What's That Awful Smell?!!!

"Pretty much all the compounds you could draw out of thioacetone are going to reek."
"Not a lot of us have smelled a gem-dimercaptan. It could well be intense."
"It [combining dimethyl sulfide with silicon] smelled like what you'd imagine the exhaust of a U.F.O. to smell like."
"It was spectacularly weird and horrible."
Derek Lowe, medicinal chemist, director in Chemical Biology Therapeutics, Novartis Institutes for BioMedical Research

According to a expert chemist Derek Lowe, it can be difficult to know what chemicals produced the odour in an incident dating to 1889 that related to a substance called thioacetone, the subject of experiments in a German laboratory. One reaction from the use of the chemical produced an awful odour, so potent it was escaped the laboratory and contaminated the entire city where the laboratory was located. The reaction it caused among the residents was so impressive the resulting panic ended in mass evacuation.

Mr. Lowe theorizes that the thioacetone would have been converted into another chemical, one he suspects was gem-dimercaptan, which itself would have been subject to further reactions in a chain that resulted in a truly revolting smell. Despite the speculation over the incident, much discussed by chemists, there are none among them willing to figure out which molecules would have been produced by the reactions, by repeating the experiments.

Aroma strength is measured by the "odor detection threshold" associated with particular substances, determining the amount required to add to air before ordinary people are able to smell it. Gasoline, as an example, has an odour detection threshold of about 100 micrograms per cubic meter, so if three litres of it evaporated into the air from on high, it would produce vapour sufficient to give the air an odour like gasoline for 180 meters in all directions.

Ethyl mercaptan, added to natural gas so that leaks become detectable, has an odour detection threshold of just 1 or 2 micrograms per cubic meter, while a few pools of ethyl mercaptan the size of the reservoir in the middle of New York's Central Park, could, spread evenly throughout the atmosphere give the entire planet the smell of a gas leak. Methyl mercaptan, even smellier, might take merely one reservoir to make the globe reek.

On a more acceptable level, one of the substances with the lowest odour detection threshhold is vanillin, the major component of vanilla extract and while estimates vary, its odour detection threshold is likely around 0.1 or 0.2 micrograms per cubic meter, quite a bit lower than ethyl or methyl mercaptan. One or two oil tankers full of vanillin might be used conceivably to render the entire Earth smelling enticingly with the fragrance of vanilla.

In 1998 Pamela Dalton, a cognitive psychologist at Monell Chemical Senses Center in Philadelphia was tasked with developing a stink bomb by the U.S. Department of Defense. She discovered in her studies, that people of different backgrounds from various parts of the world whose culture surrounded them with odours and foods specific to time and place frequently disagreed in descriptions of good or bad smells.

Dr. Dalton eventually discovered a candidate for a universally distasteful smell to be something named "U.S.Government Standard Bathroom Malodor", a substance designed to mimic the 'scent' of field latrines linked to the military for the purpose of testing cleaning products. That aromatic liquid was what she chose as the base of her recipe for a stink-bomb, and the resulting formula, Stench Soup, may represent the most rancid smell ever created.

The odour was described as "Satan on a throne of rotting onions", by science writer Mary Roach, one of the few people curious enough to make an effort at inhaling Stench Soup. Dr.Lowe recalls the worst thing he ever smelled came about when he combined dimethyl sulfide with some silicon he was experimenting with; the two odours combined, each of which is known to stink, produced a final odour beyond foul.

The second that ammonium sulphide breaks down to hydrogen sulphide and ammonia you've got yourself a stinky problem. Joe Schwarz, McGill, Office for Science and Society