tom, sides, and ends of the boiler. This
very much exceeds the proportion usually adopted; and in scarcely any
instance are boilers stayed sufficiently to be safe when the shell is
composed of flat surfaces. The furnaces should be stayed together with
bolts of the best scrap iron, 1-1/4 inch in diameter, tapped through both
plates of the water space with thin nuts in each furnace; and it is
expedient to make the row of stays, running horizontally near the level of
the bars, sufficiently low to come beneath the top of the bars, so as to be
shielded from the action of the fire, with which view they should follow
the inclination of the bars. The row of stays between the level of the bars
and the top of the furnace should be as near the top of the furnace as will
consist with the functions they have to perform, so as to be removed as far
as possible from the action of the heat; and to support the furnace top,
cross bars may either be adopted, to which the top is secured with bolts,
as in the case of locomotives, or stays tapped into the furnace top, with a
thin nut beneath, may be carried to the top of the boiler; but very little
dependence can be put in such stays as stays for keeping down the top of
the boiler; and the top of the boiler must, therefore, be stayed nearly as
much as if the stays connecting it with the furnace crowns did not exist.
The large rivets passing through thimbles, sometimes used as stays for
water spaces or boiler shells, are objectionable; as, from the great amount
of hammering such rivets have to receive to form the heads, the iron
becomes crystalline, so that the heads are liable to come off, and, indeed,
sometimes fly off in the act of being formed. If such a fracture occurs
between the boilers after they are seated in their place, or in any
position not accessible from the outside, it will in general be necessary
to empty the faulty boiler, and repair the defect from the inside.

305. _Q._--What should be the pitch or numerical distribution of the stays?

_A._--The stays, where the sides of the boiler are flat, and the pressure
of the steam is from 20 to 30 lbs., should be pitched about a foot or 18
inches asunder; and in the wake of the tubes, where stays cannot be carried
across to connect the boiler sides, angle iron ribs, like the ribs of a
ship, should be riveted to the interior of the boiler, and stays of greater
strength than the rest should pass across, above, and below the tubes, to
wh