The photo-elastic method of determining the rock pressure, which was previously reported, has been tested in mines, the results of which have proved that this is a reliable method, but to attain our ideal, easier determination of the order and colour of the highest isochromatic line is hoped. To meet this demand, the authors have originated a new method, which is characterized by adopting two or more measuring pieces, each rectangular prism of different length, silvered on the bottom surface. Each piece shows a certain colour of an isochromatic line over the field, instead of a series of isochromatic lines, under a certain state of stress, when observed with white light. The combination of the colour appearing on each piece determines the rock pressure. In connection with this measurement, the authors have analysed the relation between the colour of an isochromatic line and the principal stress difference at a point in a measuring piece.

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The purpose of this paper is to study the characteristics of pyrite in flotation, as related to the fundamental study of differential flotation of copper sulphide ore.
From the above reason, the following experiments were carried out mainly: 1) the change of floatability of pyrite by the addition of quartz particles as gangue mineral, 2) the effects of presence of copper ion and chalcopyrite on the floatability of pyrite, etc.
Through these experiments, it was found that the existence of chalcopyrite or quartz or both, together with pyrite. had serious effects upon the floatability of pyrite toward activation, and that the increasing addition of copper ion, in neutral pulp, caused both effects of activation and depression of pyrite according to its added quantity.

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The effects of the diameter of underflow nozzle(d_u)upon various performances of a wet cyclone were experimentally investigated using quartz pulp and 60-mm rubber-lined wetcyclone unit at the Mineral Dressing Laboratory, University of Tokyo. The results obtained are summarized as follows:
1)The underflow discharge observed was of vortex spray type when the underflow nozzle larger than 16-mm was used, whilst the rope type underflow was obtained for the nozzle diameter of less than 14-mm (Fig.2 and Fig.3), indicating that the transition point about nozzle diameter lay between 14 and 16-mm under the conditions applied.
2) For a particular diameter of underflow nozzle, flow ratio(Q_u/Q₀)was independent of feed inlet pressure (P)(Fig. 4), and the relationship between flow ratio and the ratio of discharge area(d_u²/d₀²)was different with the types of underflow (Fig. 5).
3) The ratio of underflow discharge velocity (v_u) to inlei velocity(v_i)in relation to nozzle diameter(d_u)took its minimum value around the transition point of underflow type (Fig. 8).
4) The thickening ratio (δ_u/δ_f)decreased linearly with increasing nozzle diameter (Fig. 9)
5) Solid-liquid separation was best around the transition point (Fig. 12).
6) The classification performance of a wet cyclone was highly dependent of underflow nozzle diameter. It was shown by Tromp distribution curves obtained that the separation size(d_T)and Terra index (ècart probable)(E_T)became larger with reducing diameter of nozzle (Fig. 13 and Pig. 14). Generally speaking the vortex-spray type underflow was superior to the rope type one from the viewpoint of classification operation.

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We investigated on the elimination of arsenic from scheelite by roasting which iscommonly found in tungsten ore and detested as an impurity that decreases the recovery of tungsten from alkali leach solution and lowers the quality of finished product.
Following results were obtained.
1) The roasting in oxidizing atmosphere to volatilize as arsenic trioxide was notcompletely successful, because unvolatile arsenate was partly formed. Dearsenizing ratio was 50-70% at 700-1000°C for 1 hr.
2) The roasting in nonoxidizing atmosphere (N₂, CO₂, SO₂) to volatilize mainly as arsenic sulphide was very effective. Dearsenizing ratio was almost 100% at 900-1000°C for 1hr.
3) The fluosolid roasting process was applied. The very fine flotation concentrate (-325 mesh) was fluidized together with larger particles of pyrrhotite (60-100mesh) which was used to make stabilized bed and SO₂ atmosphere. The cinder of concentrate was caught in the cyclone as carry over and pyrrhotitee was discharged as over flow. Dearsenizing ratio was90% at 800-900°C.
The coarse jig concentrate (-100mesh) was fluoroasted in the charcoal producer gas. By the roasting of 1000°C for 20 minutes arsenic content decreased from 0.13% to 0.02% and it was superior to the oxidizing roasting.

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In the previous papers we reported on the formation and the constitution of zincferrite, and in this paper we report on the solubility of Fe₂O₃ and ZnO in zinc-ferrite at a high temperature that was ascertained with the Xray-and magnetic analysis.
In conclusion: The excess of Fe₂O₃ makes a solid solution with zinc-ferrite and this solid solution is ferro-magnetic and at above 1200°C a part of the excessive Fe₂O₃ decomposes to Fe₃O₄ and also this Fe₃O₄ makes a solid solution, but ZnO is slightly soluble in zinc-ferrite and this is not ferromagnetic.

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