lod 
PROCEEDINGS OF SECTION J. 719 
abie deflection, when on the point of fracture, for a bar l-inch 
square and 3 feet span,and ,°, for a bar 2-inches deep and the same 
span. It is to be noted that the best results are obtained from 
a test-bar when so placed that the side in tension is that which 
was lowest in the mould during casting. 
The test for wrought-iron is usually by direct tension, and, 
unless the test-piece be made most undesirably small, requires 
comparatively powerful appliances, such as are usually found only 
in a well-equipped engineering laboratory. Such a laboratory 
exists at the best engineering colleges, and also at important 
arsenals and the works of some of the leading manufacturers in 
Europe and America. The Universities of Sydney and Melbourne 
are provided with these appliances, and are frequently. resorted to 
by the colonial Governments and private engineers. 
What, then, should be the specified tenacity of iron for bridge 
and boiler work? The various authorities, English and American, 
give from 44,800lbs., or 20 tons, to 60,000, or nearly 27 tons, per 
square inch in various cases, the lower values being usual in plate 
and the higher in bar iron, as is to be expected when the mode of 
manufacture is considered. Further, with the same quality of 
iron the tenacity of large masses is always somewhat less than 
that of smaller or thinner portions, so that the same requirements 
cannot be fairly made in the case of large and thick as in that of 
smaller or thinner rods and plates. Again, mere tenacity, apart 
from other properties, is not a sufficient criterion of quality, for, 
as was pointed out by Kirkaldy about twenty years ago, a high 
tenacity may be exhibited by a hard, brittle iron, utterly untrust- 
worthy for bridge or boiler work ; consequently, the ductility 
must be carefully observed and numerically determined. 
Let us now, therefore, consider and compare a number of actual 
specifications of iron. Those which merely state in vague terms 
that the\material shall be of the best quality and subject to the 
approval of the engineer may be at once dismissed as belonging 
to a bygone chaotic era in engineering, and so may those others 
which simply name the material supplied by some particular 
manufacturer, followed by the words, “or of equal quality.” 
The specification under which the majority of the railway 
bridges in this country have been built reads as follows :—“ The 
whole of the wrought iron used shall be of good quality, capable 
of bearing compression equal to 16 tons per square inch, or a 
tensile strain of 20 tons per square inch, without decreasing or 
increasing more than 1-625th part of the length of any bar or 
plate tested. Plates and bars will be selected by the super- 
intending officer, which must be cut to the required form, and 
submitted to the above-mentioned tests. The contractor will 
have to find all labour, machines, and instruments required for 
these experiments, and every lot of iron will be rejected the 
