eaky part. When emptied again, all the joints should be painted with a
solution of sal ammoniac in urine, and so soon as the seams are well rusted
they should be dried with a gentle fire, and then be painted over with a
thin putty formed of whiting and linseed oil, the heat being continued
until the putty becomes so hard that it cannot be readily scratched with
the nail, and care must be taken neither to burn the putty nor to
discontinue the fire until it has become quite dry.

372. _Q._--How should the brickwork setting of a wagon boiler be built?

_A._--In building the brickwork for the setting of the boiler, the part
upon which the heat acts with most intensity is to be built with clay
instead of mortar, but mortar is to be used on the outside of the work. Old
bars of flat iron may be laid under the boiler chime to prevent that part
of the boiler from being burned out, and bars of iron should also run
through the brickwork to prevent it from splitting. The top of the boiler
is to be covered with brickwork laid in the best lime, and if the lime be
not of the hydraulic kind, it should be mixed with Dutch terrass, to make
it impenetrable to water. The top of the boiler should be well plastered
with this lime, which will greatly conduce to the tightness of the seams.
Openings into the flues must be left in convenient situations to enable the
flues to be swept out when required, and these openings may be closed with
cast iron doors jointed with clay or mortar, which may be easily removed
when required. Adjacent to the chimney a slit must be left in the top of
the flue with a groove in the brickwork to enable the sliding door or
damper to be fixed in that situation, which by being lowered into the flue
will obstruct the passage of the smoke and moderate the draught, whereby
the chimney will be prevented from drawing the flame into it before the
heat has acted sufficiently upon the boiler.

373. _Q._--Are marine constructed in the same way as land boilers?

_A._--There is very little difference in the two cases: the whole of the
shells of marine boilers, however, should be double riveted with rivets
11/16ths of an inch in diameter, and 2-3/8th inches from centre to centre,
the weakening effect of double riveting being much less than that of single
riveting. The furnaces above the line of bars should be of the best
Lowmoor, Bowling, or Staffordshire scrap plates, and the portion of each
furnace above the bars should consist