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"I think we ought to erect a monument to Monsieur Clay?" |
"It would be a fitting thing to do, because at the end we are all bound to go back to him." |
"I believe you said, Professor, that we should have to grind up the coke and then mix it up and make plates out of it?" |
"Yes; we can use either carbon or copper for the negative plates." |
"What are the other plates?" |
"The positive. That is what I wanted the zinc for, which we made several weeks ago." |
"Why should we have positive and negative plates in a battery?" |
"Everything must have an opposite. If there is an up there must be a down; there would be no darkness without light; no heat without cold; no strength without weakness, and no joy without sorrow. Like all these things, the electric current flows from one to the other." |
"But in electricity the current flows only one way, does it not?" |
"In the primary battery that is the case; but when electricity is generated and sent over the wires, the natural current flows in both directions -- that is, it goes in one direction as much as in the other." |
"I do not understand what you mean by that." |
"The current alternates. What is meant by that is this: For an instant the current flows from the positive to the negative, and the next instant it flows from the negative to the positive, and so on, making the alternate current." |
"Then the primary battery we are going to make will be another kind of current?" |
"We shall make what is called the direct current which goes in one direction only -- that is, within the battery it moves from the positive plate, the zinc, to the copper plate, or negative, and outside of the battery it moves from the negative to the positive plate." |
"Why does it do so?" |
"In order that you may understand, I shall make a drawing so Harry will not have so much trouble in arranging the parts. So if you will examine the sketch (Figure 25), you will see that the clay cell, which we are to make, has in it the two electrodes, A and B. That is what they are called when they are spoken of toget... |
Fig. 25. PRIMARY BATTERY |
"The liquid in the cell, marked C, is used as the electrolyte, and for that we shall take some of the sulphate of copper which the copper ore furnishes. A good strong salt solution would also answer the purpose. The two electrodes are separated, and a wire connects the two outside of the cell. Now you will notice that ... |
"I can understand it now. The current from the battery will always go from the negative to the positive pole." |
"You are mistaken. I am glad you referred to that. It shows the importance of using correct terms. You must not confound the terms 'negative plate' with 'negative pole.' All currents leave the battery or dynamo from the negative plate, but that negative plate is called the positive pole of the dynamo." |
"It seems to me that is a curious way to do it." |
"Such is the case, however; but there is no real positive or negative in the alternating current, so that either side may be termed positive or negative." |
Work on the battery continued for some days, as lack of fine tools made much of the work difficult, and in doing this work, as in everything else, a certain amount of preparation was necessary. They had no screws, and no facilities for making them, so a substitute had to be devised, but the difficult part now to encoun... |
"A battery is of no use unless we can have wire, and it will be a big job to beat out wire long enough for our purposes," Harry observed as the battery neared completion. |
"Then we must draw some wire?" |
"From what?" |
"From the copper?" |
"Is that better than iron?" |
"Copper should be used for several reasons; first, because electricity travels through a copper wire more easily than through iron, and second, for the reason that copper is more ductile than iron, and can be drawn into a wire with greater facility." |
"Doesn't electricity flow through different substances at the same rate of speed?" |
"Yes; but it retards the amount or the force." |
"You say, 'Amount' or 'Force.' I can understand that if applied to water, that there might be a large or small quantity of water, or a greater or less pressure, but I do not see how this applies to electricity." |
"In measuring the pressure of water, calculation is made by taking the height of the water in the tank. For every 28 inches in height a column one inch square weighs one pound. This represents the force of the water when it issues from the orifice below. Now the orifice may be large or it may be small. The amount or qu... |
"Yes; I understand the difference, now." |
The drawing of wire is not a difficult task where facilities are at hand, but it must be remembered that all their tools were of the crudest kind. Harry had prepared a number of bars of copper, each having been beaten out to form pieces about ten inches long and a half inch thick. A steel plate about three-eighths of a... |
Fig. 26. Template for Drawing Wire. |
When all was ready Harry was instructed to hammer out one end, so it would go through the largest hole. The projecting end was then grasped by a pair of heavy pliers, and pulled through, so that the bar was formed the size and shape of the first hole, and of course the bar was lengthened. The end was then hammered out ... |
It was laborious work, and a long time was consumed in fully drawing out each bar. In this way a quantity of serviceable wire was prepared. |
"Why does this plate get so hot when we pull the wire through?" |
"Why do you make a fire by rubbing together two substances?" replied the Professor. |
"On account of the friction." |
"For that same reason you are making the heat in drawing the copper through the die." |
"But I notice that if I hammer a piece of cold iron it will get hot. There is not any rubbing motion there to make friction." |
"Do you think not? You have by that means made the most intense friction. The iron is composed of tiny particles, called atoms, and molecules. When you strike a piece of iron you force these particles in among themselves, and the friction caused by this movement produces the heat." |
"Is that true of all substances?" |
"Yes." |
"Well, if air is forced together will it heat in the same way?" |
"Yes, and for the same reason. The tiny particles, of which air is composed, move among each other with such rapidity, under compression, that the heat their frictional contact develops is dependent on the pressure exerted." |
"You used the terms 'atom' and 'molecules' a moment ago. What is the difference between them?" |
"A molecule is always composed of two or more atoms. An atom is smaller than a molecule, for this reason. Furthermore, an atom comprises only one substance. A molecule has two or more substances in its make-up. For instance, water is composed of two parts of hydrogen and one part of oxygen. One molecule of water, there... |
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