You want to find 69_ron on dmt nexus, he was the king of mescaline extraction
I've attempted twice with no luck, even though I confirmed mescaline present.
My initial thoughts on what went wrong was I had my stuff too concentrated while boiling it down.
Don't work with more than 500 mL at a time unless you have serious equipment, but you should approach this as a fairly difficult extraction - harder than mimosa hostilis.
Heat whole cactus in an oven on lowest setting for an extended period, in side a pot.
This causes the cactus to experience stress and produce more alkaloids, if you can do this for 24 hours, good.
Then chop off the outer layer, the inner core has nothing.
Chop / blend / freeze / thaw / boil (or boil in a pressure cooker).
Extract mescaline with pH 2-4 water (HCl)
Do this 3 times, combine water
Basify with NaOH (lye) until black - pH >11
Extract with either: Ether, ethyl acetate, naptha (not the best), xylene, toluene
Then evaporate (or add acid for the salt, but you'll get a shit load of salts that aren't mescaline.)