rod is 6 feet long between the centres, and is fitted with bushes of white metal.  The eccentrics are formed of wrought iron, and have 4-1/8 inches of throw.  The link of the link motion is formed of wrought iron.  It is hung by a link from a pin attached to the framing; and instead of being susceptible of upward and downward motion, as in the case of the link represented in fig. 57 a rod connecting the valve rod with the movable block in the link, is susceptible of this motion, whereby the same result is arrived at as if the link were moved and the block was stationary.  One or the other expedient is preferable, according to the general nature of the arrangements adopted.  The slide valve is of brass, and the regulator consists of two brass slide valves worked over ports in a chest in the steam pipe, set in the smoke box.  The steam pipe is of brass, No. 14. wire gauge, perforated within the boiler barrel with holes 1/12th of an inch in diameter along its upper side.  The blast pipe, which is of copper, has an orifice of 4-1/4 inches diameter.  There is a damper, formed like a Venetian blind, with the plates running athwartships at the end of the tubes.

[Illustration:  Fig. 58.  SAFETY VALVE.  Gooch.]

662. Q.—­Of what construction is the safety valve?

A.—­There are two safety valves, consisting of pistons 1-3/16 inch in diameter, and which are kept down by spiral springs placed immediately over them.  A section of this valve is given in fig. 58.

663. Q.—­What are the dimensions of the feed pumps?

A.—­The feed pumps are of brass, with plungers 4 inches diameter and 3-1/4 inches stroke.  The feed pipe is of copper, 2 inches diameter.  A good deal of trouble has been experienced in locomotives from the defective action of the feed pump, partly caused by the leakage of steam into the pumps, which prevented the water from entering them, and partly from the return of a large part of the water through the valves at the return stroke of the pump, in consequence of the valve lifting too high.  The pet cock—­a small cock communicating with the interior of the pump—­will allow any steam to escape which gains admission, and the air which enters by the cock cools down the barrel of the pump, so that in a short time it will be in a condition to draw.  The most ordinary species of valve in the feed pumps of locomotives, is the ball valve.

Notwithstanding the excellent performance of the best examples of locomotive engines, it is quite certain that there is still much room for improvement; and indeed various sources of economy are at present visible, which, if properly developed, would materially reduce the expense of the locomotive power.  In all engines the great source of expense is the fuel; and although the consumption of fuel has been greatly reduced within the last ten or fifteen years, it is capable of being still further reduced by certain easy expedients of