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DENJIRO: Do you know which castle this is?
BOY: I know! It's Himeji Castle!
DENJIRO: Yes. It's Himeji Castle. Castles like this one or warehouses with white walls are coated with plaster.
NARRATOR: What is plaster? Let's do an experiment to find out.
DENJIRO: Here, we have some quicklime. It is made by burning limestone, a naturally occurring rock, at a high temperature. When you pour water on it...
It reacts with water and becomes slaked lime. When slaked lime reacts with a certain substance, it becomes hard and durable plaster.
NARRATOR: So, what is this certain substance? We've prepared two boards with slaked lime pasted on them. The board on the left has been dried for a day, and the board on the right has been dried for seven days. When we spray water on them...
DENJIRO: The one that has just dried begins to crack and dissolve. It proves that it still hasn't become plaster.
On the other hand, the one that's been dry for a couple of days does not dissolve.
This has become hard and durable plaster. Why does drying the slaked lime for a few days turn it into plaster? The key is the carbon dioxide in the air.
NARRATOR: Since slaked lime is water-soluble, it dissolves when it isn't completely dry. But when slaked lime is dried for a certain period of time, it reacts with carbon dioxide in the air and changes into calcium carbonate.
DENJIRO: Calcium carbonate is hard and does not dissolve in water. This is what we call plaster.
Limewater helps us see the reaction between slaked lime and carbon dioxide very well. Slaked lime has been dissolved in limewater. When you blow air into this...
BOY: It turned white!
DENJIRO: The carbon dioxide that you exhale reacts with the slaked lime and creates calcium carbonate, turning the limewater white. This is the mechanism that creates plaster.
I hope energy will bring you all happiness. Our magic word is "Happy Energy!"