I assume you're talking about measuring a substance by dissolving a known amount of solute into a known amount of water (or any solvent).
Because I like K:
You have weighed out 2 grams of ketamine (lucky bastard). You dissolve it into 20mL of water measured by syringe(s). You now know that every mL has 100mg of ketamine dissolved in it.
What you can do with this knowledge. Inject it (preferred method) or squirt some onto a plate and re-evaporate it and snort it.
[This message has been edited by wickedclown_stl (edited 18 July 2001).]