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Island General Store



Every tropical island needs a general store. This one is stocked with lots of useful items to help you and your customers have fun in the sun and enjoy yourselves after dark. Everything on the shelves is a rough science product.

The Challenges!



Make Candles

If you didn't build a flashlight in the Island Power Plant scenario, you'll still be able to function in the dark if you make some candles — for yourself and the general store customers.

You'll need:

  • paraffin wax or beeswax
  • colored crayons or dye
  • powdered stearin
  • wick
  • wide, shallow pan
  • two tall cans
  • thermometer
  • paper towel
  • waxed paper
  • pencil
  • metal washer
  • newspaper
  • essential oil or perfume
  • water

What you do:
Spread the newspaper over your work area. Heat water in the pan. Cut the wax into small chunks and add them to one of the tall cans. Set the can in the warm-water pan. Heat slowly, adding more chunks as the wax melts. When the wax has melted, stir in about 3 tablespoons of stearin for each pound of wax. For color, melt in the wax crayons or add dye. Use the thermometer to maintain the temperature of the molten wax between 150 and 180°F. Prepare the wick by cutting it into lengths 5 inches longer than the candle you want to make. Attach a metal washer to one end of the wick to weight it, and tie the other end to a pencil. Dip the wick into the molten wax, lift it up, and let the wax drip along the wick. Dip the coated wick into the second tall can, filled with cool water. Lift the wick out, and use some paper towels to remove excess water. Place your candle on waxed paper for 30 seconds and then repeat the dipping process. Dip each candle 40 to 50 times until your candle is about 1 inch. As the size of the candle increases, you may need to straighten it by rolling it on waxed paper. When the candle is about 1 inch thick, add a tablespoon of stearin to the wax for one final dip. The added stearin will make the final wax coating of your candle dripless. If you want to make scented candles, add a few drops of essential oil or perfume.

What's going on?
The Romans used beeswax to make candles, but modern candles are made from a mixture of hard paraffin and stearin (added to increase the melting point and to prolong burning time). Stearin is a substance that changes the melting point of the wax. This allows the candle to harden faster. Stearin also makes candles firmer, dripless, and brighter burning. It is harder than tallow. Wicks must be naturally absorbent to absorb liquid wax and move it upward while the candle is burning. The heat of the flame vaporizes the wax, and it is the wax vapor that burns. The wick does not burn because the vaporizing wax cools the exposed wick and protects it.

For other candle-making activities, see:

For more information, see Rough Science episode 10: "Sustenance and Sayonara"



Concoct Homemade Toothpaste

Fail to pack for your island vacation? Don't panic. Toothpaste doesn't have to come in a tube. You can make it from a few simple ingredients if you know the basic principles.

You'll need:

  • baking soda
  • water
  • calcium carbonate
  • peppermint oil, mint, or lemon juice
  • glycerin (optional)
  • teaspoon
  • a bowl

What you do:
In the bowl, add 3 parts of baking soda to 1 part calcium carbonate. Add 2 teaspoons of glycerin and 5 to10 drops of peppermint oil. Test for taste. If you like your toothpaste to tingle, add a bit more oil. Mix all of the ingredients thoroughly and add enough water to give a smooth, toothpaste consistency. You could use other flavorings, such as mint or lemon juice.

What's going on?
Baking soda causes dirt and grease to dissolve in water. This cleansing action combines with the abrasive calcium carbonate (chalk) to produce an effective cleaning agent. The glycerin thickens the mixture to give it a paste consistency. The peppermint oil is for flavor.


For more information, see Rough Science episode 10: "Sustenance and Sayonara"


Make Glue

Even island dwellers must make simple repairs. You never know when one of your customers might break something. Making this glue is so easy, you'll never run out.

You'll need:

  • 1/2 cup warm milk
  • 1/4 teaspoon baking soda
  • 2 tablespoons vinegar
  • water
  • saucepan
  • cup
  • cheesecloth or coffee filter

What you do:
Slowly heat the milk until it is hot. Remove it from the heat and add 4 teaspoons of vinegar for every cup of milk. Place the curds in cheesecloth and then squeeze out the water. Rinse the curds with cool water. Squeeze out all the water and put the curds in a cup. Add a pinch of baking soda and mix with a little water to make the glue smooth.

What's going on?
When vinegar is added to milk, the acetic acid in the vinegar causes thick lumps (curds) of casein to develop and coagulate from the proteins in the milk. The acid separates the milk into curds and whey. The acid causes constituents of the proteins (amino acids) to react with each other, resulting in adhesion. Also the fibers in paper or other objects attract the casein that makes them stick together.

Activity adapted from Lawrence Hall of Science. Secret Formulas. Regents of the University of California, 1996. See also http://www.howstuffworks.com.

For more information, see Rough Science episode 10: "Sustenance and Sayonara"



Make Insect Repellent

Insects are everywhere in the tropics and some carry diseases. You need to stock an effective insect repellent. This one really works. Watch it fly off the shelves!

You'll need:

What you do:
Mix all the ingredients together in the bowl. Stir thoroughly until everything has dissolved. Before you go outside, apply the repellant to your skin but avoid getting any lotion near your eyes. Be sure to discontinue use at the first sign of an allergic reaction.

What's going on?
Camphor is a powerful natural repellent. It is an extract from the camphor laurel tree. Insects don't like the smells of the volatile oils (vapors) in the camphor.

For more information, see Rough Science episode 7: "Mediterranean Mystery"



Suggestion for other activity:

  • Make your own filtered water and bottle it for sale. See the Water Quality Control Center scenario for directions on how to make a water filter.