SOLIDS

"Their time in envious search of colors lose, Which, when they find, they lack the skill to use."

     —Shee.

The solids applied as paint to iron may be classified as (1) stimulators of corrosion, (2) preventives, or inhibitives of corrosion, and (3) inerts. Stimulators embrace some natural pigments that are either slightly soluble themselves, like gypsum, or that contain soluble impurities. Many manu-factured pigments also must be included on account of the presence of traces, at least, of stimulative acids and salts employed in the process of manufacture, or resulting therefrom. Inhibitives include chromates of the alkaline earths, and a few other pigments not so certainly determined. Zinc yellow, which   is   a  double   chromate   of  zinc