As I wrote recently, I got COVID, which hasn’t been fun. I had a miserable day, but started feeling better by the next. After a week the symptoms had mostly subsided.

But then last week I got worse, with a grinding headache, sinus problems, and coughing. It’s autumn here and that always plays havoc with my sinuses, but I’m pretty sure this was COVID related — I have lost my sense of smell and taste, which is classic COVID.

That’s temporary, but in the meantime, while it isn’t fun, it’s interesting. I can’t taste most foods, but some I can kinda sorta taste. Dots are a chewy fruit-flavored candy, and I had some — I can’t really taste the flavor exactly, but I get enough of a sense of them that I can tell them apart, like lime from orange. It’s weird, like trying to remember a dream; the flavor is right there (literally on the tip of my tongue) but hard to make it coalesce. I tried a mint chocolate bar, and the chocolate was hopeless, but definitely got that cool feeling from the mint. That was weird! I also sense the sourness of lemonade, and my wife made some hot buffalo chicken last night and I definitely felt the heat even though the flavor was completely absent. 

I’ve read the recovery time for this can be weeks, so I’m settling in for it. Hopefully it’ll be quicker. In the meantime I’ve also read that COVID isn’t contagious after 10 – 14 days after the symptoms kick in, so I’m good on that front. Of course I will still wear a mask out in public, because I don’t wish to be a vector, and even if I’m not contagious I still think it’s important to be seen masking.

So stay safe out there. Get your vaccinations, and mask ‘em if you’ve got ‘em.

I have a recurring (and very irritating) medical issue called stenosing tenosynovitis, or more commonly trigger finger. It occurs when a finger tendon swells up a bit and then won’t slide easily in its protective sheath. Think of it like a trying to lace a shoe when the lace has a knot in it, and it won’t fit through the hole. It can make your fingers feel tight, or create an unpleasant clicking or snapping feeling when you bend your finger. In severe cases can make it painful to make a fist or grab objects. Mine’s never been that bad, but it still kinda sucks.

An immediate if temporary fix is to introduce a steroid into the tendon to reduce the swelling. This is done via injection. I’ve had these done, and the procedure hurts. Well, just for a few seconds until the lidocaine mixed with the steroid numbs the nerves. Still though, ouch.

I had an injection recently, and the doctor did something I hadn’t seen before: before the procedure, she sprayed the injection site on my hand with a small can of “compressed air” first. That spray was cold, and I mean cold. The purpose is to temporarily deaden the nerves in the skin so the injection doesn’t hurt as much. I’ll note the cold spray hurt too, but not as much as the needle, so it’s still a win.

Curious, I looked at the spray can to see the ingredients: it contains ethyl chloride, also called chloroethane. I thought about it for a second, and realized it must have a very high vapor pressure — and when I looked it up later I found I was right!

How did I know, and what does that mean?

Vapor pressure is related to how much a liquid “wants” to evaporate at a given temperature. Some liquids, like water, are pretty stable at room temperature, and evaporate slowly. Others, like alcohol, evaporate much more rapidly.

Now imagine you put his liquid into sealed container. As the liquid evaporates, the pressure in the air above it increases. That’s the vapor pressure, and for a liquid that evaporates more readily that pressure will increase to a higher level than for a liquid that doesn’t evaporate as much.

Water has a vapor pressure of about 2 kiloPascals at room temperature (a Pascal is a unit of pressure, and at sea level air pressure is about 100 kP). Chloroethane, on the other hand, has a vapor pressure of 135 kP at room temperature! That’s way higher than water, which means it evaporates really rapidly. Alcohol has a vapor pressure of about 5 kP, for comparison, which is why it feels cooler than water, but nowhere near chloroethane.

The important bit here is that evaporation is a cooling process: it takes energy to convert liquid to gas, and the evaporating gas removes that energy from the liquid, cooling it (that’s why sweat cools you off). Since chloroethane evaporates really vigorously it can really cool off whatever it touches — it boils at about 12° C, too, so it is an extremely efficient coolant when it hits your warm skin. I read it can drop skin temperature to about -20° C!

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