“The cause of the explosion and the bursting of the bottle was the steam, which, having no way of escape, accumulated and exerted against its prison walls a stronger and stronger pressure as the temperature rose. A time then came when the vial could no longer resist the pressure of the steam, and it burst to pieces. They call elastic force the pressure exerted by steam on the inside of pots that hold it prisoner. The greater the heat, the stronger the pressure. With heat enough it may acquire an irresistible power, capable of bursting, not only a glass bottle, but also the thickest, most solid pots of iron, bronze, or any other very resistant material. Is it necessary to say that under those conditions the explosion is terrific? The fragments of the pot are thrown with a violence comparable to that of a cannon-ball or a bursting bomb. Everything standing in the way is broken or knocked down. Powder does not produce more terrific results. What I have just shown you with the glass vial is also not without some danger. You can be blinded with this dangerous experiment, which it is well to see once under proper precautions, but which it would be imprudent for you to repeat. I forbid you all, understand, to heat water in a closed vial; it is a game that might cost you your eyesight. If you should disobey me on this point, good-by to stories; I would not keep you with me any longer.”
“Don’t be afraid, Uncle,” Jules hastened to interpose; “we will be careful not to repeat the experiment; it is too dangerous.”
“Now you know what makes the locomotive and a great many other machines move. In a strong boiler, tightly closed, steam is formed by the action of a hot furnace. This steam, of an enormous power, makes every effort to escape. It presses particularly on a piece placed for that purpose, which it chases before it. From that a movement results that sets everything going, as you will see in the case of the locomotive. To conclude, let us remember that in every steam engine the essential thing, the generator of the force, is a boiler, a closed pot that boils.”
CHAPTER XLIX
THE LOCOMOTIVE
UNCLE PAUL showed his nephews the following picture, and explained it to them.
An old-time Locomotive
“This picture represents a locomotive. The boiler where the steam is generated, the boiling pot, in short, forms the greater part of it. It is the large cylinder that goes from one end to the other, borne on six wheels. It is built of solid iron plates, perfectly joined together with large rivets. In front the boiler terminates in a smoke-stack; behind, in a furnace, the door of which is represented as open. A man, called a stoker, is constantly occupied in filling the furnace with pit-coal, which he throws in by the shovelful; for he must keep up a very hot fire to heat the volume of water contained in the boiler and obtain steam in sufficient quantity. With an iron bar he pokes the fire, arranges it, makes it burn fast. That is not all: skilful arrangements are made to utilize the heat and warm the water quickly. From the end of the furnace start numerous copper pipes which traverse the water from one end to the other of the boiler, and terminate at the smoke-stack. You will see some in B where the picture supposes a part of the casing taken away to show the interior. The flame of the furnace runs through these pipes, themselves surrounded by water. By this means the fire is made to circulate through the very midst of the water, and so steam is obtained very quickly.
