Part 22 (2/2)
”How can that be done?”
”Several ways are open; one would be to tap the floor and drain the gas out, which would be difficult to do with our resources. Another plan would be to force in a lot of air, so as to render the gas inert, or we might put in enough air to make it burn, and consume it.”
”Why, will it burn?”
”Most a.s.suredly; all it needs is enough air; but I am afraid this plan will not be a very safe one for us. If the floor of the cave is not at any place more than four feet below the entrance, we can go about safely, but in such case we must move about with the utmost caution, so as not to get too much of the gas in the system.”
”I am afraid it will be a difficult thing to go in unless we know absolutely where the low places are, or unless we survey the bottom of the cave,” said George, brightening up at the idea.
”What would happen if we threw a light into the bottom where the gas is?”
”It would be extinguished instantly,” remarked John.
”That gives me an idea,” a.s.serted George. ”Why not take a lamp, and carry it ahead of us, about three feet from the ground, and whenever that goes out, it will show there is gas there?”
”That is a good observation; but I am afraid it would be very dangerous to do that.”
”Dangerous? I thought you said that the carbonic gas would put out the light?”
”So it will; but if three parts of air should be added to one part of the gas it will make an explosive mixture,--that is, a mixture which will burn, as there has been enough oxygen added to support combustion.”
”In what way could enough air mix with the gas to make it burn?”
”By stirring it; the movement of the body might make an admixture just above the surface of the gas, which would burn, and that might mean a catastrophe for us.”
”Then we are certainly stopped at this cave.”
”Not by any means,” rejoined John, and he saw the boys' faces smiling again. ”We must make a safety lamp.”
”Do you mean a lamp that will not explode the gas, although it has enough oxygen to 'support combustion,' as you say?”
”Exactly. Have you ever heard of the Humphrey Davy lamp? Well, that was invented to meet the very condition found here.”
”Tell us about it.”
”In 1816 Davy discovered that a flame would not pa.s.s through a fine wire gauze, while conducting some experiments. It occurred to him that use could be made of this discovery by surrounding the flame of a lamp with gauze, and the well-known lamp was built on that principle.”
”What I am curious to know is, that if it will not burn the gas, will it go out if it gets down in the gas?”
[Ill.u.s.tration: _Fig. 13. Types of Safety Lamps._]
”Yes; because enough air, or oxygen must go through the mesh to support combustion of the flame itself. If it does not get enough it is smothered.”
”Then why not make a lamp of that kind?”
”But where can we get enough gauze to make a cylinder big enough to go around a lamp?”
John laughed at the serious predicament, which expressed itself in the faces of the boys. ”That is true,” he said; ”but if we can get a small piece of tin, we can punch it full of fine holes, and probably make that answer.”
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