The Indians surrounded the house, but there were loop-holes on each side. Mr. Kilburn and Mr. Pike took two of the sides, and the two boys the others. Bang! bang! went the guns of Mr. Kilburn and Mr. Pike. Bang!

bang! went the boys' guns. They could fire at a rest, and take deliberate aim. The Indians could not see the muzzles of the guns, and the moment one of the red men peeped from behind a tree his skull was in danger.

One by one they fell, which enraged them all the more, and they crept nearer, firing rapidly, riddling the shingles, hoping, quite likely, that a bullet might glance down from the roof, and hit those inside.

"The roof looks like a sieve," said John Kilburn, as he looked up and saw the holes.

Mrs. Kilburn and her daughter were loading the extra guns the while, and handing them to the men and boys, who kept up such a rapid fire that the Indians came to the conclusion that there were a large number of men in the house.

"We shall soon be out of bullets," said Mrs. Kilburn.

A thought came: why not catch the bullets that were coming through the roof? The b.a.l.l.s had nearly spent their force when they came through, and they hung up a blanket, with thick folds, which stopped them entirely; and the girl, gathering them as they fell harmlessly upon the floor, put them into a ladle, melted them, and ran new bullets, which soon were whizzing through the air, and doing damage to the enemy.

All through the afternoon the fight goes on, the Indians aiming at the loop-holes. Their bullets pepper the logs around them. One comes in, and inflicts a ghastly wound in Mr. Pike's thigh, but the Indians do not know it, and the brave defense is kept up till the Indians, foiled in all their efforts, defeated, with several of their number dead and many wounded from the volley fired by Colonel Bellows and his men, and by those in the house, set Mr. Kilburn's wheat on fire, kill his cattle, bury their dead, and slink away, not having taken a scalp or a prisoner.

They have only wounded one man.

When everything goes well with the Indian he can be very brave, but when the tide is against him he quickly loses courage and becomes disheartened, and so Captain Philip made his way back to Canada, very much crest-fallen at the repulse received at the hands of two men, a woman, two boys, and a brave-hearted girl.

[TO BE CONTINUED.]

CAMBRIDGE SERIES

OF

INFORMATION CARDS FOR SCHOOLS.

No. 3.

About Combustion.

BY

W. J. ROLFE, A.M.

Combustion is only another name for burning, and burning in all ordinary cases is _oxidation_, or union with oxygen, one of the gases that make up our atmosphere. It is a _chemical_ change; that is, one by which we get a new substance entirely unlike any of the substances united. Common salt, for instance, is formed by the chemical union of a yellow, bad-smelling gas and a soft silvery metal. When coal and wood are burned, the chief products of the union with oxygen are carbonic acid and water. The former is a colorless gas, and the latter is in the form of invisible vapor, and both go up the chimney and mix with the outer air. The ashes left behind are only what can not be burned or united with the oxygen. If we collect all the products of the burning, together with the ashes, we find that they weigh more than the coal or wood, the increase being exactly equal to the weight of the oxygen consumed. No kind of matter can be destroyed by any power known to us; it may unite with other matter, and take many new forms, but its weight can be neither increased nor diminished. The amount of matter in the universe is always the same.

Oxygen must be heated before it will unite with coal or wood. The air is at all times in contact with them, but they will not burn unless they are first kindled. The chemical process itself, when once started, generally produces heat enough to raise more oxygen to the proper temperature, and thus the combustion is kept up. The point to which the oxygen must be heated varies much with different substances, as is well shown in kindling a coal fire. The heat produced by rubbing a match on a rough surface suffices to make the oxygen unite with the phosphorus on the end of the match; the burning of this causes heat enough for the union of the oxygen with the sulphur, and the burning of the sulphur enough to set the wood of the match on fire. The shavings, the kindling wood, and the charcoal are in turn ignited, and the burning charcoal develops heat enough to enable the oxygen to combine with the hard coal.

Each step in the operation requires more heat than the preceding step.

This seems a very simple thing now, but the anthracite beds of Pennsylvania long remained useless because no one had found out how to kindle the fuel, and the discovery was at last made half by accident.

There are some forms of combustion which are very unlike ordinary burning, and yet are essentially the same, being cases of union with oxygen. The only difference is that the process goes on slowly instead of rapidly. We know that vegetable and animal substances decay when exposed to the air; and decay is a slow burning. The oxygen of the air gradually combines with the substances, converting them into carbonic acid and water, and leaving only a small remnant of matter as the ashes of the lingering combustion. The _heat_ produced in this case is found to be precisely the same as in ordinary burning, but it is set free so gradually that it escapes our notice.

We know that green wood decays much sooner than dry wood. Indeed, if wood is kept perfectly dry, it will not decay for ages. In the dry climate of Egypt wooden mummy cases have been preserved for more than three thousand years. On the other hand, dry wood burns much quicker than green wood; it is not easy to set the latter on fire. Why this difference, if decay and burning are similar processes? The decay of the green wood is due to the fact that the presence of moisture causes certain changes in portions of the wood, which enable the oxygen to attack it at a low temperature; and the slow combustion, once started, is self-sustaining. But in ordinary burning the temperature must be raised to a certain point before the oxidation can begin, and this point can not be reached until the moisture is evaporated, which uses up a good deal of heat.

This process of decay is continually going on in our bodies; but during life the matter which is burned up is being constantly renewed from the food we eat. The body is not only decaying, as dead animal matter decays, but it is also wearing out. With every motion a part of the muscles is actually consumed, and must be replaced by fresh material.

The heat of the body is likewise due to combustion, and must be kept up by proper fuel, like the fires in our stoves and furnaces. The products of all this burning are carbonic acid and water, which pa.s.s out of the body through the lungs.

The rusting of metals is a slow combustion, and scientific men have proved that, like decay, it develops heat. Iron can be easily burned in pure oxygen, with the production of intense light and heat. Zinc and some other metals can be burned in the air if heated very hot, and most metals are rapidly consumed in the flame of the oxyhydrogen blow-pipe.

Indeed, every form of matter known to us can be burned, unless it has already been burned. All substances belong to one of these two cla.s.ses--those that will burn, or unite with oxygen; and those that have been burned, or are products of oxidation. Water belongs to the latter cla.s.s, and so do nearly all the rocks and solid matter of the earth.

Slow burning sometimes becomes rapid, and then we have what is called _spontaneous combustion_. When cotton or tow which has become soaked with oil is laid aside in heaps, the oxygen of the air begins to unite with it; but the heat developed causes the oxidation to go on faster and faster, until in some cases the ma.s.s bursts into a flame. The same thing sometimes takes place in moist hay, the moisture starting the process, as explained above, and the confined heat increasing until it is sufficient to set the heap on fire.

[_By special arrangement with the author, the cards contributed to this useful series, by_ W. J. ROLFE, A.M., _formerly Head-Master of the Cambridge High School, will, for the present, first appear in_ HARPER'S YOUNG PEOPLE.]

[Ill.u.s.tration: GETTING WEIGHED.]

DAVE'S GREAT LUNCH.

BY J. B. MARSHALL.

It was the great day at the State Fair, and the sidewalks were nearly deserted as Dave Burt went down Main Street toward the post-office. As Dave approached the Town Hall, or the City Hall, as the good people of Rawley were pleased to call that fine building, he glanced up at it, and saw Mr. William Henry Barrington, the great lawyer, standing at one of the large windows of his office. Mr. Barrington was frowning, and looked up the street and down it as if impatiently waiting for some one.

"I'll bet he's mad 'cause he can't go to the fair," thought Dave.

A few days before, Billy Barrington, a nephew, had been telling the boys of that fine office, with its bra.s.s-studded revolving chairs, great bookcases of books, and a private room where the great lawyer ate his dinner, which was sent up to him on a dumb-waiter from the restaurant in the bas.e.m.e.nt of the City Hall the moment he touched an electric bell.

Dave was recalling all the delightful possibilities of such a room, when click! went something on the pavement before him.

"A penknife," said he, picking up the article, and then, looking in vain among the branches of the tree for its owner. Examining the knife, he noticed a slip of paper shut in under the largest blade, and on which was written:

"Five Dollars Reward! I am on the City Hall roof, and can't get down, as the spring-latch door has blown closed. Please send the janitor to release me.

"CHARLES M. WILSON."

"Why, he's our Governor!" said astonished Dave, aloud, and started to look for the janitor. Dave had been on the roof with his father only the day previous, and knew just how the door would act if it was not fastened back.

Stout old Billy Simms, the janitor, in his shirt sleeves, had comfortably propped himself back in an arm-chair to take a nap, when rap-rap-rap sounded on the door. Billy's "office," as he called it, was on the ground-floor of the City Hall.

"Well, boy, what's wanted?" gruffly demanded old Billy, having opened the door and discovered Dave.

"Why, the Governor's shut out on the roof, and can't get down," said Dave, handing Billy the paper. "He must have been looking at the Fair Grounds."

Old Billy lowered his great silver-rimmed gla.s.ses from his forehead to his nose, and read the paper. He gazed for a moment in a queer way over his gla.s.ses at Dave, and then laying his hand pretty heavily on Dave's shoulder, said, "Come with me."

"I haven't time; and, besides, I don't want any reward," answered Dave.

There was a small room, or closet, back of Billy's "office," toward which he moved, holding fast to Dave.