[arcane]

Hello all,
Kind of a random question not sure if any of you will be able to help but I'm thinking of making a remembrall for my friends birthday present.

For those of you who don't know what it is it's from harry potter.

"A Remembrall is a glass sphere filled with white smoke. If you hold the ball in your hand, the smoke will turn red to indicate you have forgotten something. The name is apparently a portmanteau of "remember", "all", and "ball"."

Link of a pic: http://www.harrypotterfanzone.com/assets/item_remembrall.jpg

I was a little suprise that I couldn't find a toy company that makes them but it doesn't seem like it be impossible to make.

I'm thinking all I'll need is to inclose to colourless gas into a sphere and when you shake it'll react to make red gas and then after awhile eventually separate. Any ideas on two possible  gas or any other suggestion a gas mixed with a colourless liquid perhaps?

Lol actually that sounds pretty hard, could always get her flowers....

[Borek]

Search forums for colored gases, this question appears now and then.

In short: whatever exists, is poisonous and/or dangerous.

[Arkcon]

As I recall, the gasses dinitrogen tetroxide and nitrogen dioxide, exist in equilibrium with one another: N₂O₄ ⇌ 2NO₂ and nitrogen dioxide is brown.  My chemistry text book had a sealed glass cylinder of the mix, that went from light brown to dark brown, when put in a warm water bath.  Like Borek: says, these gasses are toxic, and I wouldn't let kids play with them.  Perhaps someone makes a sphere with liquid crystals on the inner surface, we used to find disks of this sort of substance fascinating, back in the '70's.  But we were easily amused, back then.

[nj_bartel]

I think that equlibrium is too far shifted in one direction at room temp Arkcon - I've seen the same picture, and it's placed in ice bath to get it to shift from brown to clear.  At any rate, like Borek said, the gas Arkcon mentioned, and other colored gases are pretty much all toxic.