n of the hammer and the latter a plan, partly in section, of the
cross girder, while Fig. 4 is a cross section showing the arrangements
for operating the hammer. In the center is a cast iron guide for working
the ram, the guide being extended on two sides to receive the disk crank
journals, 2 in. in diameter by 31/2 in. long. The disk cranks are
connected to a hollow steel ram by a connecting rod. The ram is divided
inside into two compartments, each having a phosphor bronze air piston.
These are connected together by a steel piston rod, the top air piston
forming a connection for the small end of the connecting rod. The
outside diameter of the ram is 33/4 in., and the diameter of the air
pistons 23/4 in. and 2-7/8 in. respectively. Cottered into the bottom of
the ram is a steel pallet holder with a dovetail, so that the pallet can
be renewed or exchanged for one of another shape when required. Keyed on
to the crankshaft is a flanged pulley 10 in. in diameter by 31/4 in.
between flanges. There is also an overhead countershaft with strap
shifting arrangement. At the side of one of the columns a hand lever and
quadrant are provided, as shown in the perspective view and in Fig. 2,
for working an arrangement for tightening the belt when the machine is
working. To this arrangement is connected a powerful brake which stops
the machine in a few revolutions. It will be seen that the brake is
applied as the belt is slackened for stopping the machine. For
planishing pipes or tubes a long wrought iron mandrel is provided
mounted on two cast iron carriages, each having four flanged wheels for
running on rails. The hammer is arranged so that tubes 4 feet in
diameter can be worked for planishing plates. A pallet is fastened on
the top of one of the mandrel carriages, Figs. 5 to 8 showing the
details of the carriages. The general dimensions are: Distance between
pillars, 6 feet; height under girder, 5 feet; height from ground to top
of mandrel, 4 feet 13/4 in.; and length of stroke, 5 in. This machine is
capable of delivering 500 blows per minute. The constructors are Messrs.
Thwaites Brothers, Limited, Bradford, Yorkshire.

[Illustration: FIG. 1.]

[Illustration: SUSPENSION PNEUMATIC POWER HAMMER.]

* * * * *

SIBLEY COLLEGE LECTURES.--1890-91.

BY THE CORNELL UNIVERSITY NON-RESIDENT LECTURERS IN MECHANICAL
ENGINEERING.

COMPRESSED AIR PRODUCTION.

By WM. L. SAUNDERS, C.E., of New York.