Charlotte Connelly, University of Cambridge
We are moving forward in time a few more years now, to a discovery that changed the lives of countless people. In 1799, scientists discovered a way to generate something that today, we just couldn’t live without - electricity. Speaking with Chris Smith, historian Charlotte Connelly assembled a replica of the first ever battery; but she began by explaining what people understood about electricity in the 1700s...
Charlotte - Everyone knew about thunderstorms and lightning. They knew that that was electricity. They knew about things like electric eels, but most importantly, in 1780s, an Italian called Luigi Galvani had been doing experiments with frog’s legs and he discovered that if you take two pieces of different metal and place them at either end of a frog’s leg’s nerve, it makes the frog’s leg twitch.
Chris - Wasn't this the same guy who used to hang frog legs on metal hooks on the metal fence in his garden and he saw them twitching during thunderstorms?
Charlotte - Everyone’s got to have a hobby. Absolutely, yeah. He did that after he made this discovery. So, he had seen the twitching. He thought, “Oh, I wonder if this is electrical” and he made the link and then he was doing the experiment with the thunderstorms. And his theory was that there was a special kind of animal electricity that was coming from the frog’s legs and was causing this reaction.
Chris - How was that then taken from the concept of animal electricity to the electricity manifest in the environment and then also making electricity on tap?
Charlotte - Well, lots of people got very excited by what Galvani had discovered and one particular person, Alessandro Volta was doing some more experimenting. To begin with, he thought, “Yeah, this animal electricity makes sense.” And then as time went on, he began to question it and thought, “Well, maybe it’s not as universal as it might be.” So, he thought, “Is there a way of getting similar results without using the frog’s legs?” he thought there was maybe something about the two different metals. So, he came up with a contact theory of electricity, about contact between two different metals.
Chris - Can you recreate this experiment for us?
Charlotte - I can. So, I've got slightly different ingredients. What Volta did, it was a real kitchen top experiment. He took some silver coins that were in circulation at that time. He got some zinc, cut to the same size because he thought contact between two different metals, that's important. He placed one on top of the other and then he thought, well, there was some fluid in the frog’s legs. So, he took some cardboard and made it damp. He found it worked better with salt water.
Chris - So actually, just looking at this, what we have in front of us are a whole load of squares. These are an inch, an inch and a half square pieces of – what metal is that one? That's quite heavy. So, that's zinc. That's a silvery colour and then we’ve got these coppery coloured sheets. Are they copper?
Charlotte - They are copper. Copper is rather cheaper than silver and lots of people later on went to use copper.
Chris - And then we’ve got these things that look like the kind of thing you'd put on a wound in the hospital. They are the things you put on a wound.
Charlotte - Precisely. They happened to be exactly the same size and unlike cardboard, they don't stick to the zinc.
Chris - So, these are Volta’s bits of cardboard.
Charlotte - Exactly. So, we take a piece of zinc, we place that down. And then because we’ve got a slightly more advanced theory than Volta, we put our bits of cardboard in between the two. So, we first dip it in our saltwater and we place that on top.
Chris - And so then what we’re going to do is put on top of the cardboard piece a piece of copper.
Charlotte - That's right. So, we have a layer of three things, zinc, cardboard, copper and then we carry on, we do it again – zinc, cardboard, copper, zinc, cardboard, copper.
Chris - And here’s one magically you made earlier. This is quite big. This is 6 inches high of these.
Charlotte - This is a 20-cell layer. So, I've done that 3 layers 20 times over.
Chris - Scientifically speaking, what’s actually going on in each of the little layers in the battery?
Charlotte - So, in each cell, you get some free electrons that move by potential energy to one side of the surface so from the zinc to the copper. And because we’ve got lots of them piled up, that happens more so you get – in today’s terminology – higher voltage and no marks for guessing where voltage comes from, given that we’re talking about Alessandro Volta. So, the greater your pile, the more layers you have, the more voltage or electromotive force you have. And then what happens when you create a circuit is all of that potential energy discharges and you get a bit of a sensation which I think we should probably get someone to experience.
Chris - Who would like to volunteer to help us with our battery? What's your name?
Amelia - Amelia.
Charlotte - We’re going to get Amelia to put one finger from each hand in the saltwater. So, she’s a really good conductor. Now, with your left hand, I would like you take this piece of zinc wire which is attached to the bottom piece of zinc in the pile. With your right hand, I’d like you to touch the very topmost piece of copper.
Amelia - It felt like a static electricity shock which I just had twice.
Charlotte - Very good and I think we can get a stronger shock if you're feeling brave, do you think?
Amelia - Yeah.
Charlotte - So, I'm giving you a piece of copper to take in your right hand. So, Volta discovered that if you touched the pile with pieces of metal that he got a stronger shock. So, same again.
Amelia - It did feel much stronger.
Charlotte - Very good. So Volta didn’t have a way of measuring how much electricity was coming out of these things. So, he said things like, “I got a shock up to my knuckle or a shock up to my wrist.” Do you think that would be a good way to describe it? Did it feel like it went further?
Amelia - Yes, it did.
Chris - Thank you very much, Amelia. Is there any way we can measure this or prove that we are actually making some electricity so people at home believe us?
Charlotte - Well, I have got a buzzer and if I attach it, hopefully, it’s going to make funny noise. Now, I'm just going to dip the ends in our saltwater to help it conduct a bit. So, if I take the negative side and attach it to the zinc and the positive side and attach it to the top, (beep).
Chris - No. the fire alarm has not gone off. It is working. Charlotte, how did this change people’s perception of electricity and also, what did it enable them to do once they could make cells like this and batteries like these voltaic piles we’ve created here?
Charlotte - Well, it took off really quickly because it was something you could do at home with really simple equipment. So, loads of people started experimenting and within weeks, a couple of people, Nicholson and Carlisle were their names, took a pile like this, stuck their ends in water and found out that it gave off hydrogen and oxygen which as we learned earlier, if you put them together, you get water. And this led to all sorts of experiments and a new discipline called electrochemistry. So, Humphrey Davy was famous for having a massive pile. In 1807, so only 7 years later, he started coming up with all sorts of new elements that he isolated and potassium and sodium were the first ones.