nterposition
of a little red lead to make them quite tight when screwed together. Lead
or canvas joints, if of any considerable thickness, will not long withstand
the action of high pressure steam; and the whole of the joints about a
locomotive should be such that they require nothing more than a little
paint or putty, or a ring of wire gauze smeared with white or red lead to
make them perfectly tight. There must be a mud hole opposite the edge of
each water space, if the fire box be square, to enable the boiler to be
easily cleaned out, and these holes are most conveniently closed by screwed
plugs made slightly taper. A cock for emptying the boiler is usually fixed
at the bottom of the fire box, and it should be so placed as to be
accessible when the engine is at work, in order that the engine driver may
blow off some water if necessary; but it must not be in such a position as
to send the water blown off among the machinery, as it might carry sand or
grit into the bearings, to their manifest injury.

420. _Q._--Will you state the dimensions of the tube plate, and the means
of securing the tubes in it?

_A._--The tube plates are generally made from five eighths to three fourths
of an inch thick, but seven eighths of an inch thick appears to be
preferable, as when the plate is thick the holes will not be so liable to
change their figure during the process of feruling the tubes: the distance
between the tubes should never be made less than three fourths of an inch,
and the holes should be slightly tapered so as to enable the tubes to hold
the tube plates together. The tubes are secured in the tube plates by means
of taper ferules driven into the ends of the tubes. The ferules are for the
most part made of steel at the fire box end, and of wrought iron at the
smoke box end, though ferules of malleable cast iron have in some cases
been used with advantage: malleable cast iron ferules are almost as easily
expanded when hammered cold upon a mandrel, as the common wrought iron ones
are at a working heat. Spring steel, rolled with a feather edge, to
facilitate its conversion into ferules, is supplied by some of the
steel-makers of Sheffield, and it appears expedient to make use of steel
thus prepared when steel ferules are employed. In cases where ferules are
not employed, it may be advisable to set out the tube behind the tube plate
by means of an expanding mandrel. There are various forms of this
instrument. One form is that