82. _Q._--From all this it appears that a combination of cast iron and
malleable iron is the best for the beams of engines?

_A._--Yes, and for all beams. Engine beams should be made deeper at the
middle than they are now made; the web should be lightened by holes pierced
in it, and round the edge of the beam there should be a malleable iron hoop
or strap securely attached to the flanges by riveting or otherwise. The
flanges at the edges of engine beams are invariably made too small. It is
in them that the strength of the beam chiefly resides.




CHAPTER I.


GENERAL DESCRIPTION OF THE STEAM ENGINE.

* * * * *

THE BOILER.

83. _Q._--What are the chief varieties of the steam engine in actual
practical use?

_A._--There is first the single-acting engine, which is used for pumping
water; the rotative land engine, which is employed to drive mills and
manufactories; the rotative marine engine, which is used to propel steam
vessels; and the locomotive engine, which is employed on railways. The last