The following took place at Eastercon in 1965.
At Eastercon, Carl Frederick and I were chatting when we were accosted
by two middle aged ladies who each prominently wore an Ankh suspended
from their necks. The ladies announced that they were witches. Since
neither Carl nor myself believed in the supernatural, we quickly eased
ourselves away. Minutes later though, fellow caver Barry Greene
appeared, fully dressed in caving gear. He had come straight from a
cave and had not even had a chance to wash off the cave mud yet.
We chatted for a while and told Barry about the witches we had met a few
minutes earlier. We were sitting at a table which was empty except for
a half full bottle of beer. As we spoke, Barry shifted his caving kit
bag and a bottle of calcium carbide rolled out. I think that we all hit
on the idea simultaneously. Calcium carbide combines with water to form
the highly flammable acetyle gas. Beer is essentially mostly water. We
reasoned that calcium carbide should work just as well with beer as with
water to produce acetylene gas. We accordingly hatched a plot to have
some fun with the witches, hopefully leading them to believe that they
were witnessing a supernatural apparition...
My task was to engage the witches in conversation and lure them over to
our table. Barry was to surreptitiously drop the calcium carbide in the
beer bottle as he saw us comming. Carl's task was to casually wave a
lit cigarette over the mouth of the beer bottle to ignite the gas.
Timing was critical. If Barry dropped the calcium carbide in the bottle
too early, the area would become suffused by the telltale smell of
acetylene gas. If he dropped the calcium carbide too late, air might
remain in the bottle possibly causing it to explode.
Everything worked like a charm. Carl (a non smoker) ignited the gas,
resulting in a spectacular three foot flame continuously errupting from
the bottle. The witches displayed the utmost cool. One said "I see
this happen all the time."
We drew the attention of a crowd of people. None had ever seen flames
errupting from beer bottles before. A few tried to blow the flame out
but the force of the gas was such that this was impossible. Another
inverted an empty glass over the bottle but this merely caused the flame
to shoot aroud the gas. One of the attendees remarked that he smelled
acetyle gas. We thought the jig was up but then Barry said "Yes, but
where does the gas come from?" No one had an aswer to that.
We pulled away from the table as more and more people crowded around.
When we returned a few minutes later, the witches had everyone sitting
around the table holding hands while they conducted a seance.