n these gage
readings. The sum of the readings divided by the number of readings
taken will be the average steam pressure during the test.

A recording steam gage is best and makes its own readings.

WORKING UP THE TEST.

After the boiler test has been made, so as to find the weight of
coal burned, weight of feed water used, feed-water temperature and
steam pressure, the efficiency, the horsepower, and the economy
must be obtained by calculation from the test results. The process
of figuring the desired results from the test data is called
"working up the test."

To illustrate the method used in finding the efficiency, etc.,
suppose that the data obtained from the test are as follows:

Length of test hours 10
Total weight of coal fired pounds 5,000
Total weight of water evaporated do. 35,000
Average temperature of feed water deg.F 180
Average steam pressure, gage pounds per square inch 100

The efficiency of any process is always a comparison, or ratio, of
the output to the input. In the case of a steam boiler the
efficiency is the percentage of the heat supplied in the coal that
is usefully employed in making steam. The output of the steam
boiler is the heat represented by the quantity of water evaporated
by a pound of coal, taking into account the feed temperature and
the steam pressure, and input is the amount of heat contained in a
pound of the coal used. The efficiency of the boiler is the output
divided by the input.

The heat contained in a pound of coal is called the "calorific
value" or "heating value" of the coal. It can be found by taking a
fair average sample of the coal used during the test, as explained
in connection with weighing the coal, and sending the sample to a
chemist, who will make a calorimeter test to determine its heating
value.

At the end of the test the sample fuel should be spread out on a
clean floor and all lumps broken up, so that no pieces are larger
than 2 inches maximum diameter. Then the gross sample should be
very thoroughly mixed by shoveling, after which it should be spread
out in the form of a square of uniform depth and quartered down
until a final average sample is obtained for shipment to a
competent chemist, experienced in fuel analysis. (See Bureau of
Mines Technical Paper No. 133.)

About 2 quarts of the chemist's sample