The kinetics and mechanism of filiform corrosion occurring on polymer coated AA2024-T3 aluminium alloy are investigated using a scanning Kelvin probe technique (SKPT). Repeated scanning by SKPT is used to generate a time-lapse animation showing the dynamic evolution of localised free corrosion potential (E corr ) patterns. E corr values in the head region of propagating filaments are up to 150 mV lower that the intact polymer coated surface, indicating local depassivation. However, E corr values in the filament tail are ca. 100 mV higher than background, indicating superpassivation. Spatial analysis of instantaneous E corr distributions indicates that anodic metal dissolution is concentrated at the leading edge, and cathodic oxygen reduction at the trailing edge, of active filament heads. Temporal analysis of time-dependent E corr distributions shows that filaments propagate at a constant speed and do not intersect.

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micro-Dumas method of Pregl (S) has an enviable reputation for producing accurate results on a variety of substances. Properly handled, it was considered an accurate method for any organic nitrogen-containing compound.This method was used in this laboratory on a wide range of compounds without any known discrepancy until a certain series of pyrimidines of known purity failed to give the required amount of nitrogen. The nitrogen values obtained were from 0.4 to 2.0 per cent below theory and were reproducible under uniform treatment of the sample. The carbon and hydrogen values for these compounds agreed with the theoretical values within the limits of experimental error.Several papers have appeared recently in the literature in which references were made to the fact that there were certain types of compounds which could not be analyzed properly by the Dumas method. The nitrogen values ob-

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