When one or some kinds of gas are contained in a limited range of an underground airway, they are diffused by being conveyed by the air current and their rates of flow become lower and lower with the distance of flow. This diffusionhas been discussed by making use of the rates of flow of CO and CO₂ gas measured at the exhaust shaft mouth of the Yamano coal mine for two and a half hours after the explosion of June 1, 1965. It has been found that it needs 0.3 times the average flow time l/v for a small amount of gas conveyed by an air current of a mean velocity v to pass entirely through a cross-section at a distance of l.

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The temperature of exhausted air from the rock drill (60mmφ leg hammer) was measured with a resistance thermometer of a platinum fine wire, and the results were apllied to the calculation of the temperature change of air in the cylinder by means of an analytical method.
The results obtained are as follows.
Generally, the temperature in the fore room of the cylinder are higher than that of the rear room, and with increasing the input air pressure, the initial temperature during compression becomes lower, the maximum temperature higher and the minimum exhaust temperature lower. For instance, in the case that the input pressures are 5 and 2kg/cm² (gauge), temperatures of air in the cylinder when input air tempe-ratures are about 20°, are as follows.

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For the purpose of using laterite ores as raw materials of iron production, it is necessary to remove nickel and chromium minerals from the ores. In the previous paper, denickelizing of laterite ores was investigated by means of sufuric acid leaching after the selective reduction.
The present paper is concerned with the removal of chromium mineral from laterite ores by means of selective grinding followed by classification and magnetic roasting followed by magnetic separation.
The results obtained are as follows.
1) Chromium mineral contained in laterite ores is chromite replaced by aluminum ion for chromium ion and is insoluble in hot solution of concentrated hydrochloric acid. 70 to 80 percent of its particles is in the size range of 35 to 200 mesh.
2) For the preferential size reduction mineral of iron mineral particles to that of chromite particles, an attrition machine is more effective than a ball mill. When the ores ground by attrition machine are sized by a sieve of 200 mesh, about 80 percent of iron is recovered into a fine size fraction and about 50 percent of chromium is removed into a coarse size fraction.
3) The magnetization of the magnetic roasted samples of laterite ores is lower than those of goethite and limonite. This low magnetization may be due to the solid solution replacement of impurity such as aluminum ion.
4) In the magnetic separation of the magnetic roasted samples of laterite ores, using a ferrogum magnetic separator, 90 to 95 percent of iron is recovered into magnetic product and 40 to 45 percent of cromium is removed into nonmagnetic product. This unsatisfactory results are explained by the fact that the magnetization of the magnetic roasted samples of laterite ores is low.

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In order to explain several observations in hydrometallurgical processes, a new type of reaction based on the galvanic interaction through contact of solid particles suspended in the aqueous solution has been proposed.
As a special case of this interaction, a quantitative investigation was carried out on the suspension system of powdered pyrite and zinc dust in 1N-H₂SO₄.
Reductive dissolution of pyrite with generation of hydrogen sulfide gas was observed in this system. To know the extent of the interaction between pyrite particles and zinc dust, experiments were also carried out on the cathodic dissolution of pyrite blocks, cathodic polarization of pyrite particles, the reaction of pyrite block made contact with zinc panel, electrode potential determination of pyrite blocks in the solution suspended with zinc dust and on the behavior of zinc panels in the solution suspended with pyrite particles. From results obtained, it is found that the dissolution of pyrite is caused by the galvanic interaction with zinc dust and that the amount of reaction corresponds to the one when the area equals to several percent of total surface of pyrite particles is always responsible for the dissolution.

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The anodic dissolution of chalcopyrite concentrate from anode (a mixture of chalcopyrite concentrate and graphite powder) in sulfuric acidic solution as electrolyte was investigated.
At pH<3, the anodic dissolution recctions occurred well, when the electrolytic condition was 1). apparent anodic current density=0.5-1.0A/dm², and 2). graphite percentage in mixture of CuFeS₂ and graphite≥20%.
Anodic dissolution current efficiency for Cu (II) was 80-90%.

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