How to Spot a Psychopath

A reader writes:

Most cigarettes have a wrapping around the filter that looks like cork, because apparently the earliest filter cigs had a filter made of cork.

How the hell did that work, though?

Isn't cork used for, well, corks, because it's impermeable? How could you suck smoke through a cork? Perhaps smokers in 1940 were more health-conscious than we thought, and enjoyed these Unsmokable Health Cigarettes!

Luca

Today, most cigarette filters are made of cellulose acetate fibre, a substance of many uses (from cloth for garments to stuffing cushions) which is made by reacting plant cellulose with acetic acid.

But cigarette filters are, as you say, usually covered with a layer of paper printed with a cork pattern. And yes, that's because in the olden days the filters were made of cork. (This makes the printed-paper filter a "skeuomorph", an object with cosmetic design elements held over from an older version of the same thing.)

Cigarette filters were, however, never solid cork; as you say, that would be ridiculous. Instead, the filter was actually filled with loosely-packed cork granules, or a loosely-rolled piece of paper, which might itself have been made from cork.

There's nothing about cork that makes it a particularly excellent filter material. It was just a relatively cheap substance that wouldn't do anything very alarming if the smoker smoked all of the tobacco and sucked the flame back into the filter.

Cigarette filters have the peculiar task of blocking some bad stuff from getting into the smoker's lungs, without blocking the bad stuff that the smoker's paying to put into their lungs. (See also guns, which are generally designed to be simultaneously as safe, and as dangerous, as possible.)

So a really good filter material, like activated carbon, would be no use in a cigarette. Instead, filter materials with relatively low surface area are used. Activated carbon works so well as a purifying filter because it's immensely porous, giving it an enormous surface area per gram and allowing it to "adsorb" a surprising amount of stuff. Cellulose acetate fibres, of a similar consistency to cotton wool, adsorb rather more "tar" than the old cork filters, while letting various other compounds through.

Both cigarette filters and long cigarette holders do catch some particulate matter and "tar", but their actual effect on smokers' health is difficult to detect.

(See also "light" cigarettes that have air holes in the paper around the filter to dilute the smoke. In theory, they could actually be somewhat healthier than regular cigarettes, but in reality, there's no good evidence that "light" cigarettes are any better. Smokers cover the holes with their fingers, or just smoke more, or more deeply; however it happens, health outcomes are the same no matter what mainstream-Western-market cigarette you smoke.)

Psycho Science, as I have brilliantly decided to call it, is a new regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

A reader writes:

I was walking down the street at three in the morning after a night out, in the middle of winter [here in Australia], and there was twinkling frost all over the top of a parked car. And the next parked car. But not the one after that.

I kept looking, and the difference was that cars that were parked under a tree had no frost, but cars that were in the open were frosty.

The air temperature was pretty low, but it wasn't below freezing - I checked later and the local weather station said it got down to about 4 degrees C.

Did frost fall down out of the sky and somehow... stay?

Finn

It was a clear night with no breeze, right?

On a clear night, the sky above you is a window to deep space. There's no sun keeping things warm, no diffuse sky radiation making the sky blue and at least a bit warm wherever you look; just a blanket of air, and then space.

Heat can pass by convection, conduction and radiation. Radiation, for most items humans encounter, is the least important of these three paths. But if an object has a wide view of something which, like deep space, is close to absolute zero, then it can radiate enough heat to drop below zero Celsius, even if the ambient air temperature is a little above freezing.

If there's even a light breeze, the passing above-freezing air will keep surfaces too warm for frost to form, by allowing heat to move by convection - in this case forced convection (as in the case of a computer CPU's heat sink cooled by a fan). Likewise if a surface is directly connected to something with a large heat capacity, allowing that surface to stay warm by conduction (as in the case of the CPU itself, in physical contact with its heat sink). The thin steel roof of a car will form frost in these conditions; a solid block of steel would not, because radiation wouldn't be able to cool all of it enough before the sun came back up.

The less of a direct view a surface has of the sky, the smaller this already-small effect will be. So cars - or rubbish bins, or other thermally-isolated surfaces - that're in the "shade" of a tree or building probably won't frost up. (There could be some interesting odd cases, if for example a car is parked next to a skysraper covered with IR-reflective glass.)

This same phenomenon can be used to make ice in a desert, if that desert has clear, still nights. Wide shallow trays of water held up off the sand by narrow supports can freeze surprisingly quickly.

Psycho Science, as I have brilliantly decided to call it, is a new regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.