its close should be weighed so far as
possible in a dry state. If wet the amount of moisture should be
ascertained and allowed for, a sample being taken and dried for this
purpose. This sample may serve also for analysis and the determination
of unburned carbon and fusing temperature.

The method above described for sampling coal may also be followed for
obtaining a sample of the ashes and refuse.

12. CALORIFIC TESTS AND ANALYSES OF COAL

The quality of the fuel should be determined by calorific tests and
analysis of the coal sample above referred to.[70]

13. ANALYSES OF FLUE GASES

For approximate determinations of the composition of the flue gases, the
Orsat apparatus, or some modification thereof, should be employed. If
momentary samples are obtained the analyses should be made as frequently
as possible, say, every 15 to 30 minutes, depending on the skill of the
operator, noting at the time the sample is drawn the furnace and firing
conditions. If the sample drawn is a continuous one, the intervals may
be made longer.

14. SMOKE OBSERVATIONS[71]

In tests of bituminous coals requiring a determination of the amount of
smoke produced, observations should be made regularly throughout the
trial at intervals of 5 minutes (or if necessary every minute), noting
at the same time the furnace and firing conditions.

15. CALCULATION OF RESULTS

The methods to be followed in expressing and calculating those results
which are not self-evident are explained as follows:

(A) _Efficiency._ The "efficiency of boiler, furnace and
grate" is the relation between the heat absorbed per pound of
coal fired, and the calorific value of one pound of coal.

The "efficiency of boiler and furnace" is the relation between
the heat absorbed per pound of combustible burned, and the
calorific value of one pound of combustible. This expression of
efficiency furnishes a means for comparing one boiler and
furnace with another, when the losses of unburned coal due to
grates, cleanings, etc., are eliminated.

The "combustible burned" is determined by subtracting from the
weight of coal supplied to the boiler, the moisture in the coal,
the weight of ash and unburned coal withdrawn from the furnace
and ashpit, and the weight of dust, soot, and refuse, if any,
withdrawn from the tubes, flues, and combustion chambers,
including ash carried away in the gases,