Preliminary data indicated that titanium had superior corrosion resistance to the experimental condition of the synthesis of acetic acid from methanol and carbon monoxide. In the present study, in order to examine the existence of chemical resistant materials other than titanium, and to confirm the utility of titanium, laboratory corrosion tests were performed.
The data in this paper covered 24 kinds of metals and alloys.
For test environment, pure acetic acid solution and acetic acid solution containg a small amount of cobalt acetate and potassium iodide (catalyst in this synthetic reaction) were selected. Corrosion specimens were immersed in the solution admitted to an autoclave, and the air in the autoclave was replaced by carbon monoxide; then the solution was heated to a temperature between 200 and 300°C is temperature was usually maintained for 48 hours. The pressure was maintained in the equilibrium value for a given temperature except for some special cases.
At elevated temperatures the corrosivity of acetic acid increased, especially under the existense of the catalyst. However titanium, zirconium and tantalum produced only a slight weight gain assuming interference colours, and the prominent corrosion resistance of these metals was recognized.
From the viewpoint of price, titanium alone became the subject of practical use; then the welded specimens and the U-from specimens of titanium were tested furthermore. At the result of these tests it was observed that the corrosion resistance of titanium was not affected by welding, cold working and stress, and the utility of titanium which had been infered from the preliminary data was confirmed. In pure acetic acid solutions, besides titanium, Hastelloy B showed excellent corrosion resistance.

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Despite of exhaustive studies and numerous trial applications carried on in the past with respect to the presentive measures against the electrolysis corrosion of the railway track materials, many cases of corrosion damages are still encountered in the railway tunnels. In order to find out the keys to this problem, we have been conducting following tests at “Tanna” tunnel and other places; namely.
(1) Durability tests of track materials by applying various kinds of conventional corrosion control methods.
(2) Preventive tests of track materials against the electrolysis corrosion by applying the selfregulated forced drainage system.
From the observations of the above tests gathered until now, no decisive conclusion cannot be drawn yet as to (1), the same tests having been started quite resently, while fairly good prospects can be expected as to (2), judging from the results of the rail to earth potential measurements.

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