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8. Ella. I-am sure there is nothing but clean water; I saw it put in myself.
9. Mr. W. But is it not very extraordinary that simple clean water should blow the lid off?
10. Thom. Not at all, father. When you told us about the expansion of cold water below forty degrees, we wondered; because we could not think that ice was more bulky than water; but there seems no reason to doubt that the hotter water becomes, the more room it takes up.
11. Mr. W. How does the heat do this?
12. Thom. By expanding the water.
13. Mr. W.- We know that; but how?
14. Thom. By driving the particles of steam further and further apart. •
15. Mr. W. Precisely so. The moment the particles of a drop of water become steam, they occupy eighteen hundred times as much room as they did before.
16. Thom. Therefore they press upon the lid eighteen hundred times more forcibly than water.
17. Mr. W. Its force is altogether irresistible. If this kettle were composed of iron an inch thick or more, the steam, if it could not escape, would burst it with ease.
18. Thom. Is that the reason why steam-boilers burst?
19. Mr. W. It is one reason, but not the principal one. If all the water in this kettle were boiled out, and it were full of steam, and if we corked it up tightly, and soldered the lid down, and still kept the fire blazing fiercely under it, it would burst at the weakest part. Perhaps the lid would fly off, or the side burst. The steam would rush out; and, if we were very near, we might be scalded.
20. Thom. Then when a boiler grows old and thin, if the pressure is very great, it bursts in the weak part, does it?
21. Mr. W. Just so; and ingenious men have made some portion of the boiler of a weaker metal; so that, if it should burst from the pressure of steam, it would hurt no one.
22. Amelia. I can not understand what you mean.
23. Mr. W. You see this kettle on the fire; now if we cork up the spout, and fasten the lid down, and let it boil, it will probably blow the cork out, and hit some one of you; but if, on the backside of the kettle, we have a part of it made of lead or tin, it will explode there.
24. Am. O, I see now.
25. Thom. But, father, this can not account for the tremendous explosions by which the boiler itself is thrown to a great distance, and even buildings are blown down.
26. Mr. W. I think not; but I will try to explain this. I need not tell you, who read the newspapers, of any particular accidents from the bursting of steam-boilers. Scarcely a week passes without an accident of this kind. Let us refer to the tea-kettle again.
27. Thom. It boils; and the steam is escaping from both the lid and the spout.
28. Mr. W. You recollect, I dare say, when we explained what the little explosions were, which were heard when the red-hot wick of a candle was wetted?
29. Thom. O yes! perfectly. The water, you told us, was composed of two gases, — oxygen and hydrogen,* — and that the heat of the candle converted the drops of water into these gases.
30. Mr. W. Quite correct; and I also explained that whenever oxygen became mixed with hydrogen, and a burning light was applied, the explosion was loud and violent.
31. Am. I recollect well being stunned by the explosion of a bladder filled with these two gases.
32. Mr. W. Well, I believe that steam-boilers burst simply from the pressure of steam; but when lives are lost, and
• pieces of the boiler are hurled with the violence of artillery, I believe the same thing takes place as when a drop of water falls into a candle.
* Ox'y-gen and Hy'dro-gen, the two gases which compose water, being In the proportion, by weight, of eight parts of oxygen to one of hydrogen, and by volume, 01 one of oxygen to two of hydrogen.
33. Thom. This might happen if the hoiler were nearly empty and the fire very fierce; but how could it happen when water was in the boiler? If there were only a table-spoonful of water left in the kettle, it would boil away, or be turned into steam.
34. Mr. W. All very good; but I believe it is not the water which is turned into these exploding gases, but the heated steam. You know the water is never at a temperature above two hundred and twelve degrees; afterwards it becomes steam.
35. Thorn. And also, what is very wonderful, the water keeps the bottom of the kettle from becoming hotter than itself.
36. Mr. W. But steam may be heated up to almost any degree. In Papin's Digester, which is only a steam-kettle with enormously strong and thick iron sides, the steam will rise to the height of six hundred degrees, — a heat which converts solid bone into jelly!
37. Thom. I think I see it; so long as there is water in the kettle, the bottom can not become red-hot; but there is nothing to prevent the sides from becoming so, if the fire be hot enough.
38. Mr. W. Certainly not.
39. Thom. Then, why may not the red-hot side of the kettle convert the steam into oxygen and hydrogen, and at last, having filled the boiler with this decomposed water, glow with a heat sufficiently intense to explode hydrogen? And when I remember with what violence a small bladder, filled with it, bursts, I can believe the explosion of a large steamboiler, filled with it, would be tremendous!
40. Mr. W. And so could I; and I firmly believe this to be the chief cause. Notwithstanding all these accidents and all this power, it has done for man what no other agent has ever equaled. It is his patient, unfed, untiring slave, requiring neither wages, nor food, nor raiment. Its power is truly wonderful, — almost sufficient to overturn mountains; and yet it sinks, powerless, into utter nothingness, at the touch of a little cold water!
Questions.—What is the subject of this lesson? 1-8. What is the first experiment in proof of the power of steam? 9 - 16. Explain why the lid of the tea-kettle was blown off? 17-20. What reason is given why steam-boilers sometimes burst? 21-24. How are steam-boilers made, and why are they made so? 25-40. !Iow are the explosions by which tbe boilers themselves are thrown great distances illustrated and accounted for? What are oxygen and hydrogen ? — What is the character of this lesson? Point out the first question. Which kind Is it? With what luflectionr should it be read? What is its answer? What inflection does it require? What is the next question? &c, &c. Point out the first exclamation. What Inflection doe* it require? Point out the next, fro'
LESSON XXIII. 1 %
1. Har'ness, to confine by harness.
1. Pu'xr, weak, small.
2. Way'ward, changing, uncertain. 2. Peas'Ant, a rural laborer.
S. Coors'er, a swift horse.
8. Cou'ri-er, a messenger sent in haste.
3. Out-strip'pa-d, outrun.
5. Ori-ent, eastern.
6. Fath'om-less, too deep to be measured. 7- Forge, to shape by hammering.
7- Fur'nace, a place for melting ores.
Articulate the cousonant combinations distinctly In the pronunciation of tbe fbl lowing words:—scorns, marked, outstripped, throne' wind, yielded, floods, depths muscles,
THE SONG OF STEAM. —G. W. Cutter.
1. Harness me down with your iron bands;
Be sure of jour curb and rein!
As the tempest scorns a chain !.
For many a countless hour,
And the pride of human power I
2. When I saw aij army upon the land,
A navy upon the seas,
When I marked the peasant fairly reel
As he feebly turned the tardy wheel,
Or tugged at the weary oar, — >
3. When I measured the panting courser's speed,
The flight of the courier-dove,*
Or the lines of impatient love, —
As these were outstripped afar,
Or chained to the flying car!
4. Ha, ha, ha! they found me at last;
They invited me forth at length;
And laughed in my iron strength!
On the earth and ocean wide,
Nor wait tor wind and tide.
5. Hurra! hurra! the waters o'er,
The mountain's steep decline,
The world — the world is mine ! —
Or those where his beams decline,
And the Orient floods divine.
* Cou'r'i-er-dovo. The courier-dove and carrier-pigeon ( Columba tabellaria) mean the lame bird. It is a native of Asia, and may be trained to perform the omce of a tatter-carrier. The letters are written upon the finest silk paper, and properly tied to the wing, It has been known to fly two thousand seven hundred miles in a day.