Re: what gas is needed for a plasma ball?

By "plasma ball", I assume you mean one of these nifty physics toys. After a bit of research, I've concluded two things. One is that the manufacturers don't seem too keen to tell you what they load their products with. But that doesn't matter that much, because you can make a good guess at it. this site has a very nice presentation of the different gases that are used in plasma balls (they vary) and what colors they produce. If you want to see the noble gases (commonly found in plasma balls) lit up, try this page. Also, another Mad Scientist answered a similar question about 5 years ago. Here is his answer.

Two points I found interesting:

• The pressure of the gases inside the ball are below atmospheric pressure. This is to allow the balls to operate at lower voltage. (It takes more voltage to make it through thicker air.)
• The most common gases inside the plasma balls seem to be noble gases, like neon, xenon and argon. To understand why, I need to explain a little bit about how the plasma ball lights up. The central ball inside the plasma ball is fixed at some voltage, while the glass is grounded. Electrons want to jump from one of the surfaces to the other to try to balance the charges. As they jump through the gas in the ball, they bump into atoms of the gas. When the electrons bump into the atoms, they give them some of their energy. When you give an atom energy, it gets excited (it's own electrons change their orbits, in effect). Atoms don't like to stay excited for long, so they soon settle back down. In order to do that, they have to emit a photon of light. So why the noble gases? When the electrons strike the atoms, we want the electrons to give some of their energy and move along. Noble gases don't want any more electrons, but other gases often are happy to take electrons in. They would still emit photons, but the colors would be different. With a noble gas you know what you'll get. I also suspect that other atoms might react chemically inside the ball, which might cause the colors to change as the ball grew older or gunk building up on the glass. (That would all depend on the what gases you put in there, of course.)

I hope that answers your question. Thank you for asking it, I had never stopped to find this out myself!