[chris (OP)]

Why do acetylene cylinders contain other materials such as acetone or (historically) asbestos? I was asked recently about acetylene cylinders in fires becoming unstable - can the gas react with itself and trigger a chain reaction?

Chris

[rosy]

Well, for one thing anything-cylinders are unstable in fires. Temperature goes up=pressure goes up=cylinder and anyone near it laminated across room. And then the explosive gas can catch fire.
Don't know about the rest.

[daveshorts]

They put acetone in the cylinders because acetylene is quite soluble in acetone, so you can get a lot more of it in the bottle, and it will stay at a more constant pressure as it is used up. It also means that if you heat it to the pressure above which it wants to come out of solution, the pressure will increase enormously - a bit like when you boil water, hence it is particularly dangerous in a fire.

[Infamous]

Why do acetylene cylinders contain other materials such as acetone or (historically) asbestos? I was asked recently about acetylene cylinders in fires becoming unstable

daveshorts has answered that question rather well in the forgoing post. With regard to your last question:

- can the gas react with itself and trigger a chain reaction?

No; it must have an oxidizer such as oxygen with which to react.
....................Infy

[lightarrow]

Why do acetylene cylinders contain other materials such as acetone or (historically) asbestos? I was asked recently about acetylene cylinders in fires becoming unstable - can the gas react with itself and trigger a chain reaction?

Acetylene cannot be stored as it is at high pressures, because it can easily decompose and become explosive; even a small collision of the cylinder with something could make it explode. So, the only way to store big amounts of it in little volumes is, as Dave said, to dissolve it in acetone (or something similar) that dilute it.
So the answer to your second question is yes.
At high densities it can also polymerize.

[Bored chemist]

"No; it must have an oxidizer such as oxygen with which to react."
No It doesn't. Acetylene is (unusually) unstable with respect to the elements it is made from. As lightarrow says it can go off bang all too easilly.

[Infamous]

"No; it must have an oxidizer such as oxygen with which to react."
No It doesn't. Acetylene is (unusually) unstable with respect to the elements it is made from. As lightarrow says it can go off bang all too easilly.

Ah yes, so right you are Bored chemist. That's what I get for not checking before making an assumption. Wiki has information on this at:

http://en.wikipedia.org/wiki/Dissolved_acetylene

....................Infy

[chris (OP)]

"No; it must have an oxidizer such as oxygen with which to react."
No It doesn't. Acetylene is (unusually) unstable with respect to the elements it is made from. As lightarrow says it can go off bang all too easilly.

And what would be the equation for such a reaction please?

[Bored chemist]

There are lots of possibilities.
2C2H2 --> butadiene or ethene + soot
Acetylene can be trimerised to benzene (but the yeild is low)
Almost any combination of the elements that doesn't contain the triple bond is energetically favoured.