some time back a report was made here or on physshare that a candle flame
in a bell jar turned blue before it went out. I saw no explanation following
that report.
I had occasion to do another demo that required the bell jar and vacuum
pump so I stuck a candle under the jar and evacuated the aie.
It does indeed turn blue. However, I also observed that the blue color
started at the bottom and worked its way up the otherwise orange flame until
it got near the top.
The flame when orange had the typical shape which tapered to a point
at the top. As it turned blue the flame became spherical and lost the
top point shortly before it went out altogether.
I seem to recall that the orange color is sometime attributed to the
carbon particles that have not yet burned, i.e. the ones that make the
soot deposit if you stick a cool beaker in the flame. I can't stick anything
in the flame through the bell jar so I don't know if soot is being formed.
Does anyone have an explanation of the shape and color ??
Jim Braunsdorf