[Wil"]

I really don't understand what's the use of the glass beads in the fractional distillation.

I've a thought but I don't know if it's correct

Suppose the solution contains ethanol(bp 78'C) and water(bp100'C)
When we heat the flask, all the ethanol will be vaporized at 78'C. So at 78'C, the ethanol vapour will rise up to the glass bead, and since the glass bead is cooler than the ethanol vapor, the vapor condenses back to liquid ethanol. However, the temperature of the flask is now over 78'C, ethanol is still being vaporized and at 100'C, the water is also being vaporized.
Now, both of them will be condensed when are in contact with the glass bead(since it's still below the bp of the two substances). As the time goes on, the glass beads will become hot enough(suppose it's now at 100'C). Therefore, when the ethanol vapor is in contact with the glass beads, the vapor won't condense but it goes up and up to the condenser and so on.
Since water is not volatile when compared with the ethanol, water will be vaporized later than ethanol.
We possibly get 90% of pure ethanol.

Is my assumption correct? Please correct me if you see any mistakes. I really hope I can get this mechanism clear and correct.

Thank you.

[enahs]

http://en.wikipedia.org/wiki/Fractionating_column