468|3.902|4.335|4.769|5.202|
| 75 | 73 | 4677 |2.138|2.565|2.993|3.420|3.848|4.275|4.703|5.131|
| 76 | 74 | 4741 |2.110|2.532|2.954|3.376|3.798|4.220|4.642|5.063|
| 77 | 75 | 4807 |2.082|2.498|2.914|3.330|3.746|4.162|4.578|4.994|
| 78 | 76 | 4869 |2.054|2.465|2.876|3.286|3.697|4.108|4.518|4.929|
| 79 | 77 | 4932 |2.027|2.433|2.838|3.243|3.649|4.054|4.460|4.865|
| 80 | 78 | 4996 |2.002|2.402|2.802|3.202|3.602|4.003|4.403|4.803|
| 81 | 79 | 5060 |1.976|2.371|2.767|3.162|3.557|3.952|4.348|4.743|
| 82 | 80 | 5124 |1.952|2.342|2.732|3.122|3.513|3.903|4.293|4.683|
| 83 | 81 | 5187 |1.927|2.313|2.699|3.085|3.470|3.856|4.241|4.627|
+------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+

[Illustration: City of San Francisco, Cal., Fire Fighting Station. No.
1. 2800 Horse Power of Babcock & Wilcox Boilers, Equipped for Burning
Oil Fuel]

Many tables have been published with a view to comparing the two fuels.
Such of these as are based solely on the relative calorific values of
oil and coal are of limited value, inasmuch as the efficiencies to be
obtained with oil are higher than that obtainable with coal. Table 47
takes into consideration the variation in efficiency with the two fuels,
but is based on a constant calorific value for oil and coal. This table,
like others of a similar nature, while useful as a rough guide, cannot
be considered as an accurate basis for comparison. This is due to the
fact that there are numerous factors entering into the problem which
affect the saving possible to a much greater extent than do the relative
calorific values of two fuels. Some of the features to be considered in
arriving at the true basis for comparison are the labor saving possible,
the space available for fuel storage, the facilities for conveying the
oil by pipe lines, the hours during which a plant is in operation, the
load factor, the quantity of coal required for banking fires, etc., etc.
The only exact method of estimating the relative advantages and costs of
the two fuels is by considering the operating expenses of the plant with
each in turn, including the costs of every item entering into the
problem.

Burning Oil Fuel--The requirements for burning petroleum are as follows:

1st. Its atomization must be thorough.

2nd. When atomized it must be brought into contact with the requisite
quantity of air for its combustion, and this quantity must b