The Student Room Group

Reply 1

If you have too much of the solvent, the ink or whatever you're trying to separate will dissolve back into the solvent and won't travel up the paper therefore no longer leaving a thin line of the solvent. It makes it hard to work out an accurate Rf value after.

As for the capillary tube, I'm very inclined to say yes since it's a device with which you take measurements so why not?

Hope that helps!!