herefore for the aqueous nitric and sulphuric acid
is found by multiplying the ammonia by 2.65 and adding 13 calories for
each 0.01 gram of sulphur in the coal. This total correction is to be
deducted from the heat value as found from the corrected range and the
amount equivalent to the calorimeter.

After each test the pan in which the coal has been burned must be
carefully examined to make sure that all of the sample has undergone
complete combustion. The presence of black specks ordinarily indicates
unburned coal, and often will be found where the coal contains bone or
slate. Where such specks are found the tests should be repeated. In
testing any fuel where it is found difficult to completely consume a
sample, a weighed amount of naphthaline may be added, the total weight
of fuel and naphthaline being approximately one gram. The naphthaline
has a known heat of combustion, samples for this purpose being
obtainable from the United States Bureau of Standards, and from the
combined heat of combustion of the fuel and naphthaline that of the
former may be readily computed.

The heat evolved in burning of a definite weight of standard naphthaline
may also be used as a means of calibrating the calorimeter as a whole.

COMBUSTION OF COAL

The composition of coal varies over such a wide range, and the methods
of firing have to be altered so greatly to suit the various coals and
the innumerable types of furnaces in which they are burned, that any
instructions given for the handling of different fuels must of necessity
be of the most general character. For each kind of coal there is some
method of firing which will give the best results for each individual
set of conditions. General rules can be suggested, but the best results
can be obtained only by following such methods as experience and
practice show to be the best suited to the specific conditions.

The question of draft is an all important factor. If this be
insufficient, proper combustion is impossible, as the suction in the
furnace will not be great enough to draw the necessary amount of air
through the fuel bed, and the gases may pass off only partially
consumed. On the other hand, an excessive draft may cause losses due to
the excess quantities of air drawn through holes in the fire. Where coal
is burned however, there are rarely complaints from excessive draft, as
this can be and should be regulated by the boiler damper to give only
the draft necessary f