From the results obtained in this investigation, the following conclusions can be drawn: 1. A substance inhibits corrosion only under certain conditions, and under other conditions it may not be an inhibitor, but may be inert or an accelerator. 2. No compounds tested in concentrations of 0.01 and 0.10 percent nitrogen, were found to inhibit the corrosion of steel in 5 percent phosphoric acid at 25°C. and under the conditions of aeration and agitation used. 3. Sodium chromate is an inhibitor in concentrations of 1 percent for the corrosion of steel by a 5 percent, aerated, agitated, phosphoric acid solution at 25°C. 4. The mechanism of the corrosion of copper proposed by Whaley is not substantiated. Chelation probably is not the mechanism by which 2-nitro-l-butanol inhibits the corrosion of copper in a 5 percent phosphoric acid solution. 5. Inhibitors that are used and are efficient for one acid under certain conditions cannot always be said to work for other acids under other conditions. / M.S.