Sipe's Japan oil, most of the other driers being a detriment rather than a help, especially to red-lead paints.*

Best Colors for Paints

Practice seems to have decreed that dark paints are more suitable for bridges than light ones, notwithstanding the well-known facts that they absorb much heat, and that excessive heat is one of the most active agencies in paint deterioration. The main reason for the reluctance to use light paints is their tendency to fade and to show the dirt that inevitably accumulates on all bridge metal; but the fading is avoidable by a proper study of the finishing coat, and it cannot be denied that dirt shows more or less on dark paints as well as on light ones. It must not be forgotten that the selection of paint color for any bridge is a matter of aesthetics as well as of expediency; for in some structures dark colors give the finer effect, and in others light ones provide a better appearance. An old favorite color of the author's is olive green; and he has employed it on a number of occasions with satisfaction to all concerned. Canary yellow and pearl gray are often suitable colors for the finishing coat.

There is one important point about paint colors that should never be ignored, viz., that, no matter how many coats are given to any steel-work, all of them should be of essentially different shades or colors, in order to make sure that all the coats called for are really applied. In one of his early bridges, the author caught the erection superintendent trying to palm off on him a single coat of rather thick paint instead of two field coats of the same color. Ever since then his bridge-erection specifications have called for distinctly different shades or colors of paint coats.

Elasticity of Paint Coats

The matter of elasticity in paint coats is one of extreme importance; because, if neglected, the paint is liable to crack and permit moisture to reach the metal, thus starting rust. As before indicated, there should be a gradual increase in the elasticity of the different, coats from the priming one outward.

Covering and Spreading Powers of Paints

One of the most effective claims of paint-selling agents is that the special paint which they handle has a very large spreading power; and this

*Concerning driers Dr. Sabin writes as follows:

Three or four years ago I sent a circular letter, asking confidential opinions as to driers, to about a dozen of the chemists of the really big mixed-paint companies. Without exception they agreed that if price is left out of account the best drier is free from rosin, and contains lead and manganese, from three to twenty-five times as much lead as manganese, but must contain both.

I myself would not object to a drier made by a responsible concern, which contained a little rosin, as most commercial driers do. The trouble is to draw the line.