KC beat me to it. Dictionary.com lists the root word etymology as “pur” (long u), which also seems to be the source for the prefix pyro, having to do with fire. You may be talking about a cermony or rite, of which there seems to be no shortage of hits on Google when paired with “fire”. Merriam-Webster Online lists “baptism of fire”, and the Christian Purgatory is supposed to cleanse the soul by fire (thus we have purge). Refine is the word you’re looking for if you’re talking about metallurgy, and boil if talking about purifying water.