Monday, April 18, 2011

A sappy story

Last weekend we took a jar of used turpentine to our recycling center to be disposed of. The jar's lid wasn't on perfectly, the jar tipped as I drove around a curve, and a tiny splash of turpentine spilled, filling the car with a sent reminiscent of a pile of fir branches. The smell took me back to when I was a kid exploring the forest. Fir trees are sappy – a fact I learned early while climbing them. The fir trunk has sap blisters that burst under my hands when I grabbed the branches. The sap left sticky residue on my hands, so climbing a fir tree quickly became a inferior choice compared to the maples and alders. But, something about the sap intrigued me, so I would collect it by lancing the blisters with my pocket knife and capturing the drips in a large clam shell. When I had enough, I would light the sap to see the black smoke (probably not the smartest of ideas).

The smell of turpentine started me wondering if it's made from fir sap. It didn't take much digging to learn that what I'm calling sap is actually resin, a hydrocarbon secreted by predominantly coniferous trees and a few other plants (both the biblical frankincense and myrrh are resins). Resin is also known as pitch and it has some neat properties. It behaves as a solid normally, but if a force is imposed on it long enough the deformation will increase indefinitely, just like a liquid. Cool, but how does it become turpentine?

Resin is converted to turpentine by distillation, a process where the parts of a liquid are separated using heat – for example if you want to make a fortified wine like brandy, you would need to heat the wine and collect the alcohol as it evaporated away. Generally, turpentine is made from pine trees, but it's also a byproduct from reducing coniferous trees to pulp.

Turpentine is commonly used as a solvent; we use it for cleaning brushes coated in oil paints. It could also be used to thin out oil paints.

As a tangent, I pulled out an old country skills handbook to see what they suggested one could do with turpentine. Apparently, it was used as an ingredient in mosquito repellent along with some other nasty stuff – I was relieved to see that this concoction was to be used by saturating cloth with it and placing it by the door instead of putting in on your skin.

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