The testing gurus will surely get to this one, but to answer quickly:
The liquid should quickly (less than ten seconds definitely; less than five even better) turn to a bluish or purplish black. A colour chart should have come with your test kit.
And um, it shouldn't ruin the pill if you're doing it correctly. You don't drop the liquid directly on the pill; that most certainly would ruin it, since the testing reagent is quite definitely poison to humans. To test a pill, you scrape a little bit off of it, and drop the liquid on that scraped-off powder.
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Coitus ergo sum.
[This message has been edited by stardragon (edited 17 July 2001).]