ts of the setting. If the draft is increased above that which such a
stack will give, difficulties arise from excess air for combustion with
consequent loss in efficiency.

A poor mixing or laneing action in the furnace may result in a pulsating
effect of the gases in the setting. This action may at times be remedied
by admitting more air to the furnace. On account of the possibility of a
pulsating action of the gases under certain conditions and the puffs or
explosions, settings for this class of work should be carefully
constructed and thoroughly buckstayed and tied.

Natural Gas--Natural gas from different localities varies considerably
in composition and heating value. In Table 50 there is given a number of
analyses and heat values for natural gas from various localities.

This fuel is used for steam generating purposes to a considerable extent
in some localities, though such use is apparently decreasing. It is best
burned by employing a large number of small burners, each being capable
of handling 30 nominal rated horse power. The use of a large number of
burners obviates the danger of any laneing or blowpipe action, which
might be present where large burners are used. Ordinarily, such a gas,
as it enters the burners, is under a pressure of about 8 ounces. For the
purpose of comparison, all observations should be based on gas reduced
to the standard conditions of temperature and pressure, namely 32
degrees Fahrenheit and 14.7 pounds per square inch. When the temperature
and pressure corresponding to meter readings are known, the volume of
gas under standard conditions may be obtained by multiplying the meter
readings in cubic feet by 33.54 P/T, in which P equals the absolute
pressure in pounds per square inch and T equals the absolute temperature
of the gas at the meter. In boiler testing work, the evaporation should
always be reduced to that per cubic foot of gas under standard
conditions.

TABLE 50

TYPICAL ANALYSES (BY VOLUME) AND CALORIFIC VALUES OF NATURAL
GAS FROM VARIOUS LOCALITIES

+----------------+-----+-----+-----+-----+-----+----+-------+------+--------+
|Locality of Well| H |CH_{4}| CO |CO_{2}| N | O | Heavy |H_{2}S|B. t. u.|
| | | | | | | |Hydro- | | per |
| | | | | | | |carbons| | Cubic |
| | | | | | |