penetration of water by suitable overcoats, is promising good results, and a final solution of the problem is confidently looked for.

The tendency of rust to grow and spread out from a centre has an adequate explanation in the electrolytic theory. This phenomenon is especially pernicious, as it results in pitting, or, under a paint coat, in a growth which finally flakes off the paint and exposes large areas of the iron.

Some agencies that have been observed greatly to hasten corrosion are:

1. Alternate exposure to air and water.

2. "Constant or alternately occurring

heavy rains with drying winds, hot sun,

frost or snow."

3. "Collection of soot,  dust,  or anything

that will retain moisture in sheltered

places."