My best guess is that it's supposed to be a chimney - you could put a candle in the bottom and it would heat the air in the cylinder, driving it up and replacing it with fresh air from the bottom, driving its own circulation. At the same time, it would heat the contents of the bulb like a retort.

But there's no fitting to attach anything to the top of the bulb, so any vapours would just be exhausted upward with the combustion products of the candle. I also don't get the point of the serpentine tube - if it were just for support, why would it be hollow and matched to an orifice in the side of the cylinder? If it's for filling the bulb, why not just use the orifice at its tip, since you can't have anything attached to that anyway? Were it straight, you could maybe use it to stick a thermometer into the bulb, but the bends in the tube prevent that.