Anyway there's a trick with the 2 solvents. If you add 20mls of one solvent to the other, a certain amount of the chemical will be transferred to the new solvent. However, if you add 2 lots of 10mls (one after another), more of the chemical will be transferred. Weird huh?
Anyhow, I was teaching this to class and when I explained this, I got a gasp out of the class, when they got it. It really cheers me up when this sort of thing happens.