NURSE BALLOON CONTAINING 5,000 CUBIC FEET OF GAS.
It is used in the field to replenish kite balloons with hydrogen.
Previous to the entrance of the United States in the war, preliminary experiments in France were being made with the view of putting the telephone wires in the center of the main cable, thus doing away entirely with the second cable and windlass. But there had never been developed a satisfactory cable of this construction. American inventiveness at the John A. Roebling Sons Co. and the American Steel & Wire Co. was set to work on this problem with the result that not only was a satisfactory cable developed but a steady production was attained, 50,000 feet per week being delivered regularly by the John A. Roebling Sons Co. alone. This new cable consisted of 114 separate wires of special steel besides the telephone center of 3 copper wires properly insulated and armored. The specifications demanded a breaking strength of 7,200 pounds while the actual test of the finished Roebling cable showed 8,250 pounds.
Another of the balloon problems was the supply of hydrogen gas. Before the war only a little hydrogen was used in this country, the element being a by-product in the manufacture of commercial oxygen. We met the additional demand for millions of cubic feet of hydrogen for our balloons by establishing Government gas plants and expanding privately owned plants already in existence. There were two methods of supplying hydrogen to our balloon units at home and abroad. One of these was by furnishing portable plants which would generate hydrogen at the place where it was to be used. The other was to take the hydrogen from the stationary plants, condense it by pressure in steel cylinders, and ship it to points of demand. By far the greater part of the gas which we used not only in this country but in France was produced at the permanent supply stations and shipped in cylinders. Each cylinder held about 191 cubic feet of gas under a pressure of 2,000 pounds per square inch at 68° F. temperature. When the war ended we had placed orders for 172,800 of these cylinders, of which 89,225 had been delivered and were in use. We developed a manifold filler which would take the gas from 12 to 24 cylinders at the same time and quickly inflate a kite balloon, a speed of 23 minutes for a complete inflation having been reported from one training camp.
In the production of portable hydrogen generators we had to produce not only the machine but the chemicals required in the process. We adopted the ferrosilicon and caustic soda process by which it was possible to produce 10,000 cubic feet of hydrogen per hour in a field generator. There was plenty of caustic soda to be had, but high grade ferrosilicon, a production of large electrolytic furnaces, was scarce, because of its heavy consumption in the steel industry. We procured, however, 2,482 tons of it for our generators, of which over 2,360 tons were supplied by the Electro-Metallurgical Sales Corporation alone.
An interesting feature of the gas supply in the field was the use of "nurse balloons." The nurse balloon was simply a large rubberized-fabric bag with a capacity of 5,000 cubic feet of gas. It was used for storage of gas, and the observation balloons were fed from it. We have not received the exact figures of the quantity of gas used by the entire Balloon Service; but, as one item alone, private manufacturers previous to the signing of the armistice produced and delivered 17,634,353 cubic feet of hydrogen and were in position to meet practically any demand for the gas. This figure is only a small part of the total, since it does not include the hydrogen produced in the permanent Government stations or by the field generators.
Hydrogen itself, while the lightest of cheap gases, and therefore the one universally used in balloons, has the grave fault of being dangerous to the balloonist. When mixed with the air it is highly explosive, if touched off by a spark of fire or electricity. For years balloonists have dreamed of a gas light enough to have great lifting power, but which would not burn nor explode. There was such a gas known to chemistry, and this was helium, discovered first in spectroscope examinations of the corona of the sun, but later found by chemists to exist rather freely in the atmospheric envelope of the earth. Although one of every 100 parts of air is pure helium, it was not until comparatively recent years that this light nonexplosive gas was discovered in our atmosphere.
Now helium was rare and expensive, and until the United States entered the war no one had considered its production as a commercial possibility. Up to two years ago the total world production of helium since its discovery had not been more than 100 cubic feet in all, and the gas cost about $1,700 per cubic foot.