HEATS OF COMBUSTION
| Substance. | Calories. | B. T. U. |
| Hydrogen | 34,500 | 62,100 |
| Carbon to carbon dioxide | 8,137 | 14,647 |
| Carbon to carbon monoxide | 2,489 | 4,480 |
| Carbon monoxide | 2,435 | 4,383 |
| Methane | 13,343 | 24,017 |
| Ethylene | 12,182 | 21,898 |
| Cellulose | 4,200 | 7,560 |
| Acetylene | 12,142 | 21,856 |
| Peat | 5,940 | 10,692 |
| Naphthalene | 9,690 | 10,842 |
| Sulphur | 2,500 | 4,500 |
When it is understood that heat is transmitted in three different ways, the value of a measuring instrument, or a unit, will become apparent.
Thus, heat may be transmitted either by conduction, convection, or radiation.
Conduction is the method whereby heat is transmitted from one particle to another particle, or from one end of a rod, or other material to the other end. Some materials will conduct the heat much quicker than others, but if we have a standard, such as the calorie, then the amount of heat transmitted and also the amount lost on the way may be measured.
Convection applies to the transmission of heat through liquids and gases. If heat is applied to the top or surface of a liquid, the lower part will not be affected by it. If the heat is applied below, then a movement of the gas or liquid begins to take place, the heated part moving to the top, and the cooler portions going down and thus setting up what are called convection currents.
Radiation has reference to the transference of heat from one body to another, either through a vacuum, the air, or even through a solid.
By means of the foregoing table, which gives the heats developed by the principal fuels, it is a comparatively easy matter to determine the calorific value of fuels, which is ascertained by making an analysis of the fuel.
The elements are then taken together, and the table used to calculate the value. Suppose, for instance, that the analysis shows that the fuel has seventy-five per cent. of carbon and twenty-five per cent. of hydrogen. It is obvious that if we take seventy-five per cent. of 8,137 (which is the index for carbon), and twenty-five per cent. of 43,500 (the index of hydrogen), and adding the two together, the result, 14,727, would represent the calorific value of the fuel.