Peter Dureen had a great idea to modify the experiment. He wrote:
I wanted to test Avogadro's hypothesis by doingthe following. I would take a piece of burning charcoal, throw it in aglass, and immediately cover the glass with plastic wrap. I hoped thatsome carbon monoxide would be produced. In that instance, I expected anincrease in volume, or pressure, as the case may be, since every oxygenmolecule that entered into the reaction would produce two carbon monoxidemolecules. In any case, to the extent that carbon dioxide was produced,there would be no change in pressure, I thought, since each molecule ofoxygen would be replaced by a molecule of carbon dioxide.fully expected the plastic wrap to bulge upward with the increase ingas pressure, even after the piece of charcoal ceased to burn due tothe lack of oxygen, and the temperature fell to room temperature again.What happened amazed me. The plastic wrap bulged downward into the cup.This indicated, to me, a reduction in pressure exerted by the gas in theglass, and thus indicated a reduction in the number of molecules. Youmay try this interesting and simple experiment yourself.I have no explanation for what happened, although one conjecture is thatthe carbon absorbed the carbon dioxide.The stoichiometry for coal is different than for paraffin. In the case ofonly carbon, one has
C + O2 = CO2and one would indeed expect that the volume would stay the same.Since the pressure decreases afterwards, this could indicate thatindeed some air has gone out when the heat has expanded the inside.After cooling, the plastic wrap collapses.
Peter Dureen again:
The second experiment is a parallel one to the candle experiment. I andan associate made a little stand from aluminum foil, so that it couldsupport a piece of burning charcoal. This little stand basically replacesthe candle in the burning candle experiment.We had a shallow reservoir of water in a pan, the water surrounding thelittle stand. I took a piece of charcoal, which I had fetched earlier frommy fireplace, and took a propane torch to all sides of it to ensure itwas well lit, and then placed it on the stand. My accomplice then quicklyplaced a jar over the assembly. Remarkably, water eventually rose in thejar after the apparatus had a chance to cool down. It, in fact rose toprecisely the same level as it had in a candle experiment using the samejar. So it seems that charcoal has the same effect as a candle. Now inyour analysis, you mention that the candle burns hydrogen, and produceswater, and that seemed quite reasonable to me at the time. But afterconducting this experiment, I must ask why burning carbon alone shouldproduce precisely the same result.It is hard for me to explain to my students these two experiments. I nowawait further discussion of this matter, and hopefully, an analysis thatexplains the results of these recent experiments.I think this is more indication that some hot air has left the container before it started to cool down. I have repeated the experimentsalso with different type of containers and seen also some air, as otherteachers have observed too.
I thank you for posting your explanation. I hope the above adds somethingto the discussion. Maybe we should consult Faraday. Did he not writesomething called the history of the candle?Faraday had been a fantastic experimenter and assisted as a chemist before for a long time. Lavoisier was definitely a great pioneer in this context.
