Also another METHod of figuring out how pure it is would be simply smoking the first hit (or more if it's really nasty stuff...). Pure meth
feels just like air, but if it's cut, it tastes like chemicals and is harsh so at least Swim
tends to cough a bit.
Also, Swim watches the stem in particular. Much like tweakerbell's finger test, if the stem clouds up in the first few hits and covers the inside with the white chalky shit, that is from the cut.
HCL is produced by combining other dangerous/toxic/etc chemicals, but it takes real chemistry skill to be able to perform the reactions necessary to make the final (entertaining) product. Like the classic table salt example; Sodium and Chlorine are both poisonous, but stick them together and you can sprinkle it on your breakfast. It isn't about what goes in, it's about what comes out.
Swim is tweaked out so he talks too much. I'm sorry I wrote such a long reply. I hope it helps