The way I have always heard recommended is to make the "stock" solution. I don't think you need quite 20 grams of sodium sulfite to preserve it either, but I will have to check.(posted 8564 days ago)10 grams to a volume of 100 ml makes a nice 10% solution to use. A tip, use some alcohol to dissolve the phenidone than dilute with water. The little bit of alcohol won't hurt any formula and will really help to dissolve the phenidone. That tip from Ctein's "Post Exposure."