In the study of metallic corrosion much use is made of specimens exposed at outdoor research stations, but wide variations in the results observed can often be attributed to differences in climatic conditions. Obviously a major factor in corrosion is the persistence of free or even of absorbed moisture on the surfaces of the exposed specimens, and the interpretation of exposure data from a number of locations would be made very much more reliable if an instrument could be developed to record the period of time in which a specimen is actually corroding due to the presence of moisture.

The need for such a device was recently realised by the ASTM Committee on Corrosion of Non-Ferrous Metals, and an offer to undertake its development was made by P. J. Sereda of the Division of Building Research, National Research Council, Ottawa. Two progress reports have now been published describing the investigations leading to a successful means of measurement of time-of-wetness (ASTM Bulletin, No. 228, February 1958, p. 53, and No. 238, May 1959, p. 61).

The method adopted, based on a suggestion by F. L. LaQue, involves the measurement of the potential developed between a corroding metal specimen and a platinum electrode placed in immediate proximity, surface moisture serving as the electrolyte. Preliminary trials have proved promising, and an attempt is being made to develop a field instrument in which periods of wetness would be indicated by a time recorder.