I can't find it now, but my favorite of TIWWW was this chemical that just smelled terrible and did so in exceedingly small quantities. Like, a stray drop of this gets the building evacuated kind of bad, and people are asking what that smell is a mile or more downwind.
> To convince them otherwise, they were dispersed with other observers around the laboratory, at distances up to a quarter of a mile, and one drop of either acetone gem-dithiol or the mother liquors from crude trithioacetone crystallisations were placed on a watch glass in a fume cupboard. The odour was detected downwind in seconds.
How is the smell able to travel so quickly? And through walls no less?
Nigel of the NileRed youtube channel has just the other day disputed this claim. Diffusion isn't very fast and the wind would have to have been going 15mph or more. He says he wants to create this compound and test it, as he has done with a few other "horrific smell" compounds.
However, there's a running theory that he has kinda burnt out his nose working with certain compounds, as he seems mostly unphased by smelly chemicals that other people very much struggle working with.
In the thioacetone TIWWW, Lowe says that "the workers in the laboratory did not find the odours intolerable". It sounds like in higher concentrations it just overwhelms and numbs a strong reaction people have at even extremely low concentrations.
> the wind would have to have been going 15mph or more
15 mph really isn't much for wind, though? In fact that's about how much wind there is where I am right now, so that doesn't strike me as an unreasonable condition.
Individual molecules of air travel at speeds in the hundreds of meters per second (https://pages.mtu.edu/~suits/SpeedofSound.html). So it seems quite possible that individual molecules may be found quite far away from their origin quite quickly, even if the bulk is much slower in mixing (I'm not an expert here and would love to hear more if someone knows more about this).
It sounds like this substance is bad enough that a couple of molecules per Litre would make the air smell awful, which together with the previous point may explain how the bad smell could be detected at such a distance so quickly.
There's a section of "Ignition!" where the rocket scientists try out mercaptans as a rocket fuel, and get exiled to the far end of a huge empty field for the duration of their experiments.
Ignition! is a fantastic read. Not related to mercaptans (or bad smells), but this passage from the book has always made me chuckle:
> [Chlorine trifluoride] is, of course, extremely toxic, but that’s the least of the problem. It is hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water –with which it reacts explosively. It can be kept in some of the ordinary structural metals — steel, copper, aluminum, etc. — because of the formation of a thin film of insoluble metal fluoride which protects the bulk of the metal, just as the invisible coat of oxide on aluminum keeps it from burning up in the atmosphere. If, however, this coat is melted or scrubbed off, and has no chance to reform, the operator is confronted with the problem of coping with a metal-fluorine fire. For dealing with this situation, I have always recommended a good pair of running shoes.
