al. | 22 | 34.8 | 0.73 | 0.16 | 6.84 | 8.06 | 6.02 | 14,430 | 54.0 |
| | " | | 24 | 29.9 | 0.35 | 0.12 | 7.62 | 9.00 | 5.75 | 14,240 | 61.2 |
| | " | | 20 | 19.9 | Nil | 0.21 | 7.30 | 8.33 | 3.66 | 14,240 | 58.6 |
+----------------------------+-------+--------+--------+-----------+---------+---------+-------+--------+----------+---------+------+

[1] In the first three trials no retarders were used in the tubes. In
the last trial retarders were used.

[2] In this trial retarders were used in the tubes.

[3] The first four trials were made with horizontal baffles above the
tubes; the last two trials with the baffling described in the text.

BOILER MAKING.

The practice of the boiler, bridge and girder shops may here be
conveniently treated together, because similar materials and methods are
employed in each, notwithstanding that many points of divergence in
practice generally relegate them to separate departments. The materials
used are chiefly iron and steel. The methods mostly adopted are those
involved in the working of plates and rolled sections, which vastly
predominate over the bars and rods used chiefly in the smithy. But there
are numerous differences in methods of construction. Flanging occupies a
large place in boilermaking, for end-plates, tube-plates, furnace flues,
&c., but is scarcely represented in bridge and girder work. Plates are
bent to cylindrical shapes in boilermaking, for shells and furnaces, but
not in girder work. Welding is much more common in the first than in the
second, furnace flues being always welded and stand pipes frequently. In
boiler work holes are generally drilled through the seams of adjacent
plates. In bridge work each plate or bar is usually drilled or punched
apart from its fellows. Boilers, again, being subject to high
temperatures and pressures, must be constructed with provisions to
ensure some elasticity and freedom of movement under varying
temperatures to prevent fractures or grooving, and must be made of
materials that combine high ductility with strength when heated to
furnace temperatures. Flanging of certain parts, judicious staying,
limitation of the length of the tubes, the forms of which are
inherently weak, provide for the first; the selection of steel or iron
of high percentage elongation, and the i