524. Q.—­At what part of the boiler is the feed water admitted?

A.—­The feed pipe of most locomotive engines enters the boiler near the bottom and about the middle of its length.  In Stephenson’s engine the water is let in at the smoke box end of the boiler, a little below the water level; by this means the heat is more fully extracted from the escaping smoke, but the arrangement is of questionable applicability to engines of which the steam dome and steam pipe are at the smoke box end, as in that case the entering cold water would condense the steam.

525. Q.—­How are the pipes connecting the tender and locomotive constructed, so as to allow of play between the engine and tender without leakage?

A.—­The pipes connecting the tender with the pumps should allow access to the valves and free motion to the engine and tender.  This end is attained by the use of ball and socket joints; and, to allow some end play, one piece of the pipe slides into the other like a telescope, and is kept tight by means of a stuffing box.  Any pipe joint between the engine and tender must be made in this fashion.

526. Q.—­Have you any suggestion to make respecting the arrangement of the feed pump?

A.—­It would be a material improvement if a feed pump was to be set in the tender and worked by means of a small engine, such as that now used in steam vessels for feeding the boilers.  The present action of the feed pumps of locomotives is precarious, as, if the valves leak in the slightest degree, the steam or boiling water from the boiler will prevent the pumps from drawing.  It appears expedient, therefore, that at least one pump should be far from the boiler and should be set among the feed water, so that it will only have to force.  If a pump was arranged in the manner suggested, the boiler could still be fed regularly, though the locomotive was standing still; but it would be prudent to have the existing pumps still wrought in the usual way by the engine, in case of derangement of the other, or in case the pump in the tender might freeze.

527. Q.—­Will you explain the construction of locomotive wheels?

A.—­The wheels of a locomotive are always made of malleable iron.  The driving wheels are made larger to increase the speed; the bearing wheels also are easier on the road when large.  In the goods engines the driving wheels are smaller than in the passenger engines, and are generally coupled together.  Wheels are made with much variety in their constructive details:  sometimes they are made with cast iron naves, with the spokes and rim of wrought iron; but in the best modern wheels the nave is formed of the ends of the spokes welded together at the centre.  When cast iron naves are adopted, the spokes are forged out of flat bars with T-formed heads, and are arranged radially in the founder’s mould, the cast iron, when fluid, being poured among