the
piston rod with the crank pin?

_A._--The cap for attaching the piston rod to the crank pin, is formed
altogether of brass, which brass serves to form the bearing of the crank
pin. The external diameter of the socket by which this cap is attached to
the piston rod is 3-5/16 inches. The diameter of the crank pin is 3 inches,
and the length of the crank pin bearing 3-7/8 inches. The thickness of the
brass around the crank pin bearing is 1 inch, and the upper portion of the
brass is secured to the lower portion, by means of lugs, which are of such
a depth that the perpendicular section through the centre of the bearing
has a square outline measuring 7 inches in the horizontal direction, 3-7/8
inches from the centre of the pin to the level of the top of the lugs, and
2-1/2 inches from the centre of the pin to the level of the bottom of the
lugs. The width of the lugs is 2 inches, and the bolts passing through them
are 1-1/4 inch in diameter. The bolts are tapped into the lower portion of
the cap, and are fitted very accurately by scraping where they pass through
the upper portion, so as to act as steady pins in preventing the cover of
the crank pin bearing from being worked sideways by the alternate thrust on
each side. The distance between the centres of the bolts is 5 inches, and
in the centre of the cover, where the lugs, continued in the form of a web,
meet one another, an oil cup 1-5/8 inch in diameter, 1-1/8 inch high, and
provided with an internal pipe, is cast upon the cover, to contain oil for
the lubrication of the crank pin bearing. The depth of the cutter for
attaching the cap to the piston rod is 1-1/4 inch and its thickness is
3/8ths of an inch.

627. _Q._--Will you describe the means by which the air pump rod is
connected with the crank which works the air pump?

[Illustration: Fig. 50. AIR PUMP CONNECTING ROD AND CROSS HEAD. Messrs.
Penn.]

_A._--A similar cap to that of the piston rod attaches the air pump crank
to the connecting rod by which the air pump rod is moved, but in this
instance the diameter of the bearing is 5 inches, and the length of the
bearing is about 3 inches. The air pump connecting rod and cross head are
shown in perspective in fig. 50. The thickness of the brass encircling the
bearing of the shaft is three fourths of an inch upon the edge, and 1-1/8
inch in the centre, the back being slightly rounded; the width of the lugs
is 1-5/8 inch, and the depth of the lugs is 2 inches up