Monday, December 27, 2010

The No-Frog Battery

In Lecture 12 of The Joy of Science, Prof. Robert Hazen tells the story of the first electric battery. In 1799, Alessandro Volta was the first person to devise a way to chemically generate electricity without the use of frogs. I decided to try this experiment at home.

Luigi Galvani and his wife Lucia discovered that dissecting frog legs
with a scapel near an electrostatic generator caused the muscles to jump.

We had tried to make a Lemon Battery back when we were doing chemistry. We were not successful. I was all ready to go out and buy a bag of lemons and try again, when I came upon this Tiny Lemon Battery Instructable. The author shows many different ways to create what one commenter dubbed "nano-batteries" using the bare minimum of materials and only a few drops of lemon juice. Since I had a bottle of lemon juice in the fridge, and the other materials were easily scrounged from our science and art supplies, we were able to make a few different types of batteries in the course of a morning -- two of which actually worked!

Method One: Copper and Aluminum Foil Batteries


copper foil (available in craft stores)
aluminum foil (from the supermarket)
facial tissue (Kleenex)
multimeter or voltmeter
disposable plate (to work on)
dish soap or lemon juice

  1. Cut a piece of copper foil about 1 inch by 2 inches.
  2. Separate the tissue into layers. Cut a piece about 1 inch by 3 inches.
  3. Cut a piece of aluminum foil about 2 inches square.
  4. Layer the materials so that the aluminum foil is on the bottom, the tissue is in the middle, and the copper is on top. Fold the aluminum foil so that the edges wrap around the tissue and copper foil as shown above. This is your battery.
  5. Place the battery on a plate. Soak the paper with either dish soap or lemon juice. (We tried one of each.)
  6. With your voltmeter, measure the voltage generated by placing one terminal on the copper and one on the aluminum. We got up to half a volt of electricity from our primitive Galvanic cell batteries.

Method Two: Copper and Zinc Wire Battery

2 inch long piece of zinc-plated steel wire ("galvanized" picture-hanging wire works well)
4 inch long piece of uncoated copper wire, as thin as possible
a layer of Kleenex (see above)
disposable plate
lemon juice or dish soap

  1. Cut a piece of tissue about 1 1/2 inches long and 1/2 inch wide.
  2. Wrap the tissue layer around the steel wire, leaving the ends uncovered.
  3. Coil the copper wire around the tissue, being sure not to touch the steel wire inside. Make the coils as close together as possible without overlapping. 
  4. Soak the paper in lemon juice or soap as above and measure the voltage!
The Instructables page has directions for several variations, which include making several batteries and attaching them in series to light an LED, and flower and animal "sculptures" which use lemon juice to light up attached LEDs using the same techniques. One variation which we tried but did not (yet) get to work was to make tiny batteries from coils of wire inside lemon juice-filled drinking straws sealed with hot glue. Although the cells we made looked right, we could measure no voltage from them. We'll write an update post when we've got a few more designs to show off!

Wednesday, December 15, 2010

Second Law of Thermodynamics -- Keeping Butter Cool with Evaporation

The setup. Left to right: the control, Anthony's experiment (The cup of butter was kept in wet sand,) and John's experiment, (The butter was put in a bowl of water, and covered by a ceramic pot and a cloth.)

After watching The Joy of Science lecture about the Second Law of Thermodynamics, I decided to spend a week focusing on entropy. Entropy is a concept that has always interested me, although I don't understand very well. I first read about it in a short story by Thomas Pynchon, and then ran into it again when I saw Tom Stoppard's play Arcadia. But despite its interest for writers, it doesn't seem to have inspired a lot of popular science videos we could watch. The only mention I could find in the archives of what is now my favorite science show, NOVA, was a show about Absolute Zero. Luckily, this topic proved to be interesting in its own right.
The Teachers Guide for NOVA programs often contain good hands-on science activities. In this case, however, I thought the activity -- using a thermometer to calibrate a homemade thermometer -- was a tad lame. But a mention in the show about the discovery that evaporating chemicals could be used to produce refrigeration did catch my attention. I started Googling for safe classroom-type activities the kids and I could do to recreate the 1823 experiment by Michael Faraday, but perhaps without the potentially explosive chlorine.

Taking the temperature of butter in a Butter Keeper
And then it occurred to me that I could use the concept of a Butter Keeper -- a porous terracotta holder that keeps butter cool through water evaporation -- to achieve the same purpose. (Ironically, the type of Butter Keeper which inspired this activity actually keeps the butter cool by sealing out air, not by cooling it!)

We looked at some different types of evaporative coolers, including a similar metallic evaporative cooler invented by a student when she was in high school. We then gathered some materials and tried making our own. Although we did get some cooling, the Butter Keeper works is most effective in hot, dry climates. Here are the directions for our experiments:

The materials.

  • room-temperature butter (we made a bowl of butter by whipping heavy cream; you could also soften some store-bought butter)
  • plastic wrap
  • digital food thermometer (about $15)
  • terracotta flower pots
  • terracotta flower pot dishes
  • disposable bowls and cups
  • sand
  • cloth (we used a bandana)
  • water
  1. Fill a small disposable cup with softened butter. Cover with plastic wrap
  2. Use the food thermometer to punch a hole through the plastic wrap and take the temperature of the butter.
  3. Use the materials on hand to design and assemble a Butter Keeper that will hold the cup of butter. The Butter Keeper should hold and absorb for an extended period. See the photos for ideas.
  4. Place the cup of butter in the Butter Keeper. Place another cup of butter next to it as a control. Check the temperature of both cups at regular intervals to see whether the butter in the Butter Keeper is cooler than the butter sitting outside at room temperature.

What We Did:

John built one using a cloth to wick up water from a dish holding the terracotta pot. This design was apparently used in Great Britain and Australia in the 20th century.

The preparation of John's experiment. The cloth wicked the water up over the pot to keep it wet.

John's experiment.
Anthony used a smaller container set into a terra cotta pot filled with sand and then dampened. That version comes from Africa, where it is known as a zeer, and is used to keep produce fresh in areas where electricity is unavailable.
The setup for Anthony's experiment.
The sand in this experiment serves the same purpose as the cloth in John's.
 What Happened: We assembled the Butter Keepers and set them out on a bench, next to an unprotected cup of butter. We kept the pots wet by periodically refilling the bowls as needed. When we started, the butter was 65 degrees. Within a few hours it had decreased to 62, while the control cup was at 70. While not a gigantic difference, it does show a noticeable drop in temperate, from both the un-refrigerated control and the actual room temperature. After a few days the butter did begin to smell bad, and we ended the experiment. Note: Our first thermometer, from Wal-Mart, died soon after we started. We bought a slightly better version from an upscale cooking equipment store, which worked fine.

Friday, December 3, 2010

Our Galileoscope

In Lecture 3 of The Joy of Science, Prof. Hazen talks about how Galileo used his telescope to explore the heavens, and was the first to observe the craters of the moon, sunspots, and Jupiter's moons. (In the process upsetting medieval European society by suggesting that the celestial bodies were not "perfect.")

We happened to have on hand a reproduction of Galileo's telescope, the Galileoscope. This inexpensive instrument was designed for student use during the International Year of Astronomy in 2009. Although it claims to have decent lenses, it is very lightweight and doesn't come with a stand, which makes it hard to use. We had never really used it, but this seemed like a good time to try again.

First, we set up the telescope for projecting sunspots on a piece of paper. (NEVER point a telescope at the sun!) Unfortunately, after checking, we found that we had picked a day that the sun really did have no spots! However, we were able to see the disc of the sun. We will have to try this experiment again.

A few weeks later on a particularly cool crisp night, I noticed that Jupiter was clearly visible near the almost-full moon. I set up the Galileoscope on our front lawn. The moon and Jupiter were so bright that they could be observed even with the streetlights shining. I had never seen the moons of Jupiter through a telescope before, but they were clearly visible in the Galileoscope. The four Medici moons were lined up horizontally, three to the left of Jupiter and one to the right. About a month later, with the conditions almost the same, I pulled the telescope out and took another look. This time the line of moons was tilted down towards the left, and there were two moons on either side of Jupiter.

I was unable to take any photos of Jupiter with my little digital camera. (The image above is from Wikipedia.) So instead I pointed the Galileoscope at the moon and took some photos of it. The craters of the moon can be seen along the right edge. To get the photo, I held the set the camera for landscape (so the focus would be infinity) and held the lens a little bit away from the eyepiece. I lined up the image of the moon on the screen and then shot the photo. Pretty nice, right?

We also watched Bertoldt Brecht's play Galileo, which I have seen performed live. It does a good job of showing the conflict between the scientist and the Church. A good book for younger kids, which we read many years ago is Starry Messenger by Peter Sis. That is the title of a work by Galileo, which was part of a museum exhibit we saw called A Very Liquid Heaven. I was very impressed with the large meteorite (below) which was part of the combination art and science exhibit.