By Richard Bleil
This morning, as I was exiting my car in the parking lot, I noticed the distinct smell of “pole-cat”. “Pole-cat” is a slang term for “skunk”, because they look like cats, but with a white “pole” down their back. And they smell like cats if cats smelled very different than they do.
So, let’s take a moment out of our lives to discuss…skunks. Or rather, their defining characteristic; their smell. We all know that skunks have a special gland in their hind quarters that can spray out a solution of rather odoriferous chemicals that the skunks use to defend themselves. It might seem odd that something that makes their nearby presence so painfully obvious would be a defense mechanism from hungers, but when they spray, what they are wanting to get is the olfactory senses of the predator, making it nearly impossible for them to smell anything else until that smell wears off. This means their hunting skills will be very much hampered, and they know that. When they smell skunk, they avoid it because they will want to eat after the skunk encounter.
A skunk can spray ten to fifteen feet away, and up to six times in rapid succession. Yup, got a li’l six-shooter back there, so if it sprays once, you’re STILL not safe. The active ingredient in skunk spray is called a “thiol”, which is an organic compound that has a -SH functional group, which means that somewhere on the molecule is a sulfur that is also attached to a hydrogen. Our sense of smell is highly sensitive to thiols. We can smell them at a few parts per billion, so a nice concentrated blast and we’re going to have trouble smelling anything else. Animals with the ability to smell better than us can easily smell it in the parts per trillion level, or even beyond that.
Thiols show up in some of the most interesting of places. For example, natural gas is actually odorless and colorless. This is a problem, and engineers recognized the dangers involved. If an odorless, colorless gas fills a house, it can displace all of the oxygen and the occupants could slowly suffocate without even being aware it was happening. They would feel drowsy, and slip off into sleep, never the wiser. Until a spark CAUSES THE HOUSE TO EXPLODE. Then they would die a horrible fiery death. Not pleasant. So, the gas company adds a smelly chemical to the gas so if there SHOULD be a leak, the occupants could smell it. That chemical? It’s a thiol. A different thiol than that of the skunk, to be sure, but related nonetheless.
Many years ago, I left a tiny and very conservative medical arts college to go to a state university. A student that I had had my last year in that institution sent me an email with a simple question: “why does asparagus make your urine smell so pungent?” It’s an interesting question, and back then Google wasn’t quite so prolific as it is today, so I turned to an old chemist’s tool (since I am an old chemist, after all), the Merck Index. The Merck Index (yes, published by the drug company, or at least an affiliate company) has a marvelous, well, index in the back. See, chemicals have highly technical names, and some handbooks require that you know specifically what that name is. The Merck Index is my preferred handbook because in the back of the book, you can look up common names, like, well, “asparagus”. It will take you to an entry that gives you all of the formal names (that you can use then in other reference books for more information), and describes a bit about the relevant chemical in the entry. Asparagus, as it turns out, creates a thiol during the digestive process that your body excretes, you got it, in your urine. Same class of compounds, and I’m sure it’s created in a very low concentration, but because our sense of smell is so sensitive to it, that’s all it takes. I explained this in my reply, and she responded saying “I knew you would know. I asked all of the science professors here, and all they said was, ‘oh, that’s gross.'”
Why would you say that to a student? These are the questions that can turn students, and especially kids, on to science. So now, if YOUR child should ask about the smell of skunks, or gas, or urine after asparagus. you’ll have a little bit of a background to share with them.