplish it. However as the reactivity between NiO and SiO₂ is small, the former reactant remains reducible even after being subjected to a preliminary heat treatment of above reaction at the several temperatures. But when magnesium oxide is added to NiO and SiO₂, and this admixture is heated even at relatively low temperatures above 900°C (Mg, Ni)₂SiO₄ is easily and rapidly formed, and NiO contained in this silicate becomes hardly reducible at these temperatures. As the result, experimentally it is found that the brown garnierite is not so reducible an ore as the free oxide of nickel. Because when the garnierite is heated in a current of reducing gas, the chrysotile fraction of the ore undergoes an exothermic phase transformation to olivine, Mg₂SiO₄ at about 800°C and any nickel oxide present in the ore as substitution for part of the magnesium oxide, and that has not reduced, is then chemically combined as part of this olivine structure and rendered more difficult to reduce.
(4) In order to avoide formation of unreducible compounds of nickel, it is of importance to know to what temperature the ore may be heated for the selective sulfatization of MgO. If the garnierite is sulfatized prior to reduction selectively, further increase in the reducibility is obtained.

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