The Ideal Gas Law is just that: "ideal." The equation pV = nRT may look like perfect math but, in the real, messy world of the practical physics of pressure, temperature and volume, actual results come close to predicted results, but they never conform exactly. Why is that? Together with the formula, this painting depicts two 18th Century lads having a laugh blowing up a pig bladder. The boys appear in a Goya tapestry cartoon. Also don't miss the two embryonic puffer fish, and the green alchemic kettle.