Gaseous and Liquid Fuels.
—Gaseous and liquid fuels used for domestic illumination and heating may be divided into three general classes—coal gas, including carburetted water gas and producer gas and their various mixtures; oil gas, acetylene and gasoline gas. Of these the first is the most important as an illuminating gas, while for industrial and domestic purposes producer gas is of no importance as a fuel gas. Gasoline, acetylene and oil gases are generated and used to a remarkable extent in isolated dwellings as fuel and for illumination.
The value of any gas for domestic purposes will depend on the amount of heat that is produced when it is burned. In the earlier days of its use coal gas was employed entirely as an illuminant and its value was expressed in illuminating power; at the present time the standard often prescribed by regulation is that of its illuminating capability and is stated in candlepower. There is, however, a tendency to establish the more consistent standard of expressing the value of gas by its heat value. The reasons for this is the general use of mantle gas burners which depend on the heating value alone for their efficiency and the fact that coal gas is very extensively used for domestic fuel.