In the previous report, it has been made to evaluate the corrosion rate of steel and other metals in sulfamic acid solution and to search for the corrosion inhibitor for steel in this solution. Resulting from these tests, thiourea derivatives and acetylenic compounds were found to be most effective inhibitors.
In this study, we have investigated in detail the inhibiting effect of these inhibitors for iron and other metals in various corrosive environments of sulfamic acid solution. The results were as follows:
(1) Ca⁺⁺ ion has no influence on the corrosion of steel and the effect of inhibitors.
(2) An increase in amount of Fe⁺⁺⁺ ion results increase in the corrosion rate and decrease in the effect of the inhibitors.
(3) Inhibiting effect on cast iron is the nearly same as that on steel, although the corrosion rate of the former is greater than that of the latter.
(4) The corrosion of Cu, Al, and Cu-Zn alloy in sulfamic acid in the presence or absence of the inhibitors is smaller than that of steel.
(5) The effect of the inhibitors for steel is not lowered by recycled run of the same solution (5 times), but it is slightly lowered by aeration.
(6) The synergistic effect of some surface active agents on the inhibiting effect of 1, 3-diethyl-thiourea for steel is observed only in inhibitor concentration of below 0.2m mol/l.

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Stray current corrosion of reinforced concrete, which was immersed in tap water and 10% Na₂SO₄ solution, was studied. The steel electrode in the mortar and the auxiliary electrode made of steel plate ware connected to the anode- and cathode-terminals of the battery respectively, and the voltage applied between two electrodes was 1.2 or 1.5 volts. The mortar containing either none or 2% CaCl₂ was used. The mortar containing 2% CaCl₂ cracked even in the small degree of corrosion (15-20mg/cm²) of the steel in the mortar. It seems that cracking of the mortar is caused not only by increase in volume of rusty steel, but by the corelated effect of change in volume of rusty steel and contractibility of the mortar.
The corrosion of the reinforcing bar within the mortar (mortar-S), prepared with sea water or 3% NaCl solution, were studied by the socalled R. G. Y. test. Following results were obtained:
1) By immersing the mortar-S into tap water, the reinforcing bar was slightly corroded.
2) Since, in sea water, the corrosion behabior of the reinforcing bar within the mortar-S was equal to that within the mortar (mortar-C) prepared with tap water, seemingly, the mortar-S may be useful in sea water.
3) The early mechanical strength of the mortar-S was larger than that of the mortar-C, but the final strength of these mortars was reversed.

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