the particles of pigment and adjacent particles of the steel surface may cause a difference of electrical potential, and thus establish electrolytic corrosion.

In the inhibitive class are willow charcoal (on account of alkaline ash), one grade of Prussian blue, zinc oxide and notably zinc chromate, and barium and calcium chromate.

Pigments fit for use in structural oil paints are of two general classes, as they relate to the oil, viz., those which react more or less with it, notably the carbonates and all of the lead pigments; and those that have no chemical action on the oil or binder, called inerts, such as the carbons, silicates, probably ferric oxides, etc. The former class produces the quicker drying and the less durable paints the latter, the slower drying and the more durable coat-