iameter of the cylinder.
But a somewhat larger proportion than this appears to be expedient: Messrs.
Rennie make the area of their eduction pipes, in oscillating engines, 1/22d
of the area of the cylinder. In the oscillating engines of the Oberon, by
Messrs. Rennie, the cylinder is 61 inches diameter, and 1-1/2 inch thick
above and below the belt, but in the wake of the belt it is 1-1/4 inch
thick, which is also the thickness of metal of the belt itself. The
internal depth of the belt is 2 feet 6 inches, and its internal breadth is
4 inches. The piston rod is 6-3/4 inches in diameter, and the total depth
of the cylinder stuffing box is 2 feet 4 inches, of which 18 inches
consists of a brass bush--this depth of bearing being employed to prevent
the stuffing box or cylinder from wearing oval.

635. _Q._--Can you give any other examples?

_A._--The diameter of cylinder of the oscillating engines of the steamers
Pottinger, Ripon, and Indus, by Miller & Ravenhill, is 76 inches, and the
length of the stroke 7 feet. The thickness of the metal of the cylinder is
1-11/16 inch; diameter of the piston rod 8-3/4 inches; total depth of
cylinder stuffing box 3 feet; depth of bush in stuffing box 4 inches; the
rest of the depth, with the exception of the space for packing, being
occupied with a very deep gland, bushed with brass. The internal diameter
of the steam pipe is 13 inches; diameter of steam trunnion journal 25
inches; diameter of eduction trunnion journal 25 inches; thickness of metal
of trunnions 2-1/4 inches; length of trunnion bearings 11 inches;
projection of cylinder jacket, 8 inches; depth of packing space in
trunnions, 10 inches; width of packing space in trunnions, or space round
the pipes, 1-1/2 inch; diameter of crank pin 10-1/4 inches; length of
bearing of crank pin 15-1/2, inches. There are six boilers on the tubular
plan in each of these vessels; the length of each boiler is 10 feet 6
inches, and the breadth 8 feet; and each boiler contains 62 tubes 3 inches
in diameter, and 6 feet 6 inches long, and two furnaces 6 feet 4-1/2 inches
long, and 3 feet 1-1/2 inch broad.

636. _Q._--Is it the invariable practice to make the piston rod cap of
brass in the way you have described?

_A._--In all oscillating engines of any considerable size, the cover of the
connecting brass, which attaches the crank pin to the connecting rod, is
formed of malleable iron; and the socket also, which is cuttered to the end
of the piston