Spider head

I took this scanning electron micrograph of a spider head back at Smith. It’s a little bleached-out-looking (I hadn’t really mastered the instrument) but nonetheless gorgeous and creepy.

Before you image a biological specimen, you have to dry it using a gizmo called a critical point drier. Simply evaporating off the water doesn’t do the trick, because the surface tension at the interface between water and air damages the spider as it dries out and you end up with a wrinkly specimen — not so pretty. If you bring water to its so-called critical point, where the density of water and air are the same, you can avoid the surface tension issue. But then you have a really-dangerous-conditions issue: the critical point for water occurs at 374 degrees C (705 degrees F) and 3,212 psi (about 219 times the atmospheric pressure at sea level). The poor little arachnid corpse isn’t likely to make it through that experience intact.

Enter the critical point drier. Conveniently, carbon dioxide has a much more reasonable critical point than water: 31 degrees C (88 degrees F) and 1,072 psi. So flood in some liquid CO2 (after using acetone to purge all the water, because water and liquid CO2 refuse to get friendly), crank up the heat and pressure, and BOOM — dried spider corpse.

Then sputter-paint the corpse gold and stick it in the microscope.

I had a arachnophobic boyfriend in high school who used to attack spiders with compressed air from his paintball gun (yeah, I dated real winners). The critical point drier somehow seems like a much more satisfying way to exact revenge, if that’s your thing. And then you get a trophy, too.

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