unched to receive the projections on the tips of the
blades, which are rivetted over pneumatically.

[Illustration: FIG. 27]

The foundation rings themselves are of dovetail shape in cross-section,
and, after receiving the roots of the blades, are inserted in dovetailed
grooves in the cylinder and rotor, where they are firmly held in place
by keypieces, as may be seen at C in Fig. 27. Each keypiece, when driven
in place, is upset into an undercut groove, indicated by D in Fig. 27,
thereby positively locking the whole structure together. Each separate
blade is firmly secured by the dovetail shape of the root, which is held
between the corresponding dovetailed slot in the foundation ring and the
undercut side of the groove.

[Illustration: FIG. 28]

Fig. 29, from a photograph of blading fitted in a turbine, illustrates
the construction, besides showing the uniform spacing and angles of the
blades.

[Illustration: FIG. 29]

The obviously thin flanges of the shroud rings are purposely made in
that way, so that, in case of accidental contact between revolving and
stationary parts, they will wear away enough to prevent the blades
from being ripped out. This protection, however, is such that to rip
them out a whole half ring of blades must be sheared off at the roots.
The strength of the blading, therefore, depends not upon the strength of
an individual blade, but upon the combined shearing strength of an
entire ring of blades.

[Illustration: FIG. 30]

The blading is made up and inserted in half rings, and Fig. 30 shows two
rings of different sizes ready to be put in place. Fig. 31 shows a
number of rows of blading inserted in the cylinder of an Allis-Chalmers
steam turbine, and Fig. 32 gives view of blading in the same turbine
after nearly three years' running.

[Illustration: FIG. 31]

[Illustration: FIG. 32]

The Governor

Next in importance to the difference in blading and balance piston
construction, is the governing mechanism used with these machines. This
follows the well-known Hartung type, which has been brought into
prominence, heretofore largely in connection with hydraulic turbines;
and the governor, driven directly from the turbine shaft by means of cut
gears working in an oil bath, is required to operate the small, balanced
oil relay-valve only, while the two steam valves, main and by-pass (or
overload), are controlled by an oil pressure of about 20 pounds per
square inch, acting upon a piston