Topic: Purify Substance a too expensive version of Purify food?

[munchy]

I was wondering (weird how I begin all my posts with this phrase) why someone should learn the Purify Substance spell from the Codex for 17 PPs when he could as well use the Purify Drink and Purify Food cantrips from the Grimoire for mere 2 PPs in total.
The mass is different 5 cubic foot compared to only 1 pint and 1 pound but otherwise the effect seems to be the same.

[Rasyr-Mjolnir]

Purify Substance can be used on things other than food and water....

And at higher levels it can be used to separate out the components (i.e. like separating mercury out from tainted water, or separating iron out of raw ore, etc...)

[Willen]

...like obtaining pure silver out of regular silver, or aluminium, or iron out of ore...

I believe that spell would be the basis of every alchemical profession, ensuring purity of your ingredients. And also the only way of obtaining some very-high quality steel, etc.