Available: From the point where you join the College.
Speak to Tolfdir and choose "What was it you were missing?" if available. He seems to have lost his Alembic, which is an alchemic still (two vessels connected by a tube). You won't get a quest marker, but oh well, here are the places I've found it so far:
- Top floor of the Hall of Attoinment, in the room directly across from the stairs, on top of a barrel.
- Top floor of the Hall of Countenance, in the chamber with the Arcane Enchanter, under a display case.
- Ground floor of the Hall of Countenance, in the room with the large cask, on top of a crate.
Note: This is a repeatable quest that you can do once a day. Also, you can FIND the item before even taking the quest, which can be handy. And yes, he really losses that shit once a day. How bad of a memory would THAT take!?