nt 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.

Among the steels, those that are softer are more serviceable and
reliable than the harder ones, especially whereever shocks and
concussions or rapidly alternating strains are to be endured. In other
words, the more nearly steel resembles good wrought iron, the more
certain it is to render lasting service when used within appropriate
limits of strain. Indeed, a wrought iron of fine quality is better
calculated to endure fatigue than any steel. This is particularly
noticeable in steam hammer pistons, propeller shafts, and railroad
axles. A better quality of wrought iron, therefore, has long been a
desideratum, and it appears now that it has at last been found.

Several years since, a pneumatic process of manufacturing wrought iron
was invented and patented by Dr. Chapin, and an experimental plant was
erected near Chicago. Enough was done to demonstrate, first, that an
iron of unprecedentedly good qualities was attainable from common pig;
and second, that the cost of its manufacture would not exceed that of
Bessemer steel. Nevertheless, owing to lack of funds properly to push
the invention against the jealous opposition which it encountered, the
enterprise came to a halt until quite recently, when its merits fo