Part 2

As the match was pretty well burned by this time, Johnny applied the flame to a spirit-lamp upon the table, which was the principal purpose for which he had lighted the match.

"A very moderate amount of heat will cause phosphorus, which is the substance on the end of the match, to form a chemical union with the oxygen in the air: brimstone requires a little higher temperature than phosphorus, but not so high as wood requires. The heat produced by a little friction is enough to light the phosphorus, the heat produced by the burning phosphorus is enough to cause the brimstone to take fire, and that produced by the burning brimstone is enough to cause the wood to burn; that is, to form a chemical union with oxygen. And, although the burning phosphorus or brimstone would not have produced sufficient heat for lighting the lamp, the burning wood furnished the necessary temperature; so that the alcohol in the wick began the union at once, when the blaze of the wood came in contact with it."

"I see now how it is that we kindle a coal-fire," replied Alec. "First we put some paper in the grate, and then some pine-kindlings, and then some charcoal, and then the hard coal: then we set the paper on fire with a match, and presently the coal is burning."

"And we separate the kindlings so that the oxygen can get to them more easily," said Johnny.

"How queer we never understood exactly why a fire was kindled in that way, until now," said Belle. "And I should never have thought of fire being a chemical union."

"You can carry on the same principle a good deal farther," said Johnny. "From having a fire of coals, you might have a house on fire, and this would produce heat sufficient to set the neighboring houses on fire; and the uniting of such a quantity of carbon and hydrogen with oxygen, to make carbonic-acid gas, would create such a vacuum by the rising of the heated air and gas, that so much oxygen would rush in about the fire, in the form of a high wind, as to make the fire hotter and hotter, until, if it surrounded an iron building, it would burn it up just as easily as wood houses are burned in an ordinary fire; as was the case at the great Chicago fire, where so many fire-proof blocks were totally destroyed."

"But the iron buildings did not actually burn: they only melted down in the great heat," said Alec.

"Oh, no! they burned," said Johnny: "there is no trouble about burning iron up, if you get the right degree of heat."

"I should think there was a good deal of trouble about it, if great buildings they didn't mean to have burned, if there was a fire, did go and burn up right before their eyes," said Sue.

"Do you mean that the iron really burned as wood does?" said Belle.

"Why, certainly," replied Johnny: "iron will burn up more completely than wood; for when wood is burned, the earthy part remains in the form of ashes: but pure iron, which has no earthy matter in it, will burn up completely; it will all combine with the oxygen in the air to form gas. When iron is in a mass, it takes a very intense heat to produce this chemical union with oxygen; but when it is separated into very small particles, it will burn in an ordinary fire."

"If iron will burn up, I wonder we never see it burning so," said Alec. "I've been in blacksmiths' shops and foundries, and I never saw any iron burning up, although I've seen it at a white-heat."

"The fires in blacksmiths' shops and foundries are not hot enough to burn iron in the mass," replied Johnny; "or, if they are, they can't get enough oxygen near enough to combine with it. At the great Chicago fire, the intense heat caused such a high wind,--that is, such a flow of oxygen toward the fire,--that the fire became so intensely hot there was no difficulty in the iron blazing and burning more completely than the wood."

Here Johnny looked rather disconcerted at Alec's apparent incredulity.

"But, Alec," said he, "if little particles of iron, such as you would file off of a bar of iron, will burn up, of course the whole bar could be burned if it was all filed up; and if the filings could be burned in an ordinary lamp like this, why couldn't the whole bar be burned in a fire that was hot enough?"

"Yes," said Belle, who was troubled at Alec's being so impolite as to seem to doubt Johnny's word: "it's just like the difference between a log of wood and the sawdust produced by sawing the log in two; you couldn't burn the log without building a hot fire under it, while you could set the sawdust on fire with a match."

"That is a very good illustration," said Johnny. "Now, I lit this lamp to show you how nicely iron will burn."

Johnny took a large-mouthed bottle from the shelf, which was about half full of rather bright particles.

"These are steel-filings I got at a machine-shop; but, if you prefer, I will get a nail and file, and let you make some iron-filings yourself, which will answer just as well. I keep the steel-filings because they are so handy. I just ask the men for them, and they give me a whole lot that last ever so long."

Johnny then opened his knife, and, taking out some of the filings on the end of the blade, dropped them, or rather shook them, slowly into the flame.

"Oh, how pretty!" exclaimed Belle: "they burn something like gunpowder."

"So they actually burn up, and don't just get red-hot and fall down and cool?" said Alec.

"Oh, yes!" replied Johnny: "they burn up just like so much sawdust, only more so; for there would be some ashes left of sawdust, even though they might be invisible."

"So the filings have combined with the oxygen in the air, and gone off in gas?" said Belle.

"Yes," replied Johnny.

"I wish you would file some iron," said Sue, "because that experiment makes such pretty fireworks."

"Very well, I will, if you will go down and bring me a piece of iron from papa's tool-box."

Sue ran off, and Johnny continued,--

"I think I'll show you now how I make gas on a small scale."

"What kind of gas?" inquired Alec.

"Oh! such gas as we burn in stores and houses. I've got my pipe already prepared: if I hadn't, I couldn't show you that experiment very well to-day. I got the pipe ready to show to a boy who was coming to see me last week; but he was sick and didn't come, so I didn't use the pipe."

Johnny took a common clay pipe from his closet, and showed Alec and Belle that the top of the ball of the pipe was closed with plaster of Paris.

"I pounded a little piece of bituminous coal, such as they use at the gas-works," said Johnny, "and nearly filled the bowl of the pipe with it; then I wet a little plaster of Paris, and closed the end of the bowl to make it air-tight,--that is, to keep out the oxygen. There are carbon and hydrogen in the coal, and they will both combine with oxygen very quickly at the right degree of heat: the hydrogen will form a flame, and the carbon will look bright as you see it in a piece of burning wood or coal. But you see the pipe is fixed so that the oxygen can't get at the coal at that end."

"Is the flame of a fire or a lamp caused by the burning of hydrogen?" inquired Belle.

"Yes: the flame is the hydrogen combining with oxygen, and the glowing coal or wick is the carbon uniting with oxygen. The gas from the gas-works is the hydrogen of the coal separated from the carbon. When we heat it with a match to set it to uniting with oxygen, we have nothing but a flame. You know the coal is heated in air-tight retorts; it is heated hot enough to burn, but it can't burn because there is no oxygen for it to unite with; but the heat causes the hydrogen to separate from the carbon, and then it finds its way out through the opening in the retort into the pipes, and when it reaches the air at the end of a pipe, you can heat it a little with a match, and it will begin to unite with the oxygen."

"And the coal that is left in the retort is called coke. I have seen it very often," said Alec: "the reason it looks different from coal, and burns differently, then, is because it has lost its hydrogen?"

"Yes," replied Johnny: "almost all ordinary combustibles are composed of carbon and hydrogen,--wood, coal, oil, etc.; and there are a great many other things that oxygen has a great affinity for, and will combine with at the right temperature: the things that it won't combine with are such as have all the oxygen in them that they will contain, like dirt and stones and ashes."

"And how about the pipe?" asked Alec.

"Why, after Sue gets back with the piece of iron, we will go down and set the ball of the pipe in Katie's fire. When it gets hot, we shall see a smoke coming out of the pipe, which will be composed chiefly of hydrogen gas: we will touch a match to it, and there will be a flame at the end of the pipe until all the hydrogen which was in the coal in the ball of the pipe has united with oxygen. That is one way to make gas on a very small scale."

"And then, if we break the plaster of Paris, and take out what is left of the coal, we shall have some coke," said Alec.

"Yes," replied Johnny.

Sue now appeared, bringing a small cold chisel. Johnny took a file from the closet, and, placing the chisel over the flame of the lamp, began to file it briskly: beautiful little points of light at once commenced to play about the file and chisel at the point of contact.

"Why don't the filings fall down into the flame?" inquired Alec.

"I suppose the current in the flame blows them up, they are so small," replied Johnny, "or perhaps the motion of the file does."

Alec, Belle, and Sue then took turns at making the "fireworks," as Sue called them.

"I think I understand now about fire being a chemical union between oxygen and other substances," said Alec; "but I don't understand about the heat. What makes heat? or why does a chemical union of that kind produce heat?"

"Why, friction makes heat," replied Johnny; "particles of matter coming against each other violently. You know the Indians used to get the oxygen to combining with the carbon and hydrogen in two pieces of dry wood, by rubbing them together briskly; and before matches were invented, they kindled a fire by striking flint and steel over tinder; and a steel peg in your shoe-heel sometimes strikes fire on the pavement by the heat produced by friction; and I think I have seen it stated, that, when oxygen is uniting with other substances, it is the very quick motion of the little particles of matter among themselves that produces the heat."

"I shouldn't think such little invisible particles as those of oxygen and hydrogen could make friction enough by their motion as to produce heat," said Alec.

"Why, Alec," replied Belle, "don't you remember what terrible force the air has in hurricanes, and even in a common gale?"

"But that is in an immense volume," replied Alec.

"Oxygen is in a comparatively mild and harmless state when it is by itself," said Johnny; "but when it gets to combining with any thing it has a great affinity for, it is in a sort of rage. I think myself that there must be some pretty rapid motion going on in a fire, even if we can't see it."

Johnny had handed the chisel to Sue, telling her to put it right back where she found it.

"Well, I will," replied Sue; "but I guess things won't be put back in their right places much after Felix gets here."

Sue had no sooner said this, than she clapped her hand over her mouth. "Oh!" she exclaimed, "if I haven't gone and told!"

Johnny's face had grown very long in an instant.

"Is that your bad news?" he said. "When is Felix coming?"

"I don't know," replied Sue: "you'll have to ask mamma, for she was to decide."

Sue then went back with the chisel, and Alec said,--

"So your cousin Felix is coming again, is he?"

"I suppose so," replied Johnny briefly, as if it was not a very pleasant topic.

"What a funny boy he is!" said Belle. "I never saw him but once, and only for a few minutes; but he seemed to be ready for any kind of mischief."

"Yes," replied Johnny: "he's as fond of noise and mischief as oxygen is of carbon and hydrogen; but I guess he won't stay very long."

This latter reflection seemed to console Johnny, for he began to look tolerably cheerful again.

"Shall we go and make hydrogen gas now?" said he.

But at that moment, Sue came running back, exclaiming,--

"Some folks in a carriage are having an accident right out by our front-door!"

"What kind of an accident?" inquired Johnny.

"Is it a runaway?" inquired Belle.

"No, it isn't a runaway, for they can't get the wagon to move: at any rate, I heard a man say the wheel wouldn't turn around."

"Let's go and see," said Alec.

So they all went out at the front-door to see what was the matter.

They found a carryall and a span of horses standing near the sidewalk. A lady and a little girl were in the carryall. Two gentlemen were examining one of the wheels, and several boys stood near looking on.

"I don't know what ails it," said one of the men; "but the wheel won't turn around, that's sure. I think we'll have to go and ask a blacksmith to come and see to it."

Johnny and Alec went out on the sidewalk, while Belle and Sue stood on the doorstep.

"I guess it's a hot wheel," said Johnny to Alec.

"What did you say?" asked one of the gentlemen, turning around quickly.

"I said perhaps it is a hot wheel," replied Johnny.

"Oh, no!" said the gentleman, looking rather perplexed: "the wheel is not hot at all."

"No," said Johnny, "it isn't hot now; but perhaps it has been hot, and that caused the wheel to get welded to the axle so that it wouldn't turn; and after it wouldn't turn, there was no friction, and so the wheel cooled."

"I shouldn't wonder if he is right," said the other gentleman: "that often happens to car-wheels on a fast train, and we have been driving pretty fast, you know."

"Well, young man," said the other gentleman, "since you know so much about wheels, can you tell me why this wheel should act so, while the others are all right?"

"I presume it wasn't greased so well as the others," replied Johnny.

Just then a man who was passing by stopped to see what was the matter: he was a mechanic coming home from the rifle-factory, which closed at five o'clock. He asked a few questions, looked at the wheel, and said, "Oh! that's a hot wheel: you'll have to prop the carriage up, and pound it off from the axle. You've been doing a little blacksmithing as you came along. I presume the wheel and the axle are pretty neatly welded together, but yet not so much so but that a little artificial blacksmithing will set it all right again."

Then there was considerable stirring about: the carriage was propped up under the directions of the mechanic, and, after a good deal of hammering, the wheel was pronounced all right. Johnny brought out an oil-can; and, after the wheel was well oiled, the gentleman thanked everybody around, and offered to pay all who had helped, including Johnny. But every one refused to take any pay, except two or three boys who had hindered more than they had helped.

"That was a pretty good illustration of the effect of friction," said Alec.

"Yes," replied Johnny. "Now let us go in and make the gas."

"I sha'n't be able to stop any longer now, thank you," said Alec, "as my father told me to be home by half-past five. But I'll get a pipe and fix it myself, if I can find a piece of the right kind of coal, and that will save your pipe until another time."

"Sawdust, or almost any thing that will burn well, will answer to fill it with," said Johnny.

"I am ever so much obliged for your illustrated lecture," said Alec. "I've learned a good deal, and I wish you would come over to our house some day before long. I can't perform many experiments yet, but we'll have a good time somehow. I mean to begin to perform experiments, and study up about these things. I am two years older than you are, but I don't know half as much as you do."

"You know ever so much more than I do about history," said Johnny, "and Dick knows more about carpentry, and Fred about printing."

"And that's the way it is with grown-up folks," said Belle: "one takes to one thing, and another to another; and so, between them all, the different kinds of work in the world get done."

"As for me," said Sue, "I like to have a good time most any way."

After their visitors were gone, Johnny went in to ask his mother about Felix.

"Why, my dear," replied Mrs. Le Bras, "your aunt Mary is in very poor health, and is going to Europe on a three months' trip with your uncle Louis. Your uncle thinks she will be much better if she does not have the care of Felix; and yet she is unwilling to leave him behind, unless we will let him come here. Of course, we could not refuse; although it will be a great care for me, and a worry to you; but we are well, and aunt Mary is ill."

Johnny tried not to cry, but the tears rolled down his cheeks in spite of all his efforts to restrain them.

"There won't be any peace and quiet and comfort in the house after Felix comes," he said; "and to stay a whole three months'--But then, if aunt Mary is sick"--

"Perhaps he has improved since we saw him," replied Mrs. Le Bras: "if not, your father says he shall be made to mind and behave himself. Since his father and mother will not be here, he will be obliged to obey your father and me, and we shall be decided with him."

"When will he come?"

"In about two weeks."

"I shall try to enjoy myself as well as I can before he comes, because I know it won't be very pleasant after he gets here."

Mrs. Le Bras said nothing, because she was afraid Johnny was about right. As Johnny went up to the laboratory to put up his pipe and the other articles, he looked very sober and thoughtful: he was already planning how he could escape from Felix's racket and nonsense.

When Johnny came down again, Sue said,--

"You didn't explain, after all, how the rug put out the lamp last night."

"Put out the light, you mean. Why, don't you see? The rug prevented the air from reaching the fire, and, as there was no more oxygen to combine with the hydrogen and carbon, there could be no fire."

*CHAPTER III.*

*THE SKY-ROOM.*

Johnny felt so badly about the coming of Felix, and begged so hard to be allowed some place of refuge during the stay of this wild guest, that his father said he might have the large back-room in the French roof, if his mother was willing. Mrs. Le Bras said she had no objection, if Johnny did not mind having all the things about that were stored in that room, since there was no other place to put them in. Johnny said all he wanted was somewhere to go when Felix got too rude, where he could be sure Felix would not follow him: he said, too, that he should like to keep the chemicals be was using in the same place; because, if they were not out of the way, Felix would be meddling with them.

"I will have a lock put on the door of the room, and give you the key," said his father; "and then if you let in any one you don't want, it will be your own fault. You can carry the things from your laboratory into this private domicile, and whatever else you wish."

"I will carry most of my books, then," said Johnny; "for I haven't a single book that Felix will want to read."

"But you must not put your mother or me to any trouble about fixing up the room," added his father; "you must be contented with the bare floor; and if you want the things which are stored there put up out of the way, you must re-arrange them yourself, and be sure they are as neatly and safely placed as they were before."

"I am perfectly willing to agree to that," returned Johnny, looking brighter than he had before since the announcement that Felix was to spend the summer with them. "Can I begin to get the room ready to-day?"

"Yes," replied his mother. "I have no objection, since I am not to do any thing about it, and can trust you not to put any thing out of order in moving the articles about."

Johnny went up into "the attic," as it was called, immediately, followed by Sue. There was only one finished room in the French roof: this was in front, and was occupied by Kate. The remaining space was not plastered, and had great beams overhead: it was called "the storeroom," and was separated from Kate's room by a narrow hall formed by the placing of a light board partition about four feet distant from the finished room in front. A thin plank door, without lock and key, was in the end of the partition, near the head of the stairs. There were four large windows in the room,--one at each side, and two in front.

"It's a real pleasant room, isn't it?" said Johnny, looking about with interest for the first time; for he had never entered the room before except for the purpose of storing something there, or getting something which had been put away in some of the trunks or boxes. These trunks and boxes, some old furniture, and a large cedar chest in which his mother kept furs and other expensive articles liable to be disturbed by moths, were scattered about rather promiscuously, without regard to any particular order.

"I'll tell you what I've a mind to do," said Johnny. "I think I will put all the things that are stored here at the back part of the room, and then I'll take the old clothes-line, and draw it across in front of them, and hang some of mother's old drapery curtains on it: I don't believe but that she has enough to go clear across the room; only I shall leave an opening in front of the door to get through."

"Mamma's got a set of old cretonne, real pretty, too, with bright red flowers on them; and I know she'll let you have them," said Sue.

"And she's got another set, of cheese-cloth, that she won't use again," said Johnny. "There's four more: I'll alternate them,--that will be prettiest. I guess they'll go clear across, and be a little full too. And then see what a monstrous room we shall have left all to ourselves!"

"But you won't let me come in, will you? I thought you wanted it all to yourself."

"Oh! I shall let you come in sometimes, when you don't want to romp; and perhaps I will let Felix in once in a great while, when I am sure he won't stay long: but, as I shall have a lock and key, I can keep folks out when I am reading or busy.

"How far off you can see at these front windows!" said Sue. "I can see way up the river, and all those blue hills, and over hundreds and hundreds of houses, and lots of sky!"

Johnny came and stood by her side, and looked out at the landscape.

"It is beautiful, isn't it?" said he. "Why, I do believe it's the very handsomest view I ever saw! It is queer I never noticed before how fine it was. I wonder if father and mother know we've got such an observatory!"

"Wouldn't it be a pretty picture?" said Sue. "I wish it was a picture instead of real; for then I could carry it down in my room, and hang it up."

"Oh, no! it wouldn't be half as nice as it is now it is real. Just think how many changes we can see on all that great sweep of sky, how many clouds altering their shapes and colors every minute, and what glorious sunsets! We must come up here after supper to-night, and see the sunset. Let's surprise father and mother, Sue. If we can get the curtains, I'll have them up by that time, if you'll help me."

"Won't that be nice!" exclaimed Sue, dancing about. "And just see, Johnny! here's furniture enough to furnish your room right off: there's that red plush chair that isn't faded very badly; and that great, comfortable old wicker rocker that we used to like so much, because it would hold both of us easy,--and all that ails it is that it looks kind of old; and there's mamma's old toilet-table and a big ottoman;--and, O Johnny! there's our lounge in the corner that I've missed so much, because the new sofa isn't half so big."