As a step to realize the rationalization of postwar copper smelting, the Nippon Mining Co., Ltd. formed in the spring of 1949, a plign of producing contact process sulphuric acid by treating waste gases in their two plants at Hitachi and Saganoseki smelter. The plants at Hitachi and Saganoseki smelter were respectively completed and began operation in January and February, 1951 producing 6, 000metric tons of acid Der month.
This plan is significant in that it has the following two meanings. Firstly, the construction of contact sulphuric acid plant which had been prohibited after the wer, was once again permitted by GHQ and again, that 338, 000, 000 yen equivalent to 55 per cent ofthe total construction cost was met by the counterpart fund. Secondly, the plan of producing sulphuric acid by contact process of directly treating copper smelting converter waste gasses with high fluctuation in SO₂ and gas volume was the first of its kind attempted in Japan.
This plan brought about an extremely satisfactory result in that both of these smelters succeeded in recovering sulphur equivalent to about 40 per cent of the amountin the waste gases in the form of sulphuric acid and thus at Hitachi smelter, they were able to reduce the gas polution to less than 20 per cent when compared with that of five years before its installation.
Report was made on the circumstances which led to the construction of the waste gas sulphuric acid plant and on the construction plan, outline of new plant, points of special considerations paid in connection with the plan and the outline of operation.

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The leakage of air from the wall of air ducts has grave effects on the air ducts ventilation. The authors carried out experiments to investigate the theory governing the phenomena of air leakage. As the results of this investigation, it was ascertained that the pressure differene causing the leakage is proportional to 1/n th power of the volume of leakage, where n is a constant, and the value of n was determined for a range of Reynolds' numbers and of dimenesions of the openings.

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According to the fact that the underflowing voltextube which exists between tha cyclone wall and overflow finder and the upcasting vortex tube in the region of diameter of the finder, are continuous at the the bottom of the cyclone, the distribution of the tangential velosity and the static pressure in wet cyclone can be explained by the Theorem of Kelvin and Helmholtz about the vortex motion. In addition, the anther describes numerical culculation using the results of the experiment excecuted by H. F. Yancy.

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The Equilibrium diagram of the system nickel sulfide-copper sulfide-iron sulfide is determined by thermal analyses and microscopic examinations, and a new diagram is proposed as shown in Fig. 8. There are four reactions in this system.
Liq.+(FeS)=γ-Ni₃S₂+Cu₂S at 880°C
(FeS)+γ-Ni₃S₂+Cu₂S+(FeS)₂S·Ni₃S₂ at 575°C
γ-Ni₃S₂=(FeS)₂·Ni₃S₂+Cu₂S+β-Ni₃S₂ at 495°C
β-Ni₃S₂=(FeS)₂·Ni₃S₂+Cu₂S+α-Ni₃S₂ at 477°C

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We studied extractive methods which were not based on the usual acid process-the decomposition by the roasting with a mixture of sodium carbonate and carbon and the autoclavesoda process. Tested are is flotation concentrate from Otani mine that has 26-28% WO³ and the particle size is minus 150mesh.
Following results were obtained.
1) roasting process The maximum value of extraction, 97.46%, was obtained when she mixture of 2g ore, 2g sodium carbonate and 0.5g charcoal powder was roasted at 750°C. At the same condition without carbon, the value of extraction was 91.48%. The amount of sodium carbonate required was 7.7 times the theoretical one.
2) autoclave-soda process Effects of concentration of sodium carbonate solution, temperature, pressure, keeping time, pulp density and r.p.m. of the stirrer on the extraction and the dissolution of impurities were studied. The best result was obtained at the under condition and the extraction was 96.5%. pulp density-400g/l; concentration of solution-20% sodium carbonate; temperature-190°C; pressure-13atm.; keeping time-4hrs.; 45r.p.m.
The amount of soda required was about 4 times the theoretical one.

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