Rarefy vs Purify - What's the difference?

As verbs the difference between rarefy and purify

is that rarefy is to make rare, thin, porous, or less dense while purify is to cleanse (something), or rid (it) of impurities.

* rarify

(en-verb)

To make rare, thin, porous, or less dense

To expand or enlarge without adding any new portion of matter to.

* stretch

* condense

To cleanse (something), or rid (it) of impurities

To free (someone) from guilt or sin

* defile