ombination or
decomposition of the same elements, so that the heat evolved during
the combination of two simple or com-pound substances is equal to the
heat absorbed at the time of their chemical segregation."

TABLE I.--SUBSTANCES ENTERING INTO THE COMPOSITION OF FUEL.

-----------------------+-------------+-----------+-------------------+
| | Heat evolved in |
| Symbol and Atomic |the Combustion of |
| Weight. | 1 lb. of Fuel. |
+------------+------------+--------+----------+
| | | |In Pounds |
| | | In | of Water |
| | |British |Evaporated|
| Before | After |Thermal | from and |
| Combustion | Combustion | Units. | at 212 deg.. |
+------------+------------+--------+----------+
Hydrogen burned | H 1 | H2O 18 | 62,032 | 64.21 |
in oxygen. | | | | |
-----------------------+------------+------------+--------+----------+
Carbon burned to | C 12 | CO 28 | 4,451 | 4.61 |
carbonic oxide. | | | | |
-----------------------+------------+------------+--------+----------+
Carbon burned to | C 12 | CO2 44 | 14,544 | 15.06 |
carbonic acid. | | | | |
-----------------------+------------+------------+--------+----------+
Carbonic oxide burned | CO 28 | CO2 44 | 4,326 | 4.48 |
to carbonic acid. | | | | |
-----------------------+------------+------------+--------+----------+
Olefiant gas (ethylene)| C2H4 28 | 2CO2 124 | 21,343 | 22.09 |
burnt in oxygen. | | 2H2O | | |
-----------------------+------------+------------+--------+----------+
Marsh gas (methane) | CH4 16 | 2CO2 80 | 23,513 | 24.34 |
burnt in oxygen. | | 2H2O | | |
-----------------------+------------+------------+--------+----------+

Composition of air--

by volume 0.788 N + 0.197 O + 0.001