Today marks one year since I started this blog, and thus the end of this project. I am pleased to have successfully learned one new thing every day for a year (including the two month break for summer, even if what was learned was not chronicled for lack of internet). Updates will now stop. They may resume at some point in the future, however for now Pansophism has ended. It was a fun ride!
Alcohol strength is usually quantified in terms of 'Alcohol by Volume' (or ABV), however we still sometimes hear strength quoted in units of 'alcohol proof'. This is a somewhat arcane unit of measurement that was quite interesting. A pellet of gunpowder would be soaked in alcohol, and if it could still be lit the alcohol was said to be 'above proof', and as such taxed more heavily. The point at which the gunpowder would still burn was called 100 proof, and corresponded to about 57.15 % ABV. Knowing this, it is fairly easy to switch between Alcohol proof and ABV:
Proof = $\frac{ABV}{57.15} \times 100$
A typical beer, at about 5% ABV, works out to be around 8 proof. Understandably, soaking gunpowder pellets turned out to be a somewhat impractical way of measuring alcohol strength, and the unit was phased out in the 1800s in favour of ABV. For old time's sake, you will still sometimes see proof alluded to on the labels of spirits.
-E