Do Brand's "on hit" effects work with spells?

Like if i cast prismatic bolt, it proc's a burn, i cast prismatic bolt again, and i have Fire brand skill, will the fire brand proc extra damage from the prismatic bolt cast? Or does the "hit" mean a physical hit, like with a wand or staff, cause if thats the case, brands seem worthless imo.

it works for spells, at least for ice brand.

great, gonna make a pure prismatic bolt mage then, and max all the brands with elemental attunement and shit.