It's indeed on p.40 of the Mysteries (second page of the Alchemy section). It's called Divide the Gathered Essence, and its main purpose is to split vis into multiple containers. It seems that T:Group is necessary because of this splitting. RoP:I, on p.122, has a T:Ind spell called Cleanse the Verminous Vis that transfers vis from one container to another in bulk (incidentally "scrubbing" it of Infernal influence).