We purchased a time station from national geographic. It is one of the coolest projects we have gotten for him. For his first time using it we just filled it with water, but as you can see it actually works. You can fill the tubes with pretty much any type of kitchen substance (Ketchup, soda, toothpaste, and lemon juice. Just to name a few) He loved it. He loves science and is trying to learn how to tell time. This was a perfect gift and can not wait to try out more substances.