I'm not entirely clear on how some of the ways there are for an alchemist to learn new formulae work. Here's what I know:
I gain 1 new formula each time I gain a level of alchemists (beyond those I get at level 1).
I can copy formulae from other alchemists' formulae books and from wizards' spell books (where their spells also appear on the alchemists' extract list).
I can write formulae into my formulae book using a formula alembic to derive a formula from a potion (again, as long as the potion is from a spell that is on the alchemists' extract list).
An alchemist can also add formulae to his book just like a wizard adds spells to his spellbook, using the same costs and time requirements. An alchemist can study a wizard's spellbook to learn any formula that is equivalent to a spell the spellbook contains.
This is what raises some questions for me that I hope you can help answer.
1. Do I need to make spellcraft check to successfully learn a formula by any of the methods above?
2. Can I learn a formula from a scroll?
3. What about from a divine scroll? (Some alchemist extracts appear on the spell lists of divine casting classes, but not the sorcerer/wizard list).