analysis carried
further with a view to ascertaining whether there is CO present. As the
percentage of CO_{2} in these gases increases, there is a tendency
toward the presence of CO, which, of course, cannot be shown by a CO_{2}
recorder, and which is often difficult to detect with an Orsat
apparatus. The greatest care should be taken in preparing the cuprous
chloride solution in making analyses and it must be known to be fresh
and capable of absorbing CO. In one instance that came to our attention,
in using an Orsat apparatus where the cuprous chloride solution was
believed to be fresh, no CO was indicated in the flue gases but on
passing the same sample into a Hempel apparatus, a considerable
percentage was found. It is not safe, therefore, to assume without
question from a high CO_{2} reading that the combustion is
correspondingly good, and the question of excess air alone should be
distinguished from that of good combustion. The effect of a small
quantity of CO, say one per cent, present in the flue gases will have a
negligible influence on the quantity of excess air, but the presence of
such an amount would mean a loss due to the incomplete combustion of the
carbon in the fuel of possibly 4.5 per cent of the total heat in the
fuel burned. When this is considered, the importance of a complete flue
gas analysis is apparent.

Table 34 gives the densities of various gases together with other data
that will be of service in gas analysis work.

TABLE 34

DENSITY OF GASES AT 32 DEGREES FAHRENHEIT AND ATMOSPHERIC PRESSURE
ADAPTED FROM SMITHSONIAN TABLES

+----------+----------+--------+---------+----------+---------------+
| | | | | | Relative |
| | | | Weight | | Density, |
| | | | of | Volume | Hydrogen = 1 |
| | |Specific|One Cubic| of +-------+-------+
| Gas | Chemical |Gravity | Foot |One Pound | |Approx-|
| | Symbol | Air=1 | Pounds |Cubic Feet| Exact | imate |
+----------+----------+--------+---------+----------+-------+-------+
|Oxygen | O | 1.053 | .08922 | 11.208 | 15.87 | 16 |
|Nitrogen | N | 0.9673 | .07829 | 12.773 | 13.92 | 14 |
|Hydrogen | H | 0.0696 | .005621 | 177.90 | 1.00 | 1 |
|Carbon | | | | |