prevent their ever reaching the bridges; but this has not yet been done. It is a matter which should be investigated promptly; and, if an effective remedy for the trouble be found, it should be utilized without delay by all railroads, because the damage done by the drippings is not confined to the floor-systems, but in deck truss-bridges extends also to the upper chords. The total value of the annual damage to all the steel bridges of North America by brine drippings must amount to a goodly sum.

The railroads are now struggling with the owners of the refrigerator-car lines in an endeavor to force them to lead the brine to one side so far that it will not drip on the track rails and their fastenings; but nothing of any account is being done to protect steel bridges with open timber decks, excepting sometimes to cover each stringer and each floor-beam with a wide plank or to daub thickly the top surface of the endangered metal with some paint or other compound that has no chemical affinity for the brine.

Protection Against Locomotive Gases

Another deadly agent of destruction to steel bridges is the gas from steam locomotives, especially when they pass beneath the structure, in which case the gas collects in semi-enclosed spaces where it remains and steadily attacks first the paint and then the steel beneath.

As before mentioned, the surest method of protection against such attack is to enclose the entire metalwork below the elevation of track-rails in concrete or gunite. Another method is to use special paint beneath the floor and to hang wooden or sheet-iron protecting platforms close to the deck. If the tops of the smoke-stacks of the locomotives come very near to the floor of the bridge above, especially where there is a heavy up-grade, cinders are driven out of the stacks at high velocity, combined with smoke and steam, thus forming the most effective possible kind of blast for cutting first the protection and then the steelwork itself.

Causes of Paint Deterioration

The main causes for deterioration of bridge paint, as stated by the late Mr. Houston Lowe, are as follows:

1. Water. (Dissolution.)

2. Action of light and heat. (Chemical and physical change.)

3. Chemical action between pigment and binder. (Disintegration.)

4. Abrasion or mechanical injury. (Motion.)

5. Action of deleterious gases. (Foul air.)

It is impracticable to keep water away from a bridge, but the design can be so made that there are no pockets to hold it, in which case it quickly runs off and evaporates.

The deleterious action of light and heat can best be combated by a proper choice of color for the finishing coat.