IMPORTANT CAUTION: caffeine is a drug. it's not a controlled substance, it's not illegal, but it's still a drug. as with all drugs, don't try to prove your manhood by gobbling three grams (that would be near instant death in nearly everyone), and make sure that you always weigh it exactly to avoid overdoses. also, repeated use can be addictive (no studies to cite, just personal experience with withdrawal symptoms), and can cause insomnia (again, personal experience). don't use this in situations where you wouldn't drink two cups of coffee, because that's basically what's going on here.
Step 1: Quick Notes and Things You'll Need
what you'll need (apart from readily available things):
itty bitty bottle
--(mine is a bottle from some candy flavoring, but any will do) - mine was .125 fl. oz, and it worked extremely well.
--(make sure it can read down to at least ten milligrams [.01 grams]. you'll want to be exact.)
--(note on caffeine powder: it's really not hard to get. it's not a controlled substance at all, and my brother got me 100 grams [1000 100-mg doses] for around 7 dollars. ebay would be a grand place to get it.)
Step 2: Weigh Out Caffeine
to weigh out the caffeine, we'll want to flash back (or forward, depending on who's reading this) to high school chemistry. the easiest way that I've found to meter and dispense caffeine is to use the weigh paper method. this basically entails turning on your scale, placing a piece of paper on it (make sure it's of ample size - make one that covers the whole scale surface to be safe), "zeroing" it (that's what the "tare" button does), then measuring the dosage onto the paper using a very small spoon or a chemistry spatula (a butter knife would be and OK substitute). be careful at first; it's rather difficult to conceptualize 200 milligrams (the weigh paper itself weighs around 300-ish before zeroing the scale).
Step 3: Place Caffeine and Water in Bottle
Step 4: MAGIC!
well, just calm down, you fuzzy little man-peach. no need to get all "bleh" on me. I told you it would be supersaturated; now it's time to supersaturate.
obtain one microwave. got it? good. put the bottle in (cap off). go for ten seconds at first, and, if necessary, five second intervals after that. you want it to be hot to the touch, but not so hot that you can't hold it. once it's hit this point, remove the bottle, cap it, and shake. after a couple seconds, all the caffeine should dissolve. if not, try more heat. if that doesn't work, you're just going to need to use less caffeine (or more water).
SCIENCE EXPLANATION TIME!
basically, when something is supersaturated, it means that there is more of a substance dissolved in a liquid than could normally be dissolved. this can be shown by the fact that the caffeine wouldn't completely dissolve at room temp, but later on, after heated and brought back to room temp, it had total dissolution. in most cases, cooling it back down would make some of the caffeine go back to crystal form. however, due to the fact that it is in a smooth glass and plastic container and that there are no caffeine crystals left, there is no place to crystallize, so it just.... doesn't. it stays supersaturated.
UPDATE ON SAFETY:
it has been brought to my attention that it may not be a good idea to microwave random glass bottles. while I'm not sure about the probability of the glass exploding/cracking in this situation (I believe it is caused by uneven heating [and thus uneven expansion], which I don't think this particular situation provides much of), it would probably be a good idea to microwave the water and caffeine into a pyrex or plastic container, just to be safe.
quick note on the shattering: like I said, I think it's caused by uneven heating, which causes uneven expansion across the glass (cold liquid on the inside, hot on the outside, outside expands, inside stays contracted, boom). however, there's just so little liquid inside the glass bottle (and so little time in the microwave) that I don't think the bottle would easily crack. but in the interest of safety, let's just say it's not recommended.
another interesting microwave science tidbit: one time when I did this, I attempted to use the microwave to dry out the bottle after cleaning. when I put the bottle in the microwave, however, there was a large plasma arc across the top lip of the bottle. I believe this was due to water on the inside and outside of the bottle creating a leyden jar-like effect, and a charge was built up on either the inside or outside, which sparked between the two. I've seen a similar thing done with a grape that's cut almost in half (just connected by the skin).
Step 5: You're Done
yep. that's all there is to it.
as a final note, I would like to mention that, although it hasn't happened to me, I would assume that if any caffeine crystals were left undissolved (or if any were added afterwards), the supersaturation would collapse and a bunch of caffeine would precipitate out. but I'm not educated on the dissolution properties of caffeine, so this may be a bunch of hogwash.
happy (safe) caffeinating.
Step 6: UPDATE: 300 Milligrams... Doesn't Work Well.
I attempted to remedy this by microwaving it again, which, again, seemed to fix it. however, I let it boil, and I believe this removed just enough water to entirely crystallize it, turning the entire thing into a weird watery gel-like substance (but not really gel like- it's hard to explain, it's like a bunch of really thin fibers holding water together. weird.)
so unless you can find a way to keep it supersaturated, I'd stick to 200 mg.