STATE GEOLOGIST. 145 
‘ by volume by multiplying the numerator by 100, making the expression 
TooN— (N—3.760). We must remember that N here is always the per 
cent. by volume of nitrogen as found by the gas analysis, and O the per 
- cent. of oxygen. The resulting expression is a value either above or below 
100, depending on whether the conditions of firing are oxidizing or reduc- 
ing. For theoretically perfect conditions, that is, when only just enough 
air is admitted to- burn the fuel, no oxygen is shown by the analysis, and 
hence the ratio is 100 NN or 100. Therefore 100 per cent. of air is the 
ideal towards which all in charge of purely heat producing furnaces must 
strive. If, for example, a ratio of 160 per cent. is shown by the above cal- 
culation, it tells that an excess of 60 per cent. of air has been admitted. 
On the other hand, an amount of air lower than 100 per cent. stands 
for a deficit of air proportional to the lack of oxygen. Such an analysis 
shows but little oxygen, and indicates the presence of combustible gases, 
especially of CO. Any amount of combustible gases present will thus 
stand for minus oxygen, so that the formula becomes 10ooN~[N— 
(==3.76©)) | or 100N=N-F3.700: 
To illustrate, a gas analysis shows the following composition by 
volume: 
Carbon dioxide, TA (Der Cent, 
Carbon monoxide, Ant PSR Gem, 
Oxygen, O12) per cent: 
Nitrogen. 79.0 per cent. 
To calculate the amount of air entering the furnaces. Carbon mon- 
oxide represents an unburnt gas consuming for complete combustion 
one-half its volume of additional oxygen, or 4.I~2—2.05 volumes of oxy- 
gen, which is necessarily minus in sign. But as the analysis shows 0.2 
per cent. of free oxygen the minus oxygen will be 2.05—0.2— 
Substituting in the formula we have, 100 79.80.—79.80-+ (3.76 1.85) = 
QI.9 per cent. of air admitted, or the deficit of air as shown by this analysis 
is 8.1 per cent. These simple calculations are the ones most commonly 
required in the examination of the firing conditions of boilers and kilns, 
and all the data for it are furnished by the Orsat apparatus. More com- 
plicated and accurate apparatus, while important for scientific research, 
is unnecessary in practice, though the Elliot apparatus may be used to 
determine the hydrocarbons without difficulty. 
In some investigations it is desirable to know just what part of the 
oxygen of the air is used for converting the carbon of the coal to carbon 
dioxide, and what part burns the hydrogen of the coal to steam. ‘This 
calculation is illustrated by the following example. Assuming that the 
coal used contains 
83.75 per cent. carbon 
4.13 per cent. hydrogen 
2.68 per cent. oxygen. 
10—S. G. Bull. 3. 
