strain which was at any time liable to come
on them was 22,000 pounds per inch, or 3,000 pounds more than the
elastic limit. The fracture of the tested rods, which, it is stated,
broke with a single blow of the hammer very much in the manner of
cast-iron, showed a very inferior quality of metal. The rods broke in
the bridge exactly where we should look for the failure; viz., in the
screw at the end. No ordinary inspection would have detected this
weakness. No inspection _did_ detect it, but a proper specification
faithfully carried out would have prevented the disaster.

Look now at an extract from the specification for bridges upon the
Cincinnati Southern Railway:--

"All parts of the bridges and trestleworks must be proportioned to
sustain the passage of the following rolling-load at a speed of not
less than 30 miles an hour: viz., two locomotives coupled, each
weighing 36 tons on the drivers in a space of 12 feet, the total
weight of each engine and tender loaded being 66 tons in a space of
50 feet, and followed by loaded cars weighing 20 tons each in a space
of 22 feet. An addition of 25 per cent will be made to the strains
produced by the rolling-load considered as static in all parts which
are liable to be thrown suddenly under strain by the passage of a
rapidly moving load. A similar addition of 50 per cent will be made
to the strain on suspension links and riveted connections of
stringers with floor-beams, and floor-beams with trusses. The
iron-work shall be so proportioned that the weight of the structure,
together with the above specified rolling-load, shall in no part
cause a tensile strain of more than 10,000 pounds per square inch of
sectional area. Iron used under tensile strain shall be tough,
ductile, of uniform quality, and capable of sustaining not less than
50,000 pounds per square inch of sectional area without fracture, and
25,000 pounds per square inch without taking a permanent set. The
reduction of area at the breaking-point shall average 25 per cent,
and the elongation 15 per cent. When cold, the iron must bend,
without sign of fracture, from 90 to 180 degrees."

A specification like this, properly carried out, would put an
absolute stop to the building of such structures as the Tariffville
Bridge, and would prevent a very large part of the catastrophes which
so often shock the community, and shake the public faith in iron
bridges. Reference has been made above to the proper loads to be
plac