This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1896 Excerpt: ...of moisture. Professor Carhart of Ann Arbor, Michigan, in answering a question in regard to the destructive tendency of rust and the length of time that a rail will resist its effects, says: "It is well known that a polished iron or steel surface does not rust so soon as a rough surface when exposed to the same conditions. Rough lines and sharp points appear to serve as nuclei, about which water condenses. Moist air when expanded suddenly precipitates its vapor as a cloud, if dust is present to furnish centers of condensation. Frost crystals form first along scratches on glass. So moisture appears to condense more quickly and freely on a rough surface of iron than on a clean polished one. Trusting takes place only in the presence of moisture. A clean plate in dry air never rusts. Mixture of explosive gases do not explode when the electric spark passes, unless vapor of water is present. When a metal surface is once covered with rust, the rusting proceeds much more rapidly than at first, because the rust is hydroscopic; moisture is taken up and conducted inward toward the metal; hydratic oxides of iron are thus formed, and fresh metal underneath is attacked because of the presence of moisture or of the hydratic oxides on the outside. A coat of iron rust hastens the rusting process except when the metal is coated with the black oxide of iron. It can then be exposed to any weather without rusting. But the black oxide is formed only at a high temperature. The scales that fall from the rails as they come from the rolls are largely black oxide of iron." In a climate such as we are treating of, it is probable that fifty years of exposure would render a rail unsafe for use. If this is so, the deterioration from natural causes is two per cent. annually. Wit...