out of its place.  The air pump barrel is of brass to which is bolted a cast iron mouth piece, with a port for carrying the water to the hot well; within the hot well the delivery valve, which consists of a common flap valve, is situated.  The mouth piece and the air pump barrel are made tight to the condenser, and to one another, by means of metallic joints carefully scraped to a true surface, so that a little white or red lead interposed makes an air tight joint.  The air pump bucket is of brass, and the valve of the bucket is of the common pot lid or spindle kind.  The injection water enters through a single cock in front of the condenser—­the jet striking against the barrel of the air pump.  The air pump rod is maintained in its vertical position by means of guides, the lower ends of which are bolted to the mouth of the pump, and the upper to the oval in the top frame, within which the air pump crank works; and the motion is communicated from this crank to the pump rod by means of a short connected rod.  The lower frame is not set immediately below the top frame, but 2-1/2 inches behind it, and the air pump and condenser are 2-1/2 inches nearer one edge of the lower frame than the other.

622. Q.—­What are the dimensions of the cylinder?

A.—­The thickness of the metal of the cylinder is 9/16ths of an inch; the depth of the belt of the cylinder is 9-1/2 inches, and its greatest projection from the cylinder is 2-1/2 inches.  The distance from the lower edge of the belt to the bottom of the cylinder is 11-1/2 inches, and from the upper edge of the belt to the top flange of the cylinder is 9 inches.  The trunnions are 7-1/4 inches diameter in the bearings, and 3-1/2 inches in width; and the flanges to which the glands are attached for screwing in the trunnion packings are 1-1/2 inch thick, and have 7/8ths of an inch of projection.  The width of the packing space round the trunnions is 5/8ths of an inch, and the diameter of the pipe passing through the trunnion 4-5/8ths, which leaves 11/16ths for the thickness of the metal of the bearing.  Above and below each trunnion a feather runs from the edge of the belt or bracket between 3 and 4 inches along the cylinder, for the sake of additional support; and in large engines the feather is continued through the interior of the belt, and cruciform feathers are added for the sake of greater stiffness.  The projection of the outer face of the trunnion flange from the side of the cylinder is 6-1/2 inches; the thickness of the flange round the mouth of the cylinder is 3/4 of an inch, and its projection 1-3/8 inch; the height of the cylinder stuffing box above the cylinder cover is 4-1/8 inches, and its external diameter 4-3/8 inches—­the diameter of the piston rod being 2-1/8 inches.  The thickness of the stuffing box flange is 1-1/8 inch.

623. Q.—­Will you describe the nature of the communication between the cylinder and condenser?