| On both pistons, | 13,572 lbs. |
| And finally, 13572 × .2122 = | 2,880 lbs. |
| The requirement being | 2,823 lbs. |
By table 6, we see that five feet wheels at twenty-five miles per hour, use 33,600 cylinders of steam per hour.
By table 7, the capacity of a cylinder 12 × 20 is 1.31 cubic feet; also 33600 × 1.31 = 44016 cubic feet of steam per hour.
Assuming the mean cylinder pressure at sixty pounds, and the entering pressure at eighty pounds, also the loss in passing from the boiler at twenty pounds, we must generate the steam at one hundred pounds per square inch.
By table 8, we see that when steam is produced under one hundred pounds pressure per inch, each cubic foot of water makes 293 cubic feet of steam; whence
44016
293 = 150,
is the number of cubic feet of water to be evaporated per hour. At sixteen cubic feet of water per hour per square foot of grate, we thus require
15.0
16 or 9.4 feet, nearly;
and by table 9, we find the heating surface necessary to evaporate 150 cubic feet of water per hour, with nine square feet of grate surface, to be 779 square feet; and by the formula, with 9.4 square feet, we have,
S = √9.4 × 150 × 21.2 = 797 square feet,