The carbon filament is placed in a vessel surrounded by an atmosphere of hydrocarbon, such as coal gas or vapour of benzol.
Consequently they are designed to fly when filled with coal gas if necessary.
The relative cost of light from coal gas and oil gas may be estimated as one to six, at least.
But in England water gas could not compete with coal gas in cheapness.
For many reasons, carburetted hydrogen, or coal gas, is the agent employed to give levity to the machine.
Where coal gas is not available, a Dowson gas-producer can be employed.
Thirty-eight thousand cubic feet of coal gas were required to fill this balloon, charged by one company 20l., by others from 9l.
It is almost as invisible as a jet of coal gas or hydrogen is in air.
Such as can be had is either water or coal gas, neither of which is as efficient in lifting power as hydrogen.
To him the art is indebted for the introduction of carbureted-hydrogen, or coal gas, as the means of inflating balloons.