duces greater corrosion than moisture alone; (2) inhibitors, or pigments whose moist contact with steel produces less corrosion than does pure water alone, and (3) indeterminates, or pigments whose moist contact with steel produces neither increase nor diminution of rusting.

Not enough preliminary experimental work has been completed yet to classify confidently many of the pigments, but the reports available indicate very strongly that precipitated barium sulphate (Blanc fixe), second grades of barytes, some ochres, some red oxides, lampblack, graphite, in fact, all the carbons except willow charcoal, are stimulators of rusting. In the case of some pigments stimulation of corrosion is due to the acid quality of soluble constituents. In the case of other pigments, such as carbons, the unlike   chemical   action   of   moisture   on