to settle into a hard mass in the bottom of the container. These faults were due to an excessive amount of litharge in the pigment, sometimes as much as thirty per cent. Within a few years certain lead-paint manufacturers have reduced the litharge to as low as two per cent, the remaining ninety-eight per cent being true red lead, Pb₃0₄. This makes an ideal paint for the priming coat; for, being extremely fine, it fills all pores, and brushes out in a smooth, even film free from voids. Moreover, it stays in place on vertical surfaces, does not act ropy under the brush, and does not settle to the bottom of the container. It is sold generally in paste form; but, until it can be regularly furnished ready-mixed for application, it will not have attained its acme of excellence.

The amount of red lead to be used per American gallon of vehicle is still a disputed point among engineers. In some cases the amount actually employed has been as high as thirty-seven pounds; but such an unusually great quantity cannot be made to give satisfactory results, unless all the conditions are ideal. If the paint be applied under contract, which is by no means the best way but sometimes is unavoidable, it is well to limit the amount of pigment to twenty-eight, or possibly thirty, pounds per gallon of oil.

The theory one should adopt when applying the coats which follow the priming coat, as well as at any time thereafter when the bridge is to be repainted, is to have each coat more elastic than the one preceding it, so as to insure against checking and alligatoring-a term very aptly applied to what occurs when paint dries in lumps or ridges or when it shows wide, irregular cracks, giving the surface an appearance of alligator hide.

Some authorities advise adding a little non-drying oil to the final coat of paint, in order to enable it better to shed water; and the author agrees with this practice, provided that the amount used be not great enough to prevent the paint from drying thoroughly by the time an additional coat is required.

Summing up the matter of the best kinds of paint for bridgework, the author feels that he cannot do better than to quote the following from Mr. Houston Lowe's "Paints for Steel Structures" concerning the desirable features of an anti-corrosive metal coating:

1. It should hide the surface.

2. Should cement itself together, and also cement itself to either damp or

dry metallic surfaces.

3. Should expand and contract without breaking its own body.

4. Should present a hard, yet tough, outer surface.

5. Should be impervious to water, carbonic acid, or other gases.

6. Should be unaffected by sunshine, heat, frost, dew, or climatic changes.

7. Should be unaffected by ordinary mechanical abrasion.

8. Should wear evenly.