Fig. 4
In this first air-ship I had placed the gas escape valves even farther from the motor than I place them to-day. The suspension cords being very long I hung in my basket far below the balloon. Therefore I asked myself:
"How could this motor, so far below the balloon, and so far in front of its escape valves, set fire to the gas enclosed in it when such gas is not inflammable until mixed with air?"
On this first trial, as in most since, I used hydrogen gas. Undoubtedly when mixed with air it is tremendously inflammable—but it must first mix with air. All my little balloon models are kept filled with hydrogen, and, so filled, I have more than once amused myself by burning inside them, not their hydrogen, but its mixture with the oxygen of the atmosphere. All one has to do is to insert in the balloon model a little tube to furnish a jet of the room's atmosphere from an air pump and light it with the electric spark. Similarly, should a pin-prick have made ever so slight a vent in my air-ship balloon, the interior pressure would have sent out into the atmosphere a long thin stream of hydrogen that might have ignited had there been any flame near enough to do it. But there was none.
This was the problem. My motor did undoubtedly send out flames for, say, half-a-yard round about it. They were, however, mere flames, not still-burning products of incomplete combustion like the sparks of a coal-burning steam-engine. This admitted, how was the fact that I had a mass of hydrogen unmixed with air and well secured in a tight envelope so high above the motor to prove dangerous?
Turning the matter over and over in my mind I could see but one dangerous possibility from fire. This was the possibility of the petroleum reservoir itself taking fire by a retour de flamme from the motor. During five years, I may here say in passing, I enjoyed complete immunity from the retour de flamme (sucking back of the flame). Then, in the same week in which Mr Vanderbilt burned himself so severely, 6th July 1903, the same accident overtook me in my little "No. 9" runabout air-ship just as I was crossing the Seine to land on the Ile de Puteaux. I promptly extinguished the flame with my Panama hat ... without other incident.
"No. 9" CATCHES FIRE OVER THE ILE DE PUTEAUX
For reasons like these I went up on my first air-ship trip without fear of fire, but not without doubt of a possible explosion due to insufficient working of my balloon's escape valves. Should such a "cold" explosion occur, the flame-spitting motor would probably ignite the mass of mixed hydrogen and air that would surround me; but it would have no decisive influence on the result. The "cold" explosion itself would doubtless be sufficient....