Potassium nitrate produces oxygen when heated.

Toshi is a 5th grade boy and Tae is a 3rd grade girl.
A few days ago he read about how to make slime somewhere in the internet.
He decided to try this experiment. Soon he went to a library and borrowed a book.
Toshi: "The book says we can make slime by mixing three kinds of liquid together. I think I can do it by ourselves."
Tae: "I'm afraid Mom may not be pleased to see us making slimy things."
Toshi: "I've already got OK from Mom. Don't worry!"
Tae: "Really? If so, I want to make slime right now!
Toshi: "Tae, which color do you like?"
Tae: "I can see red, yellow, and green. I prefer red color."
Toshi: "I'll take green color."

And that is the glory that is Internet Version [Naruhodo no Mori]
Home science experiments for mothers of elementary school children
by Yumiko Mori.

( I have a new favorite web page. )