GAS AS A VENTILATOR.
This gas—light carburetted hydrogen—is about half the density of common or atmo spheric air, or of the same lightness and ascensional power as common air rarefied by 500° of heat: consequently, this gas always lies above all other gases or vapors in the mine, and fills all cavities and openings in the roof, or forms a stratum in the higher portions of the mine. If it could escape from thence, there would be little or no difficulty with gas in mines:—in fact, it is possible to make this gas itself a means of ventilation more available and constant in all fiery mines than any furnace can possibly be. The rarefaction of the air by means of furnaces is seldom over 200°, and often not over 100°: consequently, the ascensional tendency by increased lightness is small. But carburetted hydrogen is as light as air at a temperature of 500°, and, consequently, has the same tendency to ascend. If allowed, it would rush through the upcast shaft with great velocity and create a far better current than furnaces could effect. This is evident, since the carburetted hydrogen of the mines, if confined in a balloon, would carry it up with great velocity above the clouds.
If the gas of our mines could be used in this manner with practical effect, it would not only abate a troublesome and dangerous pest to mining operations, but become a valuable and co-operative agent.
In a mine requiring 35,000 cubic feet of air per minute, we may estimate 30,000 feet as necessary to dilute the amount of gas which may be produced,—say 1000 feet per minute, since 30,000 feet of air are necessary to render 1000 cubic feet of gas perfectly innoxious. When diluted with from 7 to 9 volumes of atmosphere, carburetted hydrogen becomes highly explosive and dangerous: consequently, a large excess of pure air is required to make the ventilation safe. "Gas-blowers" frequently break out in portions of the mine, and immense volumes of gas are thus suddenly produced. Often the fall ing of the roof in the paves forces the gas into the air-currents, and, were there not a large surplus of pure air, explosions would in such cases be imminent.
We thus find that 30,000 feet of the 35,000 required is necessary to counteract the explosive gases; while only 5000 cubic feet per minute is required to support life and remove the heavy vapors. It is, therefore, evident that a very small amount of ven tilating power would be required if the gases were neutralized, and less still if they were made effective in propelling the current instead of furnaces.
This may be a novel idea to many of our readers. It is not, however, new or untried, the system having been in use in several collieries in Staffordshire, England, with great success, and effected by simple and ordinary means.
The plan is to form the return air-courses, in all cases, above the "intake:" if in large seams, they may be made directly over the main avenues and wagon-ways; but if in small seams, then to the "rise," so that the return air may be higher than the entering or intake air. These courses or "gas-drifts" are so located that the gas readily escapes into them from all portions of the mine, and, being exceedingly light, rushes with great velocity towards the upcast shaft, provided the return air-courses have no depressions and lead invariably to higher levels.
It is also necessary that the chimney, or upcast shaft, should be comparatively small, and have no communication with the working portions of the mine. For the ventilation of a mine requiring 35,000 cubic feet per minute, a chimney three feet in diameter is sufficient if the gas is used as described, since the volume is thereby reduced from 35,000 to 5000 cubic feet per minute.
Almost any shaft can be prepared for this mode, by inserting a sheet-iron or cast-iron tube, or by cutting a recess in the side of the shaft and walling it up with brick.
Pitching seams are peculiarly adapted to this mode of ventilation ; and where gas is plentiful in the anthracite regions there is no difficulty in its use as a proper ventilating medium.