The body of the car, as has been said, was cylindrical, with sharp ends, like a mammoth perfecto cigar. This cylinder was divided in half, longitudinally, by a floor of aluminum alloy. The entire lower chamber thus formed was a big generating tank for a gas having a lifting capacity exceeding hydrogen vapor by a ratio of three to one. This gas was generated from brownish crystals formed of a compound of hydrogen-saturated alum and another chemical akin to radium, which the boys, for the present, kept a close secret. Two pounds of these crystals, when forty gallons of water were added to them, formed close to sixty thousand cubic feet of the powerful inflation gas. One hundred pounds of the crystals were carried in a special compartment of the aero-auto, and constituted an ample supply for all emergencies. To inflate the bag, then, all that had to be done was to unbolt a metal hand-hole in the floor of the front section of the car. Through this the crystals were dumped into the tank beneath and the water added. The opening of the generator was then closed and clamped down tight, hermetically sealing the tank. The gas, under compression, was explosive, and was utilized to run the motor as well as for inflation purposes. Immediately in front of the operator of the car was a gauge showing at all times the pressure in the tank, and when the gas bag was in operation the amount of gas in that also was indicated. When sufficient gas was generated, the operator turned a valve and the gas from the tank instantly began rushing into the bag carried on the framework above him. The bag was so folded that it inflated without necessitating much attention. Three broad bands of rubberized fabric of great strength encircled the gas bag proper. To these were attached wires of a tensile strength exceeding anything hitherto known. The other ends of the wires, of course, were fastened to the body of the aero-auto, so that when the bag was sufficiently buoyant the entire car and its occupants were borne aloft. By means of an exhaust pump connected with the motor, the volume of gas could be reduced at will, causing the entire aero-auto to sink at the pleasure of those directing the machine.