These experiments were dealt with to illustrate the magnetizing phenomena of iron oxide by the reduction and oxidation. Using ballistic galvanometer and specially wound secondary coil on silica tube, in which sample was packed in definite condition in powder form, insertèd in a electric tube furnace which is arranged in a magnetic field obtained by primary coil, the magnetic intensity of the sample at the different temperatures were determined relatively by the amount of the scale deflection. Artificial ferric oxide was prepared from ferric hydrate deposit from irom solution. Artificial and natural Fe₂O₃ were reduced by the current of H₂ gas, coal gas and CO gas at the temperatures varying 10°-500°C separately, and measured those magnetic intensities during the magnetizing reaction.
At the temperature 180°C-300°C the magnetizing reactions begin and attain maximum value at 350°C-400°C showing the formation of Fe₃O₄ By the further reduction of the sample, the magnetic intensity increases slowly in the case of H₂ gas and coal gas, and for CO gas it dereases slightly. And artificial Fe₂O₃ is much easily magnetized compared with natural one; magnetized at lower temperature and shorter time. By the oxidation of the reduced sample at 200°C-220°C, the magnetic intensity was increased showing maximum value at the same tempreature, and being kept constant up to 300°C it decreased suddenly from that temperature and diminished at 550°C. This change is owed to the format on of Fe₃O₄ and magnetic Fe₂O₃ at first, and non-magnetic Fe2O3 at last. The changes magnetic Fe₂O₃→non-magnetic Fe₂O₃ were determined for many samples after the magnetizing reduction and illustrated them by the temperature-magnetic intensity curves. The magnetic intensity of the reduced sample was increased also by heating it in vacum above 600°C because of the formation of stable magnetic oxide by the Eeat treatment. Natural or artificial Fe₃O₄ showed magnetic transformation at the temperatute of 600°C where Fe₃O₄ loses magnetic intensity and by cooling recovers it back again tracing the same curve as heating expressing reversible change.

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This description is illustrated the practical operation in combined steel refining process of active mixer and open hearth furnace. Especially. the writer will here give the general accounts of the operation of active mixer, combined process and ore process.
The active mixer is described about the structure of furnace, outline of its operation, chemical change in refining, result of operation and etc. This mixer is unable to rise to suitable temperature in relation of checker warks. Therefore; it is difficult to obtain the desired results. But, in order to escape from anxisty of scrap supplying in our country, of course, it will be the important problem to select for various steel making processes.
In the preliminary refining of active mixer, the silicon in molten pig iron become rapidly in trace, and the reduction of carbon is at small degree. The descending of manganese content is also one defect of this active mixer practice. Then, the Preliminary refined molten metal is introduced into the open hearth furnace, in which the time of treatment is carried on short by means of combined process, and then the furnace can attain the economical productions. But, owing to obtain the low silicon pig iron at present time, it will be necessary to study the ore process. By reason of this, the writer has bliefly compared with these processes. This ore process, however, is remained to study as well as the combined process in future.
In short, the writer believes that combined process is experimentally one of the advantageous plan to get rid of the panic for scrap supplying in present Japan.

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The cause of tuberculation of iron pipe was studied on several cast iron water supply pipes which had been in service for 36 years since 1896 at several places in Osaka city, and some experiments were performed to explain the formation of tubercles from the metallurgical, chemical and biological stand point. The following results were obtained.
1. Artificial cultivation of iron bacteria proved the existence of 2 kinds of iron bacteria which belong to Leptothrix and Siderocapsa species.
2. The rust of cast iron is more adhesive than that of steel and the greater part of corrosion product is accumulated in the place of corrosion, so that cast iron pipe has greater tendency of tuberculation than steel pipe.
3. The tubercular rust is not formed by bacteria but mainly the product of simple chemical corrosion of iron pipe.
4. The tubercular are main tained only by the outer hard magnetic shell and the inner part consists of very porous rust this magnetic oxide shell is formed by the action of iron bacteria.

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