"How do they find it out?" said Rollo.
"Why, they let a candle down," replied Jonas.
"And will the candle go out?" asked Rollo.
"Yes," said Jonas, "if there is choke damp in the well. Sometimes they make a little of it in a tumbler or a jar upon the table, and so let a little flame down into it, and it goes out immediately."
"I wish we could make some," said Rollo. "Do you know how they make it?"
"No," said Jonas; "but I believe it is pretty easy to do it, if we only knew how."
"I will ask my father," said Rollo; "perhaps he will know."
This conversation took place when Jonas and Rollo were about the fires; but now the fires had pretty nearly burnt out, and they prepared to go home.
That evening, just about sunset, Rollo went out behind the house, and found Jonas raking off the yard. The spring was fast coming on, and the grass was beginning to look a little green; and Jonas said he wanted to get off all the sticks, chips, and straws, so that the yard would present a surface of smooth and uniform green. Rollo told him that he had found out how to make choke damp.
"Did your father tell you?" said Jonas.
"No," replied Rollo.
"Who did tell you, then?" said Jonas.
"Guess," answered Rollo.
"Your mother," said Jonas.
"No," answered Rollo.
"Then I can't tell," said Jonas.
"It was Miss Mary," replied Rollo. "I met her in the road to-day, and I asked her."
"And how is it?" asked Jonas.
"Why, we make it with chalk and vinegar," said Rollo. "We pound up a little chalk, and put it in the bottom of a tumbler. Then we pour some vinegar over it. The vinegar takes the choke damp out of the chalk, and Miss Mary says it will come up in little bubbles. She says we can lay a paper over the top loosely,-she said loosely, but I think it ought to be tight."
"Why?" asked Jonas.
"So as to keep the choke damp from coming out," replied Rollo.
"No," said Jonas. "I understand why she said you must put it on loosely; that's to let the common air out."
"What common air?" said Rollo.
"Why, the air that was in the tumbler before," replied Jonas. "You see that, as fast as the choke damp comes up, it drives the common air out of the top of the tumbler; and so you must put the paper on loosely, and let it go out."
That evening Jonas and Rollo tried the experiment. First they put about two teaspoonfuls of chalk into the tumbler. Then they poured in the vinegar. It immediately began to foam.
"Ah," said Rollo, "that's the effervescence."
"The what?" said Dorothy; for they were making this experiment upon the kitchen table, and Dorothy was standing by, looking on with great interest.
"The effervescence," said Rollo. "Miss Mary said there would be an effervescence, which would be occasioned by the little bubbles of choke damp, coming up from the chalk."
"Poh!" said Dorothy; "it's nothing but a little frothing."
"It isn't frothing," said Rollo, very seriously; "it isn't frothing, it is effervescence. Don't you think Miss Mary knows?"
"Jonas," said Rollo again after a short pause, "how many of these little bubbles will it take, do you think, to fill the tumbler full of choke damp?"
"I don't know," replied Jonas; "we will wait a little while, and then try it."
"There, now, Jonas," said Rollo, "we have not got any candle."
"O, I will roll up a piece of paper, and set the end on fire, and then dip it down into the tumbler, and that will do just as well."
"What are you going to do that for?" said Dorothy.
"Why, to see it go out," said Rollo.
"It won't go out, unless you put it away down into the vinegar," said Dorothy.
"Yes it will," said Rollo; "we are only going to dip it down a little way, just into the choke damp, and it will go out."
"It won't go out, child," said Dorothy. "There's nothing to put it out."
"Well, you'll see. Won't it go out, Jonas?"
"I don't know," said Jonas.
"Don't know?" said Rollo. "Why, you told me that choke damp would put out a blaze."
"Yes," said Jonas, "I am sure of that; but there are a great many ways of failing in trying experiments."
"Well," said Rollo, "that may be; but this will not fail, I know, for I can see the little bubbles of choke damp coming up. There are millions of them."
By this time Jonas thought that the tumbler was filled with the gas, which was rising from the chalk and vinegar. So he rolled up a piece of paper, and set the end on fire, and, when it was well burning, he plunged the end of it into the tumbler. To Rollo's great disappointment and mortification, it continued to burn about as much as ever. The flame crept rapidly up the paper, and Jonas had soon to run with it across the floor and throw it into the fire, to avoid burning his fingers. Dorothy laughed aloud; Jonas smiled; and as for Rollo, he looked disappointed and vexed, and appeared to be overwhelmed with chagrin.
Dorothy continued to laugh at them, while Jonas went to the pump and washed out the tumbler. At length she said,-
"But come, Rollo, don't be so disconsolate. You look as if you had swallowed all the choke damp."
"Yes, Rollo," said Jonas, "we must keep good-natured, even if our experiments do fail."
"Well," said Rollo, "I mean to ask Miss Mary again, and then we can do it, I know."
* * * * *
Rollo accordingly went, the next day, to ask Miss Mary about the cause of the failure. Miss Mary said that she could not think of any thing which was likely to be the cause, unless it was that they put too large a flame into the tumbler.
"Well," replied Rollo, "and what harm would that do? Won't the choke damp put out a large flame?"
"Yes," replied Miss Mary, "if it only fairly surrounds and covers it; but, then, if you put a large flame into a tumbler, it makes the first instant, a great current of air, and so the choke damp might be blown out, and common air get in, and so keep the paper burning."
"How does it make a current of air?" asked Rollo.
"Why, the heat of the flame, when you first put the paper in," replied Miss Mary, "makes the air that is above it lighter; and the common air all around crowds in under it, in buoying it up; and by that means, if the flame is too large, common air is carried into the tumbler. You ought to make a very small flame, if you leave the top of the tumbler open."
"How can we make a small flame?" said Rollo.
"One good way," replied Miss Mary, "is to roll up some paper into a very small roll. I will show you how."
So Miss Mary took a piece of paper, and cut it into the proper shape with her scissors, and then rolled it up into a long and very slender roll; one end of it was not much larger than a large knitting-needle. She gave this to Rollo, and told him that, if he tried the experiment again, he must light the small end, and it would make a flame not so big as a pea.
Rollo explained to Jonas what Miss Mary had said, and they resolved on attempting the experiment again that evening. And they did so. Dorothy stood by watching the process, as she had done the evening before, but Rollo did not assert so confidently and positively what the result would be. He had learned moderation by the experience of the night before.
When all was ready, Jonas lighted the end of the slender roll in the lamp, and plunged it carefully into the tumbler. It went out immediately.
"There!" said Rollo, clapping his hands, "it goes out."
"Why, it is only because the wind blew it out."
"No, Dorothy," said Rollo, "there isn't any wind in the tumbler."
"Yes," replied Dorothy, "when you push it down, it makes a little wind, just enough to blow it out."
"Get another tumbler," said Jonas, "and let us see."
So Dorothy brought another tumbler, and Jonas put the burning end of the paper down into it, with about as rapid a motion as that with which he had put it before into the tumbler he had at first. The paper continued to burn.