The idea of recovering the iron from the magnetic sand is, generally, realized in the dry system, say, the pig-iron-steel-process or the spongy-iron-steel-process. The magnetic sand consists of a special composition and particular form, that is the TiO₂ content is remarkably high and is distributed throughout the crystal of the magnetic sand. For the purpose of the elimination of the TiO₂, many a device has been adopted. -A method of magnetic concentration, table concentration, floatation and etc; -they have never succeeded in the elimination of titanic acid mechanically.
The Microscopic research of the cryssal structure of the magnetic sand clearly shows the state of the distribution of titanic acid in the ore, to be the mixed crystal or the solid solution of ilumenite in magnetite.
From this point of view, TiO₂ must be seperated from iron content by means of the smelting and slagging off, in both cases of the dry system.
Under the advisory of Dr. T. Kawamura, the auther have already achieved a process of the treatment of the magnetic sand with electric furnace.
Another way of the elimination of the titanic acid is the wet system, that is the method of dissolving the ore with certain acid to convert it into the solution. From the solution, TiO₂ is seperated and the iron is recovered by the electrolytic or other method.
At the ordinary temperature and pressure, the magnetic sand can not be dissolved with hydrochloric acid or sulphuric acid perfectly and only a small portion of the ore is converted into the solution.
Author has attactsed a method for the treatment of the magnetic sand with sulphuric acid in autocleve. The ore can readily be dissolved at certain temperature with concentric acid, and with dilute acid only the iron content is dissolved, the titanic acid remaining sensibly unattacked.
From the experiments, auther has determined the reaction velocity of the dissolution in the autocleve for certain concentrations of the acid at the contant temperatures, the Phenomena of the hydrolysis of the titanic acid, and the temperatures of convertion of iron sulphate into the oxide and consequently the spongy iron.

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Reduction tests were carried out on 14 specimens at 460°-1, 050°C with hydrogen gas for 0.5-4 hours. Graphic structure of ilmenite in magnetite has an influence to promote the reducibility at the lower temperature, but generally the reduction percentages are retarded in proportion to their titanium contents.
The reduction of ilmenite begins at above 460°C.
No characteristic relations between titanium content and reducibility were found at the higher temperature.
Oxidation tests were carried out on 18 specimens from yarious localities with a "Thermo-balance" and a combustion furnace in oxygen gas or free air current at 0-1, 200°C. The roasted products were then reduced with hydrogen gas at 500° and 800°C.
Oxidizing reaction of magnetite was observed to begin at about 200° in this experiment and that of ilmenite at 450°C. The reaction velocity is comparatively rapid in the latter case.
The reducibilities of iron sands were notably promoted especially in those of lesser titanium contents by the previousroasting; higher in their oxidized percentages higher reductions resulted.
The effective temperature of oxidizing roasting is suggested to be 850°-1, 000°C.

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Summarizing the previous researches the author concluded the eight experimental facts as established, two of them are the reaults of the other investigators and six are due to himself. Various theories ever proposed were criticized by these eight facts and all found to be unable to explain them. These theories included (1) Hydrolysis theory (2) Affinity and cohesion theory (3) Solute catalysis theory (4) Solubility of Mg(OH)₂ theory (5) Breaking of the surface protecting film theory. Local current theory was also considered but found to be incorrect. A dual theory finally put forward by the author contains the following two fundamental chemical reactions
The existence of the surface film and its breakdown by Cl- ion are also believed. Besides, he assumed an intermediate compound with its catalitic action. By this theory he could explain the above facts satisfactorily.

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