319. It does not follow that because coke in England, anthracite in Pennsylvania, or wood in New England, is the most economical fuel, that either of the above will be so in Ohio, Indiana, or Illinois, or because wood is the cheapest in some parts of a State, that it is so throughout, or even that one fuel should be applied to the whole length of a single road.

The heat used to evaporate water in the locomotive boiler is developed by combustion; combustion is produced by chemically combining the oxygen of the air with the carbon of the fuel; whence, that material containing in a given cost the largest amount of carbon will produce heat the most economically.

From the table on page [320], we see that, by bulk, thirteen of coke are equal to sixty of wood; that one pound of coke evaporates eight and one half pounds of water; that one pound of wood will evaporate two and one half pounds of water. Tables of specific gravity give as an average weight per cubic foot of hard wood, thirty pounds. A cord of wood, by very careful measurement, contains one hundred cubic feet solid, or one hundred twenty-eight feet as piled, taking the average size of wood; whence a cord will weigh three thousand pounds. And we have as the relative evaporative efficiency of a cord of wood and a ton of coke,

2240 × 8½ =19040,
3000 × 2½ =7500.

Now if the cost of a cord of wood is to the price of a ton of coke as 7,500 to 19,040, it is immaterial which we use.

As an example of the use of the above proportion, when the absolute cost of wood, coal, coke, and labor are known, take the following.

If wood, cut and ready for burning, costs $3.00 per cord, how much may be given for a ton of coke?

As 7,500 is to 19,040, so is 300 to 762, or $7.62.

From the same proportion we form the following table.

Cost per cord of wood ready for burning.Price that may be paid per ton for coke.
(Cents.)(Cents.)
200508
225571
250635
275698
300762
325825
350877
375952
4001016
4251079
4501143
4751206
5001270