The need for Vitamin C in the diet was discovered hundreds of years ago when people came down with a dread disease known as "spring sickness" or "scurvy." The symptoms included bleeding gums and loose teeth, aching joints and sores on the skin and in the stomach. The disease can be avoided by adding citrus fruits and sauerkraut to the diet. The British navy required that these foods be taken on long ocean voyages, because sailors were particularly susceptible to the disease. For this reason British sailors came to be known as "limeys," after the limes and lemons they were required to eat.

It was not until 1932 that the pure Vitamin C was made in a laboratory. It turned out to be a fairly simple compound. It was named ascorbic—meaning "without scurvy"—acid. Ascorbic acid is water-soluble and picks up electrons easily, which makes it easy to detect in a lab test.

Materials and Equipment

• measuring cup and spoons
• cornstarch
• knife
• spoons for stirring
• stainless steel or enamel saucepan
• 2 jars with lids and labels
• iodine
• 250-milligram vitamin C tablet
• small juice glasses or test tubes
• medicine droppers or straws to be used as pipettes

Procedure

This test will not only tell you if vitamin C is present, but if you measure carefully it will also give you an indication of how much of the vitamin is present.

First, make a starch stock solution. To do this, take ½ level teaspoon of cornstarch and pass the back of the knife over the spoon to make the measurement level; then put the cornstarch in the saucepan. Add 1 cup water. CHECK WITH AN ADULT BEFORE USING THE STOVE. Heat and stir until the starch is dissolved. Pour the mixture in one of the jars and let it cool.

Next, make your test solution. Put one teaspoon of the stock starch solution in a clean jar with one cup of water. Add four drops of iodine. The blue color is the result of the starch-iodine complex and is typical of the iodine reaction to starch. It is very diluted in this solution.

To check your test solution, do a positive vitamin C test. Dissolve one 250-milligram vitamin C tablet in one cup of water. Put 2 tablespoons of your test solution in a small glass. Add 1 drop of the vitamin C solution. Stir. If there is no change, add a second drop. The color is gone. See what a sensitive test this is!

Observations and Suggestions

Test various foods for vitamin C. Here are some suggestions: fruit and vegetable juices, water extracts of fresh fruits, water extracts of liver (soak a piece of raw liver to make an extract), water extract of pine needles, milk. If you use a pipette to add extracts to starch-iodine solution, practice letting out one drop at a time.

Here's the chemistry behind the test. Both starch and vitamin C will give electrons to iodine and combine chemically with it. But of the two, the vitamin C will react more easily than the starch. Iodine that combines with vitamin C has no color, while the starch-iodine compound is bluish. So if vitamin C is present, the product that forms is colorless.