Fruit Battery

If you have fruit, a couple of nails, and wire then you can generate electricity to turn on a light bulb. Learn how to make a fruit battery. It's fun, safe, and easy.

Here's What You Need

• citrus fruit (e.g., lemon, lime, orange, grapefruit)
• copper nail, screw or wire (about 2" or 5 cm long)
• zinc nail or screw or galvanized nail (about 2" or 5 cm long)
• holiday light with 2" or 5 cm leads (enough wire to connect it to the nails)

Make a Fruit Battery

1. Set the fruit on a table and gently roll it around to soften it up. You want the juice to be flowing inside the fruit without breaking its skin. Alternatively, you can squeeze the fruit with your hands.
2. Insert the zinc and copper nails into the fruit so that they are about 2" or 5 cm apart. You don't want them to be touching each other. Avoid puncturing through the end of the fruit.
3. Remove enough insulation from the leads of the light (about 1") so that you can wrap one lead around the zinc nail and one lead around the copper nail. If you like, you can use electrical tape or alligator clips to keep the wire from falling off the nails.
4. When you connect the second nail, the light will turn on!

Learn More

• Citrus fruits are acidic, which helps their juice to conduct electricity. What other fruits and vegetables might you try that would work as batteries?
• If you have a multimeter, you can measure the current produced by the battery. Compare the effectiveness of different types of fuits. See what happens as you change the distance between the nails.
• Do acidic fruits always work better? Measure the pH (acidity) of the fruit juice and compare that with the current through the wires or brightness of the light bulb.

Baking Soda Stalactites and Stalagmites

Stalactites and stalagmites are large crystals which grow in caves. Stalactites grow down from the ceiling, while stalagmites grow up from the ground. The world's largest stalagmite is 32.6 meters long, located in a cave in Slovakia. Make your own stalagmites and stalactites using baking soda. It's an easy, non-toxic crystal project. Your crystals won't be as big as the Slovakian stalagmite, but they will only take a week to form, instead of thousands of years!

Baking Soda Stalactite & Stalagmite Materials

• 2 glasses or jars
• 1 plate or saucer
• 1 Spoon
• 2 Paper Clips
• Hot Tap Water
• Piece of Yarn, about a meter long
• Baking Soda (Sodium Bicarbonate)
• Food Coloring (optional)

If you don't have baking soda, but you can substitute a different crystal-growing ingredient, such as sugar or salt. If you want your crystals to be colored, add some food coloring to your solutions. You might even try adding two different colors to the different containers, just to see what you get.

Grow Stalactites and Stalagmites

1. Fold your yarn in half. Fold it in half again and twist it together tightly. My yarn is colored acrylic yarn, but ideally you want a more porous natural material, such as cotton or wool. Uncolored yarn would be preferable if you are coloring your crystals, since many types of yarn bleed their colors when wet.
2. Attach a paper clip to either end of your twisted yarn. The paper clip will be used to hold the ends of the yarn in your liquid while the crystals are growing.
3. Set a glass or jar on either side of a small plate.
4. Insert the ends of the yarn, with the paper clips, in the glasses. Position the glasses so that there is a slight dip (catenary) in the yarn over the plate.
5. Make a saturated baking soda solution (or sugar or whatever). Do this by stirring baking soda into hot tap water until you get so much added that it stops dissolving. Add food coloring, if desired. Pour some of this saturated solution into each jar. You may wish to wet the string to start the stalagmite/stalactite formation process. If you have leftover solution, keep it in a closed container and add it to the jars when needed.
6. At first, you may need to keep an eye on your saucer and dump liquid back into one jar or another. If your solution is really concentrated, this will be less of a problem. Crystals will start to appear on the string in a couple of days, with stalactites growing down from the yarn toward the saucer in about a week and stalagmites growing up from the saucer toward the string somewhat later. If you need to add more solution to your jars, be sure that it is saturated, or else you will risk dissolving some of your present crystals.

The crystals in the photos are my baking soda crystals after three days. As you can see, crystals will grow from the sides of the yarn before they develop stalactites. After this point, I started to get good downward growth, which eventually connected to the plate and grew up. Depending on the temperature and rate of evaporation, your crystals will take more or less time to develop.

Cloud in a Bottle Demonstration

Here's a quick and easy science project you can do: make a cloud inside a bottle. Clouds form when water vapor forms tiny visible droplets. This results from cooling the vapor. It helps to provide particles around which the water can liquefy. In this project, we'll use smoke to help form a cloud.

Cloud in a Bottle Materials

• 1-liter bottle
• warm water
• match

Let's Make Clouds

1. Pour just enough warm water in the bottle to cover the bottom of the container.
2. Light the match and place the match head inside the bottle.
3. Allow the bottle to fill with smoke.
4. Cap the bottle.
5. Squeeze the bottle really hard a few times. When you release the bottle, you should see the cloud form. It may disappear between 'squeezes'.

The Other Way to Do It Ok, here's the ideal gas law:

PV = nRT, where P is pressure, V is volume, n is number of moles, R is a constant, and T is temperature.
If we're not changing the amount of gas (as in a closed container) then if you raise the pressure, the only way for the temperature of the gas to be unchanged is by decreasing the container volume proportionally. I wasn't sure I could squeeze the bottle hard enough to achieve this (or that it would bounce back) and I wanted a really dense cloud for the photograph so I did the not-as-child-friendly version of this demonstration (still pretty safe). I poured water from my coffeemaker into the bottom of the bottle. Instant cloud! (... and a slight melting of the plastic) I couldn't find any matches, so I lit a strip of cardboard on fire, inserted it into the bottle, and let the bottle get nice and smoky (and melted more plastic... you can see the deformation in the photo). Dense cloud, no squeezing required, though of course it still worked.
How Clouds Form

Molecules of water vapor will bounce around like molecules of other gases unless you give them a reason to stick together. Cooling the vapor slows the molecules down, so they have less kinetic energy and more time to interact with each other. How do you cool the vapor? When you squeeze the bottle, you compress the gas and increase its temperature. Releasing the container lets the gas expand, which causes its temperature to go down. Real clouds form as warm air rises. As air gets higher, its pressure is reduced. The air expands, which causes it to cool. As it cools below the dew point, water vapor forms the droplets we see as clouds. Smoke acts the same in the atmosphere as it does in the bottle. Other nucleation particles include dust, pollution, dirt, and even bacteria.

Egg in a Bottle Demonstration

The egg in a bottle demonstration is an easy chemistry or physics demonstration you can do at home or in the lab. You set an egg on top of a bottle (as pictured). You change the temperature of the air inside the container either by dropping a piece of burning paper into the bottle or by directly heating/cooling the bottle. Air pushes the egg into the bottle.

Egg in a Bottle Materials

• peeled hard-boiled egg (or soft-boiled, if a yolk mess interests you)
• flask or jar with opening slightly smaller than the diameter of the egg
• paper/lighter or very hot water or very cold liquid

In a chemistry lab, this demonstration is most commonly performed using a 250-ml flask and a medium or large egg. If you are trying this demonstration at home, you can use a glass apple juice bottle. I used a Sobe™ soft drink bottle. If you use too large of an egg, it will get sucked into the bottle, but stuck (resulting in a gooey mess if the egg was soft-boiled). I recommend a medium egg for the Sobe™ bottle. An extra-large egg gets wedged in the bottle. Perform the Demonstration

• Method 1: Set a piece of paper on fire and drop it into the bottle. Set the egg on top of the bottle (small side pointed downward). When the flame goes out, the egg will get pushed into the bottle.
• Method 2: Set the egg on the bottle. Run the bottle under very hot tap water. Warmed air will escape around the egg. Set the bottle on the counter. As it cools, the egg will be pushed into the bottle.
• Method 3: Set the egg on the bottle. Immerse the bottle in a very cold liquid. I have heard of this being done using liquid nitrogen, but that sounds dangerous (could shatter the glass). I recommend trying ice water. The egg is pushed in as the air inside the bottle is chilled.

How It WorksIf you just set the egg on the bottle, its diameter is too large for it to slip inside. The pressure of the air inside and outside of the bottle is the same, so the only force that would cause the egg to enter the bottle is gravity. Gravity isn't sufficient to pull the egg inside the bottle.
When you change the temperature of the air inside the bottle, you change the pressure of the air inside the bottle. If you have a constant volume of air and heat it, the pressure of the air increases. If you cool the air, the pressure decreases. If you can lower the pressure inside the bottle enough, the air pressure outside the bottle will push the egg into the container.
It's easy to see how the pressure changes when you chill the bottle, but why is the egg pushed into the bottle when heat is applied? When you drop burning paper into the bottle, the paper will burn until the oxygen is consumed (or the paper is consumed, whichever comes first). Combustion heats the air in the bottle, increasing the air pressure. The heated air pushes the egg out of the way, making it appear to jump on the mouth of the bottle. As the air cools, the egg settles down and seals the mouth of the bottle. Now there is less air in the bottle than when you started, so it exerts less pressure. When the temperature inside and outside the bottle is the same, there is enough positive pressure outside the bottle to push the egg inside.
Heating the bottle produces the same result (and may be easier to do if you can't keep the paper burning long enough to put the egg on the bottle). The bottle and the air are heated. Hot air escapes from the bottle until the pressure both inside and outside the bottle is the same. As the bottle and air inside continue to cool, a pressure gradient builds, so the egg is pushed into the bottle.
How to Get the Egg Out
You can get the egg out by increasing the pressure inside the bottle so that it is higher than the pressure of the air outside of the bottle. Roll the egg around so it is situated with the small end resting in the mouth of the bottle. Tilt the bottle just enough so you can blow air inside the bottle. Roll the egg over the opening before you take your mouth away. Hold the bottle upside down and watch the egg 'fall' out of the bottle. Alternatively, you can apply negative pressure to the bottle by sucking the air out, but then you risk choking on an egg, so that's not a good plan.

Rubber Egg & Chicken Bones

A Mad Scientist can make a toy out of just about anything, including a boiled egg. Soak an egg in a common kitchen ingredient, vinegar, to dissolve its shell and make the egg rubbery enough that you can bounce it on the floor like a ball. Soaking chicken bones in vinegar will soften them so that they will become rubbery and flexible.
Rubber Egg Materials

• hard-boiled egg
• glass or jar, big enough to hold the egg
• vinegar

Turn the Egg into a Bouncy Ball

1. Place the egg in the glass or jar.
2. Add enough vinegar to completely cover the egg.
3. Watch the egg. What do you see? Little bubbles may come off the egg as the acetic acid in the vinegar attacks the calcium carbonate of the eggshell. Over time the color of the eggs may change as well.
4. After 3 days, remove the egg and gently rinse the shell off of the egg with tap water.
5. How does the boiled egg feel? Try bouncing the egg on a hard surface. How high can you bounce your egg?
6. You can soak raw eggs in vinegar for 3-4 days, with a slightly different result. The eggs shell will become soft and flexible. You can gently squeeze these eggs, but it's not a great plan to try to bounce them on the floor.

Make Rubbery Chicken Bones If you soak chicken bones in vinegar (the thinner bones work best), the vinegar will react with the calcium in the bones and weaken them so that they will become soft and rubbery, as if they had come from a rubber chicken. It is the calcium in your bones that makes them hard and strong. As you age, you may deplete the calcium faster than you replace it. If too much calcium is lost from your bones, they may become brittle and susceptible to breaking. Exercizing and eating a diet that includes calcium-rich foods can help prevent this from happening.

Rock Candy - How to Make Rock Candy

Making your own rock candy is a fun and tasty way to grow crystals and see the structure of sugar on a big scale. Sugar crystals in granulated sugar display a monoclinic form, but you can see the shape much better in homegrown large crystals. This recipe is for rock candy that you can eat. You can color and flavor the candy, too. Rock Candy Materials
Basically all you need to make rock candy is sugar and hot water. The color of your crystals will depend on the type of sugar you use (raw sugar is more golden and refined granulated sugar) and whether or not you add coloring. Any food-grade colorant will work.

• 3 cups sugar (sucrose)
• 1 cup water
• clean glass jar
• cotton string
• pencil or knife
• food coloring (optional)
• 1/2 tsp to 1 tsp flavoring oil or extract (optional)
• Lifesaver candy (optional)
• pan
• stove or microwave

Make Rock Candy

1. Pour the sugar and water into the pan.
2. Heat the mixture to a boil, stirring constantly. You want the sugar solution to hit boiling, but not get hotter or cook too long. If you overheat the sugar solution you'll make hard candy, which is nice, but not what we're going for here.
3. Stir the solution until all the sugar has dissolved. The liquid will be clear or straw-colored, without any sparkly sugar. If you can get even more sugar to dissolve, that's good, too.
4. If desired, you can add food coloring and flavoring to the solution. Mint, cinnamon, or lemon extract are good flavorings to try. Squeezing the juice from a lemon, orange, or lime is a way to give the crystals natural flavor, but the acid and other sugars in the juice may slow your crystal formation.
5. Set the pot of sugar syrup in the refrigerator to cool. You want the liquid to be about 50°F (slightly cooler than room temperature). Sugar becomes less soluble as it cools, so chilling the mixture will make it so there is less chance of accidentally dissolving sugar you are about to coat on your string.
6. While the sugar solution is cooling, prepare your string. You are using cotton string because it is rough and non-toxic. Tie the string to a pencil, knife, or other object that can rest across the top of the jar. You want the string to hang into the jar, but not touch the sides or bottom.
7. You don't want to weight your string with anything toxic, so rather than use a metal object, you can tie a Lifesaver to the bottom of the string.
8. Whether you are using the Lifesaver or not, you want to 'seed' the string with crystals so that the rock candy will form on the string rather than on the sides and bottom of the jar. There are two easy ways to do this. One is to dampen the string with a little of the syrup you just made and dip the string in sugar. Another option is to soak the string in the syrup and then hang it to dry, which will cause crystals to form naturally (this method produces 'chunkier' rock candy crystals).
9. Once your solution has cooled, pour it into the clean jar. Suspend the seeded string in the liquid. Set the jar somewhere quiet. You can cover the jar with a paper towel or coffee filter to keep the solution clean.
10. Check on your crystals, but don't disturb them. You can remove them to dry and eat when you are satisfied with the size of your rock candy. Ideally you want to allow the crystals to grow for 3-7 days.
11. You can help your crystals grow by removing (and eating) any sugar 'crust' that forms on top of the liquid. If you notice a lot of crystals forming on the sides and bottom of the container and not on your string, remove your string and set it aside. Pour the crystallized solution into a saucepan and boil/cool it (just like when you make the solution). Add it to a clean jar and suspend your growing rock candy crystals.

How to Make Homemade Firecrackers

Firecrackers are extremely easy and inexpensive to make yourself. You may want to make your own firecrackers because you are interested in learning how to make simple fireworks or it may be you are unable to obtain fireworks where you live. Fortunately, the materials needed to make your own firecrackers are very common.

Homemade Firecracker Materials

• tape (e.g., transparent tape)
• toy gun caps (either the tape or the rings) or black powder
• fuse 
• pin or needle

Toy gun caps are nice because the powder used in them is easy to work with. Here's how to get the powder out of the caps:

1. Gently insert a pin or needle through the back of a cap through to the front.
2. Remove the pin and re-insert it from the front, where you made the hole. Pry the powder out of the cap, tapping it onto a sheet or paper or plate or other working surface.
3. Carefully work the pin around the edge of the cap to collect all of the powder. There is a very slight chance of popping the cap, so be gentle and work slowly.
4. How much powder you need depends on the size of firecracker you plan to make. One ring of caps is more than sufficient to create a loud bang, but you really only need powder from about 3 caps for each firecracker. For the sake of safety, it's best to make one firecracker at a time (you don't need a big pile of powder).

Now let's assemble the firecracker.

One you have all of the materials necessary to make firecrackers, you are ready to start putting the firecrackers together.

1. Take a piece of tape about 2" long and pick up the gunpowder on the sticky side of the tape. Evenly coat the tape until you either run out of gunpowder or else run out of stickiness.
2. Place the fuse (about 2 inches long) so that it sticks halfway down the tape. The fuse does not need to stick to the tape.
3. Roll the tape around the fuse. Take another piece of tape and tightly wrap your firecracker. Be sure to cover the bottom of the firecracker or else the opening will give you a small rocket rather than a popping firecracker.

Alternatively, you could just fold a 2-inch strip of paper in half lengthwise, pour the gunpowder into the fold of the paper, and wrap the paper around the fuse. The paper firecracker could be secured with any kind of tape.

Now that you have a homemade firecracker, you need to light it! This is basically the same as lighting any other firecracker. Make sure you light it on a firesafe surface, far from people or pets. Don't hold the firecracker in your hand when you light it. Firecrackers that you buy contain measured quantities of gunpowder. You can estimate the amount of gunpowder in your firecracker based on how many caps you used. You won't necessarily get a louder 'bang' using more gunpowder, but you will increase the potential risk of injury, so don't go crazy making big firecrackers. Have fun!

Black Snakes or Glow Worms

Black snakes, sometimes called glow worms, are small tablets that you light, using a punk or a lighter, that burn to produce long black 'snakes' of ash. They produce some smoke (which had a characteristic, probably toxic odor), but no fire or explosion. The original fireworks used to contain salts of a heavy metal (such as mercury), so while they were marketed for kids to play with, they really weren't that much safer than conventional fireworks, just dangerous in a different way. However, there is a safe way to make black snakes. You can heat baking soda (sodium bicarbonate) with sugar (sucrose) to produce carbon dioxide gas that puffs up black carbon ash.
Soda & Sugar Black Snake Materials

• sand
• alcohol or fuel oil (I didn't have any high-proof alcohol on hand, so I used lighter fluid left over from the handheld fireballs project)
• baking soda
• sugar (I used powdered sugar, but you can grind table sugar in a coffee grinder)

Make Snakes

• Mix 4 parts powdered sugar with 1 part baking soda. (I used 4 tsp sugar and 1 tsp baking soda.)
• Make a mound with the sand. Push a depression into the middle of the sand.
• Pour the alcohol or other fuel into the sand to wet it.
• Pour the sugar and soda mixture into the depression.
• Ignite the mound, using a lighter or match.

How to Make a Smoke Bomb

Smoke Bomb Materials

• sugar (sucrose or table sugar)
• potassium nitrate, KNO₃, also known as saltpeter (buy it online or you can find this at some garden supply stores in the fertilizer section, some pharmacies carry it too)
• skillet or pan
• aluminum foil 

How to Make a Smoke Bomb

1. Pour about 3 parts potassium nitrate to 2 parts sugar into the skillet (5:3 ratio is also good). Measurements don't need to be exact, but you want more KNO₃ than sugar. For example, you can use 1-1/2 cups KNO₃ and 1 cup sugar. If you use equal amounts of KNO₃ and sugar, your smoke bomb will be harder to light and will burn more slowly. As you approach the 5:3 KNO₃:sugar ratio, you get a smoke bomb that burns more quickly.
   
   
2. Apply low heat to the pan. Stir the mixture with a spoon using long strokes. If you see the grains of sugar starting to melt along the edges where you are stirring, remove the pan from the heat and reduce the temperature before continuing.
   
   
3. Basically you are carmelizing sugar. The mixture will melt and become a caramel or chocolate color. Continue heating/stirring until the ingredients are liquefied. Remove from heat.
   
   
4. Pour the liquid onto a piece of foil. You can pour a smaller amount onto a separate piece, to test the batch. You can pour the smoke bomb into any shape, onto an object, or into a mold. The shape and size will affect the burning pattern.
   
   
5. If you aren't going to clean your skillet immediately, pour hot water into the pan to dissolve the sugar (or else it will be harder to clean). Clean up any residue you may have spilled out of the pan, unless you want mini-smoke bombs on your stovetop.
   
   
6. Allow the smoke bomb to cool, then you can peel it off the foil.

Now that you've made your smoke bomb, it's time to light it...

White Smoke Recipe

• Potassium nitrate - 4 parts
• Charcoal - 5 parts
• Sulfur - 10 parts
• Wood dust - 3 parts

Red Smoke Recipe

• Potassium chlorate - 15%
• para-nitroaniline red - 65%
• Lactose - 20%

Green Smoke Recipe

• Synthetic indigo - 26%
• Auramine (yellow) - 15%
• Potassium chlorate - 35%
• Lactose - 26% 

It's fairly easy to make colored flames by adding these chemicals to your smoke bomb recipe:
Chemicals Used to Color Flames

1. Red - strontium salts, most easily found in road flares
2. Orange - calcium chloride (laundry bleaching agent)
3. Yellow - sodium nitrate (common in chemistry lab)
4. Green - barium salts, such as barium nitrate (common in chemistry lab)
5. Greenish-Blue - copper sulfate (common in a chemistry lab, also found in many algicides for pool treatment) Blue - copper chloride (common in chemistry lab)
6. Purple - potassium permanganate (common in a chemistry lab, also used in sewage or water treatment)
7. White - magnesium sulfate (epsom salts, found on laundry aisle or in a pharmacy)