Fumigation Candles are made by melting a small quantity of
clean beeswax in a double pan and gradually stirring in 'flowers of
sulphur' until the liquid is quite thick, but will still just be able
to be poured.
Pour this mixture into a pre-wicked and pre-warmed candle
mould (a metal one will work best) allow to cool slowly and when it
has reached room temperature (about 6 hrs) place the mould and candle
in the freezer, then after a further 12 - 24 hrs the candle will come
out of the mould.
The wick is of such a size that matches the diameter about
halfway down the tapered portion. As the intent was fumigating a
greenhouse the initial state at lighting is that of no fumigant gas in
a relatively large volume that is 'leaky', so fast burning at the top
of the candle is unhindered by any pooling of molten wax. As the
candle is consumed and the burning has progressed about halfway down
the taper, the green house has filled with sulphur dioxide and there is
less need to generate it at the original rate and so the rate
automatically becomes less as the larger diameter surface allows a
small amount of liquid (wax/sulphur) to form which makes the flame
smaller and reduces the rate at which gas is produced to that required
to keep pace with losses to the atmosphere through cracks and vents.
The reduction in burning rate continues until the parallel portion
near the base is reached. An amount of time still remains for this
small rate of 'top up' gas production until the candle expires as it's
wick falls over when the supporting candle material is consumed/melted.