CHAPIN WROUGHT IRON.

By W.H. SEARLES, Chairman of the Committee, Civil Engineers' Club
of Cleveland, O.


Notwithstanding the wonderful development of our steel industries in
the last decade, the improvements in the modes of manufacture, and the
undoubted strength of the metal under certain circumstances,
nevertheless we find that steel has not altogether met the
requirements of engineers as a structural material. Although its
breaking strain and elastic limit are higher than those of wrought
iron, the latter metal is frequently preferred and selected for
tensile members, even when steel is used under compression in the same
structure. The Niagara cantilever bridge is a notable instance of this
practice. When steel is used in tension its working strains are not
allowed to be over fifty per cent. above those adopted for wrought
iron.

The reasons for the suspicion with which steel is regarded are well
understood. Not only is there a lack of uniformity in the product, but
apparently the same steel will manifest very different results under
slight provocation. Steel is very sensitive, not only to slight
changes in chemical composition, but also to mechanical treatment,
such as straightening, bending, punching, planing, heating, etc.
Initial strains may be developed by any of these processes that would
seriously affect the efficiency of the metal in service.