that this cement be made from a pigment that secures chemical action between itself and the liquid with which it is mixed, for it is only through the use of such a pigment that we can secure a skin, or covering, upon unheated metal that will be impervious to air and water.

Theoretically, red lead in competent hands is the best pigment to use with linseed oil for making a primer for naked steel. It forms a rapid-drying, firm, unyielding, impervious, non-corrosive, somewhat inhi-bitive, and receptive covering upon the metal, its only defect being that it will undergo chemical change when exposed to ordinary atmospheric conditions; therefore the necessity at all times of protecting the red lead with outer coatings of paint made from linseed oil and pigments that have no chemical  action  upon  it,  such  as the car-