7. Filter the cooled solution to remove any solids remaining. The easiest filtration uses the Büchner funnel and water suction. Read the separate section on the assembly and use of this device. Be sure to use the safety trap, because in this first filtration you must save the filtrate (the solution). If you don't use the trap and there is even a small interruption in the water flow, tap water can suck back into your solution and contaminate it.
8. Discard the dark solid trapped in the filter paper and SAVE the solution for use in the next part of the experiment. (Don't waste time trying to recover the small amount of alum that forms in the beaker or suction flask).