The disappearing rainbow¹ is a wonderful chemistry demonstration previously featured here on ChemEdX.^2-4 In this experiment, a colorless solution of NaOH is poured into a row of flasks, each containing a different acid–base indicator. The solutions suddenly flash into the colors of the rainbow—red, orange, yellow, green, blue, and violet. Then, with a pour of HCl, the rainbow vanishes just as quickly.

A few years ago, I showed how the Assassin’s teapot could be used for this demonstration.⁴ The teapot, with its two compartments, allows one to pour NaOH or HCl from the same vessel. This twist heightens the magical effect—but it’s tricky to pull off. Controlling which liquid comes out requires practice, and spills are common, so I eventually retired using it in the rainbow demo.

That’s why I was excited to try the new Assassin’s water bottle, made by the creators of the Curiosity Box.⁵ Like the teapot, it has two separate compartments for liquids, but the pouring control is much easier.

It’s a simple upgrade that adds a touch of theatrical magic. I’ll definitely be using this in classroom demonstrations, and I’d love to hear how it works for you.

Happy experimenting!

References

1. Flinn Scientific. The Disappearing Rainbow

2. Solution to Chemical Riddle #2

3. Chemical Riddle #2

4. Chemical Mystery #20: Magic Kool Aid

5. https://www.curiositybox.com/pages/assassins-bottle Use the code tom25 for 25% off! (Notice that the author will receive some compensation if this code is used).