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Some factors affecting the performance of exhaust valves are considered and the importance of improving engine design to give minimum valve operating temperature is stressed. Strength requirements are reviewed and it is shown that the advantages of higher mechanical strength and better corrosion resistance of austenitic compared with ferritic steels may be lost due to the valves operating at higher temperatures and hoop stresses. The corrosion conditions inside the cylinder head are considered and a new test is described in which lead monoxide coated specimens are exposed to atmospheres which produce valve corrosion similar to that which occurs in an engine. The order of merit established by this test agreed fairly well with the known behaviour of valve alloys when the effect of operating temperature was taken into account. Valve head corrosion has been shown to be due to surface carburization-oxidation and internal oxidation; by applying a suitable surface coating, valve life can be appreciably increased.

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Heavy corrosion resulted from the sulphur dioxide content, temperature and variation in relative humidity of the combustion gases in mild‐steel stacks, and replacement had been necessary after about two years' service. However, as this case history shows, such stacks can be free from corrosion and in excellent condition after many years' service.

The influence of variations in brinepH and concentration, cathodic current density, sodium concentration in the amalgam, and movement of the cathode on cathodic hydrogen formation in the mercury cell have been studied in a laboratory cell and by polarographic methods. The kinetics of the process have also been investigated. The results indicate that the small proportion of hydrogen normally formed in the cell is determined essentially by the rate of transfer of hydrogen ions to the cathode surface. If the cathode surface should become saturated with sodium, however, the over‐all rate of sodium amalgam formation can become limited by the rate of transfer of dissolved sodium from the cathode surface into its bulk. Hydrogen formation can then increase by the process H2O+e→1/2H2+OH−