M. Biot (Traité de Physique Experimentale, &c. tome ii, p. 435) describes the Voltaic pistol as a metallic vessel of a spheroid shape, furnished with an aperture and pipe, and with a conductor for the electric fluid, which passes through the middle of the vessel. This conductor is insulated, as it goes through a glass tube, and extends to within an eighth of an inch of the middle; and directly opposite to this conductor is a metallic wire, having, like the first conductor, a small metallic ball on its end. This conductor is placed a short distance from the first; so that, when the electric fluid is conducted, it passes from one ball to the other within the pistol, and hence inflames the hydrogen gas. With respect to the form of the pistol, it is of no moment whether it be cylindrical, conical, or globular, as the effect is the same, provided that it contain a sufficient quantity of gas, and the spark is conveyed through the gas, or the gas is inflamed by a vent. The air pistol described by Brande (Brande's Chemistry) is cylindrical, or rather in the shape of a cannon, and, where the touch-hole should be, there is an insulated conductor, which conveys the spark to the interior.
The Voltaic lamp is also a contrivance by which hydrogen gas is inflamed by the electric spark, which sets fire to a taper. The original lamp has been greatly improved, and simplified. The eudiometer of Volta is another contrivance by which hydrogen gas is burnt, in a strong tube, by the electric spark.
The detonation of inflammable air may be shown over a pneumatic tub, by filling metallic gas-holders with a mixture of hydrogen gas and atmospheric air. When flame is brought in contact with the mouth of the gas-holder, an explosion will immediately take place. Soap-bubbles, blown with hydrogen gas, mixed with atmospheric air, will take fire, on presenting a lighted taper, and give a slight explosion. The ascension of these bubbles demonstrates, that the gas is lighter than atmospheric air, and it is its extreme levity that fits it for the purpose of filling balloons. It may be made twelve times specifically lighter than atmospheric air, by passing it over dry muriate of lime, in order to absorb the moisture it may contain, provided the gas be free from carbon, or carbonic acid.
Light carburetted hydrogen gas, or fire-damp of miners, is that gas, which so often formerly produced many dreadful accidents by its explosion. The invention, by Sir H. Davy, of the safety-lamp prevents this effect.
The principle of this most valuable discovery, appears to be altogether in the fine metallic gauze case, which surrounds the flame of the lamp; so that, as it is found by numerous and repeated experiments, the inflammable air, if present, cannot take fire outside of the gauze; in other words, the flame, in the interior of the case, is prevented from setting fire to the exterior atmosphere, however explosive it may be.
Hydrogen gas, in combination with carbon, is not only generated in mines and coal pits, (in the latter of which, it is the most abundant), but is frequently found on the surface of springs in the form of bubbles, usually however combined with sulphur; and in many places on the surface of the earth. It may be inflamed by a candle. The burning springs consist of this gas which is set on fire, and the combustion is kept up by a constant supply of gas from the same source. In the East, this gas is very often conveyed under ground through hollow reeds, and is constantly kept burning. At other times, it is conveyed to the sacred temples, as with the Zoroasters, and burnt as holy fire; and in some countries, it is so abundant, that the natives employ it as fuel for boiling their pots. It is found in different parts of the United States. A striking incident, showing its effects, occurred lately near Cincinnati, in the state of Ohio. It appears, that, in making an excavation, and boring for salt water, the workmen penetrated their augur into a cavity, which contained an abundance of gas, and which, with the water, made its way to the excavation. Not suspecting that the gas was inflammable, or being unacquainted with it, and apprehending no danger, they brought a lighted taper; and the gas, being mixed with atmospheric air, exploded with a noise so considerable, that it was heard several miles in the neighbourhood. The men were much burnt, some of them dangerously.
The gas was afterwards inflamed by applying a taper, as it rose in bubbles from the surface of the water.
The philosophical candle is nothing more than hydrogen gas set on fire as it proceeds from a capillary tube, being formed in a bottle to which the tube is attached. The most brilliant flame, however, is produced by hydroguret of carbon, or olefiant gas.
Inflammable air is often generated in the stomachs of dead persons, for, on applying a lighted candle, the vapour has been known to take fire. Dr. Swediaur relates some instances of the same kind, but in living persons, in which the urine of the by standers was made use of. According to several authorities, combustion has been known to take place spontaneously in living persons. Lair, however, is of opinion, that, in these cases, it must have occurred by some slight external cause, such as the fire of a candle, taper, or pipe. There can be no question as to the developement of hydrogen gas.
Morse, (Universal Geography, article Persia, p. 588), after mentioning the Persian guebres, the disciples and successors of the ancient magi, and followers of Zoroaster, speaks of a combustible ground about ten miles distant from Baku, a city in the north of Persia, as the place for their devotion. This ground contains several old temples, and is remarkable for the quantity of inflammable air it emits, which is employed to produce the sacred flame of universal fire. If the ground be penetrated with a stick, there will issue out such a prodigious quantity of inflammable air, as, when lighted, will burn for a considerable time. This gas, we remarked, is employed there for lighting, cooking, and other purposes. The naphtha districts, in Persia, furnish this gas in abundance. See [Naphtha.]