he quantity of water and the steam-pressure in the
boiler. The longer the period over which the observations are taken the
less is the influence of errors in the estimation of these particulars.
Further, in order properly to represent working conditions, the rate of
combustion of the fuel throughout the trial must be the same as that
intended to be used in ordinary working, and the duration of the test
must be sufficient to include proportionately as much cleaning of fires
as would occur under the normal working conditions. The tests should
always be made with the kind of coal intended to be generally used, and
the records should include a test of the calorific value of a sample of
the fuel carefully selected so as fairly to represent the bulk of the
coal used during the trial. The periodic records taken are the weights
of the fuel used and of the ashes, &c., produced, the temperature and
quantity of the feed-water, the steam pressure maintained, and the
wetness of the steam produced. This last should be ascertained from
samples taken from the steam pipe at a position where the full pressure
is maintained. In order to reduce to a common standard observations
taken under different conditions of feed temperatures and steam
pressures, the results are calculated to an equivalent evaporation at
the atmospheric pressure from a feed temperature of 212 deg. F.
(J. T. Mi.)

TRIALS OF VARIOUS TYPES OF MARINE BOILERS

+----------------------------+-------+--------+--------+-----------+---------+---------+----------------+----------+---------+------+
| | | | | | Air | |Water Evaporated| Water | | |
| | | | | Coal |Pressure |Chimney |per lb. of Coal.| Evapor- | Thermal |Effic-|
| | Grate |Heating |Duration| burned |in Stoke-|Draught--+-------+--------+ated per |Units per|iency |
| Description of Boiler. | Area |Surface |of Trial|Per sq. ft.| hold-- |Inches of| |From and|sq. ft. of| lb. of | of |
| |sq. ft.|sq. ft. | Hours. | of Grate |Inches of| Water |Actual | at 212 | Heating | coal. |Boiler|
| | | | | per Hour. | Water. | | | deg. F.| Surface. | | %. |
+----------------------------+-------+--------+--------+-----------+---------