Internet version [Naruhodo no Mori] Vol.43

by Yumiko Mori

Vol. 43 January, 15th, 1999

Tincture of Iodine

Home science experiments for mothers of elementary school children

Tae: "This rice looks terrible!"
These are Tae's words, when she saw blue and purple colored rice.

Toshi, Tae, Satoshi and Mom are doing an experiment of adding tincture of iodine to rice.
Tae: "I know this is a kind of food experiment. But I am so disappointed we can not eat anything from this experiment."
Mom: "Can any of you drop your saliva on this rice?"
Satoshi: "I want to drop my saliva."
Mom: "Satoshi's saliva may be quite potent."

Mom mixes saliva and rice very well. After 5 minutes, add tincture of iodine.
Satoshi: "This time the rice didn't get stained."
Mom: "That's right. The rice starch has been digested into smaller sugar by enzymes in your saliva. Your saliva works very well."

On the next day

Tae: "Mom, are you still playing with tincture of iodine?"
Mom: "Yes, I am searching where starch can be found. Do you know even newspapers contain starch?"
Tae: "I guess newspapers are made of wood. Perhaps most plants produce starch."

Suddenly Satoshi came home. He is crying.
Satoshi: "I fell over on the road."
He has a minor bleeding from his leg.
Mom: "Well, I can put this tincture of iodine on your leg."
Satoshi: "Does this hurt?" (Mom is putting tincture of iodine on Satoshi's leg.) "Oh, no! My leg is tingling."
Mom: "You are going to be OK. Your injury will heal soon. But this time the color didn't change into purple."
Satoshi: "You must be joking!"

Materials

Diluted tincture of iodine		(Obtained in a drug store)
	* When starch is stained by tincture of iodine, it becomes blue or purple color. When you mix with fruit juice that contains vitamin C, the stained color disappears. Iodine is volatile and loses its effect as time passes.
3 disposable cups
Water		A tablespoonful
Cooked rice		2 tablespoonful (warm)
Daikon Radish, or saliva		A little amount (Daikon radish should be grated.)
A grater
A pair of chop sticks

Experiment

Experiment on cooked rice and grated Daikon radish

Required time: 15 min

Make Iodine solution by diluting tincture of Iodine.
Put a tablespoonful of water in a disposable cup.
Add three drops of tincture of Iodine.
The water becomes light orange colored.
Put one portion of rice into each of the remaining two cups.
Add a small amount of grated Daikon radish (or saliva) to rice in only one of the cups.
After 5 minutes, add Iodine solution to rice in both cups.
Compare the rice color between the two cups.

Never eat the rice that contains tincture of Iodine. Do not lick tincture of Iodine.

Using tincture of Iodine, try to find out if various food (such as potato starch, sugar, and rice cake) contains starch or not. Try paper as well.
Daikon radish and saliva contain a large amount of an enzyme called amylase, which can digest starch and convert it to sugar.
Sweet potatoes also contain this enzyme.
Slowly baked sweet potatoes taste delicious, because starch is converted into sugar.

Why do we study in school?

I saw a special TV program about Japanese education on the other day. In the program, many children were wondering why they had to study subjects such as history, math, or science. Can you answer them why they have to study these subjects? What was your reason to study these subjects? My opinion is that it is important for students to learn from direct experience.

Author	Yumiko Mori (Zushi, Kanagawa, Japan)
Illustration	Mitsue Ogata
Translator	Akira Ishihara
HTML format	Muneo Kume