any
increase is liable to reduce the efficiency and capacity more than the
equivalent proportion of such increase.

The size of the coal, especially where it is of the anthracite class,
should be determined by screening a suitable sample.

4. APPARATUS AND INSTRUMENTS[63]

The apparatus and instruments required for boiler tests are:

(A) Platform scales for weighing coal and ashes.

(B) Graduated scales attached to the water glasses.

(C) Tanks and platform scales for weighing water (or water
meters calibrated in place). Wherever practicable the feed water
should be weighed, especially for guarantee tests. The most
satisfactory and reliable apparatus for this purpose consists of
one or more tanks each placed on platform scales, these being
elevated a sufficient distance above the floor to empty into a
receiving tank placed below, the latter being connected to the
feed pump. Where only one weighing tank is used the receiving
tank should be of larger size than the weighing tank, to afford
sufficient reserve supply to the pump while the upper tank is
filling. If a single weighing tank is used it should preferably
be of such capacity as to require emptying not oftener than
every 5 minutes. If two or more are used the intervals between
successive emptyings should not be less than 3 minutes.

(D) Pressure gauges, thermometers, and draft gauges.

(E) Calorimeters for determining the calorific value of fuel and
the quality of steam.

(F) Furnaces pyrometers.

(G) Gas analyzing apparatus.

5. OPERATING CONDITIONS

Determine what the operating conditions and method of firing should be
to conform to the object in view, and see that they prevail throughout
the trial, as nearly as possible.

Where uniformity in the rate of evaporation is required,
arrangement can be usually made to dispose of the steam so that
this result can be attained. In a single boiler it may be
accomplished by discharging steam through a waste pipe and
regulating the amount by means of a valve. In a battery of
boilers, in which only one is tested, the draft may be regulated
on the remaining boilers to meet the varying demands for steam,
leaving the test boiler to work under a steady rate of
evaporation.

6. DURATION

The duration of tests to determine the efficiency of a hand-fired
boiler, should be 10 h