What Causes the Whistling Noise When Heating Iron and Sulfur?

[YSivan]

I quote from a fellow chemistry teachers' letter (Mike Thompson):
"Many colleagues will know that when solid sulphur is heated below some lightly packed iron wool in a test tube or boiling tube a standing wave is sometimes set up and a whistling noise is heard (around middle C with a boiling tube). The noise may be heard whether the reaction is incandescent or not. There is no obvious visible vibration of the iron wool or of the sulfur vapour. The noise can sometimes last for 60 seconds or more. I have tried to get the same noise using phosphorous and iodine with iron wool but without success. I have posted a clip on YouTube. "

To which I replied:
I tried two more experiments:
1. Using copper wool instead of iron wool, one gets this effect, though not as impressively. It seems to me that it only starts, in this case, when the reaction is taking place (while with iron wool I think it it can start before). Maybe it is temperature dependent.
2. Using pyrex wool, which obviously does not react with the sulphur, one can also get this effect. I think it has to be loosely packed, as it didn't work every time I tried.

Since then I came across a reference dating back over 70 years: http://www.iop.org/EJ/abstract/0959-5309/46/1/311
which may be relevant.

I don'y have solid CO2 available, but it would be interesting to try putting it in a test tube with iron wool, and seeing (!) if one gets the same effect.

I am posting this in the hope that someone can give us an explanation as to how the phenomenon is caused.

Thanks, Yehoshua

 

[AndyW]

Dear Mike Thompson and Yehoshua,

Thank you for sharing your observations and experiments on the whistling noise produced when heating solid sulfur with iron wool. This is a fascinating phenomenon that has been reported by many scientists over the years, but it still lacks a clear explanation.

After reading your post and conducting some research, I have come across a few theories that may shed some light on this interesting discovery. One possible explanation is that the whistling noise is caused by the formation of a standing sound wave within the test tube. When the sulfur is heated, it produces sulfur dioxide gas which can vibrate at a specific frequency, resulting in the whistling sound. The presence of the iron wool may act as a catalyst for this vibration, creating a standing wave and amplifying the sound.

Another theory suggests that the whistling noise is due to the release of sulfur vapors that are trapped within the iron wool. As the sulfur heats up, it vaporizes and expands, causing a pressure build-up within the iron wool. This pressure is then released in short bursts, creating the whistling noise.

However, these are just hypotheses and further research is needed to fully understand the mechanism behind this phenomenon. I also found the reference you mentioned from 70 years ago, which discusses the possibility of a chemical reaction between sulfur and iron wool producing hydrogen gas, which then creates the whistling sound. It would be interesting to try this experiment with solid CO2, as you suggested, to see if the same effect can be produced.

I hope that with continued experimentation and collaboration, we can unravel the mystery behind this intriguing phenomenon. Thank you again for sharing your observations and I look forward to any updates or further insights on this topic.

 

[sir-pinski]

Thank you for sharing this interesting observation and for trying out different variations of the experiment. It seems like the whistling noise is not solely dependent on the type of metal used, as copper and pyrex wool were also able to produce the sound. I agree that temperature could play a role in this phenomenon, as well as the packing density of the wool. It would be fascinating to see if solid CO2 could also produce the same effect. I will definitely check out the YouTube clip and the reference you mentioned. Perhaps it could be related to the vibrations of the iron wool or the sulfur vapour, as you mentioned. I hope someone can provide an explanation for this interesting phenomenon. Thank you for bringing it to our attention.