Annabella Learns about Batteries CONSTANCE SHARP SAMMIE San Marino, California
q
pink!" exclaimed the bald but geT ELL,strikeme . nialProfessor. "It's my little friend, Annabella!
Where in the world have you been all this time?" He shook her hand cordially. "Oh, Professor, I've been pretty busy. I've been, you might say, helping in the war effort. Every evening but Monday I've been on duty a t the Canteen. A junior hostess, you know. It really doesn't leave me much time for books and stuff." "No, I could see from your mid-term records that you were pretty busy!" The Professor's eyes twinkled. "But what brings you here so early in the morning?" "Because my brother is home on leave from the South Pacific. Say, he's wonderful, Professor! And he really is smart. He's an aviator, you know. And he says it's time I started to learn something besides how t-to cut a rug! Though I'm pretty good a t that if I do say so myself. Well, he says I've got to start leaning something important because he says they need smart people in the world and not just jitterbugs. But I think they are both important, don't you, Professor?" Annabella looked up a t the smiling Professor. "I certainly do, Annabella. Why can't a person be smart and like to jitterbug!" "Oh, I hoped you'd say that," answered Annabella in a relieved voice. "Then may I come in? I want to learn something special today, please." "You do! Then of course, come right in, and sit down." He indicated the little footstool Annabella
always preferred. Then he seated himself in his big
leather armchair, carefully removed his horn-rimmed spectacles, and put them on the desk in front of him. Annabella flounced down on the footstool at his feet. "Yes," she went on earnestly, "I've decided to takewhat do you call it-yes, electronics. The first thing I'd like to know about is batteries. Because we are always having trouble with the batteries in our portable radio, and if I learn about them, then I can fix them. Can you explain them to me, Professor?" "I'm afraid no one can fix dry batteries, Annabella. And furthermore, I am a chemist, and not an electrician." "Oh, but it's the chemistry part of batteries I want to learn about, Professor. About all the little ions and things inside, like you told me about last time. I lmed that! And besides," she added thoughtfully, "I think I will invent a kind that you can fix as soon as I learn about them. So-please!" And she looked up hopefully. "We--ell," smiled the Professor, "we'll talk a little about dry batteries, if you like. That is, about primary batteries. They are batteries that can't be renewed, recharged. Let's see now." He thought a moment, and then started: "Everything around us is made up of billions and trillions of atoms and molecules. All our tables and chairs, and our food, and everything, even batteries. These atoms and molecules are something like tiny solar systems, each separate, and with lots of space in between and all around. There is a positively charged nucleus of matter which would correspond more or less to our sun; and one or more infinitesimal, negative electrons, flying in definite paths around this 'sun.'
These tiny electrons would correspond pretty much to our planets, flying around the sun in set paths! In ordinary atoms, or in molecules (which are just two or more atoms joined together), these nucleus particles (the 'suns') and the electrons (the 'planets') are per-
fectly balanced. The positive (+) and the negative (-1 charges just balance and neutralize each other. "But if for any reason one (or maybe more) of these tiny negative electrons flies away from its 'sun,' the positive nucleus, the poor atom will become unbalanced. It will have more of a positive charge than a negative. Then i t is called an ion." "Oh, yes," cried Annabella, "I remember about ions from our last talk!" "Good," said the Professor, encouragingly. "Now, if this 'wandering Willie,' our little electron, attaches itself to another staid, neutral atom or molecule and starts buzzing around it, just as though it belonged there, this atom or molecule will become unbalanced too. Only it will have a more negative charge than positive. So it's not neutral any longer either, and it has also become an ion. "An interesting thing is this: A salt is made up of these positive and negative ions, fitted into a regular crystalline pattern. Take common table salt for instance, sodium chloride (NaCl): It is comprised of positive sodium ions (Na+) and negative chlorine ions (Cl-), fitted into their particular crystalline pattern. And when this salt is put into water, these little ions become free to move around independently. Long, long ago when the salt was first made, each sodium atom had lost an electron and each chlorine atom got hold of an extra electron." "How amazing!" exclaimed Annabella. "Yes, isn't it. Of course if you should put another salt, ammonium chloride (NH4Cl) into water, i t will separate into positive and negative ions too. In this case the positive ions will be ammonium (NH4+), and the negative ions chlorine (Cl-). Strange, isn't it?" "Very," agreed Annabella. "Well, now let's get a closer view of our primary battery. If we stick a piece of zinc metal and also a piece of carbon rod into a solution of this ammonium chloride (NHIC1), and connect the two with a wire, what do you suppose happens?" "Oh, I don't know, Professor. But I do wish I could become so little that I could really see what happens inside that solution. I wish I could be Alice in Wonderland!"
"Perhaps you could if you wished hard enough.
Why don't you just close your eyes and pretend you are even smaller than Alice in Wonderland?" Annabella shut her eyes tightly. "I believe I can see!" she cried. "Yes, I can see these little ion people moving around like mad. Will they bump into me, Professor?" "No, not if you're careful," smiled the Professor. "And notice, you're not even wet though you are right in the water. That is because there are such big spaces in between the water and salt ions, and if you are small enough you won't get wet a t all!" "Oh, yes. It's just like Main Street. Lots of cars but no danger if you watch out." "Do you see lots of 'little cars' crowding around the carbon rod, and lots of other 'cars' crowding around the zinc rod? Concentrate now, Annabella." "Yes, I believe I do!" Annabella cried. "It's congested trafficisn't it? But more orderly than I thought." "That's right, Annabella. They all follow the traffic laws. But seriously now-and you had better wish yourself back here on the footstool and listening with both em-this is what happens: When you put a piece of zinc and a piece of carbon rod into the salt solution, the zinc has a great desire (we chemists call it 'tend-
ency') to dissolve and become little positive ions (Zn++) in the solution. The carbon has practically n o tendency to dissolve a t all. Don't ask me now why the zinc wants to break up into ions so much more than the carbon. It has to do with the way the zinc atoms and the carbon atoms are made, relatively speaking, and that story will have to wait for another day. "Well, anyway, quitea lot of zinc becomes zinc ions (Zn++). But that of course leaves a whole lot of electrons (e-) left over. Because, as you know, Annabella, it takes negative electrons to balance positive zinc ions to make plain neutral zinc. We can picture what happens by an equation like this: You know what an equation is, don't you, Annabella?" "Oh, yes, Professor. You told me last time I was. here. It's a sort of shorthand that chemists use to tell what is happening, isn't it?" "Yes, indeed. That's exactly right. So this equation merely says that our metallic zinc breaks up into little zinc ions (Zn++) and tiny negative electrons (e-). These electrons are left high and dry, without anything positive to hang on to, when the zinc becomes Zn++ and leaves them behind. "But there is a happy solution because on the other-
hand, ammonium ions have the ability to take up electrons in this way:
resulting finally in ammonia and hydrogen gas. Now, the ammonium ions which happen to he touching the carbon rod will try to remove electrons from it. And since the carbon is connected to the zinc by a wire, through which electrons can pass freely, they will run over from the zinc, where their 'pressure' is high, so to speak, to the carbon where their 'pressure' is lower, because the ammonium ions are snapping them off." "Why don't these ammonium ions grab the little electrons right a t the zinc pole?" asked Annabella. "Because, you see, the positive zinc ions repel the ammonium ions which are also positive. I'm sure you know that positive charges repel each other, while a positive and a negative charge always attract each other. So the ammonium ions don't have the chance to reach the electrons on the zinc side. "But the wire is a good easy path for electrons to travel through. So they rush over from the 'high pressure' side to the 'low pressure' side where the ammonium ions immediately grab them off. And this stream of electrons is nothing more nor less than an electric current! Did you know that?" "For goodness' sake, Professor! You mean the same kind of current that runs my mother's vacuum cleaner, and rings our doorbell?" "Exactly,AnnaheIla,if you happen to have direct current a t your house." "Well, I'm certainly glad to know that!" exclaimed Annabella. "And say, Professor, you told me last time that nature is always trying to even things up. Is that why the little electrons rush around from the zinc, where there are lots of them, to the carbon, where there are hardly any?" "That's absolutely right. I'm glad to see you remember your lesson so well. And let's remember this time that a t the zinc pole, little zinc ions (which go into solution) and little negative electrons are both being produced. The electrons hurry over to the carbon pole where the ammonium ions of the dissolved salt immediately snap them up, forming ammonia and hydrogen gas. This hydrogen gas bubbles up through the solution and the ammonia stays down in it and is taken up by combination with the zinc ions." "I'll certainly try to remember that. It doesn't seem so hard." "Now the nice thing about all this," went on the Professor, "is that the little electrons have been streaming around from the zinc pole to the carbon pole, creating an electric current which we can use. Of course if we disconnect the wire, pretty soon the ammonium ions will have grabbed off all the electrons that are left, and since no more electrons can reach the carbon pole, all action quiets down. But if we keep this wire connected between the zinc and the carbon, electrons will keep zipping though the wire and the ammonium ions will
keep picking them off. We have then, you see, a chemical action that acts just like a pump to keep a stream of electrons surging through the wire. That is, to keep the electric current flowing. Which of course is the object of a battery. And this current can be used to light a flashlight and ring a doorbell and lots of other things. "So, if the wire remains connected, and as long as all the zinc has not gone into solution as ions, some electric current will flow through the wire. . . . "And that, my dear Annabella, is all there is to the way a primary battery makes electric current!" The Professor leaned back in his leather armchair and looked down a t Annabella. "Did you understand what I was telling you?" "Oh, yes, Professor, I am sure I did!" cried Annabella. "And it's wonderful to hear about it. But--one thing troubles me." Annabella wrinkled her brows. "Why doesn't a11 t h i s t h i s ammonium chloride solution spill out when you cany these batteries around in flashlights? That's what I want to know." "My dear child, that's easy," answered the genial Professor. "I was just telling you about a simple primary battery. There are other primary batteries too, by the way, that use different materials for electrodes and different solutions. But the way they work is just the same. "A lot of smart men did a lot of smart work on battezies years ago. The ordinary dry battery you see in flashlights uses zinc and carbon electrodes, all right, but they have it fixed so nothing leaks or gets messy a t all. The next time you find an old worn-out battery around the house, slice i t open with your little hatchet, Annahella, and look inside. It's quite interesting.'' "Oh, I will. But I can't wait, Professor. Do tell me about it now, please," urged Annabella. "All right. But I have a chemistry class in a few minutes, you know." And here he took out his large gold watch and carefully laid it down on the desk where he could watch the minute hand move around. "The dry cell we use in flashlights and portable radios isn't really dry a t all. It has ammonium chloride solution in it, hut soaked up into a porous mass in the cell. There is something else mixed with it too, around the carbon pole. It's a black powder called manganese dioxide (Mn02)." "What is that for?" interposed Annabella. "It's simple. You remember the hydrogen gas that forms bubbles around the carbon pole. You can't have gas bubbling up through a dry cell very well. So they put this black powder in there and it combines right away with the hydrogen bubbles as soon as they form. And that is one worry taken care of. This is the equation (chemical shorthand, you know) of what happens: Ha+2MnOz+MnzOa+I&O Pretty good idea, isn't it? If they didn't do that, the hydrogen bubbles would stick all over the carbon pole, and bubble up through the solution too. This would cut down the area of useful carbon. It would resist
the whole action that makes the electrical current flow sometimes called commercially. This pressure, or voltin the wire, because the ammonium ions couldn't reach age, is always about 1'/2 volts. But the important thing the carbon to pick off the electrons. When the hydro- to remember is what really happens inside that battery. gen is allowed to cover up the carbon-which it isn't in And I think you understand that now, don't you, my a good battery-it is called polarization. dear?" "So naturally this black powder is called a depolarHere the Professor peered down a t Annabella, who izer. They don't have to worry a t all about the am- was still listening intently to his every word. She monia gas (NH3 that forms along with the hydrogen, nodded slowly, still thinking about "high pressure" and because it immediately combines with the zinc ions, as "low pressure" and how nature always tries to balance things up. I told you before. "And now, I must get along to that chemistry class. "And to keep everything as simple and practical as possible, instead of a regular zinc rod, they make the I hope you have learned a lot about batteries. It will whole battery can out of zinc. Really then, the whole be a good start to your new career." Here the Professor can acts as the zinc pole. Then they connect binding smiled, and reached over to pat the top of Annabella's posts to the carbon pole (which isn't allowed to touch golden head. Then be picked up the big watch and the zinc can of course) and also to the zinc, so that wires slipped i t into his vest pocket. Replacing his spectacles can easily he attached to them. The carbon binding carefully on the bridge of his nose, he rose slowly from post is called the positive pole, the zinc post the nega- his comfortable armchair. Annabella roused herself from thoughts of electrons. tive pole. "A piece of heavy corrugated paper is often placed on She jumped up and grasped the Professor's hand, her top of the zinc can, and on this is sometimes put a layer face beaming her gratitude. "Oh, this was wonderful, Professor! And so very, of sand. Over all this is poured melted pitch or wax. This keeps everything inside from spilling out, and very interesting. I don't think it's hard a t all when you everything outside from getting into the battery and get i t straight. Thank you so much! Batteries are spoiling the chemical action. fun! I certainly am going to like my new career! "Well, Annabella, these batteries keep right on pro"Now I'm going right home to tell my brother all ducing electric current until, theoretically, all the zinc about it. Will be be surprised!" is dissolved. But before this actually happens, the manganese dioxide usually fails to absorb all the hydrogen, and the hydrogen then bubbles up all around the carbon and slows down the battery action almost to a stop. "Incidentally, the pressure (the voltage as electricians call it) of the current of electrons zipping through the wire doesn't depend a t all on whether the battery is a great big one or a very little thing. It is always about the same as long as it is made of zinc and carbon and And off she ran. ammonium cbloride-'sal ammoniac,' as this solution is 19,490 (1942).] [Editor's Note: For a previous article in this series see Tms JOURNAL,
