[Chris3333]

So, I was wondering what would happen if you lit the burner and the air holes were not closed.  Would the gas excape from the holes and not ignite?

[mike]

Possibly, although I have often lit the bunsen burner with the air holes open....

[Donaldson Tan]

with airholes open, you get a non-luminious flame.

with airholes close, you get a luminious flame.

with airholes open, the gas burns more efficiently. however, with airholes close, there is significant incomplete combustion. the soot formed from incomplete combustion burns to produce orange/yellow light. this is responsible for the luminious flame.