Alchemist potion bonus type

[Xerxes1]

What kind of bonus does an alchemist's potion of bull strength give? is it +4 enchantment even though he doesn't use magic? Is it a +4 alchemical bonus? and if so does it stack with a mutagen effecting strength?

[Doggan]

Enhancement bonus. And yes it stacks with Mutagen because Mutagen gives an alchemical bonus.