Fire assay gold analysis (MIT historical curriculum)

Tom's account of the centuries-old gravimetric technique still standard for referee gold analysis: digest in lead bath, oxidize off base metals, separate gold-silver button, dissolve silver in nitric, weigh refined gold. One part in 5,000 accuracy. Tom notes he was tasked 25–30 years ago with developing a replacement; inductively coupled plasma is finally getting close.

If I'm analyzing gold, they still use the fire assay technique. If you were in the materials department 120 years ago, you'd have taken a course in fire assay. There's a safe down in the basement where they used to keep the gold. The buildings were built in 1917, and they were probably still teaching fire assay as part of the undergraduate labs. You weigh the karat gold on a very precise balance — one part in about 5,000 if you do it properly.