Good work, Pans-Advocate; I wasn't aware of this reagent until you mentioned it. This is definitely pretty exciting stuff. :D Makes me wish that I had a formal education in chemistry so that these things would be more obvious than amazing, heh. Oh, and yes, this will also raise a positive for caffeine, but I suppose that's not too terrible.
Alkaloids often contain multiple amine groups. In the case of the recreational piperazines, most contain both a secondary and tertiary amine group, but
DBZP and
MBZP only contain tertiary amine groups. I doubt those ones will show with the Dragendorff reagent, but at least BZP, TFMPP, and mCPP (the most common pipes afaik) will show up. By the way, you can tell if a compound has an amine group by looking for any nitrogen atoms.
If the nitrogen has two hydrogens on it, it's a primary amine group. If it has one, it's a secondary amine group. No hydrogens means it's a tertiary amine, in which case the group's only contribution to the compound's chemical properties is the lone pair off of the nitrogen atom.
(By the way, if any of you chemists out there see anything wrong with this, please correct me -- I was taught chemistry by Wikipedia and constant pestering of my ex-chem. engineering girlfriend. 8))
To any of you who're thinking about trying this out, I recommend dissolving a crushed piece of a pill (doesn't have to be huge) in a test tube of distilled water, then adding 1mL of Dragendorff reagent. The reagent should change from its normal golden/golden-brown color to a more reddish tint, and in the presence of sufficient reactant will form an opaque precipitate. Also, the kid in the video is absolutely correct -- you can indeed make it that way.