idea behind salt analysis

jd12345

How does salt analysis work? How did they divide cations into these 6 groups?
I'm confused over things like:- In a group we precipitate metals through their sulphides - but only few of the metals precipitate - why only specific emtals precipitate. Then in another group we precipitate metals as sulphates, again only specific metals precipitate

Why is this? How on earth did they divide cations into such groups?

Borek

First, they experimentally checked solubilities of salts. Then, they designed analytical procedure based on this knowledge.